Undrained Bearing Capacity Research Articles

Influence of consolidation on undrained capacity of two interfering footings on heterogeneous clays

The effect of consolidation on the undrained capacity of two interfering footings has not been investigated previously in a systematic manner, although this is particularly interest for offshore foundations, where consolidation will occur as a result of working load or preload. This paper presents results of a numerical investigation into the consolidated undrained bearing capacity of two interfering footings resting on heterogeneous clays. Finite difference code FLAC with the modified Cam Clay soil model is applied to couple the effect of consolidation and strength gain of clay beneath the footings. The results are expressed in dimensionless form of the gain in capacity, accounting for the coupling effects of the spacing between two footings, the magnitude and duration of applied preloads, and the clay strength heterogeneity. A design approach based on the data-fitting equations of the obtained solutions is proposed, and the failure mechanisms of the two adjacent footings after consolidation are also discussed.

Soft Computing-Based Models for Estimating Undrained Bearing Capacity Factor of Open Caisson in Heterogeneous Clay

Soft Computing-Based Models for Estimating Undrained Bearing Capacity Factor of Open Caisson in Heterogeneous Clay

Effect of strain-softening and strength anisotropy on the undrained bearing capacity of non-associated clay

The bearing capacity of soils is critical in the design and analysis of foundations. The classical solutions derived from methods of characteristics and bound theories are based on the rigid plasticity and associated flow rule, which may not be realistic for natural soils. The undrained shear strength of soft clays exhibits strain-softening and anisotropic behaviour in laboratory tests, which creates complexity when choosing appropriate strength parameters in the conventional design process. In addition, the stress–strain characters are non-associative and path dependent, which also affects the bearing capacity of soils. This paper investigates two classical stability problems (i.e. deeply embedded pile/pipe section and rigid strip footing) using finite-element analysis and the MIT-E3 soil model, and demonstrates the effects of stain-softening and strength anisotropy on the undrained bearing capacity of soils. The computed results are compared with analytical solutions and finite-element limit analyses, as well as those from finite-element analysis using conventional soil models. These findings have strong practical implications in predicting the bearing capacity of foundations and interpreting in situ tests.

Numerical analysis of the post-installation consolidated response of skirted foundations

The effect of the installation process on the subsequent foundation consolidation response requires assessment when the preload is initially applied. In the framework of effective stress, the influence of large soil deformations during penetration is analysed in this study using a comparison of results from large deformation finite element (LDFE) analysis based on periodic mesh regeneration (Ritss technique) and a 'wished-in-place' small strain finite element (SSFE) model. The LDFE results demonstrate that considerations of the skirt penetration and soil plug bulge lead to different soil excess pore pressure and void ratio change distributions from that of the SSFE analysis, thereby affecting the foundation settlement and consolidated bearing capacity. The normalised fully consolidated undrained bearing capacity grows linearly with the preload ratio for preloads higher than the penetration resistance, and the capacity obtained from the LDFE is higher. The settlement ratio and the proportion of partially consolidated to fully consolidated capacity gain can be represented as a hyperbolic function of a revised dimensionless time factor. The methods integrated in this study can be used to predict the increase in the vertical undrained capacity of skirted foundations after consolidation, accounting for installation effects in engineering practice.

Effect of Preloading with Consolidation on the Undrained Bearing Capacity of Ring Foundations

The undrained bearing capacity of ring foundations has received significant attention from researchers, but most of the reported studies do not reflect the effect of consolidation due to preloading. In this work, we investigated the postconsolidation undrained vertical capacity of ring foundations resting on nonhomogeneous clays using finite differential analyses and the modified Cam-clay constitutive model. The results are presented in nondimensional form and were compared with data available in the literature. The coupling influences of the internal opening of the foundation, the magnitude of the preloading, the duration of the consolidation, and the initial overconsolidation ratio of the clay were all considered. A methodology based on approximating expressions that captured the numerical results well is proposed as a way of predicting the undrained capacity gain of ring foundations for any degree of preloading and consolidation.

FELA evaluation of undrained bearing capacity of cutting edge of circular open caisson

ABSTRACT Circular open caissons are deep foundations sunk into the ground utilising the self-weight of cutting edge and steining as driving force along with the subsequent failure of soil in bearing. During the sinking of the caisson, the clay in contact with the cutting edge is subjected to undrained loading and the controlled sinking of the caisson can be achieved by evaluating the undrained bearing capacity of the cutting edge. In the study, the undrained bearing capacity factor (N) of the cutting edge for varying cutting angle (b), radius ratio of the caisson (r i /r o ), full embedment of the caisson (d), removal of soil within the caisson (d'), and different roughness (α) conditions of the steining are evaluated using finite element limit analysis (FELA). The factors affecting the undrained stability of caisson considering all practical scenarios are addressed and presented as charts to be used in practice.

Prediction of Undrained Bearing Capacity of Skirted Foundation in Spatially Variable Soils Based on Convolutional Neural Network

Skirted foundations are widely used in offshore and subsea engineering. Previous studies have shown that soil undrained shear strength variability has a notable impact on probabilistic analyses of skirted foundation bearing capacity. This study proposes an efficient machine-learning method to predict the uniaxial bearing capacity factors of skirted foundations under pure horizontal and moment loads, without relying on traditional time-consuming random finite element methods. A two-dimensional convolutional neural network is adopted to capture the potential correlation between soil random fields and bearing capacity factors. The proposed CNN-based model exhibits satisfactory prediction performance with regard to coefficients of variation and scale of fluctuations in two directions. Specifically, coefficient of determination (R2) values exceed 0.97, while root mean square error (RMSE) values remain below 0.13 for the surrogate model. In addition, more than 96% of the predictions are associated with a relative error of 5% or less, providing evidence of the proposed 2D-CNN model’s satisfactory prediction performance.

Developing soft-computing regression model for predicting bearing capacity of eccentrically loaded footings on anisotropic clay

In this investigation, the bearing capacity solution of a strip footing in anisotropic clay under inclined and eccentric load is analyzed using the numerical simulation model. The lower and upper bound finite element limit analysis (FELA) approaches are utilized to establish precise modeling and derive the numerical outcomes of a strip footing's bearing capacity. All analyses use effective automated adaptive meshes with three iteration stages to enhance the accuracy of the outcomes. The parametric analysis is performed to examine the influence of four dimensionless parameters which are taken into account in this study, namely the anisotropic strength ratio, the dimensionless eccentricity, the load inclination angle, and the adhesion factor to the bearing capacity factor. Furthermore, a new model has been proposed to predict the bearing capacity factor for the calculation of the undrained bearing capacity for footings resting on an anisotropic clay using an advanced data-driven method (MOGA-EPR). The new model takes into account the anisotropy, eccentricity, and inclination of the applied load and could be used with confidence in routine designs of shallow foundations in undrained conditions with the consideration of the anisotropic strengths of clays.

Prediction of the Bearing Capacity of Composite Grounds Made of Geogrid-Reinforced Sand over Encased Stone Columns Floating in Soft Soil Using a White-Box Machine Learning Model

Stone columns have been extensively advocated as a traditional approach to increase the undrained bearing capacity and reduce the settlement of footings sitting on cohesive ground. However, due to the complex interaction between the soil and the stone columns, there currently needs to be a commonly acknowledged approach that can be used to precisely predict the undrained bearing capacity of the system. For this reason, the bearing capacity of a sandy bed reinforced with geogrid and sitting above a collection of geogrid-encased stone columns floating in soft clay was studied in this research. Using a white-box machine learning (ML) technique called Multivariate Polynomial Regression (MPR), this work aims to develop a model for predicting the bearing capacity of the referred foundation system. For this purpose, two hundred and forty-five experimental results were collected from the literature. In addition, the model was compared to two other ML models, namely, a black-box model known as Random Forest (RF) and a white-box ML model called Linear Regression (LR). In terms of R2 (coefficient of determination) and RMSE (Root Mean Absolute Error) values, the newly proposed model outperforms the two other referred models and demonstrates robust estimation capabilities. In addition, a parametric analysis was carried out to determine the contribution of each input variable and its relative significance on the output.

Effect of Compressibility on Undrained Bearing Capacity of Circular Embedded Footings Resting on Non-homogeneous Ground

Effect of Compressibility on Undrained Bearing Capacity of Circular Embedded Footings Resting on Non-homogeneous Ground

New failure mechanism for evaluating seismic and static undrained bearing capacity adjacent to 2D slope

The seismic or static undrained slip line field theory and Cauchy, Riemann, mixed boundary value problems for undrained soil slopes are derived. A new failure mechanism is proposed to determine the undrained bearing capacity adjacent to slopes. The effects of geometric or strength parameters and seismic forces on static and seismic undrained bearing capacity are investigated. The convergence of the proposed method is proved. The static and seismic undrained bearing capacities predicted by the proposed method are close to those of the currently existing methods. The proposed method does not need to assume or search the failure modes, and a new limit state evaluation index is given.

A Comprehensive Comparison and Analysis of In-Situ Dynamic and Static Tests of a Cased Drilled Shaft

This paper analyzes the undrained bearing capacity of temporary cased drilled shaft foundations installed as part of a new tower in Zagreb, Croatia. The comprehensive analysis focuses on skin friction resistance factors using in-situ static and dynamic test loading tests, a finite-difference computational model, and multiple semi-empirical bearing capacity equations. The cased drilled shafts support a 19-story tower on a layered deposit of soft, normally consolidated clay overlying stiff, normally to slightly overconsolidated Zagreb clays. Furthermore, the finite-difference simulations complement the dynamic testing to better understand the spatial and temporal evolution of the load transfer mechanism between the cased drilled shafts and adjacent soils during testing. Although many large-diameter piles have already been installed in Zagreb for buildings or bridge support, the skin friction resistance factors have not been fully understood in local clays, while full-scale in-situ testing has rarely been disseminated to a broader public. Therefore, the presented study will help guide future designs for cased drilled shafts in clays and contribute to global databases. In addition to exhibiting satisfactory bearing capacity in the tests performed as part of this study, the foundation raft system and the tower’s superstructure performed well during the 2020 Zagreb Mw5.3 and 2020 Petrinja Mw6.4 earthquakes.

Horizontal bearing capacity factors for conical footings on clay

Many offshore foundations can be approximately treated as circular footings. There have been a number of studies in the past few decades on the vertical bearing capacity of circular foundations, however, limited work has been reported for buried footings under horizontal loading. This paper presents the results of a numerical investigation into the undrained bearing capacity of conical footings in clay for both uniform and linearly increasing shear strength profiles. In total 1296 three-dimensional finite element limit analyses were conducted to investigate the horizontal bearing capacity, considering the effects of embedment ratio, foundation–soil interface roughness, conical angle and soil strength heterogeneity. The effects of each of the above critical factors on the horizontal bearing capacity are presented and discussed. The bearing capacity factors in this study are summarized in design tables, providing new solutions to improve the current design practice for conical footings in clay soils.

An assessment of the mechanical performance of a novel sand bentonite-glass fiber composite for the avoidance of catastrophic landfill failure

• Octahedral shear stress increased higher at the fiber aspect ratio than at the fiber dosage. • At peak and residual stress, bearing capacity factors improved significantly. • Negative excess pore waster pressure increased with an aspect ratio of 40. • Energy absorption capacity was the function of fiber dosage and fiber aspect ratio. Compacted sand bentonite (CSB) blend is one of the finest materials for landfill construction. CSB mixes with a strain-softening tendency may fail abruptly, increasing soil permeability. Water movement over the shear zone can induce flow slides, triggering a catastrophic collapse. Waste glass fiber was added to the CSB mixture (90:10) in various fractions (0.5 %, 1, and 1.5 %) and aspect ratios (l/d = 40, 80, and 120) to prevent the soil structure from collapsing. A full-scale consolidated undrained (CU) test was conducted to assess (i.e., c-phi-analysis) the load-carrying capabilities of waste fiber soil composite. The octahedral shear stress was increased significantly for both stress level (i.e., peak and residual stress). Positive pore water pressure (PWP) increased progressively after initial yield, while negative PWP reduced as the aspect ratio increased from 80 to 120. Fiber dosage and fiber aspect ratio improved bearing capacity factors (N c ,N q ,N ϒ ) and undrained bearing capacity. The EAC (Energy absorption capacity) was determined using a numerical integration approach through MATLAB (version14), and the use of waste fiber resulted in a considerable improvement. Several variables contributed to the principal stress and soil modulus. Accordingly, they were framed with all the variables and built a model that matched the experimental results well.

Effect of the circular cavity on the undrained bearing capacity of shallow strip footing

Effect of the circular cavity on the undrained bearing capacity of shallow strip footing

Discussion of “Undrained Bearing Capacity Factor N c for Ring Foundations in Cohesive Soil” by Kedar Birid and Deepankar Choudhury

Discussion of “Undrained Bearing Capacity Factor <i> N _c </i> for Ring Foundations in Cohesive Soil” by Kedar Birid and Deepankar Choudhury

Failure Envelopes for Circular Foundations on Two-Layered Clay under Combined Loading

This study numerically investigates the undrained bearing capacity of circular foundations founded on a two-layered clay under combined loading of vertical, horizontal, and moment loads using three-dimensional finite-element analysis. Each clay layer has different thicknesses and shear strengths, and two types of foundation–subsoil interface are considered: an interface with (a) zero tensile capacity or (b) nonzero tensile capacity. Analysis results are presented in the form of normalized failure envelopes for a wide range of layer thicknesses and shear strength ratios. The presented normalized failure envelopes under combined loads with or without the interface tension can be considered as graphical solutions for circular foundations on a two-layered clay in offshore marine environments. Failure mechanisms under various combined loads provide further insights into foundation-layered soil interactions.

Closure to “Undrained Bearing Capacity Factor N c for Ring Foundations in Cohesive Soil” by Kedar Birid and Deepankar Choudhury

Closure to “Undrained Bearing Capacity Factor <i> N _c </i> for Ring Foundations in Cohesive Soil” by Kedar Birid and Deepankar Choudhury

Undrained stability of dual tunnels in layered soils with different strength

The stability of dual circle tunnels buried in layered soils with different shear strengths was investigated by using finite element limit analysis (FELA). The emphasis of this study is in quantitating that the existing tunnels affects the newly-built one, and design suggestions have been provided especially in the optimum location of construction. By imposing a FELA modelling, the variation trends of undrained bearing capacity with different influential factors, including the horizontal distance, vertical distance, the thickness of the top layer, the shear strength ratio of the layered soil, were further investigated. It is concluded that there exists an inclination-fixed worst-band, in which there would be a worst undrained stability once the bottom tunnel was constructed in the band. It is interested that the inclination seems constant by varying several factors but the horizontal distance would be changed with the soil properties. In addition, three patterns of collapse were summarized.

Lower bound analysis of rectangular footings with interface adhesion factors on nonhomogeneous clays

Solutions based on lower bound limit analysis provide a safe estimate of stability, and thus they are valuable for design and analysis in practice. In this paper, new lower bound solutions of the undrained bearing capacity of rectangular footings are first presented with consideration of adhesion factors at soil–footing interfaces and linearly increasing strength with the depth of clays. The new solutions of the problem are numerically derived using three-dimensional lower bound finite element limit analysis with semidefinite programming. The new solutions are expressed in terms of dimensionless parameters, including footing aspect ratios, adhesion factors at soil–footing interfaces, and normalized strength gradient factors. A statistically algebraic equation of the undrained bearing capacity of rectangular footings is also proposed for the first time.