基于统一强度理论及太沙基极限平衡原理推导了螺纹桩极限承载力,提出了螺纹桩螺牙单独承载破坏与圆柱形剪切破坏两种模式下临界螺距的确定方法和极限承载力计算方法,讨论了统一强度理论参数b与螺纹桩关键参数对极限承载力的影响.结果表明:螺纹桩的极限承载力是同外径圆桩的1.5~2倍,螺牙提供的极限承载力主要由土体黏聚力、内摩擦角及埋深决定.当b从0增加到1时,螺纹桩极限承载力理论计算值增幅约48%,考虑中主应力对土体强度的影响会使得螺纹桩承载力理论计算结果更加准确.螺纹桩的参数中,螺牙高度b_h对其极限承载力影响最大,而螺牙厚度t对承载力基本无影响.设计螺纹桩时可适当增加螺牙高度,以提高螺纹桩极限承载力.

Based on the unified strength theory and the Terzaghi limit equilibrium theory, the ultimate bearing capacity of screw pile has been deduced. The method to determine the critical pitch and calculate the ultimate bearing capacity of the screw pile in two failure modes including the independent bearing failure mode and the cylinder shear failure mode has been proposed. The influence of the unified strength theoretical parameter b and the key parameters of concrete screw pile on the ultimate bearing capacity has been analyzed. The results show that the ultimate bearing capacity of the screw pile is 1.5—2 times that of the round pile with the same outer diameter. The ultimate bearing capacity of the screw teeth is mainly determined by the cohesion, the internal friction angle, and the buried depth of the soil. As b increases from 0 to 1, the theoretical value of the ultimate bearing capacity of the screw pile increases by nearly 48%. As the influence of the medium principal stress on the soil strength is considered, the theoretical calculation results of the bearing capacity of the concrete screw pile will be more accurate. Of the parameters of the concrete screw pile, the screw height b_h has the greatest influence on the ultimate bearing capacity, while the screw thickness t has little influence on the bearing capacity. When designing threaded pile, the height of screw can be increased to some extent to improve the ultimate bearing capacity of the screw pile.