Discussion of “Stability of Long Trenches in Sand Supported by Bentonite-Water Slurry” by George M. Filz, Tiffany Adams, and Richard R. Davidson

Abstract

The authors have presented a valuable study on the stability of long slurry-supported trenches in cohesionless soil. Quite by chance, the discusser published a related paper two months ago Fox 2004 . The focus of that paper is the development of analytical solutions for trench stability under various conditions e.g., two-dimensional 2D versus three-dimensional 3D , drained versus undrained, cstrength , whereas the focus of the current paper is largely on understanding stability mechanisms. The two papers overlap in their analysis of 2D global stability of a slurrysupported trench with a fully formed filter cake in drained cohesionless soil. Both papers provide closed-form equations for the factor of safety and orientation of the critical failure plane Eqs. 26 and 27 in Fox 2004 and Eqs. 2 in the current paper . The discusser has verified that the values of factor of safety and critical failure plane angle given by these equations are identical. As stated by the authors, the 2D global stability equations are appropriate for long trenches without significant end effects. Three-dimensional stability effects that occur for shorter panels may yield substantially higher factors of safety. To illustrate, the discusser calculated the global factor of safety, FS, for various trench lengths L for the hypothetical example presented in Fig. 8 of the current paper using Eqs. 22 and 23 from Fox 2004 . In the notation used by Fox 2004 , the input parameters are as follows: H=Hs=20 m, zw=3 m, zc=0 no tension crack ,