ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 24 Aug 2019 07:30:44 GMT2019-08-24T07:30:44Z502121- Application of the probabilistic SBRA method in the steel frame designhttps://scholarbank.nus.edu.sg/handle/10635/74069Title: Application of the probabilistic SBRA method in the steel frame design
Authors: Krivy, V.; Marek, P.; Phoon, K.K.
Abstract: This paper is concerned with the alternative reliability assessment of steel frame structures using the probabilistic SBRA method (Simulation-Based Reliability Assessment). The attention is focused on the selection of appropriate reference values, which serve to define the resistance (in case of safety assessment) and appropriate limitations (in case of serviceability assessment) applied in the calculation of the probability of failure Pf of the structure and its members. Next it is necessary to evaluate the suitability of particular transformation models serving as tools for transforming the loading into the response of the structure to the load with regard to the substance of the stochastic method. In this connection attention is paid to the transition from the traditional assessment of buckling strength in compliance with contemporary standards (buckling lengths, buckling factor or stress) to the "strength stability concept" with respect to the effects corresponding to the second order theory. Possible solution based on the probabilistic SBRA method and increasing capacity of computer techniques is outlined and demonstrated using an example of reliability assessment of a multistory frame structure.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/740692007-01-01T00:00:00Z
- Characterisation of model uncertainties for laterally loaded rigid drilled shaftshttps://scholarbank.nus.edu.sg/handle/10635/74097Title: Characterisation of model uncertainties for laterally loaded rigid drilled shafts
Authors: Phoon, K.-K.; Kulhawy, F.H.
Abstract: This paper presents a critical evaluation of model factors for laterally loaded rigid drilled shafts (bored piles). Both the lateral or moment limit and hyperbolic capacity are considered to make explicit the dependence of model factors on the criterion for interpreting 'capacity' from load test data. Although the hyperbolic capacity may be closest to the theoretical ultimate state or upper bound, results indicate that it generally does not produce a mean model factor of 1. When the measured capacity is interpreted consistently from load test data, the coefficient of variation (COV) appears to remain relatively constant between 30% and 40%. The range of the mean bias for the lateral or moment limit is 0·67 to 1·49, whereas that of the hyperbolic capacity is 0·98 to 2·28. Based on available data, a log-normal probability model appears adequate for reliability analysis. Laboratory-scale load tests conducted in uniform soil deposits prepared under controlled laboratory conditions are ideal for establishing benchmarks on the probable magnitude of uncertainty arising from model idealisations alone. However, the limited range of geometric and geotechnical parameters in a laboratory load test database may not produce a representative mean model factor. A field load test database typically contains more diverse geometric and geotechnical parameters, but it entails an unknown degree of extraneous uncertainties. A comparative study indicates that model statistics are surprisingly robust and appear not to be seriously affected by the above concerns (possibly because of normalisation). Model factors from drained analysis seem to be more variable than those from undrained analysis. A more detailed examination indicates that the higher COV of about 40% for these drained model factors arises because they are not completely random. There are reasons to believe that applying a more complete force system for drained analysis could minimise some of the undesired correlations and reduce the COV to a level comparable to undrained analysis.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/740972006-01-01T00:00:00Z
- Bootstrap estimation of sample autocorrelation functionshttps://scholarbank.nus.edu.sg/handle/10635/74086Title: Bootstrap estimation of sample autocorrelation functions
Authors: Phoon, K.-K.
Abstract: It is rarely appreciated that the sample autocorrelation function is a non-stationary stochastic process with mean and variance that are functions of the lag distance. For Gaussian processes, some complex formulae for the mean and covariance of the sample autocorrelation function are available. Analytical solutions for non-Gaussian processes are probably intractable and none seems to be available. A more hopeful strategy is to exploit growing desktop computational power and increasingly powerful simulation techniques for stochastic processes to perform bootstrapping. Numerical results presented in this study show that fairly accurate mean estimates of the sample autocorrelation function can be obtained for both Gaussian and non-Gaussian processes using bootstrapping. Variance estimates are less accurate, but even crude estimates are useful in identifying the level of noise at large lags and reducing misinterpretation of how the actual autocorrelation function decays with lag distance. Copyright ASCE 2006.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/740862006-01-01T00:00:00Z
- Reliability-based design and its complementary role to Eurocode 7 design approachhttps://scholarbank.nus.edu.sg/handle/10635/123379Title: Reliability-based design and its complementary role to Eurocode 7 design approach
Authors: Low, Bak Kong; Phoon, Kok-Kwang
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1233792015-01-01T00:00:00Z
- Characterization of model uncertainties for drilled shafts under undrained axial loadinghttps://scholarbank.nus.edu.sg/handle/10635/74100Title: Characterization of model uncertainties for drilled shafts under undrained axial loading
Authors: Phoon, K.K.; Kulhawy, F.H.
Abstract: This invited paper presents a rigorous examination of model statistics for drilled shafts under undrained axial loading. To apply a model factor as an independent random variable on the predictive capacity equation, it is desirable to verify that it is not varying systematically with some underlying factors. The measured and computed capacities appear as the numerator and denominator, respectively, in the standard definition of the model factor and are the most obvious factors to check for such statistical dependencies. The Spearman rank correlation is a simple and useful method to perform this check. Even though the adhesion factor typically is expressed as a function of the undrained shear strength, this approach only is marginally acceptable from a rank correlation perspective. For undrained compression tip resistance, a generalized model factor is recommended because the existing definition produces strong statistical dependencies with the measured and computed alues.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/741002005-01-01T00:00:00Z
- Characterization of model uncertainties for for Augered Cast-In-Place (ACIP) piles under axial compressionhttps://scholarbank.nus.edu.sg/handle/10635/74101Title: Characterization of model uncertainties for for Augered Cast-In-Place (ACIP) piles under axial compression
Authors: Phoon, K.K.; Chen, J.R.; Kulhawy, F.H.
Abstract: The uncertainties in normalized load-displacement curves for ACIP piles are quantified using a pair of correlated lognormal curve-fitting parameters. To correct for simplifications in the capacity model, it is preferable to use linear regression rather than the standard multiplicative form. The former definition prevents correlation by removing variations that are explainable by the computed capacity. Copyright ASCE 2006.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/741012006-01-01T00:00:00Z
- Effect of soil microstructure on the compressibility of natural Singapore marine clayhttps://scholarbank.nus.edu.sg/handle/10635/65489Title: Effect of soil microstructure on the compressibility of natural Singapore marine clay
Authors: Low, H.-E.; Phoon, K.-K.; Tan, T.-S.; Leroueil, S.
Abstract: The effect of soil microstructure on the compressibility of natural Singapore marine clay is studied in this paper. It was found that natural Singapore marine clay can sustain higher void ratio than reconstituted Singapore marine clay at the same effective stress in one-dimensional compression. This difference is most noticeable between, yield stress and two times the yield stress. This void ratio difference is commonly attributed to soil microstructure, and the decrease in this difference at higher stresses is attributed to progressive destructuration. As a consequence of progressive destructuration, the virgin compression curve is nonlinear and the compression index along the virgin compression, range is variable, which is only noticeable during the constant rate of strain consolidation test on high-quality samples. In the absence of high-quality samples and constant rate of strain consolidation tests, an empirical method is proposed to obtain a first-order estimation of a nonlinear virgin compression curve using index properties and yield, stress. This paper demonstrates that the proposed, method works reasonably well with natural Singapore marine clay. The error bound for the predicted compression indices is approximately ±20% of the compression indices measured with constant rate of strain test on high-quality samples. © 2008 NRC Canada.
Fri, 01 Feb 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/654892008-02-01T00:00:00Z
- Effect of cementation on the compressibility of Singapore upper marine clayhttps://scholarbank.nus.edu.sg/handle/10635/65480Title: Effect of cementation on the compressibility of Singapore upper marine clay
Authors: Low, H.-E.; Phoon, K.-K.
Abstract: A series of one-dimensional consolidation tests were performed under varying pretreatments on high quality soil samples collected, from a Singapore upper marine clay layer in an attempt to evaluate the effect of cementation by amorphous materials on its compressibility. The findings from this study seem, to suggest that cementation by ethylene-diamine tetraacetic acid (EDTA) removable amorphous materials may only partially contribute to the development of soil microstructure and overconsolidation in Singapore upper marine clay. © 2008 NRC Canada.
Tue, 01 Jul 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/654802008-07-01T00:00:00Z
- Engineering judgment in the evolution from deterministic to reliability-based foundation designhttps://scholarbank.nus.edu.sg/handle/10635/65533Title: Engineering judgment in the evolution from deterministic to reliability-based foundation design
Authors: Kulhawy, F.H.; Phoon, K.K.
Abstract: Engineering judgment has always played a dominant role in geotechnical design and construction. Until earlier this century, most of this judgment was based on experience and precedents. The role of judgment in geotechnical practice has undergone significant changes over the past 50 years as a result of theoretical, experimental, and field developments in soil mechanics and, more recently, in reliability theory. A clarification of this latter change specifically is needed to avoid misunderstanding and misuse of the new reliability-based design (RED) codes. This paper first provides a historical perspective of the traditional factor of safety design approach. The fundamental importance of limit state design to RED then is emphasized. Finally, an overview of RED is presented, and the proper application of this new design approach is discussed, with an example given of the ultimate limit state design of drilled shafts under undrained uplift loading. Judgment issues from traditional approaches through RBD are interwoven where appropriate.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/655331996-01-01T00:00:00Z
- Evaluation of geotechnical property variabilityhttps://scholarbank.nus.edu.sg/handle/10635/65548Title: Evaluation of geotechnical property variability
Authors: Phoon, K.-K.; Kulhawy, F.H.
Abstract: To evaluate geotechnical variability on a general basis that will facilitate the use of reliability-based design procedures, it is necessary to assess inherent soil variability, measurement error, and transformation uncertainty separately. The inherent variability and measurement error are addressed in a common paper, and transformation uncertainty is addressed herein. A second-moment probabilistic approach is applied to combine these uncertainties consistently based on the manner in which the design soil property is derived. The design properties considered in this paper are undrained shear strength, effective stress friction angle, in situ horizontal stress coefficient, and Young's modulus. This paper concludes with specific guidelines on the typical coefficients of variation for these common design soil properties as a function of the test type and the type of correlation used.
Sun, 01 Aug 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/655481999-08-01T00:00:00Z
- Determination of optimal and stable prediction parameters values in chaotic time serieshttps://scholarbank.nus.edu.sg/handle/10635/50767Title: Determination of optimal and stable prediction parameters values in chaotic time series
Authors: Liong, S.Y.; Pasha, M.F.K.; Doan, C.D.; Phoon, K.K.; Liaw, C.Y.
Abstract: The parameters values used in the prediction method for chaotic time series play a significant role in achieving high prediction accuracy. The conventional approach derives these values using, for example, Correlation Dimension, Lyapunov Exponent or Kolmogorov Entropy methods. In the present study, a search engine based on the Genetic Algorithm (GA), is coupled with an Inverse approach to arrive at the optimal values of these parameters. An artificial chaotic Mackey-Glass time series is considered in this study to test the performance of the coupled model, GA and Inverse approach. The study shows that the coupled model yields a prediction error measure, RMSE, of 0.068 which is much more accurate than that of the conventional approach. In addition, the resulting optimal values of the state space parameters are more stable with respect to different data record lengths used in optimization and a change in forecasting lead-time. Copyright ASCE 2004.
Thu, 01 Jan 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/507672004-01-01T00:00:00Z
- On quantifying inherent soil variabilityhttps://scholarbank.nus.edu.sg/handle/10635/65923Title: On quantifying inherent soil variability
Authors: Phoon, K.K.; Kulhawy, F.H.
Abstract: An important component of geotechnical variability is the inherent soil variability that results primarily from the natural geologic processes that produced and continually modify the soil mass in-situ. The usual probabilistic model for inherent soil variability is the random field, which can be described concisely by the coefficient of variation (COV) and the scale of fluctuation. This paper presents a critical review and summary of these two soil statistics using available data from a variety of common field measurements. For the range of field measurements evaluated, the results indicate that: (a) the COV of inherent variability for sand is larger than that for clay, (b) the largest COV typically is associated with measurements in the horizontal direction and measurements of soil modulus, (c) the vertical scale of fluctuation for most field measurements is between 1 and 5 m, and (d) the average horizontal scale of fluctuation is on the order of 50 m.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/659231996-01-01T00:00:00Z
- Further contributions to reliability-based pile-settlement analysishttps://scholarbank.nus.edu.sg/handle/10635/65645Title: Further contributions to reliability-based pile-settlement analysis
Authors: Quek, S.T.; Chow, Y.K.; Phoon, K.K.
Abstract: To study the statistics of the settlement of pile foundations, the uncertainty in the Young's modulus of the soil must first be estimated. This paper considers the practical aspects of estimating the uncertainty in the model for quantifying the Young's modulus of the soil as well as the uncertainty due to the inherent variability of the basic soil property, namely, the shear strength. The uncertainty in the model is evaluated by treating the correlation parameter as a random variable; the soil is modeled as a spatially random medium. Through a numerical example it is shown how these two uncertainties can be simultaneously considered in evaluating the reliability of the pile foundation against an allowable settlement limit using design charts. The design charts were formulated based on first-order computations and validated in this paper by comparing with second-order results over the range of values of practical interest.
Fri, 01 May 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/656451992-05-01T00:00:00Z
- Early-age strength characteristics of cement stabilized Singapore marine clay at high water contenthttps://scholarbank.nus.edu.sg/handle/10635/75122Title: Early-age strength characteristics of cement stabilized Singapore marine clay at high water content
Authors: Lu, Y.T.; Tan, T.S.; Phoon, K.K.
Abstract: Cement stabilized Singapore marine clay is the material associated with the Stabilized Dredged Fill (SDF) technology practiced in Singapore. Understanding the mixture early-age strength characteristics and how the early-age and later-age strength characteristics are related will significantly improve the current SDF quality control. Flow value tests, laboratory vane shear tests and unconfined compression tests are conducted in this study. Flow value tests are conducted immediately after mixing. Laboratory vane shear tests are conducted immediately after mixing and at early curing ages. The unconfined compression test results reveal that the water/cement ratio is the appropriate parameter depicting the mixture later-age strength. The flow value test results and vane shear test results obtained immediately after mixing both suggest the current SDF quality control practice may be improved. The correlations established between the early-age vane shear strengths and later-age unconfined compression strengths may be used to improve the current SDF quality control.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751222011-01-01T00:00:00Z
- Assessment of landslide potential using steady state seepage in unsaturated soilshttps://scholarbank.nus.edu.sg/handle/10635/75105Title: Assessment of landslide potential using steady state seepage in unsaturated soils
Authors: Karthikeyan, M.; Phoon, K.K.; Toll, D.G.
Abstract: This paper presents a simple method for evaluating potentially unstable soil slopes subject to surface infiltration based on convenient closed-form seepage/stability equations containing slope geometry, soil strength, and infiltration parameters. The method is based on a formulation proposed by Lu and Godt (2008), which provides the change in the factor of safety for a slope subject to steady state infiltration. The key advantage is that no numerical modeling is needed and fairly reasonable factors of safety can be determined. Several case studies are presented to illustrate the potential usefulness of the proposed method.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751052011-01-01T00:00:00Z
- Challenges in limit equilibrium based slope reliability problemshttps://scholarbank.nus.edu.sg/handle/10635/75111Title: Challenges in limit equilibrium based slope reliability problems
Authors: Ching, J.; Phoon, K.-K.; Hu, Y.-G.
Abstract: This study addresses the challenges that may be encountered in slope reliability problems based on Limit Equilibrium Methods (LEM). The main focus is on the existence of multiple failure modes that poses difficulty to many LEM-based slope reliability methods. In particular, when weak seams are present, the failure modes associated with those seams may be difficult to detect. A systematic way of searching the failure modes is proposed, and its robustness over slopes with or without weak seams is demonstrated. It is found that in the presence of weak seams, assuming circular slip surfaces may cause underestimation of slope failure probability. The conclusion of the study promotes the use of finite elements as the stability method for reliability evaluation because it is not necessary to search for failure surfaces in finite-element stability analysis. © 2011 Taylor & Francis Group, London © 2011 Taylor & Francis Group, London.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751112011-01-01T00:00:00Z
- Beyond coefficient of variation for statistical characterization of geotechnical parametershttps://scholarbank.nus.edu.sg/handle/10635/75109Title: Beyond coefficient of variation for statistical characterization of geotechnical parameters
Authors: Phoon, K.K.; Ching, J.
Abstract: It is unrealistic to assign a single Coefficient of Variation (COV) to a geotechnical parameter. The COV depends on the quality of the site investigation and the property evaluation methodology. It is also important to recognize that the COV of a design parameter may be reduced because of: (1) availability of multiple test data in a typical site investigation and (2) spatial averaging along the critical slip curve. It is necessary to characterize the correlation structure in both cases to be able to realize COV reduction, which can be used to justify design savings using the reliability-based design framework.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751092013-01-01T00:00:00Z
- Constructing joint distributions of multivariate geotechnical datahttps://scholarbank.nus.edu.sg/handle/10635/75112Title: Constructing joint distributions of multivariate geotechnical data
Authors: Ching, J.; Phoon, K.-K.; Huang, W.-C.
Abstract: This paper presents easy-to-use tools for constructing joint distributions given multivariate geotechnical data. Two scenarios are addressed (a) complete multivariate data: the Iman-Conover method will be adopted; (b) incomplete multivariate data: the Bayes' net will be adopted. Examples of multivariate geotechnical data will be presented to illustrate the procedures for constructing the joint distributions under both scenarios and to demonstrate the practical uses of these joint distributions for the purpose of site characterization. © 2011 ASCE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751122011-01-01T00:00:00Z
- Examination of multivariate dependency structure in soil parametershttps://scholarbank.nus.edu.sg/handle/10635/75128Title: Examination of multivariate dependency structure in soil parameters
Authors: Phoon, K.-K.; Ching, J.; Huang, H.
Abstract: A typical site investigation involves sampling for laboratory tests and a variety of field tests. In other words, it is common to measure more than two soil parameters. The literature is replete with correlation equations between two soil parameters. Consistent synthesis of more than two soil parameters through construction of a multivariate probability distribution function is rare, despite obvious practical usefulness of such an approach. This paper examines the feasibility of modifying the well known multivariate normal distribution to model the dependency structure of soil parameters in two databases. © 2012 American Society of Civil Engineers.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751282012-01-01T00:00:00Z
- Effect of 1D infiltration assumption on stability of spatially variable slopehttps://scholarbank.nus.edu.sg/handle/10635/75124Title: Effect of 1D infiltration assumption on stability of spatially variable slope
Authors: Santoso, A.M.; Phoon, K.-K.; Quek, S.-T.
Abstract: Rainfall-induced landslides are often analyzed using the infinite slope model, in which each slice of the slope is treated as a soil column subjected to one-dimensional, vertical infiltration. This one-dimensional (1D) assumption means that slope inclination and lateral downslope flow of water are ignored. Some studies have shown that the impact of lateral flow on slope stability is not significant. Hence, 1D infiltration analysis is sufficient to analyze rainfall-induced landslides. However, those studies are based on homogeneous soils, i.e. soil spatial variability is not considered in the analysis. This paper investigates the significance of slope inclination and lateral flow on the stability of an infinite slope with spatially varying soil in the depth direction. Only the saturated hydraulic conductivity of the soil is assumed to be spatially varying in the form of a stationary lognormal random field. It was found that the impact of the inclination on the pressure head and the factor of safety is not significant. However, the impact on the probability of slope failure is significant for some examples studied in this paper. © 2011 ASCE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751242011-01-01T00:00:00Z
- Effective shear strengths of isotropic spatially variable soil masseshttps://scholarbank.nus.edu.sg/handle/10635/75125Title: Effective shear strengths of isotropic spatially variable soil masses
Authors: Ching, J.; Phoon, K.-K.
Abstract: The purpose of this study is to understand the mechanism of the effective shear strength for a soil mass in the presence of spatial variability. Random field finite element analyses are used to simulate spatial average shear strengths and effective (or overall) shear strengths that govern the failure of a soil mass. Based on the simulation results, it is found that the statistics of spatial average strengths can be estimated by Vanmarcke's theory as to be expected. However, the effective shear strength is found to be close to the average shear strength along the actual slip curve, rather than the spatial average shear strength over the entire soil mass. Copyright © ASCE 2011.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751252011-01-01T00:00:00Z
- Forecasting of river flow data with a general regression neutral networkhttps://scholarbank.nus.edu.sg/handle/10635/65624Title: Forecasting of river flow data with a general regression neutral network
Authors: Islam, M.N.; Liong, S.-Y.; Phoon, K.K.; Liaw, C.-Y.
Abstract: This paper proposes a simple one-parameter neural network model, General Regression Neural Network (GRNN), for forecasting chaotic time series. The approach employs the theory of phase-space to reconstruct the evolution trajectory of motion, which is used as the input. In contrast to the nonlinear prediction method (NLP), where the weight of the projected state is the same, the GRNN uses unequal weights. The nearer projected state is weighted heavier than the remotely projected state, a reasonable approximation in the phase-space. The performance of the GRNN is first verified on an artificial chaotic time series and then on a real hydrological time series. The results indicate that GRNN's performance is comparable to that of NLP.
Mon, 01 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/656242001-01-01T00:00:00Z
- Quantile framework for simplified geotechnical reliability-based designhttps://scholarbank.nus.edu.sg/handle/10635/75158Title: Quantile framework for simplified geotechnical reliability-based design
Authors: Ching, J.; Phoon, K.-K.
Abstract: This paper proposes a quantile-based framework for calibrating reliability-based design factors. The quantile framework is quite versatile: it is applicable to various design formats, such as safety factor design, partial factor design, load and resistance factor design (LRFD), and multiple resistance factor design (MRFD). The advantage of the framework is to allow a single set of design factors to maintain a more uniform reliability over a wider range of design parameters. The proposed framework does not require the capacity to be lumped as a single lognormal random variable as assumed in the LRFD format nor does it require tedious segment by segment optimization of the resistance factors in the MRFD format. The applicability and usefulness of the proposed framework are illustrated using a geotechnical design example. The results show that the proposed approach is able to maintain a uniform reliability over a wide range of design parameters with a single set of design factors. © 2011 ASCE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751582011-01-01T00:00:00Z
- Probability models for SWCC and hydraulic conductivityhttps://scholarbank.nus.edu.sg/handle/10635/75157Title: Probability models for SWCC and hydraulic conductivity
Authors: Santoso, A.M.; Phoon, K.K.; Quek, S.T.
Abstract: Direct measurement of the soil-water characteristic curve (SWCC) and hydraulic conductivity is costly and time consuming. A first-order estimate from statistical generalization of experimental data for soils with similar texture is useful. A simple approach is to fit the soil water content data with available SWCC equation and to develop an appropriate probability model of the curve-fitting parameters. This paper demonstrates that a lognormal random vector is suitable to model the variability of SWCC parameters. When experimental data of hydraulic conductivity is not available, the probability model of hydraulic conductivity can be consistently derived from the probability model of SWCC. The derivation is based on the relation between saturated hydraulic conductivity and the saturated water content. The proposed probability models can be readily used to perform probabilistic analysis of problems involving unsaturated seepage.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751572011-01-01T00:00:00Z
- Probabilistic model for overall shear strengths of spatially variable soil masseshttps://scholarbank.nus.edu.sg/handle/10635/75156Title: Probabilistic model for overall shear strengths of spatially variable soil masses
Authors: Ching, J.; Phoon, K.-K.
Abstract: The purpose of this study is to understand the mechanism of the overall shear strength for a soil mass in the presence of spatial variability. Random field finite element analyses are used to simulate spatial average shear strengths and overall shear strengths that govern the failure of a soil mass. Based on the simulation results, it is found that the statistics of spatial average strengths can be estimated by Vanmarcke's theory. However, the overall shear strength is found to be close to the average shear strength along the actual slip curve, rather than the spatial average shear strength over the entire soil mass. A probabilistic model is proposed for the average shear strength along the actual slip curve. This model considers the effects of different stress states and orientation of the spatial variability. The model is further validated by the overall shear strengths simulated by the random field finite element analyses. © 2012 American Society of Civil Engineers.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751562012-01-01T00:00:00Z
- Reliability-based design of foundations-A modern viewhttps://scholarbank.nus.edu.sg/handle/10635/75161Title: Reliability-based design of foundations-A modern view
Authors: Kulhawy, F.H.; Phoon, K.K.; Wang, Y.
Abstract: Basic concepts in the transition from allowable stress design (ASD) to reliability-based design (RBD) are reviewed. Critical issues related to RBD are noted, including their strengths and weaknesses. It is stressed that current simplified RBD methods need to be improved and expanded. Recommendations then are made for improving factor calibrations, addressing serviceability and economic limit states, and optimizing the foundation design process. © 2012 American Society of Civil Engineers.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751612012-01-01T00:00:00Z
- Updating uncertainties in friction angles of clean sandshttps://scholarbank.nus.edu.sg/handle/10635/75176Title: Updating uncertainties in friction angles of clean sands
Authors: Ching, J.; Chen, J.; Phoon, K.-K.
Abstract: It is essential to characterize the uncertainties of soil shear strengths, including friction angles of sands. In particular, it is of practical interest to reduce the uncertainties in friction angles based on all available information by correlation, given the considerable cost of a typical site investigation. This study proposes a systematic way of constructing multivariate correlations on friction angles of clean sands. A set of simplified equations are obtained through Bayesian analysis for the purpose of reducing uncertainties. The inputs to the equations are the results of field and laboratory tests, and the outputs are the updated mean values and standard deviations of the friction angles. Test databases are used to demonstrate the consistency of the proposed simplified equations. © 2011 ASCE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751762011-01-01T00:00:00Z
- Unsaturated soil seepage analysis using temporal adaptive transformation method with under-relaxationhttps://scholarbank.nus.edu.sg/handle/10635/75175Title: Unsaturated soil seepage analysis using temporal adaptive transformation method with under-relaxation
Authors: Cheng, Y.; Phoon, K.K.
Abstract: This research tends to develop robust numerical methods for solving the highly nonlinear partial differential equation describing unsaturated soil flow. Based on the research of a modified transformation method with under-relaxation, the numerical performance of this promising method with automatic temporal adaptive scheme is investigated. Example shows that such a combination approach can be a robust numerical method for practical unsaturated flow simulations, as it provides the most efficient solution at minimal computational cost; its performance is rather robust with moderate changes of several parameters introduced; and it is conceptually and computationally simple which can be easily incorporated into existing software codes based on the backward Euler scheme. © 2011 IEEE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751752011-01-01T00:00:00Z
- Uncertainty analysis in geotechnical engineering-a comparative study of selected approacheshttps://scholarbank.nus.edu.sg/handle/10635/75174Title: Uncertainty analysis in geotechnical engineering-a comparative study of selected approaches
Authors: Beer, M.; Zhang, Y.; Quek, S.T.; Phoon, K.K.
Abstract: In this paper common probabilistic methods for dealing with uncertainty in geotechnical engineering are investigated and compared with an alternative approach based on interval analysis. The selected methods are examined in view of i) an appropriate modeling of the information actually available in practical cases, ii) the transfer of the uncertainty to the computational results, and iii) the interpretation of the results. A simple nonlinear settlement problem is used for the study and considered as known in a deterministic form. This describes the input-to-output transformation of the available information in all cases. Representative available information about the parameters of the settlement model is taken from literature, and typical practical specifications for the parameters are considered. © 2011 Taylor & Francis Group, London.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751742011-01-01T00:00:00Z
- In situ evaluation of radioisotope cone penetrometers in clayshttps://scholarbank.nus.edu.sg/handle/10635/65694Title: In situ evaluation of radioisotope cone penetrometers in clays
Authors: Dasari, G.R.; Karthikeyan, M.; Tan, T.-S.; Mimura, M.; Phoon, K.-K.
Abstract: A comprehensive site investigation was performed at a 12-year-old man-made island in Singapore, which was reclaimed using dredged clay lumps. The objective of the site investigation was to evaluate the performance of the radioisotope (RI) cone penetrometers to measure in situ wet density and water content, which are the two important parameters in the characterization of soils formed from clay lumps. The site investigation program included RI cone penetration tests, high quality soil sampling, and laboratory testing. The in situ water content and wet density profiles measured with RI cone penetrometers were compared with data obtained independently from the laboratory tests on undisturbed samples. The comparison shows very good agreement, and 92% of the RI cone measurements were found to be within ±5% of the laboratory measurements. Copyright © 2006 by ASTM International.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/656942006-01-01T00:00:00Z
- Reliability analysis of pile settlementhttps://scholarbank.nus.edu.sg/handle/10635/66073Title: Reliability analysis of pile settlement
Authors: Phoon, K.K.; Quek, S.T.; Chow, Y.K.; Lee, S.L.
Abstract: The stochastic finite element method is applied to study the effect of a spatially varying soil medium on the settlement of single-pile foundations. In this study, the soil medium is assumed to be linear-elastic, and it is modeled as a homogeneous random field. The random field captures the uncertainty in the soil modulus by means of the coefficient of variation and the scales of fluctuation. Using a first-order second-moment technique, the mean and coefficient of variation of the pile head settlement are determined. It is found that the uncertainty of the pile head settlement is dependent on both deterministic and stochastic parameters. Reliability analysis is then performed to compute the reliability index and the corresponding probability of unserviceable behavior. In order to facilitate the probabilistic design of pile foundations, the results of the analysis are presented in the form of concise charts suitable for use by practicing engineers.
Thu, 01 Nov 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/660731990-11-01T00:00:00Z
- Influence of the scale of fluctuation of the friction angle on the face stability of a pressurized tunnel in sandshttps://scholarbank.nus.edu.sg/handle/10635/75143Title: Influence of the scale of fluctuation of the friction angle on the face stability of a pressurized tunnel in sands
Authors: Mollon, M.G.; Phoon, K.-K.; Dias, D.; Soubra, A.-H.
Abstract: The present paper makes use of a 2D limit analysis mechanism developped in Mollon et al. 2011 to study the influence of the scale of fluctuation of the friction angle in a soil mass on the critical collapse pressure of a pressurized tunnel face. The variability of the soil is simulated by random fields in the framework of the Karhunen-Loeve Expansion method, with various scales of fluctuation. A Monte-Carlo sampling scheme is used to examine the probabilistic impact of this variability as well as possible emergent behaviours that may be qualitatively different from well known behaviours associated with homogeneous sand. Probabilistic results show that L/D ratio (i.e. autocorrelation length of the friction angle random field, over tunnel diameter D) has an important influence on the dispersion of the critical collapse pressure. For a small to moderate value of this scale of fluctuation with respect to the tunnel diameter, it appears that there are several critical positions of the failure mechanism, whereas such phenomenon is unlikely for large values of L/D. © 2011 ASCE.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751432011-01-01T00:00:00Z
- Fast iterative solution of large soil-structure interaction problems in varied ground conditionshttps://scholarbank.nus.edu.sg/handle/10635/75135Title: Fast iterative solution of large soil-structure interaction problems in varied ground conditions
Authors: Chaudhary, K.B.; Phoon, K.K.; Toh, K.C.
Abstract: Many geotechnical problems involve a wide range of materials with vast difference in stiffness and permeability resulting in an ill-conditioned system. Existing practical preconditioners perform poorly for such problems while incomplete factorization preconditioners may show signs of instability. Recent advances in preconditioning show that the inexact block diagonal preconditioners are much less sensitive to any difference in such material properties for the iterative solution of soil-structure interaction problems. This paper highlights the general applicability of such preconditioners to large-scale geotechnical problems in realistic ground conditions with the help of a user defined solver interface in the commercial GeoFEA software. The practical observation is that nonhomogeneous soil and structural elements do not impose a problem for the new preconditioners. In fact, they can be even more effective as the system accumulates more and more stiff soil and/or structural elements.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/751352011-01-01T00:00:00Z
- Performance of Jacobi preconditioning in Krylov subspace solution of finite element equationshttps://scholarbank.nus.edu.sg/handle/10635/65982Title: Performance of Jacobi preconditioning in Krylov subspace solution of finite element equations
Authors: Lee, F.-H.; Phoon, K.K.; Lim, K.C.; Chan, S.H.
Abstract: This paper examines the performance of the Jacobi preconditioner when used with two Krylov subspace iterative methods. The number of iterations needed for convergence was shown to be different for drained, undrained and consolidation problems, even for similar condition number. The differences were due to differences in the eigenvalue distribution, which cannot be completely described by the condition number alone. For drained problems involving large stiffness ratios between different material zones, ill-conditioning is caused by these large stiffness ratios. Since Jacobi preconditioning operates on degrees-of-freedom, it effectively homogenizes the different spatial sub-domains. The undrained problem, modelled as a nearly incompressible problem, is much more resistant to Jacobi preconditioning, because its ill-conditioning arises from the large stiffness ratios between volumetric and distortional deformational modes, many of which involve the similar spatial domains or sub-domains. The consolidation problem has two sets of degrees-of-freedom, namely displacement and pore pressure. Some of the eigenvalues are displacement dominated whereas others are excess pore pressure dominated. Jacobi preconditioning compresses the displacement-dominated eigenvalues in a similar manner as the drained problem, but pore-pressure-dominated eigenvalues are often over-scaled. Convergence can be accelerated if this over-scaling is recognized and corrected for. Copyright © 2002 John Wiley and Sons, Ltd.
Wed, 10 Apr 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/659822002-04-10T00:00:00Z
- Practical reliability-based design approach for foundation engineeringhttps://scholarbank.nus.edu.sg/handle/10635/66015Title: Practical reliability-based design approach for foundation engineering
Authors: Phoon, K.K.; Kulhawy, F.H.
Abstract: A research study was completed recently that was directed toward the development of practical, reliability-based design (RBD) equations specifically for foundation engineering. Some of the key RBD principles used in the study are presented. The important considerations involved in the development of practical and robust RBD criteria are emphasized. In particular, the selection of an appropriate reliability assessment technique and the careful characterization and compilation of geotechnical variabilities are important because of their central role in the calculation of the probability of failure and the assessment of the target reliability level. An overview of a simplified RBD approach is given, and an application of this approach to the ultimate limit state design of drilled shafts under undrained uplift loading is discussed.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/660151996-01-01T00:00:00Z
- Iterative solution of intersecting tunnels using the generalised Jacobi preconditionerhttps://scholarbank.nus.edu.sg/handle/10635/74223Title: Iterative solution of intersecting tunnels using the generalised Jacobi preconditioner
Authors: Phoon, K.K.; Lee, F.H.; Chan, S.H.
Abstract: This study presents settlement analyses of intersecting tunnels using the 3-D finite element method. This study demonstrates that the reinforcing or strengthening effects due to the presence of existing tunnel(s) are significant on the problem being investigated. Any existing tunnel prior to the new tunnelling has to be incorporated into analyses if more realistic assessments on the tunnelling impacts are required. This study also shows that when multiple closely spaced tunnels are constructed, the assumption that each tunnel behaves independently and the movements that would have occurred for each tunnel acting independently can be superimposed, is unlikely to provide good estimations. Note that the linear superposition technique has been commonly used in practice to reduce the complexity of very large problems that involve construction of multiple tunnels. Consequently, the entire problem has to be modelled and large-scale computing is unavoidable. The symmetric quasi-minimal residual method (SQMR) incorporating the generalised Jacobi (GJ) preconditioner is shown to be very economical in solving such large-scale finite element problems on personal computers. © 2006 Taylor & Francis Group.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742232006-01-01T00:00:00Z
- Iterative solution of intersecting tunnels using the generalised Jacobi preconditionerhttps://scholarbank.nus.edu.sg/handle/10635/74224Title: Iterative solution of intersecting tunnels using the generalised Jacobi preconditioner
Authors: Phoon, K.K.; Lee, F.H.; Chan, S.H.
Abstract: This study presents settlement analyses of intersecting tunnels using the 3-D finite element method. This study demonstrates that the reinforcing or strengthening effects due to the presence of existing tunnel(s) are significant on the problem being investigated. Any existing tunnel prior to the new tunnelling has to be incorporated into analyses if more realistic assessments on the tunnelling impacts are required. This study also shows that when multiple closely spaced tunnels are constructed, the assumption that each tunnel behaves independently and the movements that would have occurred for each tunnel acting independently can be superimposed, is unlikely to provide good estimations. Note that the linear superposition technique has been commonly used in practice to reduce the complexity of very large problems that involve construction of multiple tunnels. Consequently, the entire problem has to be modelled and large-scale computing is unavoidable. The symmetric quasi-minimal residual method (SQMR) incorporating the generalised Jacobi (GJ) preconditioner is shown to be very economical in solving such large-scale finite element problems on personal computers. © 2006 Taylor & Francis Group.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742242006-01-01T00:00:00Z
- Large scale three-dimensional finite element analysis of underground constructionhttps://scholarbank.nus.edu.sg/handle/10635/74230Title: Large scale three-dimensional finite element analysis of underground construction
Authors: Lee, F.H.; Phoon, K.K.; Lim, K.C.
Abstract: This paper discusses the possibility of using three-dimensional finite element analyses to analyse and design underground construction works. Two common problems associated with three-dimensional analyses mean very large memory requirement and long computing times. To overcome these problems, the Authors outline some recent developments in iterative solution algorithm which can lead to large savings in memory and time. It is shown that these iterative methods offer viable and faster alternatives to Gaussian elimination approach for solving very large finite element equations in geotechnical engineering, such as those arising from three-dimensional analyses, with significantly reduced memory requirement. The convergence characteristics of ill-conditioned coupled-flow problems can be improved by using a generalized Jacobi preconditioner. Drained problems can be efficiently solved using the preconditioned conjugate gradient method with the standard Jacobi preconditioner. On the other hand, undrained problems are better solved as "nearly-impermeable" consolidation problems, using quasi-minimal residual method with the generalized Jacobi preconditioner. The advantages of iterative methods increase with the size of the problem. For very large problems, the speed-up can be very significant. The applicability of iterative methods is illustrated by the study of a tunneling project involving earth pressure balance machine. The details of face pressure application, tunnel convergence around shield and lining installation were modeled. The results show that large-scale three-dimensional analyses with iterative solution cannot only be implemented on relatively modest computation platforms with reasonable turnaround times, but they are also able to illuminate ground mechanisms which cannot be reflected by two-dimensional analyses. © 2006 Taylor & Francis Group.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742302006-01-01T00:00:00Z
- Large scale three-dimensional finite element analysis of underground constructionhttps://scholarbank.nus.edu.sg/handle/10635/74229Title: Large scale three-dimensional finite element analysis of underground construction
Authors: Lee, F.H.; Phoon, K.K.; Lim, K.C.
Abstract: This paper discusses the possibility of using three-dimensional finite element analyses to analyse and design underground construction works. Two common problems associated with three-dimensional analyses mean very large memory requirement and long computing times. To overcome these problems, the Authors outline some recent developments in iterative solution algorithm which can lead to large savings in memory and time. It is shown that these iterative methods offer viable and faster alternatives to Gaussian elimination approach for solving very large finite element equations in geotechnical engineering, such as those arising from three-dimensional analyses, with significantly reduced memory requirement. The convergence characteristics of ill-conditioned coupled-flow problems can be improved by using a generalized Jacobi preconditioner. Drained problems can be efficiently solved using the preconditioned conjugate gradient method with the standard Jacobi preconditioner. On the other hand, undrained problems are better solved as "nearly-impermeable" consolidation problems, using quasi-minimal residual method with the generalized Jacobi preconditioner. The advantages of iterative methods increase with the size of the problem. For very large problems, the speed-up can be very significant. The applicability of iterative methods is illustrated by the study of a tunneling project involving earth pressure balance machine. The details of face pressure application, tunnel convergence around shield and lining installation were modeled. The results show that large-scale three-dimensional analyses with iterative solution cannot only be implemented on relatively modest computation platforms with reasonable turnaround times, but they are also able to illuminate ground mechanisms which cannot be reflected by two-dimensional analyses. © 2006 Taylor & Francis Group.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742292006-01-01T00:00:00Z
- Modeling and simulation of stochastic datahttps://scholarbank.nus.edu.sg/handle/10635/74247Title: Modeling and simulation of stochastic data
Authors: Phoon, K.K.
Abstract: Stochastic data appear as basic components in reliability analysis and geostatistics. It is rarely emphasized that the multivariate probability distributions underlying random vectors (or processes, fields) are very difficult to construct theoretically, to estimate empirically, and to simulate numerically. This paper discusses the modeling and simulation of non-Gaussian random vectors, highlighting some useful geotechnical applications, important limitations, and outstanding challenges. Discussion is restricted to translation vectors, although emerging techniques that can potentially simulate a wider class of non-Gaussian random vectors would be briefly introduced for completeness. The translation approach is quite natural and takes advantage of the practicality, theoretical generality, and simulation speed associated with the multivariate Gaussian distribution. Nonetheless, there are fundamental limitations that must be recognized. The present focus on probabilistic analysis should be balanced by more research on statistical inference. It is acknowledged that statistical inference for correlated data is a challenging problem, but its practical significance is obvious. Copyright ASCE 2006.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742472006-01-01T00:00:00Z
- Reliability analysis of infinite slope using subset simulationhttps://scholarbank.nus.edu.sg/handle/10635/74322Title: Reliability analysis of infinite slope using subset simulation
Authors: Santoso, A.; Phoon, K-K.; Quek, S-T.
Abstract: It is important to incorporate the spatial variability of soil properties in slope stability analysis. Most studies use a random field to model the variability of soil properties and estimate the reliability using direct Monte Carlo simulation (MCS), which is not efficient for problems with small failure probabilities. The slope reliability can be more efficiently estimated using the subset simulation method, as it computes a small failure probability as a product of larger conditional probabilities. The approach is demonstrated using an infinite slope with undrained shear strength varying with depth. It will be shown that subset simulation requires much less samples than MCS to achieve a given accuracy. Subset simulation results are within the first order probability bounds derived from classical system reliability theory. It is found that the failure surface can be developed in any soil layer, not necessarily atthe soil-rock interface. Copyright ASCE 2009.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743222009-01-01T00:00:00Z
- Some critical issues in geo-RBD calibrations for foundationshttps://scholarbank.nus.edu.sg/handle/10635/74358Title: Some critical issues in geo-RBD calibrations for foundations
Authors: Kulhawy, F.H.; Phoon, K.K.
Abstract: Calibrations for reliability-based design (RBD) of foundations are critical but are largely "invisible". Some key methods of calibration are discussed, including issues ranging from the basic assumptions involved, distributions of key variables, uncertainties in both load and resistance, target reliability, etc. The goal is to assist engineers in understanding the level of sophistication, or lack thereof, in different approaches to calibrations, which then translates into the degree of confidence one can have in a particular calibration or code. Copyright ASCE 2006.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743582006-01-01T00:00:00Z
- Soil variability analysis for geotechnical practicehttps://scholarbank.nus.edu.sg/handle/10635/74357Title: Soil variability analysis for geotechnical practice
Authors: Uzielli, M.; Lacasse, S.; Nadim, F.; Phoon, K.K.
Abstract: The heterogeneity of natural soils is well known in geotechnical practice. However, the importance of quantifying the resulting variability in geotechnical characterisation and design parameters is not adequately recognised. Variability should not be approached suspiciously. Rather, it should be accepted as a positive contribution to geotechnical design as its consistent modelling and utilisation lead, with limited additional computations and conceptual effort on the part of the engineer, to more rational and economic design. The paper presents a structured - though necessarily partial - review of approaches and methodologies for the quantification of soil variability, as well as selected examples of its utilisation in reliability-based geotechnical design. © 2007 Taylor & Francis Group, London.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743572007-01-01T00:00:00Z
- Some numerical considerations in unsaturated slope stability analysis due to rainfall infiltrationhttps://scholarbank.nus.edu.sg/handle/10635/74359Title: Some numerical considerations in unsaturated slope stability analysis due to rainfall infiltration
Authors: Phoon, K.K.; Cheng, Y.
Abstract: Accurate prediction of the propagating wetting front arising from rainfall infiltration into an unsaturated soil slope is of considerable importance to stability analysis of the slope. However, difficulties exist in numerical simulations of unsaturated flow analyses because of the highly nonlinear soil hydraulic properties. This paper emphasizes the slow convergence of calculated pressure heads with the refinement of mesh sizes and time steps, and discusses possible solutions. © 2008 Science Press Beijing and Springer-Verlag GmbH Berlin Heidelberg Geotechnical Engineering for Disaster Mitigation and Rehabilitation.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743592008-01-01T00:00:00Z
- Some observations on assessment of gaussianity for correlated profileshttps://scholarbank.nus.edu.sg/handle/10635/74360Title: Some observations on assessment of gaussianity for correlated profiles
Authors: Uzielli, M.; Phoon, K.-K.
Abstract: The classical Anderson-Darling test for Gaussianity cannot be applied on correlated data. It is possible to circumvent correlation by resampling the data at wider spacing. A simple resampling criterion is developed using digitally simulated standard Gaussian realizations following a single exponential correlation structure. The effects of resampling on Gaussianity assessment are assessed on actual normalized cone tip resistance profiles from highly homogeneous soil units. Copyright ASCE 2006.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743602006-01-01T00:00:00Z
- Observations on non-Gaussian Karhunen-Loève expansionshttps://scholarbank.nus.edu.sg/handle/10635/74274Title: Observations on non-Gaussian Karhunen-Loève expansions
Authors: Li, L.B.; Quek, S.T.; Phoon, K.K.
Abstract: The non-Gaussian Karhunen-Loève (K-L) expansion has been used to generate a non-Gaussian process using an iterative scheme. Numerical results show that different non-Gaussian processes can be generated satisfying the same prescribed covariance function and marginal distribution by changing the assumed starting distribution of the K-L random variables. Non-Gaussian K-L processes produced by assuming an initial Gaussian distribution for the K-L random variables appear to be translation processes. When the K-L random variables were assigned a lognormal distribution before the iteration procedure, the resulting process is clearly non-translation. Hence, it would appear that translation processes form a subset of K-L processes. In other words, the class of non-Gaussian K-L processes is larger and potentially capable of providing better fit to observed data. © 2005 Elsevier Ltd.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742742005-01-01T00:00:00Z
- On the evolution from deterministic to reliability-based foundation designhttps://scholarbank.nus.edu.sg/handle/10635/74279Title: On the evolution from deterministic to reliability-based foundation design
Authors: Kulhawy, F.H.; Phoon, K.K.
Abstract: The key components that are in place for implementing rigorous reliability based foundation design (RBD) in foundation engineering are discussed. The characteristics of a simple second-moment probabilistic approach, which is available to combine uncertainties arising from site conditions, measurement techniques, and correlation models in a general way is also described. An important advantage of RBD is that the reliability index provides a consistent measure of risk that can be compared across different foundation types and loading nodes. With a properly calibrated simplified RBD format, a geotechnical engineer can focus on ground and construction evaluation in rigorous fashion.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/742792003-01-01T00:00:00Z
- Prediction of changes in pore-water pressure response due to rainfall eventshttps://scholarbank.nus.edu.sg/handle/10635/74309Title: Prediction of changes in pore-water pressure response due to rainfall events
Authors: Karthikeyan, M.; Toll, D.G.; Phoon, K.K.
Abstract: Global climate change is expected to result in worldwide increases in temperature and alteration of rainfall patterns. Such changes have the potential to activate rainfall triggered landslides and a study is underway in Singapore to investigate these possible effects. The main objective of this work is to calibrate a numerical model for future prediction by making use of cases where in-situ measurements of pore-water pressures/suctions have been made in Singapore. The results presented in this study show that the prediction of changes in the pore-water pressure profile is highly sensitive to the soil-hydraulic properties used in the analysis. It was found that a SEEP/W flow model is able to capture the general trend of field behaviour of the changes in the pore-water pressure profile response due to rainfall events. However, the results from the numerical models indicate that further research is warranted to improve the accuracy of the numerical analysis by better definition of critical input parameters. © 2008 Taylor & Francis Group, London.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743092008-01-01T00:00:00Z
- Probabilistic hyperbolic models for foundation uplift movementshttps://scholarbank.nus.edu.sg/handle/10635/74312Title: Probabilistic hyperbolic models for foundation uplift movements
Authors: Phoon, K.K.; Chen, J.-R.; Kulhawy, F.H.
Abstract: There is a need to consider both ultimate limit state and serviceability limit state uniformly within the reliability-based design framework. However, it is more difficult to characterize uncertainties associated with the latter, because load-displacement curves are nonlinear functions that cannot be reduced to a single random variable. This paper demonstrates that a random vector containing two curve-fitting hyperbolic parameters is an adequate probabilistic model for uplift load-displacement curves associated with spread foundations, drilled shafts, and pressure-injected footings. A simple but general computational approach, based on Hermite polynomials, can be used to simulate these hyperbolic parameters, which typically are correlated and may not follow closed-form classical distributions. Copyright ASCE 2007.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743122007-01-01T00:00:00Z
- Reliability-based design of foundations for transmission line structureshttps://scholarbank.nus.edu.sg/handle/10635/74325Title: Reliability-based design of foundations for transmission line structures
Authors: Kulhawy, F.H.; Phoon, K.K.; Prakoso, W.A.; Hirany, A.
Abstract: An overview is presented of research at Cornell University on reliability-based design (RBD) of foundations for transmission line structures (TLS). Under sponsorship of the Electric Power Research Institute (EPRI), Empire State Electric Energy Research Corporation (ESEERCO), and others, a long-term research effort was conducted to develop a comprehensive RBD methodology for TLS foundations in both soil and rock under uplift, compression, and lateral/moment loading. The results of these studies are described herein in conceptual form, illustrating the basic concepts involved and key issues of geotechnical variability and uncertainty. Many are described in more detail in the geotechnical literature, so references are provided to the pertinent works. These very useful tools are readily available to the TLS design community. Copyright ASCE 2007.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/743252006-01-01T00:00:00Z