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This document discusses a research paper that proposes a modified method for evaluating the stability of deep excavations in soft clays. The discussion raises concerns about the proposed method and questions the assumptions made by the authors. It suggests alternative explanations for the observed behavior of excavations in soft clays and criticizes the models used in the study for not accurately representing actual ground movement patterns caused by excavation. The author invites the study authors to respond to these criticisms. [Extracted from the article]

In the literature, the influence of spatial variability of the undrained shear strength of foundation soils on the bearing capacity of footings is limited to footings seated directly on the foundation. This is an unlikely arrangement in practice. This paper revisits the footing problem by considering a thin granular layer between a strip footing and soft foundation soil using analytical and stochastic numerical modeling. The analyses are extended to the case of a geosynthetic-reinforced granular layer and to the idealized case of no granular layer. The study shows that the probability that the ultimate bearing capacity for the footing is smaller than the deterministic design value is greater for all three scenarios with randomly uniform clay soil than for the same soil with isotropic or anisotropic spatial variability of strength at practical levels of reliability index β (e.g., β≥3.09 for a permanent footing). The reason for this outcome, which may appear counterintuitive, is explained. Design charts are provided to estimate the deterministic design bearing capacity of a rigid strip footing required to meet a range of target reliability index for the three footing scenarios examined in this study. [ABSTRACT FROM AUTHOR]

As a widely used taut-wire mooring system for deepwater platforms, the Vertically Loaded Anchor (VLA) has better performance in bearing capacity, angle adaptability, and deepwater installation than other systems. However, the installation process of the VLA and its motion characteristics are significantly impacted by multi-layered seabed soil. In this paper, the coupled Eulerian-Lagrangian (CEL) large deformation finite element analysis method has been applied to analyse the continuous penetration of a VLA in nonuniform clay with an interbedded stiff layer. A detailed parametric study has been carried out to explore the trajectory, drag angle, movement direction and drag force of the VLA in layered clay with different embedded depths, thicknesses and undrained shear strength of the stiff layer. The CEL numerical analysis results have been validated by comparison with the analytical solutions from the inverse catenary equation. Excellent agreement has been obtained between the results from the CEL analyses and the analytical solutions. The stiff layer leads to concave and convex shapes on the trend lines of the movement direction angle and drag forces, respectively. The embedded depth of the stiff layer determines where the concave and convex shapes appear on the trend lines, while the thickness affects the sizes of the openings of the shapes. The most decisive parameter, an abrupt variation in the undrained shear strength, causes predominant rotation at the interface of layered clay. It diminishes the final embedment depth and ultimate stable drag force, meaning that the bearing capacity of the VLA severely declined in layered clay. [ABSTRACT FROM AUTHOR]

In this paper, the finite element method (FEM) is applied to calculate the bearing capacity of two footings having the aspect ratio L/B (where L and B are the length and width of the footing, respectively) equal to 1, 2 resting on one-layer and two-layer soil. Soil profile contains two soil types including sand and clay. The soil strip is 500mm × 500mm × 350mm; however, only a quarter of the model (250mm × 250mm × 350mm) is examined in the study. Two primary situations are investigated in this study. In the first situation, the one-layer system is supposed to be sandy soil with footing overlays on medium-dense sand. The soft clay/stabilized clayey layer is supposed to be on top of the sandy soil in the second condition, with the footing resting on top of the soft clay/stabilized clay. The influence of layer thickness, aspect ratio, and material property on the bearing capacity value and footing failure mechanism is studied for eight different combinations of layered soil. The bearing capacity for a one-layer case is also estimated, and it agrees well with Vesic (1973), Hansen (1970), and Terzaghi's (1943) equations. The bearing capacity of footings is observed to decline when the height of unstabilized clayey soil increases, and it increases when clayey soil is stabilized with molasses, waste foundry sand, and lime alone and in combination with each other. [ABSTRACT FROM AUTHOR]

This paper reports the results of a series of centrifuge experiments exploring the dynamic response of pile foundations. The model tested in a centrifuge at 50g consisted of an isolated pile and two pile groups embedded in a kaolin clay, subjected to a sequence of quasi-sinusoidal waves with different amplitudes and frequencies. The results are back-analyzed through a two-step procedure. First, a one-dimensional ground response analysis is performed, in which the small-strain shear modulus is evaluated using data from air hammer tests, while a literature model is used to account for nonlinearity of soil behavior. Second, a three-dimensional finite-element analysis of the model foundations is carried out using the mobilized soil damping ratio and shear modulus determined from the previous step. The aforementioned procedure allowed to reproduce satisfactorily the response of the model foundations tested in the centrifuge, showing that the response of these models is strongly affected by the inertial oscillation of the cap connecting piles necessary to accommodate the measurement devices and to rigidly connect the piles' heads of the groups. The same numerical model was then adopted to evaluate the change of seismic motion due to pure kinematic interaction effects by setting the pile cap mass equal to zero. This allowed to check the prediction capability of simplified methods of analysis for the evaluation of the base excitation of pile-supported structures. In addition, a number of issues related to the execution of centrifuge tests aimed at investigating the kinematic interaction between pile and soil are highlighted and discussed. [ABSTRACT FROM AUTHOR]

This paper presents an alternative construction method of a highway along coastal area underlain by a thick normally consolidated very soft organic clay, which due to its remote location, mitigations to strengthen the soft clay are deemed too costly and/or require significant time to mobilize. Without mitigations, the presence of this very soft clay necessitates the roadway embankment to be constructed in phases to allow partial consolidation of clayey soils to take place before additional embankment fill can be placed. The stability of partially built embankment is evaluated, and the fill thickness and staging time for each phase are adjusted to meet the stability safety requirements. The settlement due to fill placement can be estimated at each construction phase and included as an overbuilt to the next fill placement thickness. Impacts of soil horizontal and vertical movements due to filling to pile foundations are also be discussed. [ABSTRACT FROM AUTHOR]

A ring foundation is widely used in bridges, water towers, caissons, and other engineering structures, and its ultimate bearing capacity is one of the significant concerns in engineering design. This paper is aimed at exploring the ultimate bearing capacity of ring foundations embedded in undrained clay. Based on the finite element limit analysis, effects of the inside-to-outside radius ratio, embedment depth ratio, cutting face inclination angle, and face roughness on the vertical ultimate bearing capacity of ring foundations are investigated. The results show that the ultimate bearing capacity of the ring foundation increases gradually with the embedment depth ratio. When the embedment depth ratio D / B reaches a critical value, the bearing capacity tends to be stable, and the critical embedment depth ratio is affected by the inside-to-outside radius ratio of the ring foundation, varying from 0.2 to 0.4. The ultimate bearing capacity of the ring foundation decreases with cutting face inclination angle β. When β ≤ 40 ° , the ultimate bearing capacity tends to be stable, and the bearing capacity is reduced by approximately 30%. The influence of the cutting face inclination angle on the bearing capacity is highly dependent on the roughness of the cutting face. [ABSTRACT FROM AUTHOR]

Removal of soil around a bridge foundation due to scour results in a reduction of the lateral and vertical foundation capacity due to the loss of soil support. The common approach in modeling the scour phenomenon of removal of soil springs without modifying the parameters of the remaining soil fails to consider the change of stress state of the remaining soil and the formation of scour hole geometry around the pile foundation. In practice, both of these factors impact the mechanical properties of the remaining soil and the resulting expected structural response of the pile under loadings. This paper proposed a methodology to comprehensively evaluate the combined effects of stress history and scour hole dimensions on piles under scour conditions in uniform soil. It enabled the examination of the lateral and axial behaviors of a loaded pile subject to scour and is applicable for both cohesive and cohesionless soils. The methodology was validated with results from field tests for no-scour scenarios and verified with existing numerical models for scour scenarios. Quantification of the soil effects was investigated through lateral pile deflection and load-settlement curves for lateral and axial behaviors, respectively. Load-settlement curves demonstrated that including the effect of stress history results in increases of up to 34.1% and 61.1% in estimated pile settlement for sand and clay, respectively, leading to potential unconservative designs if soil effects are not properly included in the analysis. [ABSTRACT FROM AUTHOR]

Pile foundations supporting offshore structures, such as jacket platforms and wind turbines, are subjected to cyclic lateral loading. The capacity and deformation of these pile foundations under cyclic lateral loading are important and challenging design aspects. This paper presents the results of a series of four lateral load pile tests in an overconsolidated clay at the Haga site and their back-analysis using a p-y framework based on fundamental soil behavior measured in the laboratory at the element level. This framework can account for site-specific cyclic soil properties, summarized in classic contour diagrams, and site-specific cyclic loading characteristics in design. The paper first provides a summary of the framework and outlines the important assumptions and calculation procedures. It then presents a detailed description of the test setup and soil conditions. The pile load test results and the back-analysis are subsequently presented. Generally, a good match between the test results and the model predictions was observed, demonstrating the model's capability to capture the essential behavior of pile foundations under monotonic and cyclic lateral loading. [ABSTRACT FROM AUTHOR]

This paper describes large deformation finite element (LDFE) analysis of the penetration of the T-bar penetrometer in uniform clay, identifying soil flow mechanisms around the T-bar, the extent of any cavity above the T-bar and the evolving penetration resistance profile. A trapped cavity above the advancing T-bar penetrometer and its influence on the corresponding bearing capacity factor are the crucial findings of this paper. The formation and evolution of the trapped cavity mechanism are studied extensively, exploring a large range of normalized undrained shear strength of soil and surface roughness of the T-bar. It is shown that the depths of forming a trapped cavity and being fully filled with soil increase with increasing normalized undrained shear strength of soil and roughness of the T-bar. The trapped cavity results in a reduction (up to 13%) in the commonly used bearing capacity factors based on plasticity solutions and a flow-round failure mechanism. According to the depth span of an existing trapped cavity, there are three scenarios: (1) for clay deposits with su/γ′D≤1 , a shallow failure mechanism is directly followed by a flow-round mechanism since the trapped cavity span is negligible; (2) for clay deposits with 18.3 , the trapped cavity is not fully closed up to a penetration of 30D , leading to a lower bearing capacity factor profile compared to the stabilized factors for the other two scenarios. A systematic interpretation procedure is therefore proposed to account for the effect of a trapped cavity for more accurate interpretation of soil undrained shear strength from the T-bar penetration resistance. [ABSTRACT FROM AUTHOR]

Research indicates the presence of in situ structure of soil skeleton in several natural deposits of clay. However, the effect of such in situ structure and its evolution during loading are rarely accounted for in solution of boundary value problems in geomechanics. This paper explores the effects of inherent soil structure and its degradation on bearing capacity of circular footings in structured clays. An advanced constitutive model that accounts for stress-induced anisotropy, soil structure, and their evolutions with loading is implemented within a finite element analysis (FEA) framework. FEA results demonstrate a significant increase in the bearing capacity of structured clay as compared to that in reconstituted clay. Nonetheless, such an enhancement in limit bearing capacity is subdued by destructuration of soil below the footing. A bearing capacity factor accounting for soil destructuration is proposed for inclusion in the limit bearing capacity calculation of circular footings on structured clay. Successful numerical predictions of results from an instrumented field load test on a footing resting on structured clay further substantiates the importance of considering soil destructuration in bearing capacity analysis. [ABSTRACT FROM AUTHOR]

This paper presents a field test on the axial and radial thermal responses of friction-type energy piles embedded in clay under monotonic thermal loads (2.5 and 5.0 kW). The inlet and outlet water temperature, pile temperature, and strain were monitored. The heat exchange efficiency and thermal response of the energy pile are discussed and analyzed. Further comparative analyses of friction-type energy piles embedded in compacted sand showed that the radial thermal stress of a pile is much lower than the axial thermal stress, which may not play a major role in soil–structure interaction. The axial thermal stress of an energy pile embedded in clay increases with increasing axial constraint. The constraint of the energy pile cannot be simply predicted through the shear strength of the sand. The influence of the radial thermal stress produced during the operation of the energy piles on the bearing capacity of the pile can be disregarded, especially in soft soil. [ABSTRACT FROM AUTHOR]

This paper proposes a theoretical method to estimate the long-term time-dependent bearing characteristics of a driven pile. The viscoplastic behavior of the surrounding soils is described by nonstationary flow surface (NSFS) theory. The evolution of the soil behavior due to aging is incorporated in a skin friction softening model, which is used in the load-transfer method to predict the bearing capacity evolution of a driven pile. Extensive comparisons with experimental data are performed to illustrate the effectiveness and accuracy of the theoretical method. Both the proposed method and the experimental data show that the bearing capacity of the test piles increases by 30–50% due to the aging effect. The good agreement indicates that the long-term capacity evolution can be evaluated using the proposed method. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the bearing capacity and the failure mechanism of obliquely loaded footings on sand overlying clay are determined by using discontinuity layout optimization (DLO) procedure. The solution is illustrated as a set of design charts with the use of dimensionless parameters. Parametric studies are performed to show that soil properties, geometric parameters, and load inclinations are all related to the bearing capacity and failure pattern. A simplified model is developed based on artificial data generated through DLO. Validations are carried out to demonstrate the accuracy of the developed model. [ABSTRACT FROM AUTHOR]

A cyclic-softening macro element model that represents mono-bucket foundation supporting offshore wind turbines in clay is presented in this paper. The model is formulated based on multi-surface plasticity with kinematic and isotropic hardening rule. The softening behaviour of the foundation subjected to a cyclic load sequence is captured real-timely in the macro element model through the contraction of yield surfaces. The model parameters are calibrated by uniaxial quasi-static load–displacement curves, which are obtained by finite element analyses with the cyclic behaviour of soil simulated via the cyclic contour diagram approach. The performance of the macro element model in representing the softening of a bucket foundation during a cyclic load sequence is demonstrated by comparing with parallel finite element analyses. A reasonable agreement has been achieved. The procedure to apply the model is suggested, considering different working scenarios with various cyclic to average load ratios. The macro element model developed is capable of capturing the real-time displacement of foundation in a load sequence, with high computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

Natural clay setup significantly contributes to the improvement of the bearing performance of a jacked pile. This paper presents a semianalytical solution to predict the time-dependent bearing capacity of a single pile in natural clays. The proposed solution properly incorporates the initial structure and stress-induced structure degradation of soils and the subsequent thixotropic and reconsolidation of disturbed soils. Pile penetration is simulated using the cavity expansion method (CEM) based on the Modified Structured Cam Clay (MSCC) model. The governing equations computing stress components during consolidation are established using a variable relaxation gradient function and are numerically solved by combining initial boundary conditions. A functional relationship between the ultimate strength and stress state of soils is presented according to critical state soil mechanics theory. The predicted results are validated against the results from the existing analytical approach, published centrifuge model tests, and laboratory model tests in structured clays. The excellent agreement between the measured and predicted values demonstrates that the method can properly predict the time-dependent bearing capacity of jacked piles in structured clays. Considering the impact of soil structure on soil setup plays a significant role in quantitatively evaluating the time-dependent bearing capacity of piles in natural clays. [ABSTRACT FROM AUTHOR]

Predicting the bearing capacity of a spudcan foundation under combined vertical ( V ), horizontal ( H ) and moment ( M ) loads is a challenging problem encountered by geotechnical engineers. In previous studies the combined VHM capacity was defined for a uniform soil profile, ignoring any variability in soil stratification and properties. In offshore conditions, however, both the soil profile and soil properties vary spatially. Therefore, it is of interest to account for the spatial variability of soil in the analysis of the bearing capacity of a spudcan. It is shown in this paper how the spatial variability of a clay affects the bearing capacity of a deeply buried spudcan foundation under combined loadings. Three-dimensional random fields are generated to model the spatial variability of undrained shear strength of clay and combined with a non-linear finite element analysis to investigate and define the VHM failure envelope of a spudcan foundation. Because of the random nature of soils VHM failure envelopes of different probability of occurrence are proposed. Results from this study provide guidance to the practical assessment of spudcan foundations in spatially varied soil conditions that can be encountered offshore. [ABSTRACT FROM AUTHOR]

The paper shows the increase in vertical and combined horizontal and moment bearing capacity of jack-up spudcan installed in silty clay, when a load-hold period is accounted for. The numerical implementation of a hypoplastic model for structured clays, combined with large deformation coupled analyses allowed the modelling of the spudcan installation process. Results were mapped into three-dimensional small strain analyses, conducted to investigate the combined loading capacity and describe the yield surface. The underlying failure mechanisms were investigated and increases in capacity due to consolidation determined. Experimental centrifuge data on carbonate silty clay validated the qualitative trend revealed numerically. [ABSTRACT FROM AUTHOR]

Creep as an intrinsic property of clay is non–negligible in predicting ground settlements in land reclamation construction and foundations on reclaimed land and soft soils, but it is unfortunately difficult to characterize in current self–weight consolidation analysis. This paper develops a one–dimensional (1D) finite strain consolidation model to take into account the creep of soft clay, particularly during the early stages of reclamation construction, mainly in a self-weight consolidation process. In this model, the Yin–Graham 1D Elastic Visco-Plastic (EVP) model is first extended for modelling self-weight finite strain consolidation of soft clays to describe the creep of soil skeleton under extremely high water content. The Darcian and non-Darcian flow, nonlinear compressibility and permeability of soft clays with a huge variety of water content are also considered. Governing partial differential equations using the EVP model are derived. These nonlinear partial differential equations are solved using the Crank–Nicholson finite difference method. Three case studies involving a wide range of initial void ratio values are simulated, which show that the present model, with more realistic consideration of creep feature of clays than previous ones, can capture the self-weight consolidation process well when compared with physical model test results. [ABSTRACT FROM AUTHOR]

Scour can cause the water-induced failure of fluvial and marine bridges and structures. Previous studies have focused on the scour mechanisms and their effects on the load capacity of single piles, although deep foundations consist mostly in pile groups. In this paper, scouring on pile groups embedded in soft clay is studied when piles are laterally loaded and affected by the formation of scour holes. This boundary problem is simulated using the three-dimensional finite element method. The scour depth, slope angle, and pile spacing are analyzed as main influence factors. Summary charts quantify how the dimensions of scour holes affect the lateral load capacity of 3x3 pile groups for varying pile spacing and their corresponding p -multipliers. Importantly, results indicate that it is unreasonable to design pile foundations by ignoring the influence of scour holes or directly removing the soil layer above the scour depth, as frequently assumed in practice. [ABSTRACT FROM AUTHOR]

The small-strain performance of offshore wind turbine (OWT) pile foundations under lateral loading is critical for the foundation safety and the fatigue analysis of superstructure but is less explored in recent studies. This work presents p-y curve analyses of monopiles in marine clay that account for complete nonlinear soil stress–strain relationship. Based on a small-strain stress–strain relation, Total-displacement-loading Extended Mobilisable Strength Design (T-EMSD) analyses are performed to interpret the pile-soil interaction. On the basis, an analytical p-y curve model is proposed. An elastoplastic constitutive model with small-strain non-linearity is developed, and then p-y curve validation against finite element simulations is carried out. Furthermore, by comparing to centrifugal test observations and existing p-y models, good agreement and noticeable improvement are shown. This paper provides industry engineers with a timely and effective approach for OWT foundation design, allowing for inputting soil characteristics measured at in-situ site and laboratory. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Accurately predict the resistance of caisson penetrating in stratified soil deposits is an engineering challenge for application of such foundation system. This paper performs large deformation finite element analysis to investigate the penetration behavior of caisson foundations in non-uniform clay interbedded with a sand layer. The numerical model is validated by comparing with previously testing data, in which good agreement is obtained. Parametric study is then conducted to examine potential influencing factors, including the penetration depth, the top clay layer thickness, clay properties, and the thickness of the second sand layer. It is found that the soil failure mechanism and corresponding penetration resistance of caisson foundations in clay-sand-clay are significantly different from that in pure clay or sand soil deposits, especially for the part in the middle sand layer, where the peak resistance could be overestimated by 10–40% using the current design codes without considering the influence of the weak underlying layer. In this study, based on intensive numerical modeling results, approximating expressions are proposed to describe the unique trends of the resistance profile for caisson penetration in non-uniform clay interbedded with a sand layer soil deposit, which can provide design guide for engineering application. [ABSTRACT FROM AUTHOR]

[Display omitted] An analytical method for quantitatively predicting the existing pile behavior induced by adjacent pile driving is of great engineering significance to evaluate the potential influence of adjacent pile penetration on existing piled buildings. In this paper, a simplified two-stage approach is employed to derive the vertical and lateral responses of the existing pile during adjacent pile installation. First, the free-field soil movement due to pile penetration is estimated by an improved source-sink imaging technique considering the existence of the top free surface. The validity and accuracy of this calculation approach are subsequently examined via comparison with published studies. Second, the shear-displacement method and improved Pasternak foundation model incorporating the impact of lateral soil displacement are introduced to investigate the pile-soil interaction. Moreover, based on the Randolph-Worth logarithmic attenuation function and Mindlin's solution, the pile group response considering the shielding effect of piles is analyzed. Finally, the present solution for a single pile response is validated with the existing theoretical solution and the simulation solution, and extensive parameter studies are conducted to systematically discuss the variation of the behavior of the existing single pile and pile group. [ABSTRACT FROM AUTHOR]

A novel side-rounded suction caisson foundation is proposed in this study. Compared to a conventional circular shape in plan, it has a rectangular middle section inserted in between the two circular halves for increased moment capacity. This paper presents an investigation into the bearing performance of this novel foundation in clay under uniaxial and combined loading by means of an extensive finite element parametric analysis. It is found that by adopting a dimensionless equivalent embedment ratio and a dimensionless equivalent strength heterogeneity ratio, which account for the side-rounded shape of the proposed foundation, its design approach can be unified with an existing framework established for conventional skirted circular footings. The advantage of the proposed foundation and the application of the proposed design method is demonstrated through an example application. [ABSTRACT FROM AUTHOR]