为使无杆钻具能有效支撑在孔壁土体上，探讨了支护结构施加的预应力对孔壁土体稳定性的影响，提出了采用虚拟土柱模拟桩孔并结合广义Mindlin 解的方法，推导了预应力作用下孔壁土体中任一点的附加应力向量． 基于此附加应力向量，求取了最大预扭矩和最大预压力作用下支护板下方5 mm、宽50 mm 处各点的剪切应力及其相对强度． 结果表明: 当预扭矩与预应力分别为120 kN·m 和100 kN 时，最大剪切应力为6. 52MPa; 除了支护板两端部外，剪切应力相对强度均小于1，即总体上孔壁土体为稳定状态． 与试验结果的对比验证了文中方法的正确性，文中方法比Boussinesq-Gerruti 联合求解法和有限元法更加精确

In order to make rodless drilling rigs support the hole-wall soil effectively,the stability of hole-wall soil affected by the prestress exerted on support structure is analyzed,and a method,which uses virtual soil column to simulate pile hole and combines with the Mindlin solution,is proposed.With the help of this method,the additional stress vector of any point in the prestressed hole-wall soil is deduced,on the basis of which the shear stress and its relative strength of any point in the location of 50mm in width and 5mm below the support plate are obtained under the actions of maximum pre-torque and maximum pre-pressure.The results show that,when the pre-torque and the prestress are respectively 120kN·m and 100kN,the maximum shear stress reaches 6. 52MPa; and that the relative strength of shear stress at each point is less than 1 except at both ends of the support plate,which means that the hole-wall soil is in a steady state overall.Moreover,a comparison is made between the calculated results and the experimental ones,finding that the proposed method is more accurate than the Boussinesq-Gerruti solution and the finite element method.