| The apparent dip slide landslide occurred mainly in a monoclinic limestone slope of dipping oblique introversion. The strata strike direction and main free face (cliffs) direction showed a large angle intersection. The landslide cover well in Southwestern China, and the overall stability is high, but they may also occur slide and instability under the special conditions (earthquake) or external factors (such as underground mining). The jiweishan mountain landslide in Wulong, Chongqing is such a special class of the apparent dip sliding high-speed and long-range landslide.The apparent dip slide landslide is difficult to identify with the characteristics of strong concealment, complex genetic mechanism, big controversy, strange disaster mode, difficult disaster prevention and reduction and high risk. Studing this type of landslide has very important theoretical and practical value.According to the field detailed engineering geological surveys,3D laser scanning and exploration, aerial photography, field monitoring and sampling tests, large-scale centrifuge model tests,3DEC numerical simulation, limit equilibrium and vector analysis method etc, the paper In-depth systematic studied the formation conditions and mechanism of instability, established a method for early identification of landslide critical block controlled and proposed proactive precautionary measures, and then extends the type of the large rocky, enriches the research means, provides a theoretical basis and technical support for the rock landslide in southwest mountain early recognition and emergency disposal, the following main conclusions and achievements:(1) According to the field detailed engineering geological surveys, data collection and comparative analysis, and the research of typical apparent dip slide landslides such as Jiweishan Landslide in Chongqing, the earthquake-induced Daguangbao landslide in Anxian County and the Woqian landslide, further developed and defined the concept, formation conditions and characteristics of the apparent dip slide landslide, and then the apparent dip slip type landslide is divided into the conventional apparent dip slip landslide (such as Daguangbao landslide and Woqian landslide) and the landslide key block controlled (such as Jiweishan landslide). The former has a sliding condition of location overhanging due to leading edge of the sliding direction has some gullies, mountain turns, etc. The latter is no obvious condition of location overhanging due to the blocking of the front edge of the mountain, so exist the so-called key block. The Jiweishan mode is that the slope downward creep due to the influence of gravity and lower mining, but because of the leading edge is blocked, the slope was forced to turn to the direction of apparent dip and slide. The Jiweishan mode is the leading edge of the mountain blocked type, the lower mining type and creeping type landslide. The Daguangbao mode is the free leading edge type, earthquake type and unexpected type landslide.(2) This paper takes Jiweishan Landslide as example and reveals the formation conditions, features, main influence factors and genetic model. The formation and evolution of apparent dip slide rocky landslide is revealed in terms of topography, slope structure, lithology, karst development, engineering disturbance as follows, monocline and gully on the side of slope provide free face for apparent dip slide; There is a large angle intersection between the true tendency and the free surface of cliff strike, two nearly orthogonal steep structure surfaces combined with soft rock in sliding zone, which made the rock in slide source area cut into the "building blocks" shape; The Karst zone apparent dip distribution made slip the source region and the stability mountain completely cut, a relative weak belt in apparent dip due to karst, mining goafs generate cantilever effect which accelerates slope deformation and promotes the formation of lateral deep crack ending up to landslide boundary,the paper generalized conceptual model of apparent dip slide landslide, Cracks along the surface of the native structure form unloading zone with gully on the side of slope cut and erosion, Slope evolution continue to develop and the formation of landslide. The leading edge of sliding block on the front of slope is a large "compressible" fracture karst zone, which plays a key role in the occurrence of this kind of landslide, and the "soft effects" of Karst zone apparent dip distribution provided "quasi free surface", which causes the landslide generate creep-crack deformation. The bottom sliding surface cut-through and the slope shear creep along the bottom surface in the process of the formation of landslide; The slope stress concentration toward to the "easy compression zone" on the leading edge of the slope, and the slope stress automatic adjust, Slope along the "easy compression zone" creep, perpendicular to the slope (cliff) and formed second fracture face, finally cut the Karst Rock,the landslide instant instability and the high-speed remote debris flow generat.(3) The type of slip zone, material components, micro-structural features and rheological properties of Jiweishan landslide determine the stress state and changes of intensity of slip zone. These changes eventually affect landslide activity, to some extent, these characteristics also control the landslide evolution process.(4) Taking Jiweishan Landslide as example, Qualitative and quantitative analysis is made in assessing the stability of apparent dip slide landslide, analysing the stability of Jiweishan landslide by various methods, such as stereographic projection method, software analysis of slope stability of block (SASW), wedge vector analysis method, analytical method based on the "Soft base effect", the results showed that landslides controlled by "key block" is stable through analysing the slope as a rigid body, the calculation is scientific and feasible through decompose "key block" on the front of slope and drive block in the rear of slope, and the "soft base effect" and "second fracture surface" exists. The length of slope of Jiweishan is more than110m and is not conventional wedge. Based on calculation model of "soft ground effect", there is a strong correlation between slope stability and slope length L and the angle θ between the weak band on the front and the direction of strike of the bottom surface, which provides the basis for the field identification.(5) Centrifuge modeling tests shows that the spatial and temporal characteristics of the formation and evolution of landslide is obvious. The pressure increased as centrifuge acceleration ascends; the process gradually reduced from the front to rear part at the same time. The change of displacement of each point of landslide is basically consistent, but Karst zone is obvious bulge upward due to compression, the initial failure of landslide is evolutionary process from stable to unstable with the long-term creep of bottom surface and the compression and shear of karst zone. The operating point and action time of the bottom surface and the side surface is inconsistent in the slip resistance effect. So they can be not play their role effectively at the same time, which is the main factor of slope evolution and the apparent dip slip. Jiweishan landslide is a complex failure mode with creep-tension fracture-Compressive-shear. Change of mode at Karst zone before and after compression is a sign which slope enter progressive failure, and the sign has great concealment.(6) Three-dimensional discrete element (3dec) numerical simulation results show that the displacement of slope is small and gradually converge under natural conditions, and slope is stability. Under conditions of creep, the deformation and stress continues to increase slowly, the karst zone of leading edge has a large "compressibility", and the karst zone has a bulge phenomenon under pressure increasing and a small amount of displacement, the sliding block continue squeezing karst fracture zone on leading edge, and then occur creep aging deformation along gray slate, in this process, the tension crack at trailing edge is increasing, slope adjust their stress, and then affect the stability of the slope, the sliding force significantly increase, Karst zone is squeezed and broken. Resistance body and drive block body in the rear of slope separate and form the second failure surface, Karst belt is cut off, the slope transient overall instability. All indicate that the role of control and slip resistance of the key block body is obvious,"Soft base effect" in karst zone at the leading edge of slope provide "quasi-free face", which cause this kind of landslide generate creep cracking deformation.(7) Based on field geological investigation, comparative study of similar slope in adjacent area, in-depth analysis of typical cases, analysis of key examples in numerical simulation and physical model test, and analysis of the geological structure, the structure of slope, instability mechanism. The research found five recognition characteristics associated with the apparent dip slide landslide:boundary segmentation of slope, Layered rock block inclined hill, barrier of tendency mountain, distribution of apparent dip direction of weak zone, free surface of apparent dip direction. The apparent dip slide landslide has space-time evolution law, deformation characteristics of slope at each stage is distinctness. |
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