受地震荷载扰动裂隙性黄土崩塌灾害发生机理及评估方法研究

The joint structural planes of fissured loess lead to obvious changes in mechanical behavior of loess. Moreover, earthquake will cause further damage to the micro-structure of fissured loess, which will induce collapse under the influence of rainfall, irrigation and repeated dry-wet cycles. However, the mechanism of this type of collapse is still not clear. In this project, CT scanning, unsaturated triaxial tests and drying-wetting tests will be carried out on both intact fissured loess samples and samples disturbed by seismic load simulated by a shaking table. Based on the test results, quantitative relationship between the mechanical index and fracture mechanism of fissured loess and earthquake parameters will be studied. The relational expressions between mechanical parameters of earthquake-disturbed fissured loess and water content and dry-wet parameters will be determined. Moreover, a constitutive model that can simulate damage mechanics properties of earthquake-damaged fissured loess under the influence of moisture and drying-wetting cycles will also be established. Based on this, the mechanism of fissured loess collapse induced by moisture distribution and effects of dry-wet cycles following an earthquake will be analyzed both analytically and numerically. The critical conditions of the collapse will be determined during the analysis. Further analysis will be carried out to investigate the movement feature, area influence and destructive power of the collapse to quantitatively evaluate the destruction caused by the collapse. The achievements of this project will aid to scientifically and reasonably evaluate the post-earthquake fissured loess collapse hazard and provide theoretical support for monitoring and prevention of this kind of collapse.

裂隙性黄土中的节理裂隙结构面对黄土力学行为产生重要影响，地震扰动会对其结构进一步造成损伤，导致震后在降雨、灌溉和干湿循环等致灾因子影响下会引发崩塌灾害，但目前对该类崩塌机理认识尚不清楚。课题通过开展原状裂隙性黄土和经过振动台模拟地震荷载扰动裂隙性黄土试样的CT扫描、非饱和三轴和干湿循环试验，确定裂隙性黄土力学指标及破裂机制与地震参数之间的定量关系，建立受地震荷载扰动裂隙性黄土力学参数与含水量及干湿循环参数之间的关系式；提出可以描述水分、干湿循环及其耦合效应下受地震荷载扰动裂隙性黄土损伤力学特性的本构模型；然后通过理论和数值分析揭示震后裂隙性黄土边坡在水分场、干湿循环及其耦合作用下产生崩塌的机理，确定崩塌发生的临界条件，分析其运动特征、致灾范围及破坏力，形成对该类崩塌的定量评估方法。研究成果有助于更加科学合理地评价震后裂隙性黄土崩塌灾害，为该类崩塌的防治和监测预报提供理论依据。

对黄土裂隙的分类及其发育特征进行调研分析，确定了裂隙性黄土边坡崩滑灾害形成的地质特点。对受震动荷载扰动裂隙性黄土单轴压缩和三轴剪切试验结果进行了分析，结果表明：裂隙性黄土的单轴压缩破坏模式表现为压裂破坏、滑移破坏、滑移-压裂复合破坏以及压剪破坏四种类型；单轴抗压强度随振动幅值和频率的增大均呈线性减小；构建了受振动荷载扰动裂隙性黄土的二元介质本构模型。振动扰动对裂隙性黄土的三轴剪切破坏模式无显著影响，其破坏模式主要由初始裂隙面倾角与围压控制；振动幅值、频率、持时对裂隙性黄土的三轴剪切强度指标产生显著的劣化效应。对不同含水量条件下受震动荷载扰动裂隙性黄土的单轴压缩和三轴剪切试验结果进行分析，揭示了裂隙性黄土的水敏感性特征，结果表明：裂隙性黄土单轴抗压强度随含水量增大显著降低；含水量较低时振动扰动对试样的损伤劣化效应较为明显。振动荷载扰动前后裂隙性黄土试样的粘聚力随裂隙倾角增大均近似呈现出“V”变化特征；振动荷载扰动前后裂隙性黄土试样的粘聚力随含水量增大表现出相似的水敏感性变化规律。开展了干湿循环效应下受震动荷载扰动裂隙性黄土的单轴压缩试验研究，结果表明：不同裂隙倾角试样的表面裂隙率与分形维数均随干湿循环次数增加逐渐增大，但增速逐渐减小；干湿循环效应下振动荷载扰动前后裂隙性黄土的单轴抗压强度随裂隙倾角增大均近似呈现出“双V”变化特征；振动荷载扰动前后裂隙性黄土单轴抗压强度随干湿循环次数增加表现出相似的劣化规律。基于离散元数值方法模拟震后裂隙性黄土边坡的崩滑变形破坏过程，揭示了裂隙性黄土边坡受到地震荷载扰动作用后在含水量、干湿循环等致灾因子作用下发生滑塌灾害的力学机理并提出其稳定性分析评估方法。