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Axisymmetric solutions for the bearing capacity of ring foundation resting on anisotropic and heterogenous clays are presented in this paper using finite element analysis (FEA). The NGI-ADP model in PLAXIS FEA, a widely used anisotropic soil model, is adopted to study the stability responses of ring foundations, with special consideration given to the effects of increasing undrained shear strength with the depth. Numerical results are formulated in terms of a dimensionless stability number (bearing capacity ratio) that is a function of three dimensionless input parameters: namely, the ratio of inner and outer radius, the increasing strength gradient ratio, and the anisotropic shear strength ratio. The influence of each dimensionless input parameter on the bearing capacity ratio is investigated using design charts and failure mechanisms, and they are scored by relative importance indexes in multivariate adaptive regression splines (MARS) model—a machine learning approach. A highly accurate equation generated from the MARS model is proposed as an effective tool for engineering practitioners.

New limit analysis solutions for the end bearing capacity of annular foundations in clay with linearly increasing shear strength are presented in the paper. The strength profile of clay corresponds to a typical case of a normally consolidated clay in deep water, where the strength at the ground surface is defined as zero and increases linearly with the depth. The annular foundation has internal and external radii and is embedded in clay, where the adhesion factor representing the strength at the soil-structure interface is also taken into account. Using the lower and upper bound finite element limit analysis, the end bearing capacity factor of this problem can be obtained based on three considered dimensionless parameters, which are the ratio between the internal radius and the external radius, the embedded depth ratio, and the adhesion factor. The collapse mechanisms of annular foundations in clay are also examined and discussed in the paper to portray the effects of the radius ratio, the depth ratio, and the adhesion factor.

In this paper, new limit analysis solutions for the bearing capacity of ring foundations on rock masses are presented, where the Hoek–Brown yield criterion is used as a failure criterion for rock masses. The lower and upper bound finite element limit analysis is employed to derive the bearing capacity solutions of ring foundations on rock masses. The ring foundation has internal and external radii. The considered dimensionless parameters include the ratio between the internal radius and the external radius, the yield parameter, and the geological strength index of rock, where the effects of these dimensionless parameters on the bearing capacity factor are investigated. It is found that a high yield parameter or a high geological strength index yields a high value of the bearing capacity factor. When the ratio between the internal radius and the external radius is around 0.25, the bearing capacity factor becomes the largest. The collapse mechanisms of this problem are also examined and discussed in the present study.

An upper bound (UB) and lower bound (LB) finite element limit analysis cooperating with a machine learning method is adopted as a new solution for predicting the bearing capacity of conical foundations embedded in anisotropic and heterogenous clays. The anisotropic and heterogenous clays are simulated by anisotropic undrained strength (AUS) model for capturing the anisotropic strengths of clays. The bearing capacity of the conical foundation is investigated using the dimensionless parameter approach. The bearing capacity factors, as well as the failure mechanisms of conical foundations, are examined through 1296 numerical cases with changing of four input dimensionless parameters, namely cone apex angle, embedded depth ratio, the anisotropic ratio, and the strength gradient ratio. Based on numerical results, a machine learning technique of multivariate adaptive regression splines (MARS) model is used for accessing the sensitivity of each investigated dimensionless parameter and functioning the relationship between input parameters and output bearing capacity factors. The results of the analysis are prepared in charts, design tables, and empirical equations from MARS. The paper can be the theory guidelines for initial design and provide an effective tool for practitioners in determining the bearing capacity of conical foundation embedded in anisotropic and heterogenous clays.

Exploring the behavior of conical footings is a significant aspect of geotechnical engineering, particularly in supporting wind turbine towers on mountain slopes. This study employs Finite Element Analysis (FEA) within Plaxis 3D to investigate the behavior of conical footings. The Mohr-Coulomb material is assumed, and the research focuses on two pivotal parameters of soil shear strength: c (cohesion) and φ (friction angle). The study aims to assess the impacts of geometry parameters, consisting of the conical angle ( α ), the setback ratio ( b/B ), and the slope angle ( β ), on the failure mechanisms of conical footing. Furthermore, Multivariate Adaptive Regression Splines (MARS) models are implemented with the FEA dataset to propose a predictive formula of the UBC (ultimate bearing capacity) factor, indicating the relationship between these five input parameters and the outcome UBC. A sensitivity analysis was also examined, revealing the contribution of each variable to the UBC of conical footings on slopes.

A new algorithm based on the load-transfer method is presented in this study to determine the behavior of bored piles that are strengthened by shaft grouting (shaft-grouted piles). Using an exponential load-transfer model, the relationship between mobilized loads and settlements at the pile shaft and tip is established in this study. Analysis results are compared with full-scale pile load tests on a bored pile and a shaft-grouted pile in Ho Chi Minh City, Viet Nam. A good agreement between the predicted and the measured results of the load settlement curve was found. The proposed method can be used in the preliminary design of shaft-grouted piles, and it should be of great interest to practical engineers.

Stability evaluations of soil or rock excavation are significantly affected by the shape of the underground cavity. Whilst most of the previous stability research was in circular tunnelling problems, rectangular tunnels are nevertheless seldom studied even though the latter is gaining more popularity in practices, especially in railway engineering. The purpose of the technical note is to bridge the current research gap using the robust lower and upper bound finite element limit analysis to study the undrained stability of wide rectangular tunnels in cohesive soils under both collapse and blowout scenarios in two-dimensional conditions. A dimensionless stability number is presented to define the solution and the associated failure mechanisms are examined with three distinct types of mechanisms. In addition, a machine learning model, namely, multivariate adaptive regression splines (MARS), is used to develop design equations for evaluating soil stability. The findings in this study provide a reliable solution to improve the current design standard for the stability of rectangular underground spaces in undrained clays.

Accurate prediction of wall displacements induced by deep excavations is essential to guarantee stability and safety of the excavation as well as to prevent any harm and damage to the adjacent structures. This paper proposes and validates a set of equations for determining soil parameters of hardening soil model with small-strain stiffness (HS-small model) for medium dense sand in Ho Chi Minh City (HCMC), Vietnam. The study was based on back-analysis of diaphragm walls’ displacements from three well-documented excavation cases and data from twenty boreholes. Good agreements between finite element analysis (FEA) results and field observations were obtained by assuming the E50 stiffness value to 2500N (kPa) (N is the SPT value), the small-strain shear modulus, G0, to 7000ρN0.7 (kPa) and the shear strain at which the shear modulus is reduced to 70% of small-strain modulus, γ0.7, to 0.0002. The comparisons with field measurements indicated that HS-small model can better predict the diaphragm walls’ displacements than hardening soil model (HS model). Additionally, the field displacements of diaphragm walls in medium dense sand are in the range of 0.1–0.3%H (H is excavation depth).

The uplift capacity factor of cylindrical suction caisson in anisotropic and inhomogeneous clays considering the adhesion factor at the interface is investigated in this paper. The finite element limit analysis based on lower bound and upper bound analyses is used for analyzing purposes. The anisotropic undrained shear model is employed to describe the anisotropic and inhomogeneous clay. The impact of these dimensionless parameters on the ratio of inhomogeneity or strength gradient ratio, the adhesion factor, the ratio of depth over diameter, and the ratio of anisotropic undrained shear strengths on the uplift resistance and the collapse mechanisms of suction caisson foundations are determined. The multivariate adaptive regression splines technique is employed to access the sensitivity of all considered dimensionless parameters on the uplift capacity factor and to propose an empirical design equation as an effective tool for predicting the uplift capacity factor. The results presented in this paper can be guidance for the preliminary design of suction caissons in anisotropic and non-homogeneous clays that are useful for engineering practitioners.

This paper investigates the behavior of deep excavations and damages on adjacent buildings based on an excavation in a thick sand layer in Vietnam. Firstly, measured horizontal displacements of diaphragm walls were used to calibrate soil stiffness parameters for finite element analysis (FEA). Then, the behavior of diaphragm walls, groundwater, ground surface deformation, and an adjacent building was analyzed. The analysis results and damages observed in the field were used to review the validity of the criteria for evaluating the damage potential of excavation to adjacent buildings. It can be concluded from the study that the damage potential of adjacent buildings as evaluated from FEA through the strain state chart proposed by Boscardin and Cording (1989) or the damage potential index (DPI) proposed by Schuster et al. (2009) is fairly accurate with field observations.