砂土原位应力场中的灌注桩成孔卸荷收缩理论解

为了探究钻孔灌注桩在竖向成孔时伴随的孔周土体径向应力的卸荷情况,基于SMP屈服准则及非相关联流动法则,探讨了初始原位应力场条件下砂土竖向钻孔孔周存在的2个塑性区的应力状态工况,并推导了该工况的应力场、位移场的解答,给出了工况判别标准。结果表明:静止侧压力系数K₀、土体内摩擦角φ的选取关系到孔周塑性区半径r_e,r_p的变化,对塑性区的产生和发展有很大影响;不同K₀和泥浆重度r_mud下的孔壁相对位移、孔壁应力均随着钻孔深度的增大而呈线性增大,孔壁相对位移随K₀增大而增大,随r_mud的增大而减小,但孔壁径向和环向应力并不随K₀的改变而改变;砂土竖向成孔的孔周塑性区范围几乎沿深度不发生变化,塑性半径r_p对钻孔孔壁环向应力有较大影响。提出的理论解对于砂土初始原位应力场中的灌注桩成孔卸荷问题具有一定的理论意义。

Theoretical Solution to Borehole Contraction Caused by Unloading in Anisotropic Sandy Soil

Radial unloading-induced borehole contraction is caused in the drilling process of bored pile. On the basis of the SMP yield criterion and the non-correlated flow rule, the solution for the stress and displacement fields in two stress-state conditions of plastic zone around the vertical borehole is deduced with the coefficient K₀ of lateral earth pressure considered. Parameter analysis shows that the K₀ and internal friction angle φ of soil have a great influence on the emergence and development of plastic zone as well as the radius r_e and r_p of plastic zone. The relative displacement and stress of borehole wall increase linearly along with the increase of drilling depth with different values of K₀ and mud's unit weight r_mud. The relative displacement of borehole wall intensifies with the growth of K₀, while declines with the rising of r_mud. However, the radial and circumferential stresses of borehole wall do not change with K₀. In addition, the range of plastic zone around the vertical borehole hardly changes along the depth in sandy soil, and the plastic radius r_p has a remarkable influence on the circumferential stress. The theoretical solution presented in this paper is of theoretical significance for the unloading problem of borehole in initial in-situ stress field of sandy soil.