杂填土与软土互嵌致沉机理及模型研究

Study on the mechanism of miscellaneous fill ground settlement in new urban districts with developed river systems is both the basis for the accurate prediction of miscellaneous fill ground settlement and the key to increase our ability of minimizing building damages and economy loss. The existing calculation model which counts settlement of each soil layer cannot predict the settlement caused by intermixing between miscellaneous fill and soft soil layer. To address this issue, a miscellaneous fill and soft soil settling column tester is developed, based on the characteristic that soft soil will be squeezed into the pores of miscellaneous fill under external loadings. Effects of external loadings, grain size distribution of miscellaneous fill, and the consistency of soft soil on the settlement due to the intermixing of Study on the mechanism of miscellaneous fill ground settlement in new urban districts with developed river systems is both the basis for the accurate prediction of miscellaneous fill ground settlement and the key to increase our ability of minimizing building damages and economy loss. The existing calculation theory of ground settlement cannot predict the settlement caused by intermixing between miscellaneous fill and soft soil layer. To address this issue, a miscellaneous fill and soft soil settling column tester is developed, based on the characteristic that soft soil will be squeezed into the pores of miscellaneous fill under external loadings. Effects of external loadings, grain size distribution of miscellaneous fill, and the consistency of soft soil on the settlement due to the intermixing of miscellaneous fill and soft soil, and on the transition layer thickness will be studied. The analysis model of calculating the intermixing-induced settlement and the transition layer thickness will be proposed by means of generalization and statistical analysis, and the material intermixing mechanism will be investigated with Discrete Element Method numerical simulations. Additionally, the compressibility of the transition layer will be studied with a one-dimensional consolidometer for coarse-grained soil. Data from a laboratory model will used to verify this analysis model. Finally, the calculation model of miscellaneous fill ground settlement will be obtained by combining the intermixing effect of miscellaneous fill and soft soil on settlement, and the settlement analysis of miscellaneous soil layer and the soft soil layer respectively.

水系发达地区的城市新区杂填土地基沉降灾害的机理研究是准确分析杂填土地基沉降问题的基础，也是建立和完善社会防灾减灾能力的关键所在。已有的地基沉降计算理论无法分析杂填土层与软土层互嵌作用引发的沉降。为此，针对杂填土地基在外荷载作用下，软土会挤入杂填土孔隙中的特点，采用研制的杂填土与软土沉降柱试验仪研究外荷载、杂填土粒径组成和级配及软土的稠度状态对杂填土与软土互嵌沉降大小和互嵌层厚度的影响。通过归纳总结和统计分析的方法建立杂填土与软土互嵌沉降量和互嵌层厚度的分析模型，采用离散元数值模拟分析杂填土与软土互嵌沉降机理。同时采用研制的粗粒土单向固结仪研究杂填土与软土互嵌层的压缩特性，并通过模型试验验证杂填土与软土互嵌沉降量和互嵌层厚度的分析模型的合理性。在此基础上，将杂填土与软土互嵌沉降与杂填土层、互嵌层和下卧软土层的沉降分析相结合获得杂填土地基沉降计算模型。

随着我国经济的快速发展，水量充沛的地区形成了大量的杂填土地基。在上覆荷载作用下杂填土颗粒很容易嵌入到软土中，使得杂填土孔隙变小引发互嵌沉降，传统分层总和法无法对互嵌沉降进行计算，如何预测杂填土地基互嵌沉降是地基沉降计算面临的新问题和新挑战。基于自主研发的互嵌仪，开展了一系列的室内试验，分别从杂填土、软土和荷载三个方面，揭示了不同外荷载、不同加载方式、不同杂填土颗粒粒径、不同杂填土颗粒粗糙度、不同杂填土颗粒粒径组成、不同软土含水率、不同软土中黏粒含量和不同软土中粗粒含量对互嵌沉降的影响。借助PFC、EDEM数值软件，分析互嵌动态过程中软土颗粒位移、孔隙、接触特征的变化过程，揭示了杂填土颗粒组成、颗粒界面参数、软土中粗颗粒、加载方式等对互嵌过程的影响机理，探究了互嵌产生的原因。基于静力平衡理论分析，构建了互嵌位移与荷载和颗粒粒径的理论计算表达式，并与室内互嵌试验对比验证了理论的合理性和实用性。研究工作揭示城市新区杂填土地基地表沉降致灾机理，有助于推动杂填土地基沉降量计算的发展，为杂填土地基的填埋和沉降计算或预测提供理论参考，为社会防灾体系及提高社会应急救援能力提供指导。