Mohr-Coulomb Criterion-Based Theoretical Solutions for Borehole Contraction in the Anisotropic Initial Stress Condition

Abstract

Solutions for cavity contraction are used widely in tunnel engineering but rarely in bored pile foundation which is a three dimensional problem. Traditional cavity contraction theory are based on the isotropic initial stress supposition (i.e. the lateral pressure coefficient K 0 = 1.0). However, the K 0 of the soil is not equal to 1.0 actually. In this paper, based on the Mohr-Coulomb yield criterion and the associated flow rule, the analytic solution for stress and displacement fields of borehole contraction considering K 0 was deduced. The relationship between the initial borehole radius a, the contracted radius a 0 , the plastic zone II radius r p and the internal pressure p is also analyzed, result shows that the a 0 is a function of a, r p and p. In addition, using the curves of the plastic zone radius and the stress fields versus borehole depth, the influence of the internal pressure p and the lateral pressure coefficient K 0 , and the internal friction angle ϕ are discussed. It shows that p and ϕ have great influence on the plastic zone radius and the borehole wall stress, while the effect of K0 on the borehole wall stress is limited and mainly focuses on the upright part of the borehole. It can be illustrated that traditional solutions based on the assumption of K 0 = 1.0 underestimated the plastic zone field while overestimated the stress around the cavity. Moreover, it should be noted that the effect of r p on the stress and displacement around borehole is non-negligible. This paper consummates the borehole contraction in bored pile foundation.