Research On The Damage Accumulation Effect And Dynamic Response Law Of Accumulation Slope Under The Action Of Frequent Microseism

Since 2003,the three gorges reservoir area began filling,the reservoir area water level has been increasing significantly,which lead to a huge water pressure applied to the reservoir basin rock.According to the reservoir water level scheduling plan,the reservoir water level is cyclical fluctuations every year,which greatly increases the possibility of earthquakes in the reservoir area.Because of energy release concentration,the surface intensity caused by the earthquake is significantly greater than the same magnitude of the tectonic earthquake,and more than 3 magnitude of induced earthquake epicenter intensity is up to?degrees(0.04 g).Accumulation slope is widely distributed in the Three Gorges reservoir area with loose structure,which is easy to destroy under the earthquake.At present,the main focus is on the critical instability state of the sliding body,and little attention is paid to the long-term effects of frequent microseisms on the slope of the accumulation body.Therefore,it is very important to study the damage cumulative effect and dynamic response of the reservoir slope in the reservoir.In this paper,the method of data summary,experimental analysis and numerical simulation are used.The characteristics and traits of the slope of the accumulation body are discussed,by the compilation of domestic and foreign literature;The shear characteristics of soil and stone mixture with different moisture content and different densities were studied by large-scale indoor direct shear test in a sample collected from a pile accumulation slope in Three Gorges reservoir region;a small shaking table test was adopted,with different slope structure,different moisture content,different density as the focus of simulation content,to study on the cumulative effect and dynamic response of 10 kinds of accumulation slopes with different characteristic models;The numerical model of accumulation slope was established by using particle flow code program(PFC2D),and the relevant dynamic response simulation was carried out.The main research results are as follows:(1)While the greater the normal stress when the stone mixture is sheared,the longer the near-elastic section of the shear curve is,and the greater the shear stress and displacement increment of the shear yield section is;When the remaining conditions are the same,the shear curve is softened or near elastic-plastic shape,and the different dry density of the sample after the destruction of the residual strength value are close,while the smaller the water content,the greater the tangent slope of the near elastic section of the shear curve is;The compactness has an effect on the shear strength of the mixture,while the normal stress has a weakening effect on this increase;The higher the water content,the lower the shear strength of the mixture is;when the degree of compactness increases,the cohesion of the mixture increases significantly,but has little effect on internal friction angle;The higher the water content,the smaller the cohesion and the internal friction angle of the mixture were,and there are a power function relationship between the cohesion,the internal friction angle and the water content.(2)Based on the analysis of natural frequency of vibration damage of shaking table test,it is found that whether the existence or failure of bedrock does not affect the trend of damage accumulation curve,but the initial vibration effect of bedrock model is stronger than that of bedrock model,and the total damage degree of the former is less than that of the latter;The higher the moisture content,the more rapid the development of model damage is;The higher the density,the slower the development of damage is.Based on dynamic Response Analysis of PGA Amplification Coefficient,it's found that in the initial stage,the higher the water content,the larger the PGA amplification coefficient increases with the elevation;From the whole stage,with the increase in the frequency of vibration,PGA amplification coefficient is in a linear trend with the increase in elevation,the higher the degree of compactness,the more obvious the trend is;Under the action of different frequency conditions,the variation range of PGA magnification coefficient under high frequency condition is larger than that of low frequency condition.The higher the frequency,the more obvious the phenomenon is.High water content model damage was "local integral",while low water content model damage was "collapse type",furthermore the degree of compactness was proved to be little effect on the model's failure mode(3)Based on damage analysis results of the crack propagation method by PFC numerical simulation,it was found that the failure mechanism of the accumulation model with different amount of stone and compactness was tensile-shear combined effect under the action of dynamic action.The higher the density,the slower the damage development was;what's more when the amount of stone is too high or too low,the damage developed rapidly,while the damage was found to developed slowly,when stone content is about 50% of the amount.