Influence Of The Increase Or Decline Of Water Level Front Slope On Seepage Characteristic And Slope Stability Of Carbonaceous Mudstone-Soil Layered Embankment

During the construction process of Liuzhai to Hechi highway in Guangxi Zhuang Autonomous Region first proposed the embankment construction method of carbonaceous mudstone-soil layering staggered filling.This method effectively solves the problem that is short of quality embankment filling in carbonaceous mudstone distribution area.However,Layered embankment excessive deformation or instability phenomena always occur due to the water level of reservoirs or rivers change during the highway operation.To this end,this article were studied the strength deterioration mechanism of pre-disintegration carbonaceous mudstone after immersion,the percolation characteristics and stability variation law of carbonaceous mudstone-soil layering staggered filling embankment under the condition of water level fluctuation front slope by laboratory experiments and numerical simulation method.The main conclusions obtained are as follows:(1)For the strength deterioration characteristic of carbonaceous mudstone after immersion,have carried out triaxial compression test of pre-disintegration carbonaceous mudstone under the conditions of different soaking time and different confining pressures.Having obtained the strength variation law of pre-disintegration carbonaceous mudstone that is under the condition of immersion.Which is: with the growth of soaking time,the total stress shear strength parameter of carbonaceous mudstone showed exponential type decay law in saturation state.(2)During artificial simulated the water level front slope rising process,the water content of each measuring point in embankment gradually reaches saturation and the matric suction of each measuring point continues to decrease until disappearing.After the water level front slope dropped,the water content of each measuring point gradually decreases and the matric suction of each measuring point slowly picking up.The response times that the water content and matric suction of each measuring point are directly proportional to the distance between measuring point and slopes,inversely proportional to the measuring point elevation.The variation law of thrust front slope and slope displacement during the model testing process showed that the water level front slope rising was beneficial to layered embankmentstability.Flood storage and the water level front slope drops were unfavorable to layered embankment stability.(3)Using numerical simulation analysis method and combined with saturated-unsaturated seepage theory to analyze the seepage characteristics of carbonaceous mudstone-silt layered filling embankment when the rates of water level fluctuation were different.Analysis showed that the rate of water level before slope rises faster,the response time that the water content and pore water pressure of feature point earlier.The rate of water level front slope drops faster,the water content and pore water pressure of feature point reduced more significantly.(4)Using limit equilibrium method and combined with unsaturated shear strength theory to calculate the variation law of embankment safety factor during the changed of the water level front slope.The calculation results showed that the safety factor of embankment continue to increase during the water level front slope rising process,embankment safety factor decreases rapidly at first,then slowly increased after the water level front slope dropped.The rate of water level front slope fluctuation faster,the larger of the embankment safety factor change range.Layered filling embankment safety factor decreases with the increases of carbonaceous mudstone filling layer thickness.(5)Proposed an embankment stability calculation method that can considering soaking softening and unsaturated effect,and compared the variation law of embankment safety factor during the changed of the water level front slope that obtained by using this method for the calculation with the embankment stability analysis method that only consider unsaturated effect.The results shows that the embankment safety factor that don't consider the soaking softening effect of pre-disintegration carbonaceous mudstone higher.This embankment stability analysis method is more targeted and practical for carbonaceous mudstone embankment which has softening effect.