黏性土中单桩贯入桩–土界面超孔压和土压测试现场试验

黏性土地基中静压桩沉桩过程桩–土界面受力变化是岩土工程中常见的问题。在东营某工地黏性土地基中进行了足尺静压桩的贯入试验,重点监测了桩身不同h/L位置处桩–土界面超孔隙水压力和土压力随入土深度的变化规律,并分析了桩身不同h/L位置处桩–土界面超孔隙水压力与上覆土体有效压力的关系,在同一入土深度桩–土界面土压力的变化特性,重点研究了影响桩–土界面有效土压力分布的原因。测试结果表明:沉桩引起的桩身不同h/L位置处桩–土界面超孔隙水压力与上覆土体有效压力比值最大是1.08,且该比值沿桩身向上逐渐减小;同一入土深度桩身不同h/L位置处桩–土界面土压力存在"侧压力退化"现象,且随着h/L的增加,该退化现象会越发明显,h/L=11/12位置处桩–土界面土压力仅约为10 kPa;除h/L=11/12位置处,桩身其它不同h/L位置处桩–土界面有效土压力是桩–土界面超孔隙水压力的1.88～2.20倍。研究成果对黏性土地基中静压桩施工和承载力确定具有一定的工程指导意义。

Field tests on excess pore pressure and soil pressure of pile-soil interface for a single pile during pile-sinking in clay

Stress change of pile-soil interface for jacked-in piles during pile-sinking in clay is a topic of concern in the geotechnical engineering. A full-scale jacked-in pile is penetrated into the clay in Dongying city of China and studied by monitoring the laws of the excess pore water pressure and soil pressure of pile-soil interface with depth at different pile locations of h/L. The relationship between the excess pore water pressure of pile-soil interface and the effective pressure of superimposed soil at different pile locations of h/L and the characteristics of soil pressure of pile-soil interface at the same penetration depth are analyzed. Especially the causes to influence the distribution of the effective soil pressure of pile-soil interface are studied. The test results show that the maximum ratio of the excess pore water pressure of pile-soil interface to the effective pressure of superimposed soil during pile-sinking is 1.08 at different pile locations of h/L and decreases gradually along the pile from pile tip to pile top. The soil pressure of pile-soil interface presents “lateral pressure degradation” with the relative depth of the increasing pile tip（h/L）at the same penetration depth. The “lateral pressure degradation” presents obviously with the relative depth of the increasing pile tip（h/L）. The effective soil pressure of pile-soil interface is only 10 kPa at the location of h/L=11/12, and that of certain interface at other different pile locations of h/L is 1.88~2.20 times the excess pore water pressure of pile-soil interface. The proposed solution is of great engineering significance for jacked pile construction and bearing capacity design in clayey foundation.