裂隙膨胀土渗流-应力耦合损伤致胀机理及对深基坑稳定性影响

The engineering hazards of expansive soil are a technical problem in geotechnical engineering field that should be solved urgently at home and abroad. After excavation, the fracture development of expansive soil is changed under coupled hydro-mechanical interaction, causing the change of expansive soil strength and expansive power. And the deep foundation pit support structure may be failure in expansive soil stratum by these changes. The typical deep foundation pit construction in expansive soil stratum will be as the research background. Then mineral composition and microstructure characteristics of expansive soil will be researched. Using CT real time mechanics test and other modern experimental, the damage and failure mechanism of jointed expansive soil under coupled hydro-mechanical process can be studied. The damage evolution mechanism of expansive soil at micro scale should be analyzed using statistical physics theory, digital image processing technology and damage mechanics. Large scale three-dimensional model experiment and in-situ measurement of the deep foundation pit excavation in expansive soil stratum will be conducted. And the fracture development rules of expansive soil under coupled hydro-mechanical progress, the change mechanisms of expansive soil strength and expansive power will be assessed. The interactive mechanical mechanism between the support structure and the expansive soil under coupled hydro-mechanical process will be researched. These results can be provided as important theory and experimental basis for the safety of the deep foundation pit engineering in expansive soil stratum under complex environment.

膨胀土的工程危害问题是国内外岩土工程领域亟需解决的技术难题。深基坑开挖卸荷后，渗流-应力耦合作用下引起膨胀土裂隙发展，强度改变，膨胀力发生显著变化，极易造成深基坑支护结构失稳或破坏。以典型的膨胀土层深基坑工程为研究背景，分析膨胀土的矿物组成及微观结构特征；开展膨胀土水理化与应力耦合下细-宏观跨层次渐进损伤破坏的工业CT实时力学试验等现代实验研究；采用统计物理学理论、数字图像处理技术与损伤力学揭示膨胀土细-宏观跨层次水致损伤演化机理。开展膨胀土地层渗流-应力耦合下深基坑工程开挖大尺度三维模型实验及现场实测，探求深基坑工程开挖卸荷及渗流影响下土体裂隙发展演化规律、强度特性以及侧向膨胀力变化机理；揭示渗流-应力耦合下膨胀土-支护结构相互作用的力学机制，为膨胀土地层中深基坑工程的安全控制提供重要理论与实验依据。

膨胀土的工程危害问题是国内外岩土工程领域亟需解决的技术难题。深基坑开挖卸载后，水-应力耦合作用下引起膨胀土裂隙发展，强度改变，膨胀力发生显著变化，造成深基坑支护结构失稳或破坏。本项目研究水-应力耦合下膨胀土-支护结构相互作用力学机理与计算理论。采用室内试验研究获得了体积含水率、基质吸力、干湿循环次数之间的数学表达式，探求了循环次数与裂隙面积率、裂隙长度比、裂隙分割土块数量的数学表征，建立了干湿循环次数与膨胀土抗剪强度指标的计算模型。研究了水-应力耦合作用下膨胀土锚杆的预应力损失规律，测出锚杆应力稳定值并算出相应的预应力损失比，建立锚固段-土体相互作用力学模型。采用颗粒流数值计算方法，研究了深基坑开挖过程中土拱产生、发展的细观机理，深入研究了桩间距、桩半径、距径比、摩擦系数等因素对桩土相互作用力的影响。建立考虑桩-土接触界面力学特性的数值计算模型，分析界面法向/切向耦合弹簧摩擦系数对桩体内力及变形的影响。相关成果发表在中国矿业大学学报（2017）、现代隧道技术（2017）上。研究桩-土非线性相互作用对深基坑支护结构内力与位移的影响，提出一种桩-土相互作用支护桩受力变形计算的方法，推导出了考虑桩-土-内支撑共同作用的支护结构的挠曲微分方程，结合理论土压力，采用该方法计算获得了不同开挖深度的桩体水平位移和桩体弯矩。相关成果发表在西南交通大学学报（2016）上。