scholarly journals On determining the undrained bearing capacity coefficients of variation for foundations embedded on spatially variable soil

2020 ◽  
Vol 42 (2) ◽  
pp. 125-136
Author(s):  
Marcin Chwała
Keyword(s):  
Shear Strength ◽  
Random Field ◽  
Bearing Capacity ◽  
Covariance Matrix ◽  
Three Dimensional ◽  
Random Variables ◽  
Undrained Shear Strength ◽  
Spatial Averaging ◽  
The Matrix ◽  
Undrained Shear

AbstractThis paper presents an efficient method and its usage for the three-dimensional random bearing capacity evaluation for square and rectangular footings. One of the objectives of the study is to deliver graphs that can be used to easily estimate the approximated values of coefficients of variations of undrained bearing capacity. The numerical calculations were based on the proposed method that connects three-dimensional failure mechanism, simulated annealing optimization scheme and spatial averaging. The random field is used for describing the spatial variability of undrained shear strength. The proposed approach is in accordance with a constant covariance matrix concept, that results in a highly efficient tool for estimating the probabilistic characteristics of bearing capacity. As a result, numerous three-dimensional simulations were performed to create the graphs. The considered covariance matrix is a result of Vanmarcke’s spatial averaging discretization of a random field in the dissipation regions to the single random variables. The matrix describes mutual correlation between each dissipation region (or between those random variables). However, in the presented approach, the matrix was obtained for the expected value of undrained shear strength and keep constant during Monte Carlo simulations. The graphs were established in dimensionless coordinates that vary in the observable in practice ranges of parameters (i.e., values of fluctuation scales, foundation sizes and shapes). Examples of usage were given in the study to illustrate the application possibility of the graphs. Moreover, the comparison with the approach that uses individually determined covariance matrix is shown.

Probabilistic failure envelopes of strip foundations on soils with non-stationary characteristics of undrained shear strength

Géotechnique ◽  
2021 ◽  
pp. 1-44
Author(s):  
Zhichao Shen ◽  
Qiujing Pan ◽  
Siau Chen Chian ◽  
Susan Gourvenec ◽  
Yinghui Tian
Keyword(s):  
Shear Strength ◽  
Random Field ◽  
Numerical Models ◽  
Undrained Shear Strength ◽  
Considerable Effect ◽  
Failure Envelopes ◽  
Autocorrelation Distance ◽  
Stationary Random Field ◽  
Constant Coefficient Of Variation ◽  
Undrained Shear

This paper investigates probabilistic failure envelopes of strip foundations on spatially variable soils with profiles of undrained shear strength su linearly increasing with depth using the lower bound random finite element limit analysis. The spatially variable su is characterised by a non-stationary random field with linearly increasing mean and constant coefficient of variation (COV) with depth. The deterministic uniaxial capacities and failure envelopes are firstly derived to validate numerical models and provide a reference for the subsequent probabilistic analysis. Results indicate that the random field parameters COVsu (COV of su) and Δ (dimensionless autocorrelation distance) have a considerable effect on the probabilistic normalised uniaxial capacities which alters the size of probabilistic failure envelopes. However, COVsu and Δ have an insignificant effect on the shape of probabilistic failure envelopes is observed in the V-H, V-M and H-M loading spaces, such that failure envelopes for different soil variabilities can be simply scaled by the uniaxial capacities. In contrast to COVsu and Δ, the soil strength heterogeneity index κ = μkB/μsu0 has the lowest effect on the probabilistic normalised uniaxial capacity factors but the highest effect on the shape of the probabilistic failure envelopes. A series of expressions are proposed to describe the shape of deterministic and probabilistic failure envelopes for strip foundations under combined vertical, horizontal and moment (V-H-M) loading.

Bearing capacity under increasing undrained shear strength

2020 ◽  
Vol 20 (5) ◽  
pp. 295-307
Author(s):  
André Arnold ◽  
Manuel Krähenbühl ◽  
Weiyuan Zhang ◽  
Amin Askarinejad
Keyword(s):  
Shear Strength ◽  
Bearing Capacity ◽  
Undrained Shear Strength ◽  
Undrained Shear

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.

Experimental and Statistical Study on Single and Groups of Stone Columns

2020 ◽  
Vol 857 ◽  
pp. 399-408
Author(s):  
Maki J. Mohammed Al-Waily ◽  
Mohammed Y. Fattah ◽  
Maysa Salem Al-Qaisi
Keyword(s):  
Shear Strength ◽  
Stress Concentration ◽  
Bearing Capacity ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Stone Columns ◽  
Stone Column ◽  
Dependent Variables ◽  
Undrained Shear ◽  
Improvement Ratio

In the present study, 24 laboratory models on soft clay treated with stone columns were carried out. The results for each case are analysed for the purpose of constructing a statistical model linking the variables studied. The experiments showed that the stress concentration and bearing capacity of soil treated with stone column increase with increasing the undrained shear strength (cu), number of columns and L/d ratio. The models represent a single stone column and a group of stone columns. The studied variables are three dependent variables, the stress concentration ratio (n), bearing capacity of soil treated with stone column (q) and the settlement improvement ratio (Sr) due to the existence of stone columns. The independent variables are six: the undrained shear strength of clay soil, with three values (6, 9 and 12 kPa), the number of stone columns (1, 2, 3 and 4 columns) and the length (L) to the diameter (D) of the stone column or (L/D) ratio in two values (6 and 8). Besides, the bearing capacity of the soil treated (q) with stone columns and the settlement improvement ratio were used in some statistical models as independents. After regression analysis, a set of equations that correlate the previous variables have been suggested. The incepted values for dependent variables are close to the laboratory results.

Study on the Variation Regularity of Shear Strength of Saturated Soft Clay under Cyclic Loading

2011 ◽  
Vol 250-253 ◽  
pp. 2388-2391 ◽  
Author(s):  
Xiao Ping Wang ◽  
Jian Qi Wu
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Bearing Capacity ◽  
Triaxial Test ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Saturated Soft Clay ◽  
Undrained Shear

The stiffness and shear strength of soft clay attenuate under long-term cyclic loading, resulting in reduced foundation bearing capacity of road. The variation regularity of undrained shear strength of saturated soft clay which is normally consolidated or over consolidated under cyclic loading was studied with two-way vibration triaxial test, and some useful results are obtained.

BEHAVIOR OF AN OVERPASS CARRIED ON FOOTINGS AND FRICTION PILES

1969 ◽  
Vol 6 (4) ◽  
pp. 369-382 ◽  
Author(s):  
L. S. Brzezinski
Keyword(s):  
Shear Strength ◽  
Bearing Capacity ◽  
Group Action ◽  
Undrained Shear Strength ◽  
Load Test ◽  
Soil Conditions ◽  
Single Pile ◽  
Marine Clay ◽  
Friction Pile ◽  
Undrained Shear

A long overpass structure with 32 piers between abutments was founded on strip footing and friction pile foundations in a deep marine clay subsoil of firm consistency. The piles were steel H-sections which were provided at the construction stage at 6 pier locations in lieu of footings because of unfavorable soil conditions exposed during excavation. A load test to failure on a single pile indicated the pile–soil adhesion to be considerably lower than the undrained shear strength of the clay.Post-construction observations indicated the settlement of the pile-supported piers to be about 50% that of the adjacent footing supported piers. The settlements of both types of foundations were small and within tolerable limits. The design approaches used for prediction of footing settlements and the group action of friction piles in bearing capacity and settlement are presented in the paper.

scholarly journals Determination of the Undrained Shear Strength of Sensitive Clay Using Some Laboratory Soil Data

2021 ◽  
Vol 8 (1) ◽  
pp. 14
Author(s):  
Tahar Ayadat
Keyword(s):  
Shear Strength ◽  
Soil Properties ◽  
Bearing Capacity ◽  
Fine Particles ◽  
Undrained Shear Strength ◽  
Clay Layer ◽  
In Situ Tests ◽  
Sensitive Clay ◽  
Undrained Shear

The undrained shear strength is a paramount parameter in determining the consistency and the ultimate bearing capacity of a clay layer. This resistance can be determined by in-situ tests, such as the field vane test or by laboratory tests, including the portable vane test, the triaxial, the simple compression test, and the consistency penetrometer test (i.e. the Swedish cone). However, the field vane test and the Swedish cone are the most commonly test used by geotechnical experts. In this paper, relationships between the field undrained shear strength of sensitive clay and some laboratory soil properties were developed. The soil properties consisted of the percentage of fine particles (less than 2 µm), the moisture content and the Atterberg limits. Furthermore, a correlation was proposed associating between the undrained shear strength of sensitive clay as obtained by the field vane test and the laboratory cone penetration test (Swedish cone). In addition, some applications of the proposed correlation on some geotechnical problems were included, such as the determination of the consistency and the bearing capacity of a clay layer. Comparison of the results of the developed correlations with the experimental results of the present investigation and the results reported in the literature show acceptable agreement.

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