扩底桩的上拔试验及其颗粒流数值模拟

Prototype tests and particle flow numerical simulation of under-reamed piles on uplift loading

通过原型试验和应用颗粒流理论及其 PFC2D 程序数值模拟,研究了黄土中扩底桩承受上拔荷载的宏观力学性能及其细观结构,以及扩底桩在上拔荷载下的位移、极限上拔承载力和破坏机理。结果表明:增加扩底桩扩大端的高度对提高承载力是有效的;破坏机理为土的减压软化和损伤软化的渐进性破坏。并提出了扩底桩极限上拔承载力计算式,计算值与实测值相吻合。应用颗粒流理论分析了颗粒细观结构、受影响区域、扩底桩的上拔位移和土中滑裂面。颗粒流模拟的土中滑裂面、荷载与位移关系和宏观试验实测结果相一致。

The field prototype tests have been carried out for under-reamed piles bearing uplift loading in loess. Uplift displacement of under-reamed piles bearing uplift loading, displacement of surface layer soil were measured. The ultimate uplift bearing capacity, failure mechanism of piles were studied. It was very effective on improving ultimate uplift bearing capacity of piles to raise height of belled-out section of under-reamed piles. Failure mechanism of piles and soil was solved by gradually failure to be due to damage softening and reduction pressure softening of the soil. A formula was proposed to calculate the ultimate uplift bearing capacity in the loess;and comparing the calculation results and the test data, both are basically similar. PFC2D (Particle Flow Code in 2 Dimensions) simulated numerically tests of under-reamed piles bearing uplift loading, simulated numerically distribution, displacement of particles and uplifting displacements of under-reamed piles; the change of arrangements of particles from before to after uplift loading, the directions of particle displacements were analyzed; the affected zone and surface of rupture in soils was taper of quadratic surface; load-displacement of piles was same with the test data. The characteristics of meso-structure simulated by PFC reflect response of macro-mechanics of soil.