Study On Seepage Characteristics Of Expansive Soil Cutting Slope Based On Fluid-solid Coupling

Due to the infiltration of atmospheric rainfall,the weight of expansive soil slopes increases,the soil expands,the sliding force increases and the strength of the soil decreases,thus causing the destabilization of expansive soil slopes.The effect of rainfall is undoubtedly the main reason for the instability damage of swelling soil slopes.Therefore,it is important to study the characteristics of saturated-unsaturated seepage field and spatial and temporal evolution law of swelling soil slope under rainfall conditions.At present,the research on saturated-unsaturated seepage of expansive soil either does not consider the influence of swelling or cannot consider the water-holding characteristics of the soil because heat conduction is used to simulate the seepage process.In this paper,based on a secondary highway project in Ningming,Guangxi,the evolution of saturated-unsaturated seepage of swelling soil slope under rainfall infiltration is numerically simulated based on the flow-solid coupling theory,and the saturated-unsaturated seepage law of swelling soil slope under rainfall and related influencing factors are analyzed.The specific research contents and results are as follows.(1)The soil-water characteristic curve and saturated permeability coefficient of expansive soil were obtained by pressure plate test and double ring permeability test respectively.The expansion deformation test,direct shear test and GDS triaxial test were used.The relationship between swelling deformation and water content and vertical load,shear strength parameters(c,φ)and deformation parameters(E,μ)of unsaturated expansive soil with water content were obtained,which provided data parameters support for subsequent numerical simulation.(2)Based on the Mohr-Coulumb criterion and the elastoplastic mechanics theory of geotechnical soils,the elastic-plastic principal model of swelling soils is modified by introducing swelling into the principal model in the form of additional strain,and the theory of elastic-plastic principal model is compiled into a dynamic link library file with the help of Visual studio programming software,so as to realize the influence of swelling strain on the mechanical calculation of soils in numerical simulations.(3)Based on the principle of continuous porous media and the flow-solid coupling theory in FLAC3D,the anisotropic permeability coefficient is established with the variation of saturation and volume strain,and the saturation,permeability coefficient and effective stress in the unsaturated seepage calculation module are improved by using the embedded FISH language in FLAC3D.Then,the flow-solid coupling module considering the swelling effect is constructed by invoking the modified intrinsic model,so as to realize the unsaturated seepage simulation under the effect of flow-solid coupling.(4)Taking a swelling soil rift slope of a secondary highway under construction in Ningming Beiban(Beijiang-Banlan)as the research object,a numerical model is established,and based on the unsaturated flow-solid coupling module considering the swelling effect,the spatial and temporal evolution of pore water pressure of unsaturated swelling soil is studied,and the influence of swelling deformation on soil permeability and water transport process is investigated,and the distribution of transient saturation zone of slope soil under different rainfall conditions is compared and analyzed.The distribution of the temporary saturation zone of the slope under different rainfall conditions is compared and analyzed,in order to provide some reference for the research on the seepage and stability of the slope of swelling soil under rainfall conditions.