Study On Seepage Stability Of Stope Slope With Soft Interlayer Under Dry-wet Cycle Condition

There is a soft carbonaceous mudstone mezzanine distributed in limestone mines in southwest China,which is often a key factor affecting slope stability due to its low mechanical strength,high water/thermal sensitivity,and significant rheological properties.However,the current research on the physical and mechanical properties of soft interlayers and the change law of permeability under the condition of wet and dry circulation is insufficient,and the research on the physical and mechanical properties of soft interlayers and the overall seepage stability of slope after the change of permeability is insufficient.In this paper,a typical open-pit pit slope with soft interlayers of carbonaceous mudstone in southwest China is taken as an example,and the evolution law of shear strength and permeability of soft interlayers of carbonaceous mudstone under the action of dry and wet cycles is studied by field investigation,laboratory simulation test,numerical simulation,and theoretical analysis.The influence of the variation of the saturated permeability coefficient of soft interlayer on the rainfall seepage characteristics of the slope after the wetting and drying cycle is revealed.The main research results are as follows:(1)The basic physical and mechanical parameters of the weak sandwich were obtained through field sampling and indoor physical and mechanical tests;The evolution law of shear strength and permeability of soft interlayer of carboniferous mudstone under the action of dry and wet cycles was obtained by conducting indoor wet and dry cycle simulation tests and post-cycle direct shear tests and variable head tests.The results showed that the shear strength of the weak sandwich was inversely proportional to the number of wet and dry cycles,and the saturation permeability was positively correlated with the number of wet and dry cycles.Combined with the change of shear strength parameter and saturation permeability coefficient,the seven cycles can be regarded as the worst environment of a weak sandwich affected by wet and dry cycles.(2)Using Geostudio finite element to simulate the influence of the variation of saturated permeability coefficient of weak interlayer on the rainfall seepage characteristics of the slope after wet and dry cycling,it is found that the influence is mainly as follows: As the permeability coefficient of the weak interlayer increases after the dry-wet cycle,it cannot act as a water barrier to prevent the downward intrusion of rainwater.With the increase in the number of cycles,the weak interlayer and the lower limestone are infiltrated by rainwater.As the rainwater discharge capacity of the weak interlayer and limestone is much smaller than that of the upper area,the rainwater cannot be discharged in time,and a high pore water pressure zone is formed at the rear edge of the slope body.(3)Geostudio and Flac-3D software were used to simulate the instability evolution process of mine slope with weak interlayer under the influence of rainfall under different dry-wet cycles.The results show that the slope displacement mainly occurs in the fractured weathered rock mass on the upper part of the weak interlayer.The failure mode of the slope changes from the inward collapse of the rock mass on the upper part of the slope to sliding along the weak interlayer after 5 cycles.The horizontal displacement of the slope body increases with the increase in rainfall duration and cycle times.(4)The overall slope stability coefficient decreases with the duration of rainfall,and the decreasing trend is greater with the increase of the number of cycles,indicating that the change of physical characteristics of weak interlayers after wet and dry cycles has a great impact on the stability of mine slope,and the change of permeability coefficient has a greater impact on the stability of slope after rainfall.With the increase in rainfall duration,the difference between the slope stability coefficient after 0 and 7 dry and wet cycles gradually increase,indicating that the influence of dry and wet cycles on the overall stability of the slope will become greater with the increase in rainfall duration.The research result of this paper can provide the theoretical basis and idea for a similar mine slope stability evaluation,prediction,and management in our southwest area,and has a certain scientific significance and application value.