Reducing shear strength uncertainties in clays by multivariate correlations

2010 ◽  
Vol 47 (1) ◽  
pp. 16-33 ◽  
Author(s):  
Jianye Ching ◽  
Kok-Kwang Phoon ◽  
Yi-Chu Chen
Keyword(s):  
Shear Strength ◽  
Site Investigation ◽  
Mean Values ◽  
Reliability Based Design ◽  
Economical Design ◽  
Coefficients Of Variation ◽  
Final Design ◽  
Available Information ◽  
Undrained Shear ◽  
Multivariate Correlations

Quantifications of uncertainties in soil shear strengths, including undrained shear strength of clay, are essential for geotechnical reliability-based design. In particular, how to reduce the uncertainties in undrained shear strengths based on all available information by correlation is a practical research subject, given the considerable cost of a typical site investigation. Although it is simple to reduce the uncertainties by correlation when the information is one dimensional (or univariate), it is quite challenging to reduce the uncertainties by using multivariate information through multiple correlations. This study proposes a systematic way of achieving multivariate correlations on undrained shear strengths. 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 in situ or laboratory tests and the outputs are the updated mean values and coefficients of variation (c.o.v.s) of the undrained shear strengths. Two case studies are used to demonstrate the consistency of the proposed simplified equations. Results show that uncertainties in undrained shear strengths can be effectively reduced by incorporating multivariate information. Given that reliability-based design can justify more economical design with reduced uncertainties, the proposed equations essentially link the value of more and better tests directly to final design savings.

scholarly journals CPT-Based Probabilistic Characterization of Undrained Shear Strength of Clay

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Mi Tian ◽  
Xiaotao Sheng
Keyword(s):  
Shear Strength ◽  
Correlation Function ◽  
Random Field ◽  
Site Investigation ◽  
Undrained Shear Strength ◽  
Bayesian Approaches ◽  
Probabilistic Characterization ◽  
Undrained Shear

Applying random field theory involves two important issues: the statistical homogeneity (or stationarity) and determination of random field parameters and correlation function. However, the profiles of soil properties are typically assumed to be statistically homogeneous or stationary without rigorous statistical verification. It is also a challenging task to simultaneously determine random field parameters and the correlation function due to a limited amount of direct test data and various uncertainties (e.g., transformation uncertainties) arising during site investigation. This paper presents Bayesian approaches for probabilistic characterization of undrained shear strength using cone penetration test (CPT) data and prior information. Homogeneous soil units are first identified using CPT data and subsequently assessed for weak stationarity by the modified Bartlett test to reject the null hypothesis of stationarity. Then, Bayesian approaches are developed to determine the random field parameters and simultaneously select the most probable correlation function among a pool of candidate correlation functions within the identified statistically homogeneous layers. The proposed approaches are illustrated using CPT data at a clay site in Shanghai, China. It is shown that Bayesian approaches provide a rational tool for proper determination of random field model for probabilistic characterization of undrained shear strength with consideration of transformation uncertainty.

Extended multivariate approach for uncertainty reduction in the assessment of undrained shear strength in clays

2014 ◽  
Vol 51 (3) ◽  
pp. 231-245 ◽  
Author(s):  
Rasmus Müller ◽  
Stefan Larsson ◽  
Johan Spross
Keyword(s):  
Shear Strength ◽  
Site Investigation ◽  
Undrained Shear Strength ◽  
Multivariate Approach ◽  
Total Uncertainty ◽  
Investigation Methods ◽  
Measurement Results ◽  
Strength Formula ◽  
A Site ◽  
Undrained Shear

Important features of the multivariate approach are discussed, and an extension to this approach is proposed whereby the total uncertainty in site investigation methods due to spatial averaging is assessed prior to its adoption. Results from a site investigation of spatially averaged values of undrained shear strength ([Formula: see text]) and the corresponding coefficient of variation ([Formula: see text]) in Veda sulphide clay were used as a practical illustration of the extended multivariate approach and provide a basis for discussion. The inherent variability and scales of fluctuation for different methods are presented. The study shows the usefulness of the extended multivariate approach for the evaluation of representative values of [Formula: see text] and [Formula: see text] based on results from different methods. It is also a way of implicitly reducing the transformation errors that arise when a property is derived from measurement results. Nevertheless, considerable care must be taken as a much lower COV for one method will have a significant impact on the results.

scholarly journals Spatial Correlation of Cone Tip Resistance for Soil in Nasiriyah

2018 ◽  
Vol 12 (1) ◽  
pp. 413-429
Author(s):  
Ressol R. Shakir
Keyword(s):  
Spatial Correlation ◽  
Soil Layer ◽  
Vertical Direction ◽  
Site Investigation ◽  
Linear Quadratic ◽  
Mean Values ◽  
Polynomial Degree ◽  
Reliability Based Design ◽  
Cone Tip Resistance ◽  
Tip Resistance

Background:Quantification of soil property spatial variations is an important step in any reliability-based design. Little stochastic parameter information about the soil in Nasiriyah, which is in southern Iraq, is available.Methods:In this paper, the Scale Of Fluctuation (SOF) for the site soil is examined, which is suggested for construction of the refinery fuel station project as no random parametric quantity has been studied in this region. A Cone Penetration Test (CPT) was performed as part of the site investigation to a depth of 20 m in the vertical direction, and 24 CPTs were analyzed within the site. The spatial correlation was computed using four methods, including Single Exponent (SNE), Square Exponent (SQE), Cosine Exponent (CSE) and Second-Order Markov (SOM). Identification of the soil type depended on the most recent classification chart, which is based on CPT results. The spatial correlation was evaluated for the vertical direction considering the cone tip resistance (qc) component. Three trend functions were applied to all CPT soundings, including linear, quadratic and cubic polynomials, which were utilized to transform the non-stationary data to stationary data. Three modes of soil were employed, including the eight-meter soil layer, a twelve-meter soil layer and the entire twenty meters of soil, which includes both layers.Results and Discussion:The mean values of SOF were 0.54 m, 0.53 m, and 1.73 m for soil layers 8 m, 12 m, and 20 m, respectively. The high value of the last mean is attributed to the 20 m of stratification in the ground. This study also indicates that the SOF decreases as the polynomial degree increases, which is due to enhanced fitting. The coefficient of variation (COV) for the SOF shows little variability for most of the studied soil cases.

Characterization of Singapore, Bangkok, and Ariake clays

2001 ◽  
Vol 38 (2) ◽  
pp. 378-400 ◽  
Author(s):  
Hiroyuki Tanaka ◽  
Jacques Locat ◽  
Satoru Shibuya ◽  
Tan Thiam Soon ◽  
Dinesh R Shiwakoti
Keyword(s):  
Shear Strength ◽  
Clay Mineral ◽  
Physical And Mechanical Properties ◽  
Site Investigation ◽  
Undrained Shear Strength ◽  
Mechanical Tests ◽  
Mineral Components ◽  
The Difference ◽  
A Site ◽  
Undrained Shear

A soil investigation was carried out at two sites in Singapore and Bangkok, Southeast Asia, and the results were compared with those from a site in Ariake, Japan. Soil samples at all the sites were retrieved using the Japanese sampling method to nullify the effect of sampling on sample quality. From the laboratory tests, consolidation characteristics and undrained shear strength were measured. In addition to the mechanical tests, X-ray diffraction and scanning electron microscope tests were carried out to identify clay minerals and to study their microstructure. Great differences in physical and mechanical properties of these clays were observed, which may be attributed to the difference in their clay mineral components and variation in the sedimentation environment.Key words: site investigation, marine clay, undrained shear strength, anisotropy, consolidation, clay mineral.

Multivariate stability assessment during staged construction

2016 ◽  
Vol 53 (4) ◽  
pp. 603-618 ◽  
Author(s):  
Rasmus Müller ◽  
Stefan Larsson ◽  
Johan Spross
Keyword(s):  
Shear Strength ◽  
Soft Clay ◽  
Indirect Measurement ◽  
Undrained Shear Strength ◽  
Multivariate Approach ◽  
Reliability Indices ◽  
Weighted Averages ◽  
Staged Construction ◽  
Available Information ◽  
Undrained Shear

For staging the construction of embankments on soft clay, an important aspect in deterministic or probabilistic stability analyses is the assessment of the representative average values and associated uncertainties for the undrained shear strength as the height of the embankment is sequentially increased. Assessments made prior to construction can be verified by performing observations during the construction phase. All relevant available information should be incorporated into an analysis to increase the level of confidence and the objectivity of the assessment. To this end, we apply an extended multivariate approach to assess the undrained shear strength using different indirect measurement methods during the staged construction of the Veda embankment (Sweden). This multivariate approach implies that uncertainties associated with the assessments are reduced, and objectively weighted averages are obtained. The resulting implications on the calculated deterministic safety factors and the probabilistically retrieved reliability indices of the embankment are thoroughly discussed in this work.

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