下伏空洞桥梁单排桩基桩端岩层极限承载力计算方法

Calculation Method of Ultimate Bearing Capacity for Single Row Pile Foundation Rock Layer of Underlying Cavity Bridge

针对下伏空洞桥梁单排桩基桩端岩层极限承载力问题,基于下伏空洞单桩基础桩端岩层冲切破坏理论,假定了下伏空洞桥梁单排桩基桩端岩层的破坏模式.采用空间曲面积分得到了各桩下冲切体重叠部分侧面积计算方法,进一步考虑重叠面积与桩端岩层承载力折减之间的关系,提出了下伏空洞桥梁单排双桩及三桩基础桩端岩层极限承载力计算方法 .通过试验验证了理论方法的合理性,并采用理论方法与数值模拟分析了桩间距L对下伏空洞桥梁单排双桩及三桩基础桩端岩层极限承载力的影响.结果表明:在桩间距L较小情况下冲切体局部出现重叠现象;在桩间距L为2倍桩径时,桥梁单排双桩以及三桩桩端岩层的总承载力分别为不考虑叠加效应时总承载力的75%和67%;随着桩间距L的逐渐增加双桩及三桩桩端岩层总承载能力逐渐增大,当桩间距L达到5倍桩径后其承载能力达到不考虑重叠效应时总承载力的99%以上.

Aiming at the ultimate bearing capacity of pile end rock in the single row pile foundation of underlying cavity bridge,based on the punching shear failure theory of pile end rock of single row pile foundation for underlying cavity bridge,the failure mode of pile end rock of single row pile foundation of underlying cavity bridge is assumed. The calculation method of the side area of the overlap part of the punching shear under each pile is obtained by using the spatial surface integral. Further considering the relationship between the overlap area and the reduction of the bearing capacity of the pile end rock,a calculation method of the ultimate bearing capacity of the pile end rock of the single row double pile and the single row three pile foundation of the underlying cavity bridge is proposed. The rationality of the method is verified by experiments. And the influence of pile spacing L on the ultimate bearing capacity of rock strata at the pile tip of single-row double-pile and single-row three-pile foundation of the underlying cavity bridge is analyzed by the theoretical method and numerical simulation. The results show that:(1)when the pile spacing L is small,the local overlap of punching shear occurs;(2)when the pile spacing L is twice the pile diameter,the total bearing capacity of single row double piles and three piles of the bridge is 75 % and 67 % of the total bearing capacity without considering the superposition effect,respectively. With the gradual increase of pile spacing L,the total bearing capacity of the pile end rock of double piles and three piles increases gradually. When the pile spacing L reaches five times the pile diameter,the bearing capacity reaches more than 99 % of the total bearing capacity without considering the superposition effect.