1st Edition
Reliability of Geotechnical Structures in ISO2394
The latest 4th edition of the international standard on the principles of reliability for load bearing structures (ISO2394:2015) includes a new Annex D dedicated to the reliability of geotechnical structures. The emphasis in Annex D is to identify and characterize critical elements of the geotechnical reliability-based design process. This book contains a wealth of data and information to assist geotechnical engineers with the implementation of semi-probabilistic or full probabilistic design approaches within the context of established geotechnical knowledge, principles, and experience.
The introduction to the book presents an overview on how reliability can play a complementary role within prevailing norms in geotechnical practice to address situations where some measured data and/or past experience exist for limited site-specifi c data to be supplemented by both objective regional data and subjective judgment derived from comparable sites elsewhere. The principles of reliability as presented in ISO2394:2015 provides the common basis for harmonization of structural and geotechnical design. The balance of the chapters describes the uncertainty representation of geotechnical design parameters, the statistical characterization of multivariate geotechnical data and model factors, semi-probabilistic and direct probability-based design methods in accordance to the outline of Annex D.
This book elaborates and reinforces the goal of Annex D to advance geotechnical reliability-based design with geotechnical needs at the forefront while complying with the general principles of reliability given by ISO2394:2015. It serves as a supplementary reference to Annex D and it is a must-read for designing geotechnical structures in compliance with ISO2394:2015.
Reliability as a basis for geotechnical design
Kok-Kwang Phoon
1.1 Introduction
1.2 Evolution of structural and geotechnical design
1.3 Role of engineering judgment
1.4 Reliability versus geotechnical requirements of a safety format
1.5 Some reliability applications
1.5.1 Multivariate soil databases
1.5.2 Geotechnical information: Is it an “investment’’or a “cost’’?
1.5.3 Model uncertainties
1.5.4 Scarcity of geotechnical data
1.5.5 Probability distributions that accommodate a “worst credible’’ value at a prescribed quantile
1.5.6 Spatial variability
1.5.7 Design point from the first-order reliability method (FORM) and partial factors
1.5.8 System reliability
1.6 Concluding thoughts
2 General principles on reliability according to ISO2394
Johan V. Retief, Mahongo Dithinde, and Kok-Kwang Phoon
2.1 Introduction: Background to the development of ISO2394:2015
2.1.1 Stages of development of ISO2394
2.1.2 Status and use of ISO2394
2.1.3 Objectives and fundamental principles
2.2 Overview of the standard ISO2394:2015
2.3 Conceptual basis and fundamental requirements
2.4 Key reliability concepts
2.5 Concluding summary of ISO2394:2015
3 Uncertainty representation of geotechnical design parameters
Kok-Kwang Phoon, Widjojo A. Prakoso, Yu Wang, and Jianye Ching
3.1 Introduction
3.2 Sources of uncertainties
3.3 Natural variability
3.4 Measurement error
3.5 Transformation uncertainty
3.6 Scale of fluctuation
3.7 Intact rock and rock mass
3.7.1 Natural variability of intact rock
3.7.2 Intact rock measurement error
3.7.3 Intact rock scale of fluctuation
3.7.4 Rock mass natural variability
3.7.5 Rock mass transformation uncertainty
3.8 Statistical uncertainty for site-specific natural variability
3.8.1 Statistical uncertainty in site-specific trend
3.8.2 Statistical uncertainty of site-specific COV and SOF
3.9 Bayesian quantification of site-specific natural variability
3.10 Selection of site-specific transformation model
3.11 Conclusions and future work
4 Statistical characterization of multivariate geotechnical data
Jianye Ching, Dian-Qing Li, and Kok-Kwang Phoon
4.1 Introduction
4.2 Correlation
4.3 Multivariate normal probability distribution function
4.4 Multivariate normal distributions constructed with genuine multivariate data
4.4.1 CLAY/5/345
4.4.2 CLAY/6/535
4.5 Multivariate normal distributions constructed with bivariate data
4.5.1 CLAY/7/6310
4.5.2 CLAY/10/7490
4.6 Multivariate normal distributions constructed with incomplete bivariate data
4.6.1 CLAY/4/BN
4.6.2 SAND/4/BN
4.7 Multivariate distributions constructed with the copula theory
4.7.1 Copula theory
4.7.2 Elliptical copulas (Gaussian and t copulas)
4.7.3 Kendall rank correlation
4.7.4 Estimating C using Pearson and Kendall correlations
4.7.5 Comparison between the Gaussian and t copulas
4.8 Conclusions
5 Statistical characterization of model uncertainty
Mahongo Dithinde, Kok-Kwang Phoon, Jianye Ching, Limin Zhang, and Johan V. Retief
5.1 Introduction
5.2 Exploratory data analysis
5.3 Detection of data outliers
5.3.1 Sample z-score method
5.3.2 Box plot method
5.3.3 Scatter plot method
5.4 Probabilistic model for M
5.5 Verification of randomness of the model factor
5.5.1 Removal of statistical dependencies
5.5.1.1 Generalised model factor approach
5.5.1.2 Verification of removal of systematic dependency
5.5.2 Model factor as a function of input parameters
5.6 Available model factor statistics
5.6.1 Laterally loaded rigid bored piles (ultimate limit state)
5.6.2 Axially loaded piles (ultimate limit state)
5.6.3 Shallow foundations (ultimate limit state)
5.6.4 Axially loaded pile foundations (serviceability limit state)
5.6.5 Limiting tolerable displacement (serviceability limit state)
5.6.6 Factor of safety of a slope calculated by limit equilibrium method
5.6.7 Base heave for excavation in clays
5.7 Conclusions
6 Semi-probabilistic reliability-based design
Kok-Kwang Phoon and Jianye Ching
6.1 Introduction
6.2 Survey of calibration methods
6.2.1 Basic Load Resistance Factor Design (LRFD)
6.2.2 Extended LRFD and Multiple Resistance and Load Factor Design (MRFD)
6.2.3 Robust LRFD (R-LRFD)
6.2.4 LRFD for total settlement
6.2.5 LRFD for differential settlement
6.2.6 First-order Reliability Method (FORM)
6.2.7 Baseline technique
6.2.8 Degree of understanding
6.3 Issue of variable coefficient of variation
6.3.1 Partial factors for the calibration case
6.3.2 Actual reliability index for the validation case
6.4 Issue of variable soil profiles
6.5 Quantile Value Method (QVM)
6.5.1 Robustness of QVM against variable COV
6.5.2 Pad foundation supported on boulder clay
6.6 Effective random dimension
6.6.1 Gravity retaining wall
6.7 Conclusions
7 Direct probability-based design methods
Yu Wang, Timo Schweckendiek, Wenping Gong, Tengyuan Zhao, and Kok-Kwang Phoon
7.1 Introduction
7.2 Situations of direct probability-based design methods being necessary
7.3 Expanded reliability-based design (expanded RBD) method
7.4 Reliability-based robust geotechnical design (RGD)
7.5 The new safety standards for flood defenses in the Netherlands
7.6 System reliability
7.7 Reliability target
7.8 Gravity retaining wall design example
7.9 Concluding remarks and future work
Biography
Kok-Kwang Phoon is Distinguished Professor in the Department of Civil and Environmental Engineering, National University of Singapore (NUS). He is a Professional Engineer in Singapore and past President of the Geotechnical Society of Singapore. His main research interests include statistical characterization of geotechnical parameters and reliability-based design in geotechnical engineering. He is the recipient of numerous research awards, including the ASCE Norman Medal in 2005 and the NUS Outstanding Researcher Award in 2010. He is the Founding Editor of Georisk and Chair of TC304 (Engineering Practice of Risk Assessment and Management) in the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). He was former Chair of ASCE Geo-Institute Risk Assessment and Management Committee. He is Fellow of ASCE and Fellow of the Academy of Engineering Singapore.
Johan V. Retief is Emeritus Professor in the Department of Civil Engineering, Stellenbosch University, South Africa. He was awarded DSc(Eng) and DEng degrees from Pretoria and Stellenbosch Universities and graduate degrees from Imperial College and Stanford University. His fields of interest are the development of risk and reliability to design standards as the basis of design, with applications to wind loading, structural concrete and geotechnical practice, amongst other related topics. As member of ISO TC98 he has been a member of the management group for ISO2394:2015 and is presently Convenor for the revision of the related ISO22111. He is a member of the SA Bureau of Standards TC98 on design standards, a fellow of SAICE and moderator of its journal and received the 2014 Jennings award for a geotechnical paper with Dr Dithinde.
"From a geotechnical perspective, the key departure of the current ISO2394:2015 from previous versions is the introduction of a new informative Annex D on “Reliability of Geotechnical Structures [...] The book unlocks the general principles of reliability as presented in this 4th edition of ISO 2394 for extended application in geotechnical practice effectively. The resulting systematic application of reliability based geotechnical design will consequently be soundly founded on the reputable international standard. It is a must-read for designing geotechnical structures in compliance with ISO2394."
Book Review in the ISSMGE Bulletin (Oct 2016)
"Structural and geotechnical engineers sometimes seem to live in different worlds. They use different words, different methods and different concepts. Usually the geotechnical engineer has only a very limited knowledge of steel and concrete structures while soil is an unknown material for the structural engineer. And yet: they both are working on the same structure and that structure can only function properly if all aspects are taken care of in a consistent way.
When preparing the ISO 2394, Basis of Structural Design, the writing panel had a clear vision that this document should be valid and useful for all structural aspects of design and assessment, regardless of the material and including the foundation. In every chapter and in every statement it was checked whether this indeed was the case. A special annex was completely devoted to geotechnical aspects. It is good to see that this initiative has been picked up by the authors of this book, which is in the first place a reflection on the contents of ISO 2394, but also a very useful extension with data, methods and examples. It certainly also helps to close some of the gaps mentioned above.
The book may be of a great help for everyone who wants to deal in a serious and systematic way with scatter and uncertainty in geotechnical engineering. Note finally that the book is not easy reading for beginners: having at least some knowledge of statistical methods is helpful."
Review by Ton Vrouwenvelder in "Structural Safety" 69 (2017) 34.
