黏性土中静压桩挤土时效性的室内应变保持试验研究

LABORATORY STRAIN-HOLDING TESTS OF SETUP OF JACKED-IN PILES IN COHESIVE SOIL

许多学者基于圆孔扩张理论,采用挤土应力不变的假设给出了黏性土中挤土桩承载力时效性的解析解答,但是原位试验表明:作用在桩壁上的挤土应力是不断衰减的。通过利用应力路径三轴仪进行应变保持试验,模拟沉桩及随后的桩周土体的应力状态和物理性质的改变。试验结果表明:沉桩后作用在桩壁上的作用力近似呈对数衰减,桩周土体有效应力先减小后增大,固结完成后有效应力增量仅为(0.2～0.27)倍的超静孔隙水压力。因而,采用挤土应力不变的假设将导致过高估计桩基承载力的时效性。

Based on cavity expansion theory,with the assumption that compaction stress acted on the wall of the pile was constant,some scholars proposed analytical answer to the setup of jacked-in piles in cohesive soil.But in-situ tests showed that compaction stress was decayed constantly.A series of triaxial strain-holding tests were conducted,and the results of tests showed that the compaction stress decayed linearly with logarithmic time appreciatively,the effective stress decreased at the beginning and then increased later during consolidation of the soil near to the piles,and the increment of the effective stress was only 0.20 ～ 0.27 times the excess pore pressure.So it would be overestimatied pile bearing capacity by assuming that compaction stress was constant.