考虑土体三维强度特性的静压桩周超孔压解析及演变

将饱和黏性土中静压沉桩过程近视看作柱孔不排水扩张问题,在充分考虑土体三维强度特性的条件下采用SMP准则改进的修正剑桥模型,推导得出柱孔扩张引起超孔压的基本解答。在此基础上,考虑桩周土竖向和径向固结,建立空间轴对称固结方程的定解条件,采用分离变量法求得桩周超静孔隙水压力消散的级数解答。分析桩周土体超静孔隙水压力随时间和空间的演变规律,揭示应力历史、径向和竖向固结系数以及剪切模量等因素对初始超孔压的产生和随后的固结速率的影响规律,并通过实例验证本文解答的合理性和适用性。通过与现场实测对比,本文解答较好地反映了静压桩周土体超静孔隙水压力的演变规律。此外,桩周土体的超静孔隙水压力随距桩侧径向距离增大呈对数衰减。剪切模量和竖向固结系数对桩周土体固结速率影响较小,而土体超固结比和径向固结系数对固结速率影响较为显著,表明超孔压消散主要发生在径向。研究成果对静压桩承载力的确定具有一定的指导意义。

Variation of excess pore pressure around jacked piles considering the three-dimensional strength of soil

The pile-sinking process in saturated clay is regarded similar as the cylindrical cavity expansion under undrained conditions. Considering the soil strength in three-dimensional stress state，the SMP criterion-based Cam-clay model was adopted to solve the cylindrical cavity expansion and to derive the general solution. On this basis，the fixed solution of spatial axisymmetric consolidation equation was built. A series solutions of the dissipation of excess pore water pressure were derived by using the methods of separation of variables. The development of excess pore water pressure around piles with time and space was discussed. It was revealed that the impact of the radial and vertical permeability coefficient，the stress history and the shear modulus on the initial excess pore water pressure and the rate of consolidation. The theoretical solution was proved reasonable and applicable in comparison with the measured data. The excess pore water pressure around piles decreases with the increase of logarithmic radical distance. Shear modulus and vertical permeability coefficient have little effect on the rate of consideration，but the radial permeability coefficient and over consolidation ratios has a significant effect on it，that reflects the dissipation mainly along the radial direction.