Interaction of drilled shafts in rock under the action of lateral load

Abstract

The article presents the results of numerical simulation of the interaction of drilled shafts with rock mass under the action on its head of horizontal load or bending moment. The studies were carried out using finite element method with the use of factor analysis (method of experiment planning). Numerical calculations allowed to obtain the factor dependencies (regression equation) that connect the response functions (the bearing capacity of the shaft and the displacement of its head) with the selected independent factors that have the significant effect on the behavior of shafts. As factors were taken: the ratio of modulus of elasticity of shaft to modulus of deformation of intact rock, ratio of length of the pile to its diameter and RQD of the rock mass. The equations allow to construct graphs of dependence of displacements of the head of the shaft from applied loads: horizontal force or bending moment. Considering that the regression equations are very cumbersome, for convenience of their use nomograms were constructed. On the base of the study were also obtained two factor dependencies (regression equations) that take into account the character of the shaft interaction with the rock mass. One regression equation is used to define the line separating two regions of different interaction of shafts with rock mass. The one region is the region of "short" shafts that deform into rock with rotation and the bearing capacity of this kind of shafts depends on strength of the rock. The other region is the region of "long" shafts. The bearing capacity and horizontal displacements of this kind of shafts is determined only by the strength of the shaft material. The second regression equation allows to find the boundary into the rock mass below which the shaft doesn't work (no displacements of shaft). For the convenience of use of the obtained regression equations were constructed nomograms.