Study On Non-equilibrium Seepage Characteristics And Instability Mechanism Of Macroporous Slopes Under Heavy Rainfall Conditions

The distribution of granite residual soil is very extensive in the southeastern coastal areas of China.For example,the proportion of macropore in granite residual soil is 2.40%?48.72%,which is a typical macropore structure.Under the condition of typhoon and other heavy rainfall,rainwater infiltrates into the deep soil layer preferentially from macropore,and then induces the shallow slope instability and collapse.However,the traditional unsaturated seepage theory can not describe this phenomenon reasonably.In view of this,by means of literature research,theoretical analysis,laboratory tests and numerical simulation,the mechanism of non-equilibrium water transport and shallow instability of slopes under severe typhoon rainfall is systematically studied in this paper.The main conclusions are as follows.(1)The experimental results of 10 working conditions,such as length,diameter and connectivity of macropore,were carried out by combining indoor rainfall soil column test with Dual Permeability theory show that:Considering the extreme value of macropore wetting front is almost twice as large as that of macropore,and the infiltration profile has a wide range.Increasing rainfall intensity accelerates the generation of macroporous flow,and the non-uniform wetting front is larger.The phenomenon of macropore flow decreases with the decrease of the diameter and length of macropore,and the increase of soil compactness leads to macropore flow one hour earlier.The wetting front values of fully connected macropore,up-connected macropore and down-connected macropore are 60cm,47.6cm and 33.5cm,respectively.The larger the bending angle of macropore,the slower the growth rate of water content value in the depth of 48cm.Considering that the response of pore pressure in the depth of macroporous soil column is faster and the peak value increases by nearly 0.4 kPa,In addition,it is not easy to accumulate water on the soil surface and the water conductivity is enhanced.The simulation results of working conditions 1 and 2 are basically the same as the experimental results.(2)Based on the indoor rainfall slope test,the experimental results under five conditions including macropore and rainfall intensity,are combined with the Dual Permeability theory show that:The response of water content and pore pressure of slope considering macropore is faster than that without considering macropore,and the increment range of soil pressure reaches 66%,the vertical displacement meter reaches its maximum value 85 minutes ahead of time,the runoff and velocity of flow decrease,and the slope is destroyed on a large scale nearly an hour ahead of time.Increasing rainfall intensity increases creep deformation and vertical displacement of slope,runoff and velocity of slope increase,and slope failure occurs 185 minutes in advance.Increasing slope height has less influence on water field,and the ultimate failure degree of slope is greater.With the increase of slope gradient,the runoff and velocity of slope surface increase,and the maximum damage of slope occurs earlier.The simulation results of slope test conditions are basically the same as those of test results.(3)Based on the coupled theory of Dual Permeability and stability coefficient field method,the results of the simulation calculation and analysis of slope considering five kinds of working conditions,such as macropore and parameter,are carried out show that:The stability coefficient field method can simulate shallow instability well.When the rainfall intensity is 2 mm/h,the stability of the macroporous slope is higher,the failure area of the slope decreases by 41%,and when the rainfall intensity is 10 mm/h,the stability of the macroporous slope decreases greatly,and the failure area of the slope increases by 39%.The larger the rainfall intensity is,the maximum value of slope instability area increases to 5.34 m2,and the value of section instability depth increases.Slope destabilization area increases with rainfall time.Water field has little influence with the increase of slope,but the maximum increase of destroyed area is nearly four times.With the increase of parameters ?f and ?values,the local stability of slope decreases by 44%and 6.8%respectively.The increase of parameters rw mainly affects the peak value of water exchange in two regions,and has little effect on the local stability of slope.