Study On Pore Characteristics And Strength Weakening Laws Of Cohesive Slip Soil

The development of landslide disasters is essentially a process of strength weakening of slip soil.And during this process,the pore characteristics in slip soil also change significantly.The slip soil of landslides in western and southwestern of China are mainly cohesive soils,affected by factors such as rainfall and irrigation,their structural and mechanical properties are easily weakened,eventually leading to slope instability.Therefore,it is important to study the strength weakening laws of the slip soil in specific areas for the prevention of landslide disasters in these areas;The strength of cohesive slip soils are significantly affected by the water content and the deformation rate of the landslide.However,the changes in pores under these macro mechanical properties are often easily ignored.Otherwise,the research on quantitative relationship between them needs to be improved.The residual strength of the slip soil controls the development of slope stability.And with the change of water content and deformation rate,the residual strength of the slip soil is also developing dynamically.The simulation of gradual development of landslides based on the dynamic development of residual strength can more realistically reflect the development trend of landslides with the increase of external influence factors,and this part of the research is currently under continuous development.Aiming at the above problems,this paper takes the Kualiangzi landslide and its slip soil as the object,and carried out a series of studies on the pore characteristics and mechanical properties of the clay zone.The main work and conclusions are as follows:(1)A basic geotechnical test was carried out on the slip soil samples of the Kualiangzi landslide.Through analysis of its particle composition and liquid-plastic limit parameters,the slip soil was named low liquid limit silty clay.(2)Prepared remolding samples of slip soil with different water content and carried out repeated direct shear test.The results showed that the shear strength of the sample decreases significantly with the increase of water content,and the residual strength parameter decreases by a cubic function;the sample with higher water content shows more obvious strain hardening in the first two shear cycles.However,the strain softening phenomenon is dominant in the latter part of the shear cycle and the shearing of samples with low water content.(3)Saturated the remolded sample of slip soil.It was found that the shear strength of the sample is linearly and negatively correlated with the logarithm of the shear rate from the repeated direct shear tests,and the residual strength parameter decreases exponentially with the increase of the shear rate;The samples at the lower shear rate showed relatively obvious strain hardening in the first two shear cycles,and the shear of the samples at the late shear cycle and at the higher shear rate was mainly strain softening.(4)The NMR test showed that the slip soil samples after sheared showed a downward trend in the total pore volume with the increase of water content and shear rate.Under the conditions of different water content and different shear rate,the pores inside the specimen after shearing have obvious fractal characteristics.Among them,the fractal dimension of the pore decreases linearly with the increase of the water content,and decreases and then rises with the increase of the shear rate.The residual strength of the slip soil under the two operating conditions expressed by the pore distribution rate function f and the pore fractal dimension D has high accuracy.(5)Considering the characteristics of the dynamic deterioration of the residual strength of the slip soil due to changes in external factors and the combined effect of tensile-shear failure,a strain softening model based on dynamic residual strength was improved.This model can describe the dynamic development trend of the slope when the external influence factors change after the slip soil reaches the residual strength parameter for the first time during the progressive tension and shear failure of the slope.(6)The numerical model of the Kualiangzi landslide was established.Based on the strain softening model with dynamic residual strength characteristics,and combined with the development of the plastic zone and the failure zone,the dynamic development process of the stability of the Kualiangzi landslide was analyzed under the condition that the water content of the slip soil continued to rise due to precipitation.The analysis results are consistent with the sliding history of the Kualiangzi slope.