通过开展一系列离心模型试验，对饱和粉质黏土中沉桩挤土应力和孔隙水压力分布特征进行研究.利用微型传感器监测沉桩过程中土体的应力和孔压变化，并根据试验结果对已有的圆孔扩张模型进行修正，提出考虑地表隆起的沉桩挤土模型，对其可靠性进行验证.研究结果表明，桩周土体总应力和超孔压变化特征主要由距桩的水平距离和埋深控制，对于确定埋深处的土体，当桩尖接近并经过其埋深位置时，应力和孔压先增大后减小；当水平距离相同时，埋深越大，沉桩引起的应力和孔压增量越大，分析认为是地表自由边界的存在影响了浅埋土体中应力变化；当沉桩深度达到7~7.5倍的桩径时，地表边界效应的影响不再明显.
A series of centrifuge model tests were conducted on the spatial distribution characteristics of stress and pore pressure due to pile installation. According to test data, the existing cavity expansion theory was modified, and a pile installation model, which took ground surface heave into account, was proposed. The reliability of this model was validated by the centrifuge test data. The results showed that variation characteristics of total radial stress and the pore-water pressure were controlled by the distance from the pile axis and depth of the soil element. For a certain depth, the stress and pore-water pressure of soil increased as the pile tip reached and decreased as the tip passed. For the same distance from pile, the increases of stress and pore-water pressure caused by deep penetration were larger than those induced by shallow penetration. The reason was that the free ground surface influenced the stress conditions. If the pile penetration depth in the silty clay reaches 7~7.5 times pile diameter, the influences can be ignored. The studies of this paper will provide the basis for time-dependent prediction of pile foundation capacity.
［1］HU P, WANG D, CASSIDY M J, et al. Predicting the resistance profile of a spudcan penetrating sand overlying clay［J］. Canadian Geotechnical Journal, 2014, 51(10): 1151-1164.
［2］KIAT T K, CHEN Z R, FAI L C, et al. Enhanced analysis of pile flexural behavior due to installation of adjacent pile［J］. Canadian Geotechnical Journal, 2014, 51(6): 705-711.
［3］JARDINE R J, ZHU B T, FORAY P, et al. Mea-surement of stresses around closed-ended displacement piles in sand［J］. Geotechnique, 2013, 63(1): 1-17.
［4］LIU J W, ZHANG Z M, YU F, et al. Case history of installing instrumented jacked open-ended piles［J］. Journal of Geotechnical & Geoenvironmental Engineering, 2012, 138(7): 810-820.
［5］张亚国, 李镜培. 软黏土中静压沉桩引起的侧向挤土位移分析［J］. 同济大学学报(自然科学版), 2015, 43(12): 1801-1806.
ZHANG Yaguo, LI Jingpei. Lateral displacements of ground caused by piles installation in soft clay［J］. Journal of Tongji University (Natural Science), 2015, 43(12): 1801-1806.
［6］LEE F H, JUNEJA A, TAN T S. Stress and pore pressure changes due to sand compaction pile installation in soft clay［J］. Geotechnique, 2004, 54(1): 1-16.
［7］DEJONG J T, RANDOLPH M. Influence of partial consolidation during cone penetration on estimated soil behavior type and pore pressure dissipation measurements［J］. Journal of Geotechnical & Geoenvironmental Engineering, 2012, 138(7): 777-788.
［8］孟振, 陈锦剑, 王建华. 基于修正剑桥模型的软黏土中沉桩过程欧拉-拉格朗日耦合模拟分析［J］. 上海交通大学学报, 2017, 51(3): 263-268.
MENG Zhen, CHEN Jinjian, WANG Jianhua. The coupled Eulerian-Lagrangian analysis of pile jacking process in saturated soft clay by using modified Cam-clay model［J］. Journal of Shanghai Jiao Tong University, 2017, 51(3): 263-268.
［9］CHOW S H, O’LOUGHLIN C, RANDOLPH M. Soil strength estimation and pore pressure dissipation for free-fall piezocone in soft clay［J］. Geotechnique, 2014, 64(10): 817-827.
［10］CAO L F, TEH C I, CHANG M F. Undrained cavity expansion in modified Cam clay Ⅰ: Theoretical analysis［J］. Geotechnique, 2001, 51(4): 323-334.
［11］ZHANG Y G, LI J P, LIANG F Y, et al. Modified approach to evaluation of undrained shear strength from piezocone tests in soft clays［J］. Marine Georesources & Geotechnology, 2017, 35(1): 80-88.
［12］RANDOLPH M F, WROTH C P. An analytical solution for the consolidation around a driven pile［J］. International Journal for Numerical and Analytical Methods in Geomechanics, 1979, 3: 217-229.
