开孔管桩动孔压消散特性的理论研究

可液化地基在遇到地震作用或任何其他突变应力条件下,土体会迅速丧失强度和刚度,发生液化,从而失去承载能力。传统的抗液化措施主要集中在地基处理层面,而开孔管桩则兼具抗液化性能和承载能力。在假设开孔管桩孔洞内液体流动满足Poiseuille方程且等应变假设成立的前提下,结合开孔管桩复合地基的应力集中现象,推导出地基在时变荷载作用下的径竖向组合孔压解析解。考虑到循环荷载作用下的孔压积累现象,进一步利用孔压发展的经验模型改进该解析解。在此解析解的基础上,分析、对比开孔管桩、碎石桩、不排水桩以及天然地基的孔压发展情况,得出开孔管桩具有最好的孔压消散能力。桩-土模量比、井径比等因素对孔压的发展都有重要的影响,桩-土模量比越大、井径比越小,孔压消散速率越快。桩本身开孔系数对孔压发展的影响不明显。荷载频率只影响初始孔压峰值,并不影响孔压振荡衰减的速率。

Theoretical study of dynamic pore water pressure dissipation characteristics of open-hole pipe pile

Under conditions of seismic action or any other mutation stresses, the soil of the liquefiable foundation can lose its strength and stiffness rapidly due to the liquefication, resulting in the loss of the bearing capacity. The traditional anti-liquefaction measures mainly focus on the ground treatment, while the open-hole pipe pile provided in this paper has both anti-liquefaction and bearing capacity. Firstly, the liquid flow in the holes of the pipe pile is assumed to meet the Poiseuille equation, and the equal strain assumption is applied. Then we derive the analytic solution of the pore pressure considering both radial and vertical flows under the time-varying load, combined with the stress concentration phenomenon of the pipe pile composite foundation. Furthermore, considering the pore pressure accumulation under cyclic loading, the analytical solution is improved by using the empirical model of pore pressure development. Based on the analytical solution, this paper analyzes and compares the development of pore pressure of the open-hole pipe piles, gravel piles, undrained piles and natural foundation. Thus, the results indicate that the open-hole pipe pile has the best drainage capacity. The factors such as the modulus ratio of pile and soil and the radius ratio have important influence on the development of pore pressure. The higher the modulus ratio of pile and soil is, the smaller the radius ratio is, and the faster the pore pressure dissipation rate is. The influence of open-hole coefficient on the development of pore pressure is not obvious. The load frequency only affects the peak value of initial pore pressure and has little influence on the rate of pore pressure oscillation attenuation.