真空预压加固夹薄弱透水层软土固结特性分析

Consolidation analysis of soft soil with thin permeable layer by vacuum preloading

由于土的沉积历史原因,实际软土地基中常含有薄透水层,如何分析薄透水层对地基固结过程的影响是地基处理效果评价的关键。笔者利用室内模型试验装置开展了3组真空预压法加固夹薄弱透水层软土地基效果研究,以分析不同厚度的透水层对真空预压法加固软土地基固结的影响;利用已有成层砂井地基固结理论分析透水层透水特性和土层厚度对软土固结的影响。试验结果表明,透水层可加快超静孔隙水压力的消散,消散速率与透水层的厚度密切相关;透水层可以加快软土的固结速率。计算结果表明,当透水层厚度及渗透系数与软土厚度及渗透系数的比值介于0.1~100时,透水层对加快土体固结最为显著;当比值超过100时,透水层已接近完全排水边界。加固软土层厚度与砂井半径的比值与地基固结速率和透水层作用密切相关,随着比值的增大,砂井地基固结时间增长,透水层加快软土固结速率的作用越来越不明显,当比值大于8时,透水层对地基固结速率基本影响很小。透水层可以显著改善井径比、涂抹效应增大对地基固结速率减缓的影响。因此,真空预压工程中若需要设置水平向透水层,透水层竖向间距不宜大于其厚度的8倍。

Due to the deposition of soil,the soft soil often contains a thin permeable layer in the actual project.How to evaluate the influence of thin permeable layer on the consolidation of foundation becomes the key to analyze the reinforcement effect.In this study,three sets of model tests are used to analyze effects of different thicknesses of permeable layer on the consolidation of soft soil by vacuum preloading.At the same time,the foundation consolidation solution is used to analyze effect of the permeability of permeable layer and thickness of soil layer on the consolidation of soft soil.The test results showed that the permeable layer can accelerate the dissipation of excess pore water pressure,and the dissipation rate is closely related to the thickness of permeable layer.The permeable layer can accelerate the consolidation rate of soft soil.The ratio of thickness and permeability coefficient of permeable layer to the thickness and permeability coefficient of soft soil is used in the calculation.When the ratio is between 0.1 and 100,the permeable layer is most significant for accelerating soil consolidation.When the ratio reaches 100 or is more than 100,the permeable layer is close to the complete drainage boundary.Also,when the ratio of layer thickness to the radius of sand well increases,the consolidation time of foundation increases,and the effect of permeable layer on the consolidation rate of soft soil becomes less.When the ratio is greater than 8,the performances of permeable layer are very small.When the well-diameter ratio increases or the smearing effect is serious,the horizontal drainage rate of foundation becomes slower,and the horizontal consolidation rate becomes slower.The existence of the horizontal permeable layer changes the vertical consolidation path of soil,and the acceleration of consolidation rate of soil becomes obvious.Therefore,if a horizontally permeable layer needs to be provided in the vacuum preloading project,the vertical spacing of permeable layer should not be greater than 8 times its thickness.