青藏高原东北缘新近纪盆地内旋转-平推式滑坡聚集规律与机理研究

摘要

旋转平推式滑坡在世界各地的新近纪盆地内广泛分布,致灾风险极高.在现场调查的基础上,本文系统梳理了该类滑坡在青藏高原东北缘的空间分布和变形方式,通过取样测试与数值模拟计算,探讨了旋转-平推式滑坡近水平滑动带的变形机理.研究表明:①旋转平推滑坡集中于青藏高原东北缘新近纪泥岩盆地内,其活动强度受青藏高原隆升的影响,自高原腹地至边缘盆地,滑体体积逐步减小;②滑坡均由高黏粒含量、超固结新近纪泥岩组成,趋向剪胀、渐进性破坏.在河流的侵蚀塑造的近水平剪切应力环境下,薄层剪切带内摩擦角小于10°,剪切带内随机排列的黏土颗粒的逐步定向,呈现韧、脆性变形;③滑动带的蠕变、裂隙扩展与地下水的增湿加速材料的流变,滑面沿黏粒含量高、碳酸钙含量低的软弱层扩展.滑带内黏土矿物蠕变、裂纹的扩展,导致宏观变形逐步积累,剪切面逐渐形成,是滑坡变形的动力因素之一.%The rotational-translational landslides occur widely within the Neogene basins throughout the world because of their high risk.Based on field survey,this paper summarized the distribution features and geometric strain models of rotational-translational landslide to analyze the dynamic mechanism of nearly horizontal sliding band transformation using the experiment and numerical simulation calculation.The study yields the following understanding.(1) The rotational-translational landslides mainly occur in the Pliocene mudstone basins on the northeastern margin of Tibet Plateau.The activity intensity of these landslides is mainly affected by the uplift process of Tibet Plateau,with the volume gradually reducing from the hinterland of the Plateau to the marginal basin.The giant landslides concentrate in the upstream areas of the Yellow River system,while the large ones distributed respectively in the downstream areas.(2) The slide mass of rotational-translational landslide are all composed of Pliocene mudstones with high clay contents and over-consolidation features.Under the environment of nearly horizontal shear stress of slide mass,which is controlled by water flow erosion,clay grains of over-consolidated mudstones within shear stress zones,with internal friction angle below 10,tend to directional alignment and present ductile and brittle deformation.(3) The sliding surfaces extend along weak layers with high clay content and low calcium content due to the deformation of creep and crack.This process is also accelerated with increasing content of pore water and the rheology of sliding zone.Therefore,the macro movement of sliding mass was determined by creep and glutinous flow of clay minerals in sliding zones,which is one of the driving factors of landslip deformation.