黄土高原地震次生滑坡灾害发生机理及评估方法研究

Earthquake will cause damage to the micro-structure of loess, which will lead to landslide under the influence of rainfall, irrigation and repeated freeze-thaw cycles. However, the mechanism of this type of landslide is still not clear. In this project, unsaturated triaxial tests and freezing-thawing tests will be carried out on both undisturbed loess samples and samples disturbed by earthquake loading simulated by a shaking table. Based on the test results, relationship between the strength and deformation characteristics and earthquake parameters will be determined. A elasto-plastic constitutive model that can simulate the mechanical properties of earthquake-damaged unsaturated loess will be established. Quantitative relathionship between mechanical parameters of earthquake-disturbed loess and freezing-thawing parameters will be determined. This relationship will be combined with the constitutive model to establish a freezing-thawing degradation formulation of earthquake-damaged loess. Based on this, the mechanical mechanism of landslide caused by variation of moisture distribution and effects of freeze-thaw cycles follwing an earthquake will be analyzed both analytically and numerically. The critical conditions of the landslide will be determined during the analysis. Further analysis will be carried out using a numerical model to investigate the distance and area influence by the landslide to quantitatively evaluate the destruction caused by the landslide. The outcome of this project will aid to scientificallyand critically evaluate this type of landslide hazard and provide theoretical support for monitoring and early warning of this kind of landslide.

地震扰动会对黄土结构造成损伤，导致震后在降水、灌溉和冻融循环等因素的影响下会引发滑坡灾害，然而目前对该类滑坡的机理认识尚不清楚。本项目通过开展原状黄土和经过振动台模拟地震作用扰动的黄土试样的非饱和三轴试验和冻融循环试验，建立黄土强度和变形指标及应力应变关系特征与地震参数之间的定量关系；提出可以描述地震荷载扰动损伤后非饱和黄土力学特性的弹塑性本构模型，建立地震荷载扰动黄土力学参数与冻融循环参数之间的关系式，并将两者结合起来建立地震损伤黄土的水-热-力-变形耦合关系式；在此基础上通过理论和数值分析揭示震后黄土边坡在水分场和温度场变化作用下而产生滑坡灾害的力学机理，确定滑坡发生时的临界条件，并进一步利用数值模型分析其致灾距离和致灾面积及沿程破坏力的大小，形成对该类滑坡的危险性及破坏力的定量评估方法。研究成果有助于更加科学合理地评价地震次生黄土滑坡灾害，为该类滑坡的防治及监测预警提供理论支持。

黄土高原的很多地区都处在高烈度地震设防区，历史上也发生过陕西华县地震和宁夏海原地震等强烈地震。因此研究黄土在受到振动荷载扰动后强度和变形性能的损伤劣化规律，对分析震后次生黄土滑坡灾害危险性以及采取相应防灾减灾措施至关重要。黄土在地震扰动后继而受到含水量变化、冻融循环等诱因的影响引起强度参数发生变化，本课题通过不同含水量下的原状黄土和地震荷载扰动黄土的强度试验和冻融循环试验寻找黄土受地震荷载扰动后变形和强度参数的变化规律；结合数值分析软件对扰动黄土受到含水量变化和冻融循环等因素的影响而使强度进一步降低的规律进行了初步研究。首先通过构建原状黄土与扰动黄土间的对比试验，以扰动频率、位移幅值、振动持时为控制变量，获得扰动参数对黄土强度和变形的影响及其之间的联系；进而采用地震扰动下不同含水量黄土的敏感性试验，配合有限元分析软件Geo-studio模拟分析地震作用对不同含水量边坡及震后降雨入渗对边坡的影响，得到不同节理边坡模型的安全系数变化及滑移面位置的变化，最后通过改进瑞典条分法使之适应求解非饱和土渗流情况下的边坡安全系数。通过冻融循环试验分析扰动黄土在不同冻融次数的诱导条件下强度变化的情况，结果显示冻融循环次数对扰动黄土强度进一步降低有一定影响。原状黄土及不同扰动因素下黄土三轴试验证实扰动因素和黄土强度指标之间具有一定规律。综合上述结果，本研究为探讨黄土滑坡灾害理论研究的知识体系奠定了坚实的工作基础。同时对于宏观分析次生灾害的安全性以及斜坡稳定性提供了重要的参考依据。