真空预压加固土体变形机制分析

Analysis on deformation mechanism of soft soil reinforcement by vacuum preloading

研究了真空预压加固机制,从弹簧模型中总应力及孔隙水压力变化出发,对不同边界条件下真空预压从概念上探讨了竖向和水平向土体固结变形行为。根据边界条件按K0固结和各向等压固结应力路径,分析了在真空排水固结下土体有效应力的变化及变形的发展,并依据修正剑桥模型推导了弹塑性状态下软土的静止土压力系数理论值K0MC。通过在大面积软基加固工程中的应用分析及部分工程案例统计分析,证实该机制的正确性和有效性,并发现土体的变形行为受真空排水边界条件及加固区尺度影响。对于大面积真空预压加固区中部来说,土体有效应力的改变不是各向等量改变,而是按一维压缩改变,经统计分析实际工程应用,当加固区宽度达到加固区深度(竖向排水体深度)4~5倍以上时,其中部可采用一维压缩公式计算沉降。

Based on the changes of total stress and pore water pressure in the spring model,the mechanism of vacuum preloading consolidation is studied by theoretically discussing the consolidation behavior of soil in vertical and horizontal directions with different boundary conditions.The variation of effective stress and development of deformation are analyzed for the soil under vacuum preloading under stress paths of K0 consolidation and isotropic consolidation based on the boundary conditions,respectively.Meanwhile,the theoretical earth pressure coefficient(K0 MC)at rest for soft soil is deduced based on modified Cam-clay model.With engineering applications,the correctness and effectiveness of the mechanism is confirmed by the application in large area of ground improvement for soft soil and statistical analysis of some engineering cases.It is found that the drainage boundary condition and the scale of treated area have effects on deformation of soil mass.For the middle part of the treated zone under large-area vacuum preloading,the variation of effective stress is not isotropic,but following the pattern of one-dimensional compression.According to the statistic results from some site investigations,one-dimensional compression equation(Cc-Cr method)can be applied to predict the settlement at the center of the treated zone when the one dimensional condition is found in the center of treated zone as the ratio between treated breadth and length of vertical drains larger than 4-5.