Study On Geomechanical Mechanism Of Soft And Hard Interbedded Bedding Failure Along Inclined Slope Induced By Rainfall

The soft hard interbedded slope is a kind of generalized soft hard composite structure slope which contains all kinds of fracture layers and unconformity surfaces?zones?,which is widely distributed in Southwest China.Compared with the homogeneous slope,the rock mass structure of the soft hard interbedded slope is more complex,and the interbedded combination is poor.Under extreme conditions?such as rainfall and earthquake?,the strength of soft rock in this kind of slope is greatly reduced,which is prone to"short plate effect"and then instability.Due to the different occurrence environment,geotechnical characteristics and mechanical properties,the rainfall mechanical response of this kind of slope also presents unique characteristics.As a key project in Sichuan Province,the construction and operation of the railway are seriously affected by the instability and sliding of the station slope during the construction of Gulin station section along the railway.Based on the landslide of Gulin station in Sichuan Province,this paper establishes the corresponding generalized model through field survey and data collection,carries out large-scale indoor rainfall physical test and numerical simulation calculation,and explores the different mechanical behaviors of this kind of slope under the rainfall conditions.The research results are as follows:1.Through the field survey of typical soft hard interbedded slope disasters induced by rainfall in southwest mountainous areas of China Based on the systematic data processing,the engineering geological conditions and distribution characteristics of rainfall instability of soft hard interbedded slopes are clarified,and the types and induced conditions of rainfall instability disasters of this kind of slopes are preliminarily identified.According to the failure characteristics of typical slope construction site under the action of engineering excavation and rainfall,the formation mechanism of two instability failures is analyzed preliminarily,and the corresponding modeling is constructed.2.Based on the self-developed model device and indoor atomization rainfall system,five groups of large-scale indoor rainfall model tests and numerical simulation studies were carried out.Considering the combination factors of slope height and rock stratum structure,the surface sliding of near horizontal slope,front collapse of middle inclined slope,shallow sliding multi-layer regression,gentle slope sliding,tension crack bending and gentle slope unequal thickness were reappeared There are four kinds of instability modes,i.e.displacement between thickness layers and shallow surface pushing.?3.Based on the similarity theory and dimension relation,the similarity constant of physical experiment is deduced.Through the design of orthogonal experiment and permeability experiment,the proportion of similar materials of soft rock and hard rock is determined.The proportion of similar materials of hard rock is:Barite powder:quartz sand:Gypsum:water mud:water=36:45:0.5:0.5:18;the proportion of similar materials of soft rock is:Barite powder:stone Quartz sand:Gypsum:Clay:water=40:32:9:1:18.The dynamic monitoring of the change of water content and the expansion of deformation of the slope body is carried out by using the internal and external monitoring systems,and the mechanical response and failure mechanism of the slope in the process of rainfall failure are revealed in many aspects.4.This paper discusses the dynamic damage effect of soft rock with time,reveals the failure behavior and mechanism of the rock mass in the slope,and proves the existence of preferential flow effect in the process of slope failure.By measuring the softening coefficient of the rock mass in the laboratory,the strength reduction of soft and hard rock with water is analyzed,and the power function change law of the softening coefficient with time is obtained For:_{Soft rock}=-0.095 ln??+0.323;_{Hard rock}=-0.043 ln??+0.7435.The program of this rule is introduced into UDEC discrete element analysis,and a numerical model of rainfall instability analysis of soft hard interbedded slope is constructed.5.It is concluded that the main effects of rainfall on the instability of soft hard interbedded slopes are the effect of uneven fracture cutting and the effect of fracture preferential flow.By combining the failure characteristics of slope in different rainfall periods with the numerical changes of water content,pore water pressure and earth pressure in corresponding periods of slope,the relationship between the changes of mechanical parameters in slope and the failure characteristics of slope is established,so as to provide reference for the disaster prevention and early warning work of similar slope.6.Based on the numerical simulation of the rainfall instability process of the soft hard interbedded slope by using the discrete element software UDEC,the potential influence of the slope and the thickness of the rock layer on the failure mode of the slope is revealed,and the distribution of the preferential flow channel in the slope is found out;the significant influencing factors of the rainfall instability of the interbedded slope with different slope structures are analyzed to find out that the failure depth and the damage of the gentle bedding slope are the deepest The proportion of soft rock in the slope is larger and the damage is serious.The larger the proportion of hard rock in slope,the stronger the stability of slope.