Analytical Study of a Braced Excavation in Weak Clay

Abstract

Analysis of the problem of braced excavations is complicated by the large number of variables involved and by the complex interaction and behavior of the soil and the supporting materials. For this reason a parametric study was made using the finite-element method of analysis to evaluate the influences of the variables. A rather unique computer modelling technique has been used to accommodate both the large number of variables and the problem of interaction and dissimilar behavior. An example of a computer simulation of a well-instrumented braced cut in Norway is given in sufficient detail to illustrate the applicability of the program.For the parametric study a typical excavation with fully penetrating sheet-pile walls was chosen. Of the parameters concerning soil conditions, the soil deformation modulus was found to have the greatest influence. The relative influence of shear strength, of initial in situ stress, of direction of mobilization of shear stress, and of soil-to-pile adhesion is also shown. All of the parameters concerning support conditions are important but pile stiffness and effective strut stiffness are the most important. The influence of prestressing and strut spacing is also shown.