南疆风积土浅表高位滑动成灾机理研究

A large scale of unequal thickness aeolian soils distribute at the upper mountain slopes between 2500 to 4000 meters of Western Kunlun and the valley where Tarim southwest corner and north-south mountain meet, and it’s disaster mechanism is still blank.According to the 7.6 YeCheng field investigation, there are 10 soil landslips and 2 blocked dams in the range of 1,400 meters. Long-term freeze-thaw action and peripheral multiple seismic activities destroy the structure of the aeolian slope. There existed creep cracking and it was easy to form geological disasters triggered by the heavy rainfall. We named it rainfall landslide dam burst diluted debris flow disaster. The geo-hazard chain is evolved as following: high soil slope went through long term freeze-thaw creep—seismic dynamic fracture—heavy rainstorm triggered slope—blocked into dammed lake—lake burst—diluted debris flow. Long term freeze-thaw action, seismic dynamic action and incidental heavy rainfall may make ‘Yecheng Model’ repeat at a certain range of time and space again and again. Therefore, we intend to use the quaternary aeolian soil elevation and partition, typical slope freeze-thaw monitoring, seismic dynamic simulation and numerical calculation methods to study its mechanism and conversion condition. The results are expected to promote the understanding of south Xinjiang aeolian disaster mechanism and provide basis for the regional disaster prevention and new rural construction, which is very significant and practical.

塔里木盆地西南隅近东西和南北走向山脉交汇的凹地、西昆仑北麓高程2500~4000m中高山范围斜坡分布大面积厚度不等风积土，其孕灾机理研究基本空白。对南疆7.6叶城地质灾害考察发现六村村委会至上游1400m内沟谷发生10个土质滑坡、2个滑坡坝。风积土边坡长期冻融作用和周边多发地震活动使结构破坏，滑动前有长期蠕变拉裂，大暴雨触发其快速成灾。将其定名为降雨滑坡堰塞湖溃决型稀性泥石流灾害，实质是风积土高边坡冻融蠕变-地震动破坏-大暴雨触发滑坡-堵沟成堰塞湖-坝体溃决-稀性泥石流从长期塑变到突发灾变的灾害链。长期冻融作用、地震动作用和偶发强降雨，使“叶城模式”可能会在一定时空范围内长期“复制”。拟采用第四纪风积土高程和厚度分区圈划、典型土边坡冻融监测、地震动模拟和数值计算方法，研究其发生机理和转化条件。结果可望推动南疆风积土灾变机理认识，为该区防灾减灾和精准扶贫工作提供依据，有重要理论和实践意义。

叶城黄土分布在西昆仑北麓，在冻融长期作用和强降雨突发作用下易发生地质灾害。通过地球物理探测、非饱和土水特性分析、物理试验以及数值模拟等展开黄土边坡稳定性研究。边坡蠕变高位弧形拉张裂缝，堰塞湖溃决型泥石流反演，以及亲历的1次小型灾害链过程，说明昆仑山北麓2500~4000m分布厚度不等、面积各异的风积土，发育蠕变高位拉裂-强降雨滑坡-堵沟成堰塞湖-溃坝-泥石流链生 “叶城模式”。 边坡上厚度不等风积土构成滑坡和泥石流主要组份。叶城风积土时代新、粘结力弱，水流冲刷易快速失稳，若形成堰塞湖则因滑坡坝强度低而在暴雨作用下溃坝危险性极高。六村上游1.2km范围10个滑坡、2个堰塞湖，是灾害链关键一环，构成风积土区灾害隐患。调查发现若干年前六村上游就存在两个老滑坡坝，曾构成堰塞湖和产生过溃决型泥石流。水毁灾害一般发生在河流急拐弯处（多为凹岸）。风积土和河漫滩相粉砂构成的高阶地在洪水侧蚀作用下，路基水毁，发生下陷和损毁淤塞原涵洞或埋管，泥石流漫过和破坏路面而影响交通。对六村等地质灾害高危险地段村民整体搬迁决策科学果断。建立降雨模型分析降雨下坡体内部渗流作用和稳定性特征，雨强分别为10mm/h和25mm/h，并考虑初始拉裂缝影响。观测不同降雨工况下斜坡渗流参数变化特征，记录坡面浸润线变化，综合分析映降雨对坡体含水率及基质吸力影响。用Geostudio建立有限元模型，包括seep/w渗流模块和slope/w稳定性模块。物理模型设置边界条件和初始条件及降雨情况。斜坡模拟中将冻融损伤和裂隙作用综合考虑，将风积土层表层3m设为松散层，赋予其较大渗透系数，进行渗流和稳定性分析。入渗中降雨沿坡面流失，侵蚀冲刷作用较强，在斜坡裂隙中形成水头。随入渗变形加剧，已有裂缝与坡脚侵蚀破坏渐贯通，最终破坏面在坡肩以下坡中位置。模拟结果较好地区分水土流失和滑坡发生的降水条件。