In this paper, novel stability solutions of unsupported conical slopes in anisotropic clays are presented by using the lower bound and upper bound finite element limit analyses under an axisymmetric condition. The anisotropic undrained shear (AUS) model is employed in the analysis as a failure criterion for anisotropic clays. The parameters in this model consist of three anisotropic undrained shear strengths, which are directly obtained from triaxial compression, triaxial extension, and direct simple shear. The geometry of the unsupported conical slopes involves the height of the slope, the radius at the bottom of the slope, and the slope inclination angle. The stability solutions are based on the geometry and strengths of conical slopes in anisotropic clays, which are presented in the form of dimensionless design charts. The failure mechanisms of the unsupported conical slopes, where the influence of anisotropy is considered, are also demonstrated in the paper.

Undrained Stability of Unsupported Conical Slopes in Anisotropic Clays Based on Anisotropic Undrained Shear Failure Criterion

Abstract Ring foundations are widely used to support various types of offshore structures because of the cost-effective reason. Unlike the traditional circular foundations, very few studies were re... 

Undrained Stability of Ring Foundations: Axisymmetry, Anisotropy, and Nonhomogeneity

Ring foundations are widely used to support various types of offshore structures because of the cost-effective reason. Unlike the traditional circular foundations, very few studies were re...

New numerical analyses of the vertical uplift capacity of circular anchors embedded in anisotropic and non-homogenous clay are presented in this paper. These analyses are derived based on the lower bound and upper bound finite element limit analysis under an axisymmetric condition. The anisotropic undrained shear (AUS) failure criterion is applied in these analyses. The undrained shear strength of clay increases linearly with depth. The anisotropy is adopted by changing of the ratios between undrained shear strengths determined from triaxial compression test and extension test. The variation of uplift factor (Fc) and shape of failure pattern with three parameters including embedment ratio (H/B), ratio of increasing undrained shear strength with depth (m), and the ratio of anisotropic parameters (re) are verified and investigated. These analyses will provide reliable results in order to improve the engineering calculation for plate anchor embedded in anisotropic and non-homogenous clays.

Vertical Uplift Capacity of Circular Anchors in Clay by Considering Anisotropy and Non-Homogeneity

Abstract 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. 

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Bearing Capacity of Ring Foundations on Anisotropic and Heterogenous Clays: FEA, NGI-ADP, and MARS

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.

Limit Analysis Solutions for Bearing Capacity of Ring Foundations on Rocks Using Hoek–Brown Failure Criterion

This paper presents new plasticity stability solutions of unsupported conical rock slopes, obeying generalised Hoek-Brown failure criterion. To solve the problem, a finite element limit analysis framework is selected to investigate the stability of the conical rock slopes. Four dimensionless parameters influencing the stability factor of the conical slopes including excavated height ratios, slope inclinations, geological strength index and yield parameter of Hoek-Brown model are considered in this study. The numerical solutions of the stability factor of the conical slopes are proposed as design charts. The failure mechanism of conical slopes influenced by the four dimensionless parameters is also presented and discussed in the paper.

Stability of Unsupported Conical Slopes in Hoek-Brown Rock Masses

A conical slope is widely used in many constructions of in situ piles, piers, footings, mat foundations, raft foundations, energy storages, or water tanks since this unsupported excavation is much cheaper than an excavation with supports. This paper presents new plasticity solutions for undrained stability of unsupported conical slopes in two-layered clays by using axisymmetric finite element limit analysis. Four parametric studies were performed on the slope height ratio, the slope inclination angle, the thickness ratio of two-layered clay, and the strength ratio of two-layered clay, where the stability factor of this problem is investigated. In all the cases, the exact stability factors are accurately bracketed by lower and upper bound solutions within 1%. The design charts for estimating the stability of conical slopes in two-layered clays are proposed. Three failure mechanisms, i.e., toe, based, and face failures are observed and discussed in the paper. The predicted failure mechanisms of the unsupported conical slopes in two-layered clays are presented in order to portray the impact of all considered dimensionless parameters.

Wittawat Yodsomjai

Papers

Undrained Stability of Unsupported Conical Slopes in Anisotropic Clays Based on Anisotropic Undrained Shear Failure Criterion

Limit Analysis Solutions for Bearing Capacity of Ring Foundations on Rocks Using Hoek–Brown Failure Criterion

Stability of Unsupported Conical Slopes in Hoek-Brown Rock Masses

Undrained stability of unsupported conical slopes in two-layered clays

A machine learning regression approach for predicting basal heave stability of braced excavation in non-homogeneous clay