Three-Dimensional and Two-Dimensional Stability Analysis of Bentonite Slurry Trenches Using a Shear Strength Reduction Technique and Limit Equilibrium Methods

Abstract

Bentonite slurry trenches are becoming increasingly popular in the excavation of trenches, especially for diaphragm wall construction. The problem that needs to be addressed is the stability of bentonite slurry trenches. This paper presents a stability analysis of trenches with temporary support from bentonite slurry, with unit weights ranging from 10.5 to 12.0 kN/m3 in the realistic stratum, and C3 in the Hue city area. Our analysis employs the Shear Strength Reduction Technique (SSR) with Mohr–Coulomb materials to numerically evaluate the factor of safety (FS). The finite element method (FEM) software program (RS2 v. 121 and RS3 v. 4.0) and the finite difference method (FDM) FLAC v. 7.0 software were used. Additionally, the limit equilibrium method (LEM) of Bell–Washbourne and three-dimensional (3D) Bishop were used to calculate trench stability. The results of the analysis show a good agreement between RS2 and FLAC2D, and between RS3 and FLAC3D. Secondly, upon comparison, it was noted that the factor of safety of the 3D software programs (RS3 v. 4.0, FLAC v. 7.0) was higher than that of the 2D software programs (RS2 v. 11.0, FLAC v. 7.0), ranging from 52.3 to 63.0% for trench lengths of 6 m. However, for trench lengths of 54 m, the factor of safety values in 2D and 3D configurations were nearly equal. Thirdly, the factor of safety of the Bell–Washbourne method (LEM) was lower than that of the numerical analysis methods (FLAC and RS programs). Using the three-dimensional numerical method appears to be effective for estimating stability.