Numerical Simulation Of Mechanical And Hydraulic Behavior Of Unsaturated Jingmen Expansive Soil

The mechanical behavior of soil refers to the deformation and strength characteristics of soil under the action of external forces,and the hydraulic behavior refers to the retention ability and flow phenomenon of water in the soil under the action of head in the pore.The soil mechanics and hydrodynamic behaviour are simultaneous,interacting,interrelated and integral.Compared with other soils,the mechanical and hydraulic behaviors of expansive soil are more complex due to its typical swell-shrink characteristic,Fissure property,and overconsolidation.and the numerical simulation research on the mechanical and hydraulic behaviors of unsaturated expansive soil has important scientific significance and application value.Therefore,based on the results of mechanical and hydraulic tests of the Jingmen expansive soil system,numerical simulations of unsaturated seepage and slope stability are carried out in this paper.The conclusions are as follows:Based on Geo Studio software platform,Morgenstern-Price method is used to carry out stability analysis of expansive soil slope considering the influence of initial structure and stress level,and the results show that:Factor of safety（F_s）of slope calculated by using peak strength of undisturbed sample with the same initial density is larger than the F_s calculated by peak strength of compacted sample,which is due to the effect of initial structure.The F_s calculated by residual strength of undisturbed and compacted samples obtained from the direct shear test is greater than the F_s calculated by the peak strength fully softened strength of the mud consolidation samples obtained from the direct shear test;the reason:the shear displacement of the drainage repeated direct shear test is 50 mm,which does not reach the corresponding shear displacement of the residual strength of100-500 mm,resulting in a high strength value.The F_s calculated by the residual strength measured by the ring shear test with a shear displacement of 264 mm was lower than the F_s calculated from the fully softened strength,which confirmed the above speculation.The F_s calculated by the measured peak shear strength line and the measured residual shear strength line of the undisturbed and compacted samples is smaller than the F_scalculated by the Mohr-Coulomb shear strength straight line fitting to obtain the shear strength parameters,and the latter overestimates the F_s value up to 75%,reflecting that the stress level effect of shear strength has a significant impact on slope stability.Based on the Hydrus software platform,using the existing soil-water characteristics and unsaturated permeability coefficient function model parameters,the numerical simulations of moisture absorption process in unsaturated direct shear and triaxial tests of Jingmen sexpansive soil were carried out.For the moisture absorption process of direct shear specimens for 7 d～13 d and triaxial specimens for 148 d～322 d,the simulation results were obtained with the coefficients of determination R~2of 0.79 and 0.96,respectively.On the one hand,the correctness of the unsaturated soil test results can be checked and verified,and on the other hand,the method can replace part of the long-term unsaturated soil test work,and better serve the related engineering.Based on Geo Studio software platform,the unsaturated permeability coefficient function model parameters and shear strength parameters of existing Jingmen expansive soil are used to carry out numerical simulation of unsaturated seepage and corresponding stability analysis of expansive soil slope under five rain intensities,and the results show that:the slope still has not reached overall saturation after 20 d of light rain and moderate rain,and the slope was reached overall saturated after 16 d of heavy rain,12 d of rainstorm and torrential rain;the variation law of unsaturated seepage field under heavy rain and large rainstorm conditions is similar,the reason:the rain intensity is close to the saturated permeability coefficient of the expansive soil.The rainfall duration has a significant effect on F_s,that is,the continuous rainfall significantly reduces the safety factor of the slope.If the fully softened strength is used,the slope will be unstable for 5 d for heavy rain,3 d for rainstorm and torrential rain holding time;if the residual strength is used,the slope will be unstable for 7 d for small rain,3 d for moderate rain holding time,and 1 d for rainstorm and torrential rain holding time.