加筋地基破坏机理及极限承载力计算

Reinforced soil foundations (RSFs) are a kind of economic new ground treatment technique which has been applied broadly. Compared to non-reinforced soil foundations, the bearing capacity of RSFs can be improved apparently. The present researches on RSFs mostly applied down-scaled physical modeling tests. However, due to the invisibility of the soil in the tests, the reinforced mechanism and failure mode of RSFs are still far from clear. Therefore, the equations of ultimate bearing capacity of RSFs proposed by different researchers are quite different and there are big biases between the computations and the measurements. In this research, in combination of prototype tests and numerical simulation, centrifuge modeling is to be conducted on RSFs using highly transparent sand which has the same physical and mechanical properties as the natural sand. The evolution of displacement field in the foundation, interaction between reinforcements and soil, and the actual failure mode of the RSFs under the real stress condition are investigated so as to reveal the reinforced and failure mechanism of the RSFs. Based on the findings, an analytical model of ultimate bearing capacity of RSFs is established, and a logical and unified equation of ultimate bearing capacity is expected. The research results will provide theoretical basis for the design and construction of RSFs in future.

加筋地基是一种经济和应用广泛的新型地基处理技术，其较无筋地基显著提高了地基承载力。目前国内外对加筋地基的研究多基于室内相似模型试验，但由于模型中土体的不可视性，还未能清晰认识加筋地基的加筋机理及破坏模式，导致不同学者提出的极限承载力公式差别较大，且与实际偏差很大。本项目拟采用与自然砂土具有相同物理力学性质的高透明度透明砂土，开展基于透明土技术的加筋地基离心模型试验，并结合加筋地基原型试验及数值模拟，研究符合实际应力场条件的地基内部位移场演化、筋土相互作用过程以及确切的破坏模式，以揭示加筋地基的加筋及破坏机理。在此基础上建立加筋地基极限承载力分析模型，提出一个合理和统一的极限承载力计算公式。研究成果为今后加筋地基的设计和施工技术提供理论基础。

采用高纯度熔融石英砂和白油配制了一种新型透明土，测试了其基本物理力学性质，该透明土的物理力学性质与天然砂土较为一致，且其透明度优于其它类型的透明土。开展了基于透明土技术的加筋地基1g模型试验和离心模型试验，研究其在条形基础荷载下的荷载-沉降特性、内部位移场演化规律以及变形破坏过程，发现当加筋间距过大或筋材刚度较小时，加筋区整体模量较小，筋材“自上而下”依次断裂，而当间距较小且筋材刚度较大时，加筋区整体模量较大，筋材“自下而上”依次断裂。开展了加筋地基原型足尺试验，研究其在圆形基础荷载下的荷载-沉降响应、附加应力分布、地表变形和筋材应变分布规律。基于试验结果，开展了加筋地基有限差分和离散元数值模拟，研究其承载特性、位移场演化过程、内部应力分布以及筋材的拉力分布和逐层破坏过程，揭示了筋土相互作用的细观机理，并提出了基于人工神经网络的筋材断裂次序判别方法。基于试验和数值模拟结果，建立了加筋地基力学分析模型，采用极限平衡方法推导了加筋地基的极限承载力计算公式，计算值与实际值的误差均在20%以内且优于文献中其他计算方法。