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New Generation Design Codes for Geotechnical Engineering Practice -Taipei...
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Proceedings of the International Symposium on
New Generation Design Codes for Geotechnical Engineering Practice -Taipei 2006 (with CD-ROM)
editors Meei-Ling Lin, Chung Yusuke Honjo and
Proceedings of the International Symposium on
New Generation Design Codes for Geotechnical Engineering Practice -Taipei 2006 (with CD-ROM)
Proceedings of the International Symposium on
New Generation Design Codes for Geotechnical Engineering Practice -Taipei 2006 (with CD-ROM) National Taiwan University of Science and Technology, Taipei, Taiwan
2 - 3 November 2006
editors
Meei-Ling Lin (National Taiwan University, Taiwan),
Chung-Tien Chin (Moh & Associates Inc., Taiwan),
Horn-Da Lin (National Taiwan University of Science and Technology, Taiwan),
Yusuke Honjo (Gifu University, Japan) &
Kok-Kwang Phoon (National University of Singapore, Singapore)
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World Scientific
NEW JERSEY • LONDON • SINGAPORE • BEIJING • SHANGHAI
• HONG KONG • TAIPEI • CHENNAI
Published by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE
British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.
Proceedings of the International Symposium on NEW GENERATION DESIGN CODES FOR GEOTECHNICAL ENGINEERING PRACTICE — TAIPEI 2006 (with CD-ROM) Copyright © 2006 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher.
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ISBN 981 -270-382-9 (pbk)
Printed in Singapore by World Scientific Printers (S) Pte Ltd
PREFACE Communication of design risk within a transparent and rational framework is necessary in view of increasing interest in code harmonization, public involvement in defining acceptable risk levels, and risk-sharing among client, consultant, insurer, and financier. Activities in code harmonization in particular are noteworthy. The advent of the World Trade Organization (WTO) has added impetus to the formation of trading groups that result in multilateral free trade areas or bilateral free trade agreements. Traditionally, geotechnical engineering practice has always been viewed as a localized activity under the purview of the relevant federal and/or state authorities. However, the move towards greater economic cooperation and integration will require the elimination of some technical obstacles that exist as a consequence of differences in national codes and standards, and harmonization of technical specifications. For the geotechnical engineering profession, there is added pressure to undergo significant revamp because structural and geotechnical design are increasingly incompatible. The structural engineering design community has adopted limit state design and probability-based design since the seventies and appears to be gradually evolving towards a performance-based design philosophy. The structural engineering community is also the main driving force behind international standardization activities, such as IS02394 on "General Principles on Reliability for Structures". Engineers and regulators in many countries are struggling to accommodate the complex and multi-faceted changes occurring at the international scene. The status of local design codes in view of globalization and their compatibility in view of evolving design philosophies, are issues of major concern that do not admit simple solutions. A large number of countries do not have the scale of economy, organizational structures, political support, and perhaps financial resources to solve these complex problems on their own. This conference intends to follow the spirit of IWS Kamakura (2002) and LSD2003 to promote greater awareness, to facilitate debate and information exchange, and to accelerate research and practice on important issues relating to new generation geotechnical design codes. The bottom-line is to move geotechnical engineers forward together as a community in response to significant changes occurring globally. The idea behind this symposium grew out of a discussion between Chung-Tien Chin, JieRu Chen, Yusuke Honjo, and Kok-Kwang Phoon during the 16th ICSMGE in Osaka last year. Subsequent discussion between Meei-Ling Lin and Kok-Kwang Phoon during the GEDMR05 conference in Singapore helped set the path in commencing the organization of this event. Given the gathering pace of geotechnical design code developments, there is a compelling reason to consider a follow-up symposium to LSD2003. It is also timely to discuss the possibilities of establishing a more regular series of symposiums and a joint working group to coordinate these activities. Thirty-five abstracts from thirteen countries were received during the initial call for paper. Thirty-one papers were accepted for publication after review. Topics covered include
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geohazards, geotechnical uncertainty and variability, probabilistic and reliability analysis, design code concept and harmonization, and performance-based engineering practice. In addition to the submitted papers, special invitations were extended for contribution as keynote lectures, invited lectures, and Taiwan special project lectures. A total of 11 papers were obtained for these lectures. This publication contains extended summaries of 42 papers. Complete contributions are available in the accompanying CD-ROM. This symposium is jointly organized by the Taiwanese Geotechnical Society and TC23 of ISSMGE. It is supported by the National Taiwan University, National Taiwan University of Science and Technology, Taiwan Construction Research Institute, ASCE Taiwan Chapter, JWG-DMR, ASCE Geo-Institute, TC39 of ISSMGE, and Southeast Asian Geotechnical Society. The publication of this proceedings will not be possible without the considerable efforts invested by a committed editorial committee that include Jie-Ru Chen, Jian-Ye Ching, Yo-Ming Hsieh, Chih-Ping Lin, and C.H. Wang. Papers appearing in this proceeding are subjected to technical and editorial reviews. We are also grateful for the constant support and timely assistance given by the technical reviewers (C. Hsien Juang, Kok-Kwang Phoon, Robert S.R. Lo, Liming Zhang, Kenichi Horikoshi) and editorial reviewers (Hsiang-Ju Chen, Ting-Rong Chen, Te-Wei Chen, Yu-Hua Hsieh, Wei-Nan Jian, YuehTing Lai, Jing-Hang Lin, and Mei-Ling Liu), and the secretariat (Ms Wei-Ling Lin and Tsui-Hui Chiang). The significant assistance rendered by Prof. Der-Wen Chang in the arrangement of travel visas for speakers is deeply appreciated. Lastly we would like to thank Rhaimie Wahap and his team at World Scientific for working patiently with us under a very tight publication schedule. His professional assistance is greatly appreciated.
Editors Meei-Ling Lin Chung-Tien Chin Horn-Da Lin Yusuke Honjo Kok-Kwang Phoon
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Organising committee Prof. Meei-Ling Lin, Symposium Chairperson Dr. C.H. Wang, Secretary General Dr. Jie-Ru Chen Dr. Chung-Tien Chin Prof. Jian-Ye Ching Prof. Jia-Jyun Dong Prof. Yo-Ming Hsieh Prof. Chih-Ping Lin Prof. Horn-Da Lin Advisory committee Prof. Yusuke Honjo Prof. C. Hsein Juang Prof. Chien-Chung Li Dr. Za-Chieh Moh Dr. Chin-Der Ou Prof. Kok-Kwang Phoon Dr. Ming-Teh Wang Editorial committee Dr. Jie-Ru Chen Prof. Jian-Ye Ching Prof. Yo-Ming Hsieh Prof. Chih-Ping Lin Dr. C.H. Wang
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TABLE OF CONTENTS Preface Organization
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Keynote Lectures 1 Limit states design based codes for geotechnical aspects of foundations in Canada D. E. Becker
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Risk assessment in rock engineering H. H. Einstein
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Some movements toward establishing comprehensive structural design codes based on performance-based specification concept in Japan Y. Honjo
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Development and implementation of Eurocode 7
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T. L. L. OnInvited Lectures
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New trend toward performance-based design in the construction industry K. Horikoshi, Y. Honjo, A. Iizuka Risk analysis of lining structure in large-diameter shield tunnel H. W. Huang, Q. F. Hu, Y. Y. Yang
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Energy approach to earthquake-induced slope failures for performance-based design T. Kokusho
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A preliminary study on load and resistance factors for foundation piles in Taiwan H. D. Lin
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Evaluating probability of seismic landslide based on the Chi Chi's events, Taiwan M. L. Lin, C. J. Chung, M. H. Ho
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Serviceability limit state reliability-based design K. K. Phoon
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Eurocode 7 for geotechnical design — basic principles and implementation in the European member states B. Schuppener, R. Frank
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Session I: Code Concept and Harmonization
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The study and revision of the probabilistic seismic hazard map and dam safety code of Taiwan C. T. Cheng, S. J. Chiou, C. T. Li, P. S. Lin, Y. B. Tsai
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A simple reliability assessment of pile design: resolving some Hong Kong challenges S. R Lo, K. S. Li, J. Lam
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Geotechnical standards in Hong Kong W. K. Pun, W. M. Cheung, L. S. Lui
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Implementation of Eurocode 7-1 geotechnical design in Germany N. Vogt, B. Schuppener
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Introduction to international joint study ofreliability-based design for port and harbor structure G. Yoon, T. Nagao, W. Lu, K. Lee, H. Kim
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Session II: Performance Oriented Geotechnical Analysis
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Effect of lateral cyclic load on axial capacity of pile group in loose sand S. Basak
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Evaluation of design methods for large-diameter bored piles Florence L. F. Chu and L. M. Zhang
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Engineering problems for performance-based design of earth structures Y. Honjo, M. Honda, K. Ogawa,Y Wakatuki
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Performance-oriented risk assessment and retrofitting strategy for electricity towers on slopes C. H. Wang, M. H. Chang, C. F. Chang, D. C. Wu, K. P. Hsiung
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Session III: Geotechnical Reliability Analysis
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Equivalence between reliability and factor of safety J. Y. Ching, T. R. Chen
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Bearing capacity of open ended piles in port construction in Japan Y. Kikuchi
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Variance of soil parameters: some common misconceptions K. S. Li, S. R. Lo
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Reliability analysis of excavation-induced building damage M. J. Schuster, C. H. Juang, E. C. L. Hsiao, M. J. S. Roth, G. T. C. Kung
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Session IV: Geohazards
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The assessment and prediction of landslides and debris flows in Ta-Chia river after Taiwan Chi-Chi earthquake C. T. Cheng, Y. L. Chang, S. J. Chiu, Y. S. Lin, C. Y. Ku, S. M. Shu, J. C. Chern, S. H. Yu, S. D. Yang, C. F. Wang, C. H. Chiao, L. T. Hwang
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Predicting landslides probabilities along mountain road in Taiwan J. Y. Ching, H. J. Liao
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Optimal design of sand compaction pile based on liquefaction hazard analysis J. H. Hwang, C. W. Yang, C. C. Lu
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Verifications and physical interpretations of the discriminant model for evaluating liquefaction potential on SPT-N value S. Y. Lai, M. J. Hsieh, W. J. Chang, P. S. Lin
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Seismic performance-based design for canal embankment Y. Otake, T. Hara, T. Horikawa, Y. Ito, T. Kato, M. Hosoyamada, Y. Kasai
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Session V: Engineering Practice and Challenges
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Observational design approaches for safe and economical deep basement construction in the urban environment I. Askew, J. A. Frame, D. Sein
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The performance of laterally loaded single pile in reclaimed land C. S. Chen
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Settlement calculation of large-area thick raft foundation under irregular high-rise buildings J. F. Gong, X. L. Huang, D. H. Di
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Geotechnical risk assessment and performance-based evaluation of a deep excavation in the Kaohsiung MRT system project B. C. Hsiung, H. Y. Chuay
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An essay on typification of verification methods used in the design procedure of geotechnical structures S. Kobayashi, K. Aita, T. Fujiyama, M. Honda, T. Kaneko, A. Morikage, A. Murakami, M. Nabetani, M. Nozu
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Session VI: Geotechnical Uncertainties and Variabilities
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Reducing performance uncertainties with monitoring data J. Y. Ching, Y. H. Hsieh
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Evaluation of spatial variability of weathered rock for pile design S. M Dasaka, L. M. Zhang
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Analysis of uncertainties in analytical pile design methods in South Africa M. Dithinde, K. K. Phoon, M. de Wet, J. V. Retief
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Probabilistic uncertainties in estimating the vertical bearing resistance of piles M. Suzuki, M. Shirato, S. Nakatani, K. Matsui
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Soil parameters used in the new design code of port facilities in Japan
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Y. Watabe, M. Tanaka, Y. Kikuchi Taiwan Special Project Series
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Performance design of Taipei 101 foundation D. S. Chen Design and construction issues of deep foundations for the Taiwan high speed rail S. W. Duann, J. R. Chen, T. C. Su, C. T. Chin
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Experiences from Hsuehshan tunnel constructions
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L. P. Shi, Y. S. Hsieh Author index
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List of past ISSMGE TC23 proceedings
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Keynote Lectures
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Limit States Design Based Codes for Geotechnical Aspects of Foundations in Canada Dennis E. Becker Golder Associates Ltd, Calgary, Alberta, Canada EXTENDED ABSTRACT The geotechnical engineering profession in Canada, and elsewhere throughout the world, is in the process of incorporating limit states design into codes of practice for geotechnical design aspects of foundation engineering. Primary benefits of the use of limit states design are that it provides a consistent design approach between structural and geotechnical engineers, as well as providing a rational and consistent framework for design and risk management of design uncertainty. This paper describes the needs and objectives for limit states design in Canada, and its development in codes; identifies and describes the primary Canadian Codes; discusses the role of the Canadian Foundation Engineering Manual and other authoritative references related to these Codes; discusses some of the experiences and challenges encountered in practice during implementation and application of limit states design; and outlines ongoing and proposed code development work, and associated future directions and research needs. The importance of understanding fundamental principles, effective communications between structural and geotechnical engineers, education and training is emphasized. All of these components will be required for successful implementation and acceptance of limit states design for geotechnical aspects of foundation engineering. Limit states design, based on a factored strength approach similar to that of the European practice, for geotechnical aspects of foundations was first introduced into Canadian engineering practice in the early 1980s. However, this initial introduction did not get off to a good start because factored strength concepts were not well accepted by geotechnical engineers; it also generated a fair amount of confusion and controversy because the promised economy of design was not achieved. Canadian geotechnical practitioners felt that it was not logical or rational for strength parameters to be reduced (factored) to reflect weaker "artificial" soils and then use them directly in the same equations for calculating design resistances. In the early 1990s, an overall factored resistance approach, based on a Load and Resistance Factor Design (LRFD) format, was proposed for limit states design based codes. Subsequently, a LRFD format for foundations became a mandatory requirement in the 2000 edition of the Canadian Highway Bridge Design Code (CHBDC) and in the 2005 edition of the National Building Code of Canada (NBCC). Nevertheless, confusion continues to exist concerning the objectives of limit states design as engineering practitioners in Canada struggle to undergo the transition from traditional working (allowable) stress design to design based on limit states (LRFD) concepts. The primary structural codes in Canada are the NBCC, the CHBDC and the Canadian Offshore Structures Code. These codes involve the interaction of structural and geotechnical engineers; they generally apply to the design and construction of foundations, retaining walls and other buried structures. There is no national code document for aspects in which geotechnical engineers do not normally interact with structural engineers. The current geotechnical state-of-practice in Canada does not use limit states design concepts to design slopes, earth embankments, dams and other earth structures. The code requirements are normally written as performance requirements and are based on scientific or technical principles. The codes avoid standardizing certain methods or procedures of design and construction. For example, the NBCC (2005) is published in an Objective-Based Code format where each code requirement is linked to the four basic objectives of Safety, Health, Accessibility (in particular for persons with disabilities), and Fire and Structural Protection of Buildings. Although some countries are striving to establish Performance-Based Codes, the NBCC code developers are of the opinion that current building science knowledge is inadequate to write a "true" (as per their perspective) Performance-Based Code, and that the measures to verify performance
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are not yet adequately in place. It is anticipated that it will be many years before a true PerformanceBased Code format exists in the NBCC and other Canadian Codes. The current implementation of an Objective-Based Code format in NBCC (2005) is considered to be an initial step in this regard. There appears to be a general lack of understanding, communication, education and training concerning the fundamental principles and intent of limit states (LRFD) design. In the LRFD format, it is important to note that the load and resistance factors are interrelated to each other. The values of the load and resistance factors depend on the target reliability index that the design is to achieve, the variability of the parameters that affect loads and resistances, and the statistical definition of thencharacteristic values. For consistent and rational design in practice, the selection of a given characteristic value for geotechnical resistance needs to be made in the same manner as that used to derive the specified geotechnical resistance factor. The mean or a "cautious estimate" of the mean value for the affected volume of ground (zone of influence) is generally considered to be appropriate for the characteristic value and the basis of the load/resistance factors derivation (calibration). The quantification of "cautious estimate" has not been formalized completely; there may be a need to establish an unambiguous quantitative definition for it. In general, practicing geotechnical engineers who have completed limit states design for foundations do not object to the use of the NBCC and CHBDC specified geotechnical resistance factors for shallow foundations. However, some of the specified resistance factors for deep foundations are considered to be too low. In particular, it is felt that static pile load tests are being unduly penalized by the specified resistance factor of 0.6. There appears to be support for the use of a value of 0.7, which is also under consideration by the AASHTO Bridge Code. A review of the geotechnical resistance factors is anticipated to be part of new code development work, including an assessment of the influence of class (level of detail) of geotechnical site characterization. In addition, effects such as subsurface variability, construction quality control, and previous site and construction experience would be interrogated to account for specific knowledge that an engineer has and can be utilized in design. Although it is generally recognized that site investigation, test dependent and knowledge-based resistance factors have merit, the approach for both the CHBDC and NBCC was to keep the design process simple, at least during the initial stages of transition between working (allowable) stress design and limit states design. It was felt that it is more important that the fundamental principles of limit states design for foundations be conveyed to and understood by geotechnical practitioners. The initial transition should be as gradual and smooth as possible. Providing a myriad of partial factors that cover a large range of methods used in practice may not be conducive to better understanding and acceptance of limit states design (LRFD) by geotechnical engineers. Refinements and level of sophistication and details can come later when more experience with limit states design for foundations has been gained. Without the "test" of designs in practice, there can be no substantive verification of appropriate numerical values of geotechnical resistance factors. Assessment of appropriate partial factors for serviceability limit states has not received the same kind of attention and scrutiny as applied to ultimate limit states. Currently the specified factor is 1.0 in the NBCC and CHBDC. The effects of sampling disturbance and other effects will need to be considered carefully. It is anticipated that partial factor values of both less than and greater than 1.0 may be a result of the assessment of partial factors for serviceability.
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TAIPE12006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Risk Assessment in Rock Engineering H. H. Einstein Massachusetts Institute of Technology SUMMARY Risk assessment in rock engineering is based on the formal identification of uncertainties and on their assessment and possible modification in the context of risk analysis and management. The best way to include uncertainty in the engineering design process is through the use of the basic structure of decision making under uncertainty which progresses from information collection, to deterministic and probabilistic modeling to end up with risk assessment and related decisions. These decisions, i.e. risk management range from accepting the risk as is to modifying it. Before applying this decision making process to rock engineering, it is necessary to be clear as to what criteria engineering structures have to fulfill: safety, susceptibility, economics and aesthetics and, particularly, to identify the relevant sources of uncertainty. In rock engineering, the most important sources are inherent spatial variability, measurement/estimation errors and model uncertainties. In information collection, one needs to determine the relevant parameters and associated uncertainties (distributions) through appropriate sampling procedures. Specifically, potential biases have to be avoided and corrected for. Also, one needs to relate the sample to the sample population and, most importantly, to the target population, the latter usually requiring judgement. The result of information collection are state-of-nature models, which express the natural variability. Stochastic fracture pattern models are examples. In the deterministic modeling, phase one relates parameters to outcomes, i.e. predicted performance. The performance can be related to stability, deformation, flow or economic aspects (or combinations). In rock engineering, such performance is related to the typical problems of slope stability, foundation performance, flow and tunneling. An important aspect of the deterministic phase is the concluding sensitivity analysis, which is used to identify the parameters having the greatest effect on the results. Usually only these parameters will be varied in the probabilistic phase. Probabilistic modeling is entirely analogous to the deterministic one but now the relevant parameters and their uncertainties (distributions) are propagated through the model. Hence, the state of nature models mentioned earlier provide the required input. An important issue specifically related to rock engineering is the treatment of fracture persistence, i.e. the fact that fractures and intact rock are interspersed; which has a significant effect on rock mass performance. The probabilistic approach allows one to rationally solve "the persistence problem". Probabilistic models are also well suited to deal with uncertainties affecting economics such as the cost and time to build a tunnel.
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In the final phase, one combines the uncertain performance from the probabilistic phase with its consequences; this combination is the risk. When doing this one has to be aware of the fact that a particular performance does not always have a consequence, another uncertain aspect usually called vulnerability. Also, consequences can be expressed in form of cost or, better, in form of utilities. Risk management can then be used to modify the risk through active actions which change the probability of unsatisfactory performance, or passive actions which change the consequences or the vulnerabilities. Determining and using uncertainties in predictions have a long tradition in rock engineering. Hence, quite a few procedures and models are available. It is, however, most important to put all this in the context of the decision making structure as was done here.
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TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Some Movements Toward Establishing Comprehensive Structural Design Codes Based on Performance-Based Specification Concept in Japan Y. Honjo Gifu University, Gifu, Japan SUMMARY Introduction There have been movements in Japan to develop a serious of comprehensive structural design codes which can harmonize all the major Japanese structural design codes. This movement is much motivated by the rapid development and popularisation of international and regional structural design codes such as IS02394 and Structural Eurocodes, as well as of the performance based design concept especially after the conclusion of WTO/TBT agreement in 1995. In proposing such efforts, it is much contemplated to propose a concept that can harmonize all the major Japanese structural design codes that have been developed rather separated way due to many historical reasons. The performance based design (PBD) (or the performance based specification (PBS)) and the limit state design (LSD) are the two concepts we introduced to achieve this aim. One of the final aims of this activity is to propose a new framework of structural design codes for harmonizing structural codes in regional and international levels. Two of such efforts, namely development of 'Principles for Foundation Designs Grounded on a Performance-based Design Concept' (nick name 'Geo-code 21') by JGS (Japanese Geotechnical Society) and 'code PLATFORM ver.l' by JSCE (Japan Society of Civil Engineers) are presented in this paper. The relationships among WTO/TBT, PBD/PBS and LSD in the current design framework are illustrated in Figure. 1. It is our belief that the specifications of performance of the structures would be described based on the concept of PBD/PBS, whereas the verification of design would be based on LSD/RBD for all the major design codes in the world. In order to cope with the situations explained in the previous section, movements to establish a series of comprehensive design codes have been started in Japan. One of the initial works of this kind of movements started in 1997 at JGS (Japanese WTO/TBT Geotechnical Society) as drafting of 'Geocode PBD 21'*, a proto type comprehensive foundation (Performance Ni design code that can harmonize all the major specifications Based Design) > by foundation design codes in Japan. The performance comprehensive design codes stand at the top hierarchy level in all the structural design codes RBD/ Respect in Japan to give concepts, framework and other LSD/ ; International design terminologies for structural design codes as Standards LRFD ' (IS02394etc.) methods indicated in Figure. 2. It is not intended to be legally enforced but as agreements among the professions (more specifically, the code writers) to draft structural codes based on the rules, Figure 1 WTO/TBT agreement, PBD and LSD/RBD terminologies and concepts established by the comprehensive codes. Therefore, it is thought that it is most appropriate for professional societies such as JSCE (Japan Society of Civil Engineers) and JGS (Japanese Geotechnical Society) to publish such codes.
* 'Geocode 21' is a nick name of this design code. This name has been used from the beginning of the project. The final official name of the code is Principles for Foundation Designs Grounded on a Performance-based Design Concept and the official number of the code is JGS-4001-2004.
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Geocode 21 Geocode 21 is drafted pursuing for an ideal foundation design code at present time in Japan. That is to say, the code is aiming at systematizing and harmonizing the major foundation design codes in Japan that have been developed rather independently due to some historical and legal reasons. In proposing such code, it is neither meaningful nor successful to try to develop a code at the same level to the existing major design codes: An advanced concept is definitely required in proposing such a code. The PBD/PBS concept Figure 2 Concept of the comprehensive design code is employed as the backbone of this code, and is used to harmonize the major design codes on a ground that is different from that of the present major design codes are based. The comprehensive design code is fully performance based design code; but at the same time, it can be looked at as 'a code for code writers'. The aims of this code are as follows: • To define means to specify the structure performances. • • • •
Unification of terminologies. Methods and formats to introduce the safety margin to various limit states in design. Standardize characteristic value determination in geotechnical design. Standardize information flow (i.e. documents preparation) among owner, designer, constructor, geotechnical investigator and others. • The limit state design (LSD) concept is introduced for design verification. For all the major design codes in Japan, it is principal that the design changes from the next day a revised code is enforced for the category of structures under the control of that code because of the legal background. It is too strong constraint for a code to introduce new concepts. For this reason, it is our experience that all the new concepts introduced to the codes are creepingly deformed, stripped of its essential contents in the process of drafting, and finally enforced with no substances. It is not expected that Geo-code 21 is to be used in the actual design from the day it is issued; it is rather pursuing an ideal code which all the code should finally merge into it in the near future. It is expected that various foundation design codes in Japan to accept the concepts and the formats etc. proposed in this code, and finally mildly harmonized to this code in a certain time interval. Final Remarks Some of the activities on harmonizing Japanese major civil engineering structural design codes are introduced in this paper. The authors are hoping this kind of activities are extended to Asian region so that we can cooperate together to develop our own regional codes system to promote construction industries within this region by unifying the market, and strengthen the competitiveness of our construction industry to the outside.
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Development and Implementation of Eurocode 7 Trevor L.L. Orr Trinity College, Dublin University, Dublin, Ireland EXTENDED SUMMARY Eurocode 7 for geotechnical design is one of the set of Eurocodes for structural design using different materials that are about to be implemented in Europe. The Eurocodes are all based on the same limit state design method, set out in Eurocode EN 1990, with partial factors applied to characteristic parameter values. In this paper, the development of Eurocode 7 from the initial work in 1981 to prepare a model limit state code for geotechnical design, through the preparation of the prestandard, ENV version of Eurocode 7, to the publication in 2004 of the of the full European standard, EN 1997-1, Eurocode 7 Geotechnical Design - Part 1: General rules, is outlined. The issues that arose in developing Eurocode 7 as a code that was consistent with EN 1990, took account of the special features of soil and geotechnical design, and was acceptable to the European geotechnical community were: • The scope of Eurocode 7 • The definition of the characteristic value of a geotechnical parameter • The value of the partial factor on permanent loads • The application of partial factors to material parameters or resistances • The treatment of water pressures and forces • The accommodation of national design practices. The nature of these issues and how they were overcome is discussed in this paper. Regarding the scope of Eurocode 7, it was accepted by CEN TC 250, the management committee for the Eurocodes, that the requirements for ground investigations and determining parameters from field and laboratory tests are part of the design process and should be included within the scope of Eurocode 7. The definition of the characteristic value of manufactured structural materials as the 5% fractile of an unlimited series of test results is shown to be not appropriate for geotechnical design. The principal reason for this is because the geotechnical parameter controlling, for example, a failure in the ground, is the mean strength over the failure surface, not the strength of an individual test element. Hence it is the 5% fractile of the mean strength along the failure surface that is required, not the 5% fractile of the test results. Another reason is because, in geotechnical design, only a limited number of test results are normally available and hence statistics need to be used with caution. Eurocode 7 states that the characteristic value "shall be selected as a cautious estimate of the value affecting the occurrence of the limit state". This definition is an important innovation in Eurocode 7 and some guidance on the selection of the characteristic value is provided in the paper. Since the Eurocodes are for structural design, the partial factor chosen for permanent loads in EN 1990 was 1.35. This value caused a problem for Eurocode 7 because in geotechnical designs, for example in slope stability analyses, the permanent actions due to the weight of soil are not normally factored. If they are factored, then illogical situations can arise; for example, in the case of a circular vertical failure surface below horizontal ground, if the unfavourable soil weight, treated as a permanent load, is factored by 1.35 while the favourable soil weight is not factored, then analysis of this situation can predict failure of the horizontal ground when it is not loaded. This is not logical and therefore the Eurocode 7 drafting panel successfully resolved this issue by getting TC 250 to accept a partial factor of unity for permanent actions in geotechnical design when factors greater than unity are applied to the soil strength. In the ENV version of Eurocode 7, partial material factors are applied to the soil strength parameters c', tan<j>' and c„, in the same way as partial material factors are applied to the strength parameters in the other Eurocodes. The partial factors for geotechnical ultimate limit states adopted in the ENV version are the sets of partial factors referred to as Cases A, B and C. However, many geotechnical engineers in Europe were not happy with these three Cases, with partial factors applied to the soil strength parameters. The inclusion of partial factors applied to soil resistances was sought,
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after these had been calculated using unfactored soil parameter values. Hence, in the EN version, three Design Approaches, DAI, DA2 and DA3, were introduced that allow for partial factors to be applied either to soil resistances or to the soil strength parameters. Pressures and forces due to groundwater are treated as permanent actions in Eurocode 7 and hence, in ultimate limit states involving failure in the ground, the appropriate partial factors in Eurocode 7 for permanent actions are applied to water pressures. In the ENV version, the partial factors in Case A are for use in the case of buoyancy ultimate limit states and no specific guidance or partial factors are given for ultimate limit states involving seepage. Hence, when the EN version was being prepared, it as decided to include a new section on hydraulic failure, which includes design rules and partial factors for design against seepage failure as well as buoyancy. Since Eurocode 7 is not a prescriptive codes but a code with the general rules for geotechnical design, providing the principles and only a few calculation rules in informative annexes, and since different national practices have developed in the European countries, reflecting different geologies and soil conditions, TC 250 accepted that the valuable experience embedded in these practices may be accommodated by supplementing Eurocode 7 with non-conflicting national standards. Two examples, a spread foundation with a vertical central load and an embedded retaining wall, are presented to demonstrate the effect of using the different Design Approaches. In the case of these examples, it was found that for low 0' values, DA2 is more conservative than DAI, while for high ' values, it is less conservative, as shown by the foundation widths in Figure 3 below from the paper.
0.5 0 -I 20
1 25
, 30 Friction angle !a?Jjrk!aL
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Full paper in TAIPEI-2006 CD-ROM
3.0 -i
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Figure 1. Normalized hyperbolic curves for ACIP piles: (a) measured, (b) pXix2 = -0.8, (c) pXiX2 = -0.4, and (d) pXix2 = 0. The common assumption of statistical independence can circumvent the additional complexity associated with a translation model, because the bivariate probability distribution reduces to two significantly simpler uni-variate distributions in this special case. However, the scatter in the measured load-displacement curves cannot be properly reproduced by simulation under this assumption as shown in Figure Id. On the other hand, Figure lb looks more realistic because the proper negative correlation is included in the bivariate probability model for "a" and "b". The SLS is defined as that in which the vertical or lateral displacement (y) is equal to the allowable limit (ya) imposed by the structure. The foundation is considered unserviceable if the displacement is greater than the allowable limit. Conversely, the foundation is considered satisfactory if the displacement is less than the allowable limit. These three situations can be described concisely by a performance function: P = y - y a = y(Q)-y« An alternate performance function is: P = Q . - Q = Q.(y.)-Q Figure 2 illustrates the uncertainties associated with these performance functions. In Figure 2a, the applied load Q is assumed to be deterministic to simplify the visualization. It is clear that the displacement follows a distribution even if Q is deterministic because the load-displacement
24
1.6-1
(a)
/! /[ Random allowable M\ . load caused by / \ uncertainty in loadf Jf*** displacement curve
1.6 -
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Figure 2. Serviceability limit state reliability-based design. curve y(Q) is uncertain. The allowable displacement may follow a distribution as well. In Figure 2b, the allowable displacement is assumed to be deterministic. In this alternate version of the performance function, the allowable load Qa follows a distribution even if y„ is deterministic because of the uncertainty in the load-displacement curve. The effect of a random load Q and the possibility of upper tail values falling on the nonlinear portion of the load-displacement curve are illustrated in this figure. The probability of failure (pf) at the serviceability limit state can be computed easily using the first-order reliability method (FORM) once the probabilistic hyperbolic model is established: p f =Prob(Q a . Other parties including professional institutions also produced publications on geotechnical standard. Status of the Publications For public development projects, the prevailing government policy is that the details of all permanent geotechnical works for man-made slopes and retaining walls shall be submitted to the GEO for checking. The policy also stipulates that related activities, including investigations, designs and works, shall be carried out in accordance with the prevailing standards. Some documents, including Manuals, Geoguides, and some other publications, are adopted as local geotechnical standards by the government through administrative means by the issue of Technical Circulars. The standards adopted for public development projects are generally also adopted for private building and civil engineering developments in Hong Kong. This is achieved through the Buildings Ordinance (Law of Hong Kong - Chapter 123) and its related Regulations and Practice Notes. Process of Production The GEO benchmarks against international standards and adapts the standards for local use as appropriate in the course of producing geotechnical guidance documents. New specifications and guidelines are prepared as needed to suit the specific nature of the local geological condition, works practice, and legal and environmental requirements. Stakeholders are always consulted in the setting of geotechnical standards. For Manuals, Geoguides and Geospecs, extensive consultation with consulting engineers, contractors, academics, professional bodies and other government departments are carried out. All comments are duly considered to ensure that the document would be considered a consensus document by interested parties in Hong Kong. Conclusion Numerous geotechnical guidance documents in the form of Manuals, Geoguides, Geospecs and other publications and reports are available in Hong Kong. These documents aim to promote good practice in geotechnical engineering. Some of the guidelines are adopted as the local standards by the Government through Technical Circulars for public development projects. The same standards are generally adopted for private buildings and civil engineering projects through the Buildings Ordinance and its related Regulations and Practice Notes. These standards have been benchmarked against international ones and are adapted to suit local conditions.
36
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Implementation of Eurocode 7-1 Geotechnical Design in Germany N. Vogt Technical University of Munich, Centre for Geotechnical Engineering, Germany B. Schuppener Federal Waterways Engineering and Research Institute, Karlsruhe, Germany
SUMMARY When Eurocode 7: Geotechnical Design, Part 1: General Rules (EC 7-1) is implemented in the European Member States, each state will need to make two important decisions concerning the design of geotechnical structures. Three design approaches are described in the code and each state can select the one that best suits its national design traditions and stipulate its use in geotechnical design. Furthermore, the Member States must establish the values of the partial factors in accordance with national safety requirements. Both, the choice of design approach and the selection of the partial factors, must be seen as a single unit as they are interdependent. The selection of the design approach and the numerical values of the partial factors in Germany was based on the principle that the safety level of the global safety concept that has been used successfully for decades and should be maintained as far as possible. I.e. a geotechnical design in accordance with EC 7-1 should result in more or less the same dimensions as the former global safety concept. A comparative design, in which each of the three Design Approaches in EC 7-1 is applied to a strip footing, is used in the paper to illustrate the option that has been selected for Germany. It shows that the Design Approach DA 2*, in which the partial factors are applied at the end of the calculation when the limit state equation is checked, not only best fits the tried and tested safety level of the former global safety concept but also results in the most economic design. Thanks to the Eurocodes, a single format will be used for the mathematical analysis of the ultimate limit states throughout the construction sector in Europe in future. It has to be verified that the design value of the effects of actions, Ed, never exceeds the design bearing capacity or the design resistances, Rd, i.e.: E d
(1)
In a deterministic analysis, LS < 0 would indicate that building damage will occur. In order to evaluate the model uncertainty and establish an unbiased limit state equation, the probability of damage for a given principal strain must be determined. This probability may be interpreted based on the distributions of the principal strains of the groups of intolerable and tolerable cases using Bayes' Theorem. Using the method developed by Juang et al. (2000), the following mapping function relating EP to PD can be established: P(s \D)P(D) K pl PD = P(D | ejp = ' K ' ' P{£p\D)P(D) + P(Ep\ND)P{ND)
59
(2)
Full paper in TAIPEI-2006 CD-ROM
where P(Z)|Sp) = conditional probability of damage for a given principal strain ep; P(ep\D) = probability of ep given that damage did occur; P(sp\ND) = probability of ep given that damage did not occur; P(D) = prior probability of damage; P(ND) = prior probability of no damage. The primary purpose for developing the Po-ep mapping function is to provide a basis to estimate the probability of damage for a given Ep, which in turn, provides a reference for back-figuring the uncertainty of the limit state model (Equation 2). Subsequently, an unbiased limit state can be established based on the fact that the limit state is unbiased when the mean model uncertainty (jicj) is 1.00. To account for model uncertainty in the limit state equation, a model uncertainty (or bias) factor, c1; is introduced so that the limit state model becomes: LS = A(c,,e pL ) = c,(1.67x 1(T 3 )- EpL = 0
(3)
Using the method developed by et al. (2004), the model bias factor (pcl and COVcj) is calibrated until the probability of damage calculated from the limit state (Equation 3) matches the probability of damage calculated from the Bayesian mapping functions. Based on the calibration with each of the 41 mapping functions (and thus, the results of 41 sets of [icl and COVci values), the mean values and standard deviations of JXCI and COVcl are determined for the initial limit state: fici = 0.71 with apcl = 0.03 and COVci - 0.33 with Bcovci ~ 0. In addition, the effect of the limiting principal strain is examined by redefining the limiting principal strain so that any damage greater than "Very Slight" is considered intolerable (limiting principal strain is equal to 0.75x10"3). With the new limit state, the model uncertainty is recalibrated, and the mean values and standard deviations of /xci and COVci respectively are determined: /xcl = 1.59 with apci = 0.07 and COVcI = 0.33 with Ocovd ~ 0. It should be emphasized that 0.71 x (1.67 x 10"3) for the initial limit state and 1.59x(0.75xl0" 3 )forthe new limit state equate to the same value of 1.19xl0~ 3 . This implies that the limiting principal strain of the unbiased limit state should be equal to 1.19 x 10~3. To more accurately formulate the serviceability limit state, the limiting principal strain is recalibrated using a trial-and-error procedure so that the mean model uncertainty is unbiased ( ficl = 1.00). From this analysis, the limiting principal strain is determined to b e l . l 9 x l 0 ~ 3 , and the mean values and standard deviations of picl and COVc, respectively are determined: fici = 1.00 with apcl = 0.04 and COVct = 0.33 with ocovd ~ 0. The uncertainty of the model bias can be combined and is equated to o c / = 0.37. Therefore, the unbiased serviceability limit state can be expressed as: I S = A ( c , , f p I ) = C l ( 1 . 1 9 x l 0 - 3 ) - e p , i =0
(4)
where the model uncertainty, Ci, is characterized as /xcl =1.00 and cct' =0.37. In summary, using the database collected by Son and Cording, the framework for a probabilistic analysis of excavation-induced building damage has been developed. The Po-ep Bayesian mapping functions have been established based on the distributions of principal strains for the group of intolerable cases and the group of tolerable cases. The mapping functions provide a basis for calibrating the uncertainty of the limit state model. Based on an extensive calibration process, the limiting principal strain has been determined to be i . i 9 x i o - 3 for an unbiased limit state with the model uncertainty, in terms of bias factor, characterized as fici - 1.00 and c c i' = 0.37. Reliability analysis of the excavation-induced building damage potential can be analyzed using the unbiased limit state as expressed in Equation 4.
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Session IV — * * ® « * —
Geohazards
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2—3, 2006, Taipei, Taiwan
The Assessment and Prediction of the Landslides and Debris Flows in Ta-Chia River after Taiwan Chi-Chi Earthquake C.T. Cheng, Y.L. Chang, S.J. Chiou, Y.S. Lin, C.Y. Ku, S.M. Shu, J.C. Chern Sinotech Engineering Consultants, INC., Taiwan S.H. Yu, S.D. Yang, C.F. Wang, C.H. Chiao, L.T. Hwang Taipower Company, Taiwan SUMMARY Ta-Chia river is the one of abundant water resource in central Taiwan, and there are seven branch hydro power plants of TPC (Taipower Company). After Chi-Chi earthquake took place, the follow-up typhoons also caused damages along Ta-Chia river. The disastrous typhoons for TaChia river were Toraji typhoon in 2001, Mindulle typhoon and Aere typhoon in 2004, and Haitang typhoon in 2005, which triggered new landslides and the debris flows were flushed into riverbed, the events caused the river channel silted up and the flood level raised. Those geohazards destroyed most infrastructures and villages nearby the river, especially the hydropower facility. In order to assess the impact of sediment yields from landslides and debris flows and to investigate the strategies of mitigating the geohazards, quantitative assessment was conducted by using aerial photos and satellite images obtained at 6 stages of major earthquake and typhoon events. In order not only to estimate the volume of the sediment yields from landslides and debris flows, but also to establish the relationships between the volumes of sediment yields, the rainfalls intensity, and the discharge. Elevation changes in DTM Figure presents the total elevation changes in the DTMs From Chi-Chi Earthquake to Hi-Tang Typhoon( 1999-2005). The width of the almost whole riverbed became wider and wider through those heavy rainfalls and the width of the shrunk sections were changed slightly. After Mindulle typhoon, maximum elevation change of the riverbed was situated at the front of outlet of ventilation tunnel, the change of elevation was more than 20 m. The most significant changed area is situated at the vicinities of Chingshan switchyard and office.
0
1000 2000 3000 4000 5000 6000 7O00 8000 9000 10000 11O00 12000
Distance from Kukuan Reservoir (m) The elevation changes from Chi-Chi earthquake to Hi-Tang typhoon(1999-2005). New added landslide areas The increased landslide areas of each event, and the summation of the increased landslide areas triggered by difference events is totally 24 million m2. Furthermore, the total area of the increased
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landslides became smaller and smaller, it seems that the geological condition would be more stable in the future. Volume and thickness of landslides The volume of landslide triggered by Chi-Chi earthquake is 5 times the volume of the landslide triggered by whole typhoon events. The average thickness of landslides of each event became smaller and smaller, the thickness was between 1.5-3 m. When the rocks fall down and deposit as taluses, the sliding material would be inflated. If the inflated rate was suggested to be 20%, TaChia main river and its branch river had generated the volume of landslide in 17 million m3 and 32 million m3 (lower bound estimation), respectively. Furthermore, if we suggest the inflated rate to be 33% and consider the error of DTM, Ta-Chia main river and its branch rivers had generated the volume of landslide in 24.3 million m3 and 46.7 million m3, respectively. In conclusion, the total volume of landslides within the watershed between Techi dam and Kukuan dam was approximated from 50 - 70 million m3. Estimate new landslide areas in the future In order to estimate the loss of sediment yields cased by heavy rainfall in each sub-watershed of Ta-Chia river, Uchihugi's empirical model was adopted for predicting the new landslide rate of each sub-watershed. The volume of Landslide will trigger by next heavy rainfall (200 year return period rainfall) are total 6 million m3 in this study region. The results show that new landslide areas of Pi-Ya-Sun river nearby Chingshan office is the largest quantity. Long-term prediction of riverbed erosion and deposition In order to predict the future trend of sediment yields transportation in Ta-Chia river, the computing program HEC-6 was adopted for simulation the situation of that. Actuality, there have no any real data for developing the discharge and the total load relationship for our study. Therefore, The change of landslides after 1923 great Kanto earthquake (Mw7.9) from 1896 to 1980 in Japan caused a lot of landslides and the number of the landslides kept on the high peak more than 15 years. It was took more than 40 years for the number of landslide becoming stable. It was a very good reference for assuming the discharge and the total load relationship after Chi-Chi earthquake, because the landslide area larger the total load would be more larger. In the condition that great earthquake would no more happen in study area, the annual average height of Sediment could decrease with exposure time increasing, and the result after almost 30 years would be flushing in the Ta-Chia main river. Ta-Chia main river Between Chingshan switchyard and Chingshan Office of TPC Chingshan plant will be still deposit in 50 years and 400 m upstream of Kukuan dam will become flushing from deposit after 10 years. After Chi-Chi earthquake, the geologic condition have became more vulnerable, the huge sediment yields would transport to downstream after each heavy rainfall, and landslides and debris flows will also be occurred in the next heavy rainfall. In order to predict the situation of geohazards and to mitigate the geohazards before it happens, the statistics and analysis of the information collected from the monitoring stations are very important to verify the expediency of proposed method. The results show the highest level of riverbed around the Chin-Shan area would raise more than 20 m in addition. Among the branch rivers of Ta-Chia main river, Ji-Ler river and Pi-Ya-Sun river brought the most sediment yields from landslides in the sub-watershed. In conclusion, there are at least 40% of the total sediment yields from landslides still remain in the study area. Therefore, the sediment will transported out in the near future, and monitoring should be conducted continually to mitigate the hazards.
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TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Predicting Landslides Probabilities along Mountain Road in Taiwan Jianye Ching National Taiwan University of Science and Technology, Taipei, Taiwan Hung-Jiun Liao National Taiwan University of Science and Technology, Taipei, Taiwan SUMMARY The total length of roads with elevation above 100m in Taiwan is more than 67,000 km. Some of them were built with high engineering standards, but a large number of them were built with low engineering standards. Therefore, landslides in different failure types are not unusual along mountain roads when the slopes are experiencing long period of rainfalls or torrential rain accompanied with typhoons. In this study, Route T-18 in central Taiwan is chosen to demonstrate the suitability of landslide prediction using Gaussian Process model. Two main questions are of concern: (a) Given the historical landslide data along the demonstrative mountain roads in Taiwan, where are the locations along the roads with high landslide potential in the future? (b) Given the historical landslide and rainfall data, what are the landslide probabilities of the slopes along the roads in a future heavy rainfall? The former mainly concerns with the locations of future landslides, while the latter concerns with the time of landslide occurrence in future rainfalls. Landslides along the mileage between 21.5km and 83.5km of Route T-18 are documented. In total, 55 failed unprotected slopes along T-18 were extracted from the road maintenance records. Among them, 12 slopes failed during Typhoon Herb, 18 during Toraji, 9 during Nari, and 16 during Mindulle due to heavy rainfalls. To match the number of failed slopes, 54 not-failed unprotected slopes were chosen. Note that the not-failed slopes in the database are roughly uniformly distributed over the chosen Route T-18 section. The data format is as follows: D = {(*,-,/,•): i = 1 109}, where Xj£ R15 contains the values of the 15 landslide features of the i-th slope in the database; r,- = 1 if that slope failed, otherwise U = 0; p is the total number of slopes in the database. Fifteen landslide features are categorized into natural features and man-made features. Among them, thirteen are natural features, and two are man-made features. The natural features cover the aspects of topography (4 features: slope direction, slope angle, slope height, and road curvature), geologic conditions (1 feature: outcrop strata age), bedrock structure (2 features: slope and dip direction difference and slope and dip angle difference), weathering & fracturing (2 features: block size and rock volume percentage), vegetation cover (2 features: area percentage of vegetative cover and thickness of canopy cover), drainage condition (1 feature: catchment area size), and seismicity (1 feature: peak ground acceleration). The manmade features (2 features: excavation height and change of slope grade due to toe cutting) quantify the impacts induced by road construction. A single index is used to capture the landslide potential: P(t=lbc,D), i.e. the probability that t = 1 given x and D. The Gaussian Process analysis is implemented to estimate the landslide potential. The discriminant function analysis is also implemented to compare with the Gaussian Process analysis. Common practice of examining the performance of the adopted model/analysis is to quantify the so-called training errors. For fair calculation of prediction errors, the so-called leave-oneout (LOO) prediction errors of the adopted model are adopted here. The LOO prediction error is an unbiased estimate of prediction error on unseen slopes of the trained model. The basic idea of LOO prediction error is to mimic the prediction process by removing one data point out of the training dataset and use the removed data point for prediction testing. Table 1 shows the traditional training error rates and the LOO prediction error rates induced by the Gaussian Process analysis and the discriminant function analysis. Note that both training errors are quite small (one of them is zero), but these are not realistic estimates for the actual prediction errors on
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unseen slopes. The LOO prediction errors, which more realistically reflect the actual prediction error rates, are always larger than the training error rates. It is also clear that the Gaussian Process analysis results in smaller LOO prediction error rates than the discriminant function analysis, indicating that the performance of the former is superior. Table 1 Training errors and LOO prediction errors for the landslide location analysis Methodology Discriminant Function Analysis Gaussian Process Analysis
Training errors 7.3% 0%
# of False LOO Predictions (out of 109) 13 6
LOO Prediction Error Rate 11.9% 5.5%
The analysis shows that slope height, catchment area, height of toe cutting, block size, and change of slope angle are the dominant features, among them are the two man-made features. This result implies that the slope stability along mountain roads is noticeably affected by road construction. Also note that catchment area is among the dominant features. This result is consistent with the sense that slope stability should be sensitive to the amount of seepage and surface water. Besides predicting potential landslide locations, it is desirable to predict "when" (i.e. during which typhoon) the dangerous slopes will fail. In Taiwan, landslides are mostly triggered by heavy rainfalls during typhoons. As a consequence, we propose a second stage of analysis (landslide potential is the first stage) to predict the occurrence times of landslides for the dangerous slopes. In the occurrence time analysis, the size of catchment area and "effective" rainfall amount are the two features studied. The latter is treated as the triggering feature of landslides. The goal is to develop a methodology that determines the relationship between landslide probability and the two features for a dangerous slope given past landslide and rainfall data. This relationship is called the rainfall fragility graph. Figure 1 shows the results of the Gaussian Process analysis and is called the rainfall fragility graph. In the figure, the crosses "+" indicate the failed dangerous slopes in the database (43 data points), while the circles "o" are the not-failed dangerous slopes (33 data points). Note that in the lower-left region, i.e. small rainfall and small catchment area, most slopes did not fail, while most slopes failed in the upper-right region, i.e. large rainfall and large catchment area. This observation agrees with our intuition. The contour values indicate the value of the predicted landslide probability P(t=l\x,D) by the Gaussian Process analysis based on 43 failed dangerous slopes and 33 not-failed dangerous slopes. This rainfall fragility graph can be used to predict landslide probability of a dangerous slope due to future typhoon.
£Bif«w8itflffotf Amnsm* #nro$ +'j'«' \"f^'J1* Figure 1 Rainfall fragility graph for dangerous slopes along Route T-18
66
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2—3, 2006, Taipei, Taiwan
Optimal Design of Sand Compaction Pile Based on Liquefaction Hazard Analysis J.H. Hwang", C.W. Yang2' & C.C. Lu' ; "National Central University, Chung-Li, Taiwan 2> Moh And Associates, Inc., Taipei, Taiwan SUMMARY In this paper, a fully probabilistic method for liquefaction evaluation is first proposed, in which both the uncertainties associated with the earthquake loading and the cyclic strength of soils are considered. Then, a liquefaction hazard model is established for computing the total cost of a building including the probable liquefaction loss during its service life. They are combined to form a decision framework to determine the optimal design solution of ground improvement method. A case of a damaged building in Wufeng, Taichung County that caused by soil liquefaction in the Chi-Chi earthquake was chosen to demonstrate the feasibility of the proposed methodology. The results show that the proposed methodology is workable and provides a logical and reasonable way to design the ground improvement for preventing the liquefaction hazard. Fully Probabilistic Method (FPM) The framework of the proposed FPM contains two calculation loops are implemented to calculate the probability of liquefaction for a soil layer at a site. The inner loop calculates the probability density function (PDF) of liquefaction by using a newly developed reliability model, and the outer loop is to sum the contributions from all potential seismic sources that are capable of producing significant ground motion at the site by Monte Carlo Simulation. For engineering purposes, an index is necessary to be proposed for characterizing the liquefaction severity of the "whole" ground that might consist of several layers of liquefiable soils. In this study, p the liquefaction potential index L defined by Iwasaki et al. (1982) and the post-liquefaction settlement ^ defined by Ishihara and Yoshimine (1992) are adopted to characterize the liquefaction hazard of the whole ground. Strategy of ground improvement The ground improvement method used in the paper is sand compaction pile(SCP). By this way, loose sandy soils can be compacted by squeezing sand columns and vibrating the natural soil around the columns. The design of sand compaction pile is based on the empirical relationship of the replacement ratio of sand piles, the SPT-N value of the subsoil before and after compaction for different fines content. The relationship was established by collecting reliable Japanese case history data of SCP in the past (JSSMFE, 1988). Case Study The proposed liquefaction hazard analysis model is similar to that suggested by Nishimura and Shimizu (2005) with omitting the constant initial construction cost of the structure. The case used for the study is a residential district, named the Prince's Castle, where many buildings were damaged by soil liquefaction during the 1999 Chi-Chi earthquake. The Prince's Castle residential district is in Wufeng, Taichung County and surrounded by the Kehniaokengchi, which is a 5 meters wide creek. The representative geological profile of the site is shown in Table. Based on the proposed fully probabilistic method for analyzing the liquefaction potential, the annual exceedance probability (AEP) of liquefaction potential index PL and post-liquefaction
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settlement S at this site can be calculated. The result of the hazard analysis, shown in Figure, indicated that the probable overall cost due to liquefaction hazard CL is a concave curve of the replacement ratio rs and has a minimum value of 300,000 NT where the corresponding replacement ratio rs =0.115. In the proposed hazard model, the value of rs that minimizes the CL function is defined as the optimal solution rs a, of SCP design. Thus, the optimal solution of the SCP design is rs a, = 0.115 in this case. Table: The geological profile of the Prince's Castle site soil layer No. 1 2 3 4 5
depth (m) 0-3.5 3.5-8.0 8.0-12.5 12.5-14.5 14.5-17.0
unit weight «/m3) 1.90 2.02 2.10 2.15 1.94
SPT-Ar 4 8 23 26 30
FC
(%) 46 25 40 53 32
soil classification SM SM SM ML SM
Ground water table»G.L. -2.5m
0.15
0.1
Replacement Ratio, r, Figure. Optimal analysis of sand compaction pile Conclusion This paper proposes a fully probabilistic method for analyzing liquefaction potential of a ground and a liquefaction hazard model for structures. They are combined to form a decision framework to determine the optimal design solution of ground improvement method. From the case study, the feasibility of the proposed methodology has been demonstrated.
68
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice. Nov. 2-3, 2006, Taipei, Taiwan
Verifications and Physical Interpretations of the Discriminant Model for Evaluating Liquefaction Potential on SPT-N Value S.Y. Lai Harbor and Marine Technology Center, Institute of Transportation, Taichung, Taiwan M.J. Hsieh Harbor and Marine Technology Center, Institute of Transportation, Taichung, Taiwan W.J. Chang Department of Civil Engineering, National Chi Nan University, Nantou, Taiwan P.S. Lin Department of Civil Engineering, National Chung-Hsing University, Taichung, Taiwan SUMMARY Development of statistical models from after-earthquake investigations has been an important subject in geotechnical earthquake engineering. Discriminant method, which is a multivariate statistical method, has been employed to analyze binary data related to multiple parameters. In liquefaction study, discriminant models have been developed to evaluate the liquefaction potential from in situ testing data, such as blow counts in standard penetration test (SPT-N value), cone tip resistance (CPT-qc), and Shear wave velocity (Vs). Discriminant models based on 592 cases of both liquefaction and non-liquefaction occurrences, including 288 cases from the Chi-Chi Earthquake of 1999 in Taiwan, are developed to correlate the cyclic resistance ratios with corrected SPT-N values and fine contents. Discriminant curves of different probabilities of misclassification for cases with fines content less than 10% are shown in Fig. 1. The correlations of cyclic resistance ratios with corrected blow counts (Ni)so for different fine contents are developed based on the occurrence of C(P)=0, in which the probability of misclassification is equal for both liquefaction and non-liquefaction situations. Models for 10%= FC= 20%, 20%= FC= 30%, and 30%= FCS 40% can be referred in Lai et al (2005). The evaluation models for cases with various fine contents are summarized and illustrated in Fig. 2. The curves in Fig. 2 are further simplified by regression analyses and expressed as: CISR7J=exp(A-V(N1)60-fl)
(1)
where 4 = 0.3865548+0.0072398 FC , fl = -(3.3597395 + 0.0186297FC-0.0001093FC 2 ) and the square of the correlation coefficient (R2) is 0.99. Equation (1) provides a simple way to calculate the cyclic resistance ratio using SPT data and can be easily implemented in computer code. And the factor of safety against liquefaction (F s ) can be computed by: FS=CRR1$ICSR15 (2) where CSR7.5 represents the cyclic stress ratio induced by a earthquake. The Fig. 2 shows that the liquefaction resistance CRR75 increases with an increase in fines content for the same (Ni)6o, which agrees with the liquefaction phenomena observed in the field. Moreover, the liquefaction resistance of different soils for (N!)60= 5 is almost the same. To support the discriminant model, physical meanings of the generated discriminant curves are discussed in view of the soil mechanics and the physical mechanism of liquefaction. Probability examinations are performed on both parameters to determine statistically satisfied explanatory variables. The cyclic disturbance of a soil induced by an earthquake is proportional to the logarithm of CSR1S instead of CSRTS.The logarithmic transform of the induced cyclic stress ratio is consistent with the definition of seismic intensity, which is linearly proportional to the
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logarithmic transform of the maximum ground acceleration amplitude ( ln(a m „) ) of a site. Analyses that correlate the properly transformed CRR7.5 and ( N ^ o are shown in Fig. 3. The results reveal that the logarithm of liquefaction resistance ln(CRR15) of a soil is proportional to JlNja instead of (#,)«, , implying that the logarithm of liquefaction resistance of a soil is proportional to the relative density Dr. It is consistent with previous laboratory results. The developed model is implemented to map the liquefaction potential of Taichung harbour for Chi Chi earthquake event and the results are shown in Fig. 4. The map shows that the most severe liquefied area occurred between the North Terminal and the North Pier, where the black area located. The mediate liquefied areas are located in the West Terminal and the South Terminal. The results are compatible with the damage condition at Taichung harbour during Chi-Chi earthquake. REFERENCES Lai, S.Y., Lin, P.S., Hsieh, M.J., and Jim, H.F. (2005), " Regression Model for Evaluating Liquefaction Potential by Discriminant Analysis of the SPT N value." Canadian Geotechnical Journal. Vol. 42, No. 3, p.856-875.
V*0X
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'15 % 0.3
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ju^yXy4C4.
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Discriminant curves with 0%£ FCs 10%
)
Fig.3 Physical meanings of the developed models
0.6 pc=m
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5 10 15 20 25 30 35 40 45 50 Conected Blow Count, (Ni)u
Fig. 2 Comparison of discriminant curves with fines content of 5%, 15%, 25% and 35% for C(P)=0
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Fig. 4 The result of liquefaction potential evaluation by Discriminant's model at Taichung Harbor area
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2—3, 2006, Taipei, Taiwan
Seismic Performance-Based Design for Canal Embankment Y. OTAKE, T. HARA & T. HORIKAWA CTl Engineering Co., Ltd., Japan Y. ITO, T. KATO, M. HOSOYAMADA & Y. KASAI Japan Water Agency, Japan SUMMARY Development of reasonable seismic verification and design of the countermeasure for existing structures, such as buildings, bridges, dams and etc., is an important issue in Japan because the occurrence of big earthquakes in the near future has been predicted. A type of canal, which is built on embankment, Figure 1 shows typical transverse section of the canal, is also one of the structures required the reasonable seismic treatment from the viewpoints as follows; there are many canals of such type in Japan considerable effects of the canal damage during the earthquake on human life and social economy are concerned expensive seismic countermeasures will be needed for almost all the canal if they are verified with respect to the present seismic design specification, satisfying safety factor, 1.0, of land slide analysis, thus tremendous amounts of money and time will be required for the project Therefore, a study on the proposal of quantitative seismic performance based design for the canal as a reasonable treatment of the issue has been conducted. In this paper, contents of the proposed seismic performance based design code, seismic performance, limit states, quantitative criteria for verification, and prediction methods of seismic response of the canal embankment, are introduced.
Figure 1 Typical transverse section of canals built on embankment Study on the proposal of quantitative seismic performance based design for the canal In order to verify the canal embankment quantitatively to satisfy seismic performance of the canal, both quantitative criteria for verification and prediction method of seismic response of the embankment have to be stipulated along with seismic performance and its corresponding limit states. Therefore, firstly, seismic performance, limit states and criteria for verification of the canal embankment are newly proposed from the viewpoints of soil strain for safety and reparability of the embankment, and subsidence of top of the embankment for serviceability of the canal. And then, the prediction method that can reproduce well actual seismic response of embankments was proposed from the comparison with centrifuge tests. Furthermore, because simple prediction method is valuable for practical design, applicability of several prediction methods, which are the method using static elastic FEM, the method based on Newmark proposed method (N.M. Newmark, 1965) and more simple methods adopting charts or equations as well as dynamic elasto-plastic FEM analysis, are studied. Procedure of seismic verification of canal embankments and design of the countermeasure Figure 2 shows concrete procedure of seismic verification of canal embankments and design of the
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countermeasures based on the performance criteria and the prediction methods proposed in this study. It has been expected that large amount of canal embankments would be able to be verified and treated reasonably with respect to big earthquakes, which has been predicted to occur in the near future, by the procedure of verification and design method. 1 st verification of embankments / " ' by using simple chart or equation 2nd verification of embankments ' " and design of countermeasure j Prediction of by using simple prediction method (
"\
3£ behavior
3rd verification of embankments and design of countermeasure by using more detailed analysis such as UWLC
[Design of seismic]/ [ countermeasure y
Figure 2 Procedure of seismic verification and design of the countermeasure for canal embankment
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Session V Engineering Practice and Challenges
TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Observational Design Approaches for Safe and Economical Deep Basement Construction in the Urban Environment I. Askew Lambeth Associates, Hong Kong J.A. Frame Gammon Construction, Hong Kong D. Sein Lambeth Associates, Hong Kong SUMMARY This paper presents the author's experiences of applying Observational Design (OD) approaches to substructure design and construction in the South East Asia. To illustrate the potential benefits that can be achieved, a case history is described for a deep basement excavation in Singapore. The design objectives, methodology and performance data are presented. There is an ever-growing push to gain further economies in the construction industry. Construction projects, particularly in congested urban areas, are becoming increasingly complex but with shorter expected construction periods. At the same time regulators and the public are increasingly intolerant to any form of risk. The OD approach can provide a means by which construction safety and efficiency are improved for deep excavations in the urban environment. Modern instrumentation has become more accurate and reliable and can provide real time automated monitoring which directly benefits the processes in OD. Instrumentation data loggers can remotely connect to Internet based instrumentation databases, which makes data accessible and transparent to all stakeholders in a project. The construction industry is also undergoing change in the way contracts are procured, which has lead to greater interest in OD. Design and build contracts and greater emphasis on partnering amongst stakeholders has made OD more viable compared to the adversarial nature of historical construction contracts. The excavation at a site in Singapore Central Business District involved a 20m deep basement structure. The base design required 5 layers of struts and imposed constraints on the phasing of the construction of the pile caps. Objectives of the OD were to delete the lowest level of struts and avoid the phasing constraints. The OD design approach involved a series of sensitivity analyses covering a range of design parameters so that the predicted behaviour could be benchmarked against the measured performance on site. The range of design parameters covered "most probable soil parameters" and "original design soil parameters". A monitoring control framework was developed to track the predicted against measured wall deflections during basement excavation. A "traffic light" system was implemented which reflected the status of the wall deflections at different excavation depths (green as below predicted response, amber as alert and red as action). A similar traffic light system was used in the control framework for the strut loads. Decisions to proceed with deletion of struts or implement contingency measures were made at predefined stages of the excavation based on the monitoring records. A decision flowchart was included on the construction drawings to clearly identify the key decisions. All of the stated objectives of the OD were achieved on the project resulting in safety, cost and programme benefits. Site safety benefits included reduced handling of heavy steel struts and providing more working space for manoeuvring excavation equipment. Valuable information on the importance of temperature on strut forces was also obtained. There was a daily fluctuation in strut force of about 25% recorded.
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There are a number of critical success factors. A design-and-construct project procurement approach, in which the designer and contractor are fully integrated, is best suited for OD. "Traditional" engineer designed and tendered contracts will be difficult to evaluate and administer effectively since there will be potentially a number of different outcomes depending upon the field monitoring results and speed of decision making. There must also be a clear decision framework at the outset that has been agreed by all of the stakeholders. The regulatory framework must be sufficiently flexible to allow a design approach leading to a number of potential work sequences and outcomes rather than a single design solution. The decision framework must be clearly stated on the construction drawings. Designers must have adequate experience and resources to be able to track measured field behaviour closely, report regularly, recognise anomalies and act on them if necessary. In the contractual relationship between the contractor and designer, there needs to be an acceptance on the part of the contractor that design spend will continue for the duration of the works covered by the OD in addition to costs for specific design deliverables. There must be adequate instrumentation in terms of quantum and reliability. Critical observations should be made in "real time" with all data fed into a GEOMON system or similar. It is imperative that the database is transparent and readily accessible to all stakeholders to alleviate possible concerns on manipulation of the monitoring records. Stakeholders with a partnering mindset are important. An adversarial environment without openness will not lend itself to the successful implementation of OD. There needs to be effective communication between all of the parties. In particular, the construction team must communicate timely, detailed information on the works progress to the designer to allow field observations to be evaluated. The wider application of OD approaches will improve understanding and generally result in more efficient design solutions for substructure construction provided all the necessary steps are taken. Whilst Regulators are currently exploring possibilities of general use of OD, more needs to be done to ensure robust practical frameworks are put in place to ensure maximum benefit can be obtained from OD without any compromise in safety. In addition to potential direct benefits in cost and time from OD, there may also be safety benefits from reducing the quantity of support members that need to be handled and increasing working space. Experience also suggests that because of the high level of interaction between the design and site teams general communication improves and construction issues are more readily resolved. Whilst our experience, particularly in Singapore, shows that significant cost and time benefits can be achieved as a result of applying the OD approach, it must be emphasised that OD requires the implementation of strict review and risk management processes.
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TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
The Performance of Laterally Loaded Single Pile in Reclaimed Land C.S. Chen SSP Geotechnics Sdn Bhd, Kuala Lumpur, Malaysia SUMMARY Piles are normally designed to resist axial compression and uplift forces for most of the building foundations. However, for deep foundations of structures such as towers, bridge abutments, jetties, mooring dolphins, high-rises etc, the piles are often subject to significant lateral loads in addition to the axial loads. The induced lateral deflection and bending moment not only will affect the design pile capacity but also the performance of the structure. The ultimate lateral resistance of pile depends very much on the subsoil surrounding the pile. It can be evaluated using approximate solution as proposed by Broms (1965). Extensive researches on the deformation of a single pile subject to lateral load had also been carried out and some analytical techniques have been developed too. In general, the analytical model can be grouped into two main categories: the Elastic Continuum model and the Spring Idealisation soil model (Winkler soil model or p - y curve method). Both models had been used extensively today for the prediction of pile deformation when subject to lateral load. A recent development on a tidal land required pile foundation not only to resist axial load but also to resist lateral load. The site originally was submersed at most of the time and the ground surface level was at about 0.75 mLSD (Land Survey Datum). Reclamation had been carried out by using hydraulic sandfill. The design platform level for the proposed development is about 4 mLSD. Due o the thick soft clay, long term post construction settlement was expected. In order to expedite the minimise the post construction consolidation settlement of the soft marine clay, surcharge method with the installation of prefabricated vertical drains had been adopted and more than 90% consolidation has been completed at the time of pile tests. Soil investigation carried out at the test piles locations revealed that the subsoil composed of 7.5m thick of sand below the design platform level. Underlying is the treated soft clay with thickness of about 18m. Liquid Limit and Plasticity Index of the soft clay vary from 80% to 120% and 40% to 80% respectively. A thin layer of loose silty sand was found below the treated soft clay layer follow by medium stiff to hard soil layer. In order to evaluate the pile performance when loaded laterally, in-situ full-scale lateral load tests were planned and conducted on two single piles. Test pile LTP-1 is a 600 mm diameter prestressed concrete spun pile with thickness of 100 mm. The concrete strength is about 78.5 MPa. The pile was installed using hydraulic hammer from the design platform level of 4 mLSD. The penetration depth is about 30 m, i.e pile toe level at -26 mLSD. Inclinometer of 70 mm outer diameter was installed into the spun pile and grouted. Test pile LTP-2 is a 750mm diameter castin-situ bored pile. The pile was constructed from the design platform level to 34m depth, i.e. pile toe at about -30 mLSD. After the boring depth had reached to the design depth, a steel cage consisted of 10 numbers of high yield strength steel reinforcement of 32mm diameter was installed. A steel pipe of 150mm diameter was welded to the steel cage for the installation of inclinometer in later stage. The concrete strength is 30 MPa and it was placed by tremie pipe method. Inclinometer with outer diameter of 70mm was installed into the pre-installed 150mm diameter steel pipe. The annular space between the steel pipe and the inclinometer was filled with cement grout. For both test piles, about 2m excavation was carried out for the setting up of the test. The applied load was at the level of about 2 mLSD. Reaction piles with similar diameter to the test piles were adopted as the reaction system. The test load apply to the test pile was using a hydraulic jack together with a load cell. The pile head deformation was measured by dial gauges or transducers. In addition to the dial gauges or transducers, inclinometer was installed in the test pile to measure the pile deflection at different depths.
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Test Pile LTP-1 was loaded to 225 kN and the measured pile deflection at the ground surface (at level of 2 mLSD) was about 39mm. LTP-2 was loaded to 400 kN and the pile head deflection was about 61mm. Preliminary analysis had been carried out prior to the lateral pile load tests for the prediction of the pile head deformation. The assessment methods were based on the guidance from NAVFAC DM-7.2 and using commercial available computer software. Differences between the estimated and measured results are expected. Nevertheless, for preliminary assessment purpose, guidance from some of the Standards or using computer software is still very useful. Lateral pile load test may be carried out later to verify the assumptions and to refine the analysis. In addition to the pile head deflection, the measured results on the deformation of pile at various depths indicate that the pile deformations are confined to the upper part of the piles only. Based on the results of the two tests, the deformations are confined within 6 to 7 pile diameters from the ground surface.
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TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Settlement Calculation of Large-Area Thick Raft Foundation under Irregular High-Rise Buildings J.F. Gong, X.L. Huang & D.H. Di China Academy of Building Research, Beijing, China SUMMARY With the development and utilization of the underground space, large-area frame structure with thick raft foundation under a single or multiple high-rise buildings is widely used in China. Settlement calculation method for large-area thick raft foundation under regular high-rise buildings has been already proved feasible and reasonable in studies and in-situ settlement monitoring in recent years. In fact, with the variety and complexity of high-rise buildings, largearea frame structure with thick raft foundation under irregular multi-tall buildings is increasing, for this foundation form, existing approach cannot accurately calculate the settlement of the whole range of the raft. To solve the above-mentioned problem, based on the mechanical concept of large-area thick raft foundation, a deformation analysis method is developed in this work, which can be employed in the settlement calculation of large-area thick raft foundation with irregular multi-tall buildings, and it has been successfully applied in the projects of China Petroleum Mansion and Beijing HengFu Garden Mansion. Design Principle for Large-Area Thick Raft Foundation The large scale model test proves that the rigidity of frame structure with large-area thick raft foundation as approximately equal to the rigidity of box foundation. Tests show that the dispersion through the thick raft foundation for the tall building load is limited to a certain extent under service ability limit state. When the ratio of thickness to span of the raft h/L > 1/6, if the soil is uniform, rigidity of superstructure is good, load distribution is comparatively uniform, for highrise building at the circumference connecting one-span podium symmetry, the contact pressure of foundation distributes linearly, raft design can only consider local flexure and its distribution rule of the internal force is as same as that of the global analysis method (with the consideration of superstructure). When the circumference of high-rise building exceeds one-span podium, the contact pressure under high-rise building still distributes linearly, and the value of contact pressure under high-rise building can be calculated on average with the area of further adding one span, The raft design of high-rise building may only consider local flexure and the raft design of podium needs to consider total flexure. The basic mechanical characteristics of large-area thick raft foundation require the following considerations for design: In case many high-rise and low-rise buildings are built on the same large-area integral thick raft foundation, by taking each building as the centre, and the raft thickness within the one and half span from the side of the tall building remains unchanged. When the deflection of the raft meets the requirements, and the variable-thickness raft design is needed, the raft thickness change points shall be within the second span from the side of the tall building and the gradating way is adopted for transition. If the difference in settlement between tower and the podium attached is not acceptable and it is necessary for delay poured strip, it should be within the second span next to the tower, and the raft of the podium linked with high-rise building should be as thick as that of the tower. The settlement of large-area thick raft foundation with multi-tall buildings can be calculated based on superimposition method. Calculation method of settlement for irregular multi-tall buildings Based on the mechanical characteristic of large-area thick raft foundation and deformation controlling principle of foundation designing, under serviceability limit state, settlement
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calculating method for large-area thick raft foundation under irregular high-rise buildings can be drawn as follows: Basic assumptions: The raft is limited, its deformation is irregular and continuous; Foundation is unlimited, and its deformation is continuous and elastic; Load transferred through the raft is limited. Applicable conditions: The soil is uniform, rigidity of superstructure is good, and load distribution is comparatively uniform. The ratio of thickness to span of the raft h/L>l/6. The ratio of length to height of tower is not more than 1.5. Rectangular cutting and superimposition method: According to structural characteristic, each irregular high-rise building is divided into several rectangle parts on the projected plan of superstructure. The settlement of divided portions of tower is calculated on elastic theory respectively, and then superimposition method is used for the settlement of high-rise building. Under serviceability limit state, the settlement of large-area thick raft foundation under multiple irregular high-rise buildings can be calculated by superimposition method based on the settlement of large-area thick raft foundation under each irregular high-rise building. Practical application Optimized designs using the aforementioned method for the large-area thick raft foundation of China Petroleum Mansion, which is of four high-rise buildings of L-shape, and Beijing HengFu Garden Mansion, which is of single high-rise building of Z-shape, have been carried out, and insitu settlement monitoring has been made during the construction stage. In comparison with theoretical calculation, measured settlements agree well with numerical results. From engineering applications, it is demonstrated that thick raft are capable to effectively spread the intensive highrise loading outwards to podium area, as a result to adjust the differential settlement in between. In comparison with flexible raft/plate, rigid thick raft can significantly reduce the unacceptable differential settlement occurred normally at the location of 1 to 2 span outside tower perimeter. The concept of adopting thick raft to replace the conventional delay poured strip is proved to be feasible and practical. Conclusion Under the interactions of superstructures, raft and foundation soil, the measured deformation of entire raft is irregular and continuous, the rigidity of raft foundation is limited, and the raft foundation under high-rise building is still limited rigidity. Based on the 'rectangular cutting and superimposition' method, the settlement of irregular high-rise building can be calculated by elastic theory. The settlement of large-area thick raft foundation under multiple irregular high-rise buildings can be calculated based on elastic theory and superimposition method under serviceability limit state. It is necessary to extend the thick raft of irregular high-rise building outside one-span podium to decrease the additional stress under the foundation of high-rise building, and to increase the foundation's stability of irregular high-rise building.
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TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
Geotechnical Risk Assessment and Performance-Based Evaluation of a Deep Excavation in the Kaohsiung MRT System Project B. C. Benson Hsiung National Kaohsiung University of Applied Sciences, Kaohsiung City, Taiwan H. Y. Chuay Mott MacDonald Ltd, Kaohsiung City, Taiwan SUMMARY Kaohsiung is the largest city in southern Taiwan as well as the economic and political centre. To fulfil the need of fast development of the city, the construction has started since 2000 for the Phase 1 of Kaohsiung mass rapid transit system. The system is expected to be in full operation from 2007. There are two lines in Phase 1, Red Line in N-S direction and Orange Line in E-W direction. A risk assessment was carried out in the design stage for the deep excavation of a cofferdam without any lateral strutting system, 140 m in diameter and 27 m deep, in silty sand, in order to ensure the construction safety and programme of the only interchange station in the Red & Orange lines of Kaohsiung mass rapid transit system (KMRTS). The main risks associated with this type of excavation are unbalanced ground water pressure and soil pressure outside the cofferdam before the completion of the concrete structure, which are critical to the development of the arching effect. A risk assessment was carried out for the excavation at O5/R10 station and it identifies that possible risks during the cofferdam excavation include: (1) excavation error, (2) over/underdigging, (3) collapse of trench wall, (4) design load on ground level, (5) ground conditions, (6) groundwater level, (7) direction and velocity of groundwater, (8) temperature, (9) earthquake, (10) structure buckling, (11) field measurement, (12) water pumping and draw-down of groundwater, (13) uplift failure and (14) leakage of diaphragm wall. After the identification of hazards, a performance-based evaluation of the excavation is considered. Based on the field measurements, a deflection path of O5/R10 was made and also be compared with reference envelope determined from excavations having different ground conditions and wall thicknesses in Taipei. It was found that the ratio of maximum lateral wall movement (5hmax) to the excavation depth (D) varies from 0.07% to 0.27% at O5/R10 and this ratio is much smaller for excavations in Taipei with D greater than 4m. This might be connected with a thicker wall, different ground conditions and excavation shape at O5/R10. The observational method was considered to be applied in the project. In the observation method, the design is reviewed from time to time during the construction in response to the monitored performance of the structure. It was suggested that the observation method should be taken for a project where a precise prediction of the geotechnical behaviour is difficult. The management of geotechnical works at O5/R10 is reviewed and it was recommended that the advantage and flexibility associated with a turnkey contract should be properly considered in geotechnical works. In addition, having one consultant to carry out independent checking services might reduce the risk in geotechnical design successfully. The efficiency of using circular cofferdam excavation is explored in this study. It was found that the use of circular cofferdam excavation could dramatically reduce the construction cost, even though it increased design complexity.
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Further, a two-dimensional analysis was carried out for the excavation at O5/R10 using computer software PLAXIS. Two sets of soil stiffness were used here: one is determined based on an empirical estimation of SPT-N values; the other is defined by the shear wave velocity of soils measured from the site. It indicated that the analysis using soil stiffness interpreted from shear wave velocity measured in the ground could have closer results with field observations. At the end, it was recommended that partial factors should be applied to actions, soil parameters and resistances and a sensitivity study can be conducted by the use of numerical simulation in this paper to explore influences from the partial factor.
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TAIPEI2006 International Symposium on New Generation Design Codes for Geotechnical Engineering Practice Nov. 2-3, 2006, Taipei, Taiwan
An Essay on Typification of Verification Methods Used in the Design Procedure of Geotechnical Structures S. Kobayashi Kyoto University, Kyoto, Japan K. Aita Sato Kogyo Co., Ltd., Tokyo, Japan T. Fujiyama Central Research Institute of Electric Power Industry, Abiko, Japan M. Honda Nikken Sekkei Civil Engineering Ltd., Tokyo, Japan T. Kaneko Fukken Co., Ltd., Hiroshima, Japan A. Morikage Chubu Chishitsu Co., Ltd., Kanazawa, Japan A. Murakami Okayama University, Okayama, Japan M. Nabetani Sato Kogyo Co., Ltd., Tokyo, Japan M. Nozu Fudo Construction Co., Ltd., Tokyo, Japan SUMMARY Technical committee on the performance-based design for geotechnical structures in Japan Society of Civil Engineers was founded in 2004 and has actively exchanged the ideas among the administrators, practitioners and academia. Working group 2 (WG2) of this committee has collected and investigated many verification methods used for previous practices to establish a new methodology of verification methods in the context of the performance-based design. We should notice that the preciseness of calculated results depends on not only a verification method itself but also other data qualities such as boundary conditions, initial conditions and modeled geometrical configurations. We discuss on the potential abilities of each verification methods with the unified framework. However, a verification method itself is only one factor to a solution. As a nature of a geotechnical problem is that of an initial boundary value problem, we can point out three major factors of a problem. One factor is expressed as a term " material" which includes a constitutive model and its material parameters. Another factor is expressed as a term "ground profile" including the constitution of soil strata and initial conditions of ground. External forces such as seismic motions, wind forces and tidal forces are also included in ground profile. The other factor is expressed as a term "solver" which describes how to formulate and solve a problem. In a performance-based design procedure, choice of verification method is one of the key issues for the reliability of an obtained result. From the view point of cognitive science, three typical behavior can be observed as pointed out by Rasmussen (1986) shown in figure 1.; i.e., skill-based behavior (SBB), rule-based behavior (RBB) and knowledge-based behavior (KBB). This model is convenient for our research purpose to consider qualitative classification of verification method. By
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combining three major factors and Rasmussen's model, we derive a matrix expression of qualitative levels in the verification. A desirable choice for the quality / cost ratio is that these three factors are suitably balanced in the similar level. Possible errors which will occur in the verification are also discussed based on the cognitive engineering. The obtained results in this paper indicate an important view point for the establishment of regulations and implementation of technical matters in a social system. Goal
Knowledeg-based level
Rule-based level
Skill-based level
Figure 1. Operator's three behavior modes by Rasmussen (Yoshikawa, 2003)
Ground profile
Frequency
Importance of structure
Knowledge base
rare
very high
Rule base
few
high
Skill base
lot
low
Material
Solver
Figure 2. Matrix expression of three levels of modes and three factors in geotechnical design
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Session VI —\. Please note that in the process of MCS, samples distributed asf{(p\F) snAfij^F0) can be obtained (F° denotes the non-failure event): Corresponding to the N sample sets {Z*' : /' = I...N) are the JV samples of the monitoring value {#>*' : i = 1.. .JV }. Assuming that among the N samples, there are NF failure samples, i.e. samples satisfying J?[Z"]>1, so the corresponding