The Engineering Characteristics And Disaster Significance Of Strongly Weathered Layer At Mudstone Surface In Tianshui,Gansu Province

The Tianshui city,located in Longxi loess plateau,with poor geological conditions,own frequent loess landslide which is much necessary to research deeply induced by earthquake or rainfall.What is studied systematic is that the landslide characteristics,the structure,composition,physical and mechanical characteristics in loess / mudstone contact surface from macroscopic to microcosmic,in view of mineralogy and mechanics,which is the innovationin this paper in Maiji district.It discusses how to influence the formation of landslides preliminarily.The main results include:(1)According to the lip surface profile morphological characteristics,the loess / mudstone contact surface(strip)landslides caused by rainfall is divided into three types: the spoon type,the arc type and the straight line type.The landslide formation conditions of contact surface of the Loess / mudstone is studied firstly in the area.Thinking that the two or three storey slope structure is the prerequisite for the occurrence of loess / mudstone contact surfaces landslides;The distribution of fully weathered-strong weathering mudstone is a necessary condition for the formation of the landslide;Water is the direct cause of landslides formation.It puts forward the loess / mudstone interface landslide formation evolution process: two layer/three layer slope structure formation?landslide breeding-creep period?the critical slip surface through period?landslides resurrection deform period?landslide relatively stable period.(2)This paper identifies the characteristics of loess / mudstone contact surface(strip).On the macro level,loess / mudstone contact surface(strip)is usually thin weak interlayer or smooth interfacial contact,and criss weathering fissure makes strongly weathered mudstone divided in blocks.On the micro level,strongly weathered mudstone mainly reflects flocculation structure,alignment structure,granular stacked structure and glued structure,and clay piece is mostly showed as surface-surface or side-surface form,dense or denser aggregates arranged in high directivity.(3)Mineral combination of strongly weathered mudstone is mainly composed of quartz,feldspar,calcite,illite-montmorillonite mixed-layer minerals in contact surface(strip).The specific structure of clay mineral and concentrate of illite-montmorillonite mixed-layer minerals is the leading reason of landslide creeping even loss of stability near the contact surface(strip).(4)Contact surface(strip)strongly weathered mudstone has the physical features of high natural moisture content,low density and middle-strong expandability,whose features are different from the rock mass above and below the contact surface(strip)significantly.Meanwhile,when contact surface(strip)strongly weathered mudstone is subjected to shear failure,it mainly shows brittle failure,possessing plastic failure characteristics.There is a big difference between the peak intensity before failure and residual strength after damage.The contact surface(strip)with such physical and mechanical characteristics is a potentially slippery layer.