| In the western of China, there are widely distributed the gentle-dip stratum of Jurassic, Cretaceous and Triassic.Under the long-term action of internal and external geological forces,it's become the gently inclined bedding landslide.This kind of landslide has the characteristics of hard to identify, difficulty in recognition, complex mechanism, and difficulty in prediction and predict. In view of this, with the subject of "973 project mentor western mountain landslide geological structure characteristics and disaster mode research", based on a large number case of gently dip bedding landslide and the geological survey, basic characteristics, landslide formation conditions and influencing factors were inductively analyzed. And based on it to establish the landslide formation mechanism conceptual model.and use it to research the characteristics of slow dip bedding landslide groundwater pressure distribution, the deformation and failure mode of physical simulation experiment, and then the influence factor sensitivity of numerical calculation, and finally puts forward the identification method of this type of landslide. The research results of this paper will provide some theoretical support for the identification, early warning, prevention and control of such landslides. The main research contents and results are as follows:1?The gently inclined bedding landslide typical cases was collected to research on its basic characteristics. soft and hard interbedded strata inclined outside the soft and hard interbedded slope mainly developed in Low Mountain hilly area of gently dipping Jurassic and Cretaceous and Triassic; dip angle less than 15 degrees; the average length of 660 meters, the slope was mainly the width / length of about 1.4 strip; the middle of the slope flat about 10 degrees slope and the trailing edge of slope of 30 degrees ~40 degrees, the average thickness of 25 meters; the slope mainly developed two groups of nearly orthogonal vertical joint surface, a group of nearly vertical sliding direction, a group of nearly parallel to the direction of landslide; slope layer to soft and hard interbedded lithologic. Soft and hard rock lithology difference exist between the water permeable hydrogeological structure characteristics.2?Based on field investigation and data analysis, summed up the gentle dip soft and hard interbedded landslide deformation characteristic: trailing edge form up to deep pull tension rift trough; landslide based on single level or multilevel sliding, sliding body integrity is good; slope in front of the extrusion forming uplift drumlin; pull slot and slope in the front boundary formed small collapse sliding zone. The unfavorable lithology combination of the soft and gentle slope is the geological foundation of landslide development. The relative permeability and water- separated hydro- geological structures are the main internal factors of landslide development. The strong rainfall is the triggering factor of landslide formation, and the hydrostatic pressure and uplift pressure caused by heavy rainfall are the important mechanism of this kind of landslide instability. The formation and evolution of the gentle slope and gentle slope can be divided into the following stages: the transformation stage of the valley and the lower surface of the valley, the crack propagation and the aging deformation stage. Based on the geological prototype characteristics, the deformation and failure characteristics, the inducing factors and the evolution law of the slope, the concept model of the interaction between the soft and hard.3?Based on concept model of gentle consequent landslide,the experimental model of 1:200 is built according to similarity principle. Through screening test and the seepage test, the selection and setting of the permeable material were completed. The seepage series of sand and mud rock mass, which is widely existed in the water-permeating layer in the slope with interbedded soft and hard rock beddings of low dip angles, is simulated by the medium water-permeating level, strong water-permeating level and intense-permeating level respectively. The main results are as follows:(1)The permeable layer permeability rate and the permeability has a linear relationship, as in the trailing edge permeable layer under high seepage pressure permeability from middle permeable- strong permeable and strong permeability increased, groundwater infiltration rate increased from 1mm/s-5mm/s-39mm/s linear, permeable in the same rainfall condition layer of the larger permeability coefficient, water permeable layer more quickly; the permeability of the size also affects the slope groundwater distribution curve slope groundwater distribution curve of the average slope and the permeability of the linear negative correlation with permeable layer permeability from middle permeable- strong permeability increases, water pressure distribution curve of the average slope of K value from 0.4525, 0.31, 0.14276,0.073 linearly changes, i.e. the larger the permeability of the groundwater distribution curve of average slope is small.(2)The tests indicate that the penetration rate of permeable layer is linearly proportional to permeability. Generally, The greater the permeability coefficient of permeable layer, the faster the movement of groundwater under the same condition of rainfall.The quality of permeability also has effect on curve slope of groundwater distribution in the slope: There is a negative correlativity between average slope of groundwater distribution curve and the permeability, which means the better the permeability, the smaller the average slope of groundwater distribution curve; Water-permeating level of permeable layer determines the sequence of the confined water to work: The confined water acts firstly at the foot of the slope as water permeability surpasses the intense-permeating level, and develops gradually to the middle posterior part of the slope with rise of fissure water level; On the other hand, the confined water acts firstly at the back of the slope while water permeability becomes weaker than the intense-permeating level, and develops gradually to the front edge of the slope with rise of fissure water level.(3)Under the condition of heavy rainfall, groundwater distribution of flat outside soft hard alternating layers slope after toe slope water plugging was simulated. We can get the permeable layer with different permeability under water pressure distribution of the top surface of the water,the results are as follows:The distribution of confined water in the slope is triangular, trapezoidal and rectangular, when the permeability of the permeable layer is weaker than that of the medium permeability;The distribution law of groundwater in the slope is small triangle triangle rectangle mode when the permeability of the permeable layer is between the medium permeability and strong water permeability;When the permeability of the slope is stronger than the strong water permeability, the pressure in the slope is basically in the rectangular distribution with the high head of the trailing edge and so on.(4)Based on the analysis of the pressure bearing water distribution in the slope, the effect of different water pressure on the landslide near the sliding condition is studied.Compared with the traditional formula and the correction formula, this paper introduces the hydraulic gradient parameters i,which determines the magnitude of slope of curve for groundwater distribution curve,to modify the formula, and accurate representation of the uplift pressure size.4?Through of gently inclined and soft and hard interbedded type landslide single factor sensitivity numerical calculation results: primary and secondary slope rock and soil physical factors influence on slope stability is as follows: in friction angle, cohesion, sliding bulk density, landslide permeability of; structural conditions of slope of gently inclined and soft and hard interbedded slope rock steady inclination play main role, soft and hard rock mutual layers on the stability of the slope body almost had no effect; the stability of slope caused by the heavy rainfall in the trailing edge of the head height response is larger. Under the influence of a single factor, only the internal friction angle is small, the dip angle of the rock stratum is greater than the internal friction angle, and the stability of the slope under the trailing edge crack can be reduced to below 1.5?This paper builds the orthogonal experiment table for influence factors of bedding landslide with gentle dip strata by using the statistics Principle. It studies on the sensitivity of influence factors by numerical calculation on the basis of conceptual model of these kind of landslides. The primary and secondary factors affecting the stability of the soft and hard mutual layer type landslide are summarized. Friction angle of the slope stability of the primary and secondary relations are as follows: in friction angle, and the dip angle of strata, rainfall intensity or trailing edge head height, cohesion, permeability coefficient in the dip angle of strata are less than that of the inner sliding contact; dip angle is greater than the internal friction angle under: dip angle and the weak interlayer friction angle, heavy rainfall or trailing edge head height, cohesion, permeability coefficient.6?It is a long and complicated process that the slow slope and the slope of the soft and hard mutual layer type landslide is a long and complicated process, which is under the combined action of various factors and conditions. From the point of view of the result of orthogonal experiment, under the action of strong rainfall trailing edge head elevated, if you cannot make a slope physical properties of weakening is not possible to make the slope instability, namely slope rock and soil properties is gently inclined and soft and hard interbedded slope instability of internal factors. Also, the effect for a long time, the rock and soil weakening after, if no rainfall outside conditions of the formation of hydrostatic pressure, the change of seepage field, instability of slope is not, namely rainfall is external factors of slope instability. The gentle slope and the external soft and hard mutual layer type landslide is under the action of internal and external factors.7? On the basis of the geological prototype, failure characteristics, evolution law and mechanism of the gentle slope, the identification mark of this kind of landslide is summarized. Summed up in gently inclined Cuesta landscape logo, slope delta front channel narrowing protrude, vegetation height limits or density boundaries was chair shaped, trailing edge slopes appear pull troughs or sliver shaped sink puddles, based remote sensing identification mark; summarized the erosion, denudation of low mountains and deep hilly landform slow inclined convex type Cuesta landscape logo, gently dipping Cretaceous, Jurassic, Triassic soft and hard interbedded stratum identification, typical deep fissure, exchange the puddles to slope structure etc. ground identification mark. |
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