Stability Of Expansive Soil Slope Under Cyclic Rainfall Infiltration Analysis And Disaster Law Research

With the gradual increase in human engineering and construction activities,the frequency and intensity of geological hazards are increasing.Due to the wide distribution of expansive soils in China,various types of infrastructure projects are damaged every year due to expansive soil problems.Among them,slope instability catastrophe of swelling soil has become one of the common geological hazards in China,and most of the landslides are closely related to rainfall factors.Also,due to the characteristic of weakened strength of swelling soil slope when encountering water,strong rainfall and cyclic rainfall make the suddenness and concealment of this type of landslide disaster stronger,which makes the prevention and control of landslide disaster and monitoring and early warning very difficult.Therefore,it is necessary to carry out the research on the stability analysis and disaster law of swelling soil slopes under the infiltration of cyclic rainfall,which has important guidance and practical significance for the prevention and control and monitoring and early warning of swelling soil slopes in China.This paper takes the right bank swelling soil slope at TS105+400 of the South-North Water Diversion Central Project in Nanyang City,Henan Province as the engineering background.By reviewing the geological data of the site and relevant literature,firstly,the deformation theory of dry and wet cyclic expansive soil and the destabilization mechanism of expansive soil slope under cyclic rainfall infiltration conditions were analyzed in depth.Then,the deformation and damage law of the expansive soil during the dry and wet cycles was studied.Finally,the study on the stability and catastrophic change laws of swelling soil slopes under cyclic rainfall infiltration conditions was carried out by combining indoor model experiments and numerical simulations.The main research results are as follows.(1)Through dry and wet cycle experiments and direct shear experiments on swelling soils with different water contents,it can be seen that the swelling rate and shrinkage rate of swelling soils and their increase increase increase with the gradual increase of water content.As the number of cycles increases,the expansion rate and shrinkage rate of the expansive soil are decreasing,and the variation of both is gradually becoming smaller.The expansion amount of expansive soil is greater than the shrinkage amount during the dry-wet cycle.Based on this,the concept of elastic expansion and plastic expansion is proposed.With the increase of water content and cycle times,the cumulative plastic expansion rate of expansive soil increases continuously,but the cumulative elastic expansion rate increases slightly.Both of them tend to be stable after the third dry-wet cycle.Moreover,with the increase of the number of cycles and water content,the shear strength of swelling soil gradually decreases,and the cohesion and internal friction angle both gradually decrease,but the dry and wet cycling action has no significant effect on the internal friction angle.(2)By using the self-developed model box and dry-wet circulation system,the indoor model experiment was carried out to analyze the deformation and failure evolution process of expansive soil slope under the condition of cyclic rainfall infiltration.It was found that when the 1st cycle,with the increase of rainfall duration,the soil on the slope surface showed multiple rain puddles,drip erosion and other minor damages.In the 2nd cycle,with the increase of rainfall duration,it makes the fissures produced during the drying process of slope surface gradually closed.In the 3rd cycle,with the increase of rainfall duration,the depth and length of the slope surface washout kept increasing,and local landslides occurred at the foot of the slope.In the 4th cycle,with the increase of rainfall duration,the slide range at the foot of the slope keeps expanding,the scale of the slide block gradually increases,the depth and length of the gully keep increasing,and the tension cracks keep extending toward the top of the slope,which finally causes the slope destabilization and deformation damage.(3)By analyzing the monitoring results of water content during the indoor model experiments,the water content at different depth locations such as the top of the slope,the slope surface and the foot of the slope gradually increased with the increase of the number of wet and dry cycles.During each dry-wet cycle,the water content at different depths of the slope top,slope surface and slope toe all showed a trend of first rising sharply,then gradually decreasing and finally stabilizing.And the surface water content of slope top,slope surface and slope toe increased more than the internal.At the same time,the fluctuation of water content at the foot of the slope is significantly larger than that at the top and surface positions of the slope.(4)By analyzing the pore water pressure monitoring results during the indoor model experiments,it was found that the pore water pressure at different depths of the slope top,slope surface and slope foot gradually increased with the increase of the number of dry and wet cycles.In the process of each wet and dry cycle,the pore water pressure at different depths on the slope top and slope surface first increases,then decreases,then rises again,and finally stabilizes.Both the top and the surface of the slope show hysteresis in the process of drying and water loss.And the change at the foot of the slope shows a change pattern of first increasing,then decreasing,and finally stabilizing.Meanwhile,the fluctuation of pore water pressure at the foot of the slope is greater than that at the top and surface locations,and the rate of pore water pressure decline during the infiltration and drying periods is slightly slower than that at the top and surface.(5)Through the numerical simulation of seepage field,stress field,displacement field,plastic zone and slope safety factor under different cycle times and different rainfall duration conditions.The results show that with the increase of cycle number and rainfall duration,the soil saturation and pore water pressure of slope gradually increase,but the matrix suction continuously decreases,and the horizontal stress,vertical stress and total effective stress all show a continuous decreasing trend.The total displacement,horizontal displacement and vertical displacement all increase with the increase of the number of cycles and the length of rainfall,and the increase of the total displacement becomes smaller from the foot of the slope to the top of the slope,and the displacement at the foot of the slope is the largest.With the increase of the number of cycles and the length of rainfall,the range of plastic zone gradually expands and the safety factor of slope gradually decreases.When the 3rd cycle is performed,the slope is in an under-stabilized state.After the 4th cycle,the slope is already in an unstable state and measures need to be taken to reinforce it.And,after the 3rd cycle,the decrease of slope safety factor gradually increases.And when the rainfall duration is certain,the greater the number of cycles,the greater the reduction of the slope safety factor.