Study On Direct Shear Test And Slope Stability Of Improved Salty Fine Sand By DHT Soil Condensate

Salt lakes and saline-alkali lands are widely distributed in the Qinghai-Tibet Plateau.The soluble salt in the saline soil precipitates when the water content is low and acts as a skeleton.When the water content increases,the soluble salt will dissolve and cause the destruction of the soil structure.The special engineering properties of saline soil can cause roadbed frost heave,subsidence,and mud boiling.Using soil condensate as a modifier,in order to clearly improve the mechanical properties of saline soil and improve the stability of roadbed slopes filled with saline soil,the following studies have been carried out:Firstly,the salt content determination test,sieving test,liquid plastic limit test and compaction test were carried out on two soil samples collected by drilling holes on site,and the salt type,liquid plastic limit,maximum dry density and minimum density of soil samples were obtained.Optimal moisture content,analyzed the relationship between the liquid-plastic limit,the maximum dry density,the optimal moisture content and the salt content of the soil sample,and gave the function of the maximum dry density and the optimal moisture content on the salt content,and analyzed the physical test parameters Knowing that the two soil samples are fine sands,direct shear tests were performed on these two soil samples,and the cohesion and internal friction angle were obtained.Secondly,3%,6%,9%,12% of soil condensate was mixed into plain soil,and the influence of the content on the shear strength of soil condensate improved saline soil was explored,and it was found that the content and the shear resistance of saline soil The strength presents a linear law,and then a piecewise function of the cohesion of the soil sample considering the influence of the content is proposed.Based on the results of the improved soil direct shear test,the change law of the failure strength is analyzed.Finally,a "coated" roadbed slope model for improved saline soil filling was established,and different thickness schemes of improved soil filling were proposed.The SLOPE/W module in geo-studio software was used to calculate and analyze different fillings.The influence of thickness and different slope on the safety factor of slope.The results show that:(1)With the increase of salt content,the plastic limit of soil samples has a significant downward trend,reaching 53.0%.As the salt in the soil increases,the salt dissolves in water and reaches a saturated state,and the excess salt exists in the soil in the form of salt crystals.Compared with soil particles,the plasticity of salt crystals is poor.Therefore,the plasticity of the soil The increase in salt content decreases.(2)Analyzing the direct shear test data of plain soil,it is known that the high-salinity saline soil generally exhibits brittle failure during the shear test process,and the salt content is more sensitive to the influence of the cohesive force of the soil sample.With the increase of the salt content,the cohesive force of the soil sample increases,and the increase rate reaches 13.5%.The influence of the salt content on the cohesive force of the soil sample is greater than that of the internal friction angle.Increasing,the internal friction angle of the soil sample decreased by 6.69°.(3)Analyzed the direct shear test data of soil condensate modified soil,explored the influence of soil condensate content on the cohesion and internal friction angle of the soil sample,and gave the expression of the shear strength of the soil sample considering the influence of the content The formula also summarizes the influence law of soil condensate admixture on the failure strength.(4)A "coated" roadbed slope model was established,and the improved soil was filled on the side slope surface and top of the roadbed slope.After calculation,for the LS-1 soil sample,the plain soil was used to fill the slope.The safety factor of subgrade slope is 2.356,and the best safety factor of subgrade slope filled with improved soil sample is 2.876.The improved soil sample is filled on the subgrade slope,and the safety factor increases by 22.1%;for LS-2 soil sample In other words,the safety factor of the subgrade slope filled with plain soil is 2.308,the safety factor of the subgrade slope filled with the improved soil sample is 2.877,and the safety factor of the subgrade slope filled with the improved soil sample has increased by 24.7%..It shows that the improvement effect of this model is more significant.(5)A filling plan with a filling thickness of 5cm for the top of the slope and a 10 cm filling thickness for the slope surface was determined.(6)Three slope models with different slopes of 1:1.25,1:1.5,and 1:1.75 were designed under the condition of optimal filling thickness.For the LS-1 soil sample,as the slope slows down,it is safe The coefficient first decreases and then increases.For the LS-2 soil sample,as the slope slows down,the slope safety factor shows an increasing trend.