Experimental Study On The Influence Of Montmorillonite Content On The Physical And Mechanical Properties Of Silty Clay Subgrade Filler

The railway subgrade is composed of loose earth and stone materials.In order to meet the requirements of strength,rigidity and stability,the physical and mechanical properties of the railway subgrade filler should be strictly required.The clay group in silty clay is mainly composed of clay minerals,and montmorillonite is the most active mineral component in clay minerals.the physical and mechanical properties of silty clay are very sensitive to montmorillonite content,and clay with high montmorillonite content often exhibits high liquid limit,high natural moisture content,poor compaction and low strength.It is easy to cause roadbed subsidence,slope erosion and other diseases for railway roadbed filling.There are a large number of silty clays in vast areas of China,and the mineral composition shows a large difference in engineering properties.The classification and selection of subgrade filling for different grades will have great economic benefits.Therefore,it is important to study the relationship between montmorillonite content and the physical and mechanical properties of silty clay.Mineral analysis,particle density and particle analysis tests were carried out on three kinds of test raw materials（fine sand,stone powder,montmorillonite）.Three kinds of materials were used to prepare silty clay samples with different montmorillonite contents,and a comprehensive system was carried out.Indoor geotechnical test to study the effect of montmorillonite content on the physical and mechanical properties of silty clay.The main research work and conclusions are as follows:（1）Cohesive soil samples with montmorillonite content C=0%,10%,20%,30%,40%,50%were prepared by using montmorillonite to replace the clay group in the base soil（8%fine sand and 92%stone powder mixed to form a low liquid limit silty clay）.The clay soil samples were tested for combined liquid and plastic limits.The test shows that with the increase of montmorillonite content in the sample,the clay soil and plastic limit increase continuously,and the liquid limit increases with the increase of montmorillonite content,and the plastic limit increase trend is relatively flat.In addition,the plasticity index Ip10 showed a good linear relationship with the liquid limit of 10 mm（weight 76 g,cone angle 30° conical sinking depth of 10 m m）,I_p10=0.55 w _L10-5.77.（2）Four kinds of samples with montmorillonite content C=0%,10%,20%,30%were prepared.Carry out heavy-duty Z1 indoor compaction test to study its compaction characteristics.The results show that with the increase of montmorillonite content,the maximum dry density and the optimal water content of silty clay show a nonlinear trend of accelerated reduction and acceleration.The analysis shows that the optimum water content of cohesive soil is about strongly bound water,and the montmorillonite content increases the capacity of adsorption to strongly bound water,and optimal water content increases.Under the condition of maximum dry density,the pore ratio of the sample increases with the increase of montmorillonite content,which is the main reason for the decrease of the maximum dry density of the sample.（3）For the silty clay samples with montmorillonite content C=0%,10%,20%,30%,the two compaction coefficients of 0.92 and 0.96 were developed,optimal and saturated. Consolidation fast shear tests under two vertical pressures,100 k Pa and 300 k Pa were carried out to study the effect of montmorillonite content on the shear strength of silty clay under different test conditions.The test results show that the montmorillonite content decreases the shear strength of the sample,and the attenuation effect of the montmorillonite content against shear strength is more obvious under high vertical pressure.The four influencing factors（vertical pressure,water content,montmorillonite content,compaction coefficient）affecting the shear strength of the sample were evaluated by the partial correlation analysis method.The analysis indicated the dominant factors affecting the shear strength of silty clay.In turn,vertical pressure>water content>montmorillonite content>compaction coefficient.From the microscopic angle of intergranular friction and intergranular cohesion,the microscopic mechanism of montmorillonite content affecting the shear strength of silty clay was analyzed.（4）The 10%montmorillonite content is an important turning point of the consistency limit and compaction characteristics of silty clay.At this time,the cohesive soil 10mm liquid limit is 32%.The international mainstream 17mm liquid limit（weight 76g,cone angle 30°cone sinking depth is 17mm corresponding water content）in the fine-grained soil plasticity map with 50%as the high and low liquid limit boundaries,using the empirical formula to convert the corresponding the 10mm liquid limit is 42%.In view of this,it is proposed to use the 10mm liquid limit of 32%and 42%as the middle,low and middle,high liquid limit points respectively,and the classification of fine-grained soil from the current high and low liquid limit“two types”to high,middle and low liquid limit."Three types"division.