The Study On Mechanical Properties And Stability Of Ancient Ditch Dependent Soil Improved By Colloidal Silica

This paper takes the relocation project of the Tang Dynasty ancient ditch site of Tongjin Road in Chengdu as the research background,and carries out the reinforcement scheme design of the attached soil behind the slope wall of the canal side and the slope stability research.The attached soil behind the wall is prone to collapse and collapse in the case of water,so it is necessary to select materials with excellent anti-seepage and reinforcement effects to improve the attached soil.As a new type of grouting material,colloidal silica（CS）with controllable gel time,low initial viscosity and durability has been gradually applied to civil engineering.Based on this,this paper studies the mechanical properties of CS in improving silty sand through immersion test and direct shear test,discusses the influence of CS concentration and curing time on the mechanical strength of improved soil,compares the slope stability of reinforced and unreinforced areas,the reinforcement effect of CS on attached soil was analyzed.Main research contents and conclusions:（1）Through the indoor basic test,it is determined that the attached soil behind the wall is silty fine sand with clay.Adopting the principle of"same dry density,similar permeability coefficient",it is determined that the mixed soil with a mass ratio of clay and sand of 3:7 is used in the laboratory test,and the permeability coefficient of the mixed soil is 2.72×10^-4 cm/s.（2）Immersion test was carried out on the CS improved sample.The results show that the failure time of the improved sample is affected by three factors:CS concentration,mixing ratio and curing time.The higher the CS concentration,the larger the mixing ratio and the longer the curing time,the better the water stability of the sample.Finally,the CS concentration is 20%、30%,and the mixing ratio is 1:6.（3）Consolidation fast shear tests were carried out on the improved samples with different CS concentrations.After adding 20%and 30%concentration of CS respectively,the shear strength of the modified sample is improved to some extent,and the higher the concentration of CS,the higher the shear strength of the sample.With the increase of curing time,the shear strength of the improved sample shows a further increasing trend.（4）There are differences in the reinforcement effect of CS on soil under different states.Under natural conditions,the addition of CS can effectively improve the cohesion and internal friction angle of the soil,and the effect of CS concentration on the cohesion is greater than that on the internal friction angle.Under the action of immersion,the shear strength of the soil is enhanced by increasing the cohesion.（5）The effects of different CS concentration and curing time on slope stability were discussed by limit equilibrium method and finite element strength reduction method.With the increase of CS concentration and curing time,the safety factor of the slope is increasing,and the improvement effect of the slope is better.Based on the consideration of economic cost,the slope model was finally grouting reinforced with 20%concentration of CS,and the reinforcement effect of silica sol was verified by water storage test.