| Carbonaceous mudstone has many bad characteristics such as wet deformation,water disintegration,softening,etc.Engineering problems such as road surface settlement and slope slippage are easily affected by rainfall when carbonaceous mudstone is used for actual embankment filling.Therefore,a filling method using carbonaceous mudstone-soil layered to build embankments is proposed by researchers.The purpose is to isolate rainwater by using clay with a small permeability coefficient,reduce rainwater that penetrates into embankment,prevent further collapse of internal carbonaceous mudstone soil and improve stability of embankment.This paper relies on the method of layering filling of carbonaceous mudstone-silk clay in embankment construction of Longlang Expressway project in Lianyuan,Hunan Province.However,due to the heavy and long duration rainfall in Hunan,many embankments still suffer from instability damage.Therefore,through laboratory test and numerical calculation method,seepage characteristics and stability of pre-disintegrated carbonaceous mudstone-soil layered embankment under rainfall conditions are studied,and following conclusions are obtained:(1)According to basic physical and mechanical properties of pre-disintegrated carbonaceous mudstone,natural mass moisture content is 8.79%,uneven coefficient Cu is 5.63,curvature coefficient Cc is 2.17,saturated permeability coefficient of pre-disintegrated carbonaceous mudstone is inversely proportional to compactness,cohesion and internal friction angle are proportional to soil compaction,volumetric water moisture content and permeability coefficient of pre-disintegrated carbonaceous mudstone with different compaction gradually decrease with the increase of matrix suction.(2)Rainfall increases volumetric water content of soil inside slope,at the same time,transient saturation zone is formed at slope surface;the soil moisture content of slope gradually decreases after the rainfall stops.During rainfall period,the closer to slope,the earlier the moisture content increases and the time to enter the transient saturation state,and the longer the slow rise phase lasts while soil in same level.After rainfall stopped,soil moisture content near slope began to decrease,and the closer the moisture content of the soil near the slope is,the greater the decrease.(3)During the test,soil suction of slope soil firstly decreased and then increased.in the soil of the same horizontal plane,the suction of the silty clay matrix in the edging soil decreases rapidly at the beginning of rainfall,the farther the soil from the slope,the later the response time of the matrix suction.After the rain has stopped,the magnitude of the increase in matrix suction is also proportional to the distance from the slope.(4)The foot thrust gradually increases with time during the rain and reaches the maximum after the rain stops 2 hours,the amplitude of increase and increase rate are both proportional to the elevation.The slope top soil simultaneously shifts along the vertical direction and the horizontal direction of the slope to the slope during rainfall.At the same time,the horizontal displacement is always greater than the vertical displacement.(5)Numerical simulation method is used to simulate the seepage process of carbonaceous mudstone-soil layered embankment under rainfall conditions,receiving the calculated results are compared with the model test results.The results show that the numerical simulation and model test results show that the water content of the layered embankment is basically consistent with the trend of matrix suction under rainfall conditions,but there is a certain difference between the variation range and the change time.(6)During rainfall,the safety factor of layered embankment decreases gradually with increase of rainfall time,and the safety factor of embankment decreases slowly 8 hours before rainfall.The embankment safety factor drops rapidly and reaches a minimum during 8 to 16 hours of rainfall.After rain stopped,the embankment safety factor began to increase slowly.Besides,the safety factor of carbonaceous mudstone-soil layered embankment is affected by rainfall intensity,layered filling thickness and compaction degree,among which the compaction degree is the most affected. |
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