Boonchai Ukritchon

Finite element analysis of undrained stability of cantilever flood walls

In this study, new undrained stability solutions of cantilever flood walls in clay were proposed and solved by finite element analysis with a two-dimensional plane strain condition. The analysis considered flood walls in homogeneous and non-homogeneous clay layers, where the latter corresponded to a linear increase in shear strength with depth. Two parametric studies were performed for embedded length ratios and dimensionless strength gradients. Results were summarised in the form of design charts for stability number, normalised maximum shear force and normalised maximum bending moment as a function of those two parameters. Closed-form solutions were proposed for a convenient and accurate evaluation of undrained stability of flood walls in practice, and their applications were demonstrated through a back analysis of a case study.

Undrained face stability of tunnels in Bangkok subsoils

This paper presents the analysis of undrained face stability of tunnels in Bangkok subsoils. In this study, two-dimensional (2D) and three-dimensional (3D) finite element analyses were employed to analyse the 2D plane strain conditions of transverse (2DT) and longitudinal (2DL) sections as well as the full 3D geometry, respectively. The simplified geometry of 2DT corresponds to the circular face of tunnels subjected to a uniform face pressure, while that of 2DL correspond to the plane strain heading applied by a uniform face pressure at the front plane. For the 2D plane strain transverse and longitudinal sections, the tunnel lining was not considered in the analyses. For 3D cases, tunnel linings were included in the analysis and modelled as the rigid plate element with the fully rough surface along their lengths, while the tunnel face was subjected a face pressure. For all cases, the uniform surcharge was applied all over the ground surface. Strength reduction methods in conjunction with 2D and 3D finite element analyses were employed to determine the stability and the factor of safety of this problem. The stability analyses included ranges of tunnel face pressure measured during the tunnelling process. Effects of three-dimensional stability of tunnel face were also presented and discussed in this paper. Results of analyses were verified and compared with existing methods.

Bearing capacity of shallow foundations in clay with linear increase in strength and adhesion factor

ABSTRACT In this paper, the computational lower bound (LB) limit analysis using finite element with second-order cone programming was used to investigate the LB solutions of the undrained bearing capacity of continuous footing with a linear increase in the strength profile and an adhesion factor at the soil–footing interface. A full range of parametric studies of the dimensionless strength gradients and adhesion factors at the soil–footing interface were performed in the LB calculations. The results were verified by comparison with the available solution from the method of characteristics (slip-line analysis) for perfectly smooth and rough footings. The LB analyses were able to complete a prior solution of undrained bearing capacity with a linear increase in the strength profile by incorporating the influence of adhesion factor at the soil–footing interface. Based on the nonlinear regression to the computed LB solutions, an approximate expression of the LB solution regression was proposed, which is applicable to an accurate prediction of a safe load for offshore shallow foundations in clay with an arbitrary linear increase in strength and adhesion factor at soil–foundation interface in practice.

Three-dimensional interaction diagram for the undrained capacity of inverted T-shape strip footings under general loading

This paper presents new solutions of a three-dimensional (3D) interaction diagram for the undrained capacity of inverted T-shape strip footings under general loading. The two-dimensional plane strain finite-element analysis was employed to determine the stability of this problem. Parametric studies were performed to study the interactions of the combined vertical load (V), horizontal load (H) and bending moment (M) that were applied on top of the inverted T-shape footing. The combined action of vertical forces included both tensile (upward) and compressive (downward) loadings. The results of these analyses were summarised in terms of the dimensionless factors for V, H and M. Failure mechanisms associated with different locations on the 3D interaction diagram were compared and discussed. A closed-form approximate solution of the 3D interaction diagram for inverted T-shape strip footings under the V–H–M loading was proposed and compared with the finite-element solutions.

Stability of Retained Soils Behind Underground Walls with an Opening Using Lower Bound Limit Analysis and Second-Order Cone Programming

Lower bound finite element limit analysis in conjunction with second-order cone programming is developed and employed to investigate the stability of retained soils behind underground walls with an opening in cohesive-frictional soils. In this study, two-dimensional plane strain condition is setup for modelling the problem while the lower bound solution of the problem is obtained by employing the finite element approach of lower bound limit analysis. The lower bound optimization problem is cast as the second-order cone programming, and is solved by a conic programming algorithm. For practical use, the results of lower bound solution are summarized in the form of dimensionless stability charts of the load factor that is a function of the cover depth ratio of opening, overburden stress factor and soil friction angles. Plastic yielding zones predicted from the lower bound analysis are discussed and examined for these dimensionless parameters while the computed lower bound solutions are validated with an existing solution. Finally, a closed-form approximate expression is developed for predicting the lower bound solution of the load factor for the problem with practical ranges of cover depth ratios of opening, overburden stress factors, and soil friction angles. New opening stability factors with respect to soil cohesion and unit weight as a function of cover depth ratios of opening and soil friction angles are presented.

Experimental studies of floor slip tests on soil blocks reinforced by brittle shear pins

Abstract Massive slope failures in open pit mines are essential issues for mining projects because they can cause the loss of lives, damage to machineries and the delay of works. To understand the effect of shear pins on slope stabilisation, the aim of this paper is to employ experimental models to investigate the stability and failure mechanisms of the floor slip resistance of soil blocks that are reinforced by brittle shear pins and rest on a low-interface friction plane. The soil blocks were made of humid silica sand No. 6 and placed on a Teflon sheet. Pencil leads, 2 mm in diameter, were used as the brittle shear pins and installed perpendicularly to the bedding plane. A series of tests were carried out for the floor slip resistance of the soil blocks with shear pins by gradually tilting the models until failure was observed. Parametric studies were performed by varying the number of shear pins, the shear pin installation, and the soil block thickness. The experimental studies revealed that these parameters have a significant influence on the stability and the failure mechanisms. Three different failure mechanisms were observed in this study, namely, slip failure, punching failure and detachment failure.