Analysis Of Soil-water Characteristics And Slope Stability Of Unsaturated Red Sandstone Soil Under The Action Of Dry-wet Cycle

Red sandstone soil,widely distributed in China,especially in the south of Jiangxi Province,has obvious regional features,such as swell-shrink characteristics,multiple fractured structure,and obvious weakness of its strength after wet.Affected by factors such as rainfall infiltration,evaporation process,and changes in groundwater level,the water content of red sandstone soil in the natural environment is often in a dynamic state.The soil is always in the dry-wet cycle process under the environment of repeated rainfall-evaporation and rise and fall of groundwater level.It has a great influence on the strength,water holding capacity and permeability of the soil.and will directly affect the stability of the slope and even cause engineering disasters.On this basis,in this paper,taking red sandstone soil as the study object,the experimental study is conducted on the soil-water characteristics of red sandstone soil under the action of the dry-wet cycles,and the experimental results will be applied to the seepage and stability analysis of the red sandstone slope under the action of the dry-wet cycles.The main study achievements are as follows:(1)The soil-water characteristic curve test of unsaturated red sandstone soil under drywetting cycle was carried out,analyzed study the effects of different dry-wet cycles and different compaction degrees on the red sandstone soil,and the change law of the soil-water characteristic curve(SWCC)of unsaturated red sandstone soil is obtained.It shows that the SWCC of the red sandstone soil tested has obvious bimodal characteristics;as the number of dry-wet cycles increases,its water-retention capacity decreases,and the influence of the first cycle is the greatest;the increase of the degree of compaction can improve the influence of drywet cycles on water-retention performance.There is an obvious hysteresis effect between the drying process and the wetting process of red sandstone soil SWCC,the influence of the drywet cycles on the hysteresis effect evaluated by the hysteresis loop area and attenuation rate.(2)Considered the shortcomings of the existing F-X single-peak stacking model,based on the bimodal random stacking geometric model and the drainage process theory in the pores and its single-peak SWCC model,a bimodal SWCC model that can link the two drainage processes of SWCC1 and SWCC2 together and has strong applicability and good characterization accuracy has been established.The research results show that this model can describe the bimodal SWCC of unsaturated red sandstone soil.(3)Carried out the red sandstone saturated permeability coefficient test under different dry-wet cycle times and compaction degree,combined with the measured red sandstone soilwater characteristic curve,the method of dividing the suction interval of the same matrix was used for different cycle times and different compaction,the unsaturated permeability coefficient of red sandstone is calculated.The permeability coefficient curves of unsaturated red sandstone soils with different compaction degrees under dry-wet cycles are obtained,the influence of drywet cycles and compaction degrees on the unsaturated permeability coefficients is analyzed,a bimodal soil-water characteristic curve based on the bimodal soil-water characteristic curve is established.Unsaturated permeability coefficient calculation model.The data fitting results show that the model has a high precision,the test data basically overlaps with the fitted curve,and the fitting correlation coefficients are all greater than 0.99.(4)A calculation model for the red sandstone soil slope under the dry-wet cycle was established in the Geo-studio numerical simulation software,based on the measured soil-water characteristic curve,unsaturated permeability coefficient curve and strength parameters of the red sandstone soil under the dry-wet cycle.According to Ganzhou's local climate conditions,different rainfall-evaporation conditions are set,and the effects of water holding capacity,permeability,and strength attenuation on the slope seepage and stability under the action of dry-wet cycles are obtained.It can provide a theoretical reference for the reinforcement and support of the actual natural slope and the design of the roadbed slope.The study shows that within a dry-wet cycle,the safety factor showed a trend of first decreasing and then increasing with time,and the slope stability was greatly reduced after the first cycle,the slope stability was stable after repeated dry-wet cycles.