Experimental Study On Modification Of Low Liquidity Silt Based On Reducing Deflection Of Expressway Subbase

With the development of urbanization and the development of science and technology,China's expressway industry has developed rapidly and the traffic volume has increased.It has put forward higher requirements for the design and construction of highway pavement structure.Among them,the calculation and detection of pavement structure deflection are very important.Deflection is an indicator to characterize the strength and stiffness of each layer of pavement structure,For the deflection problem of silt used in pavement subbase,improvement and reinforcement is the main solution to reduce the deflection of subbase.Based on the construction project of Gaoqing-Guangrao section of Changshen Expressway,The problems of low liquid limit silt mix material based on the improvement of subbase deflection,the variation law of subbase deflection and tensile stress and its influencing factors are studied.The results show that:(1)According to the basic indoor geotechnical test results,the soil particles are uniform,the particle size is basically distributed between 0.1-0.005 mm,the plastic index is 9.3,and the soil quality is determined to be low liquid limit silt.Due to the lack of clay filling,the porosity of the soil is relatively high,and it belongs to medium compressive soil with low shear strength.(2)According to the theoretical formula of the top deflection of subbase specified in the code,under the condition of certain axle load,load circle radius,subgrade and cushion modulus,any parameter of subbase thickness and modulus and cushion thickness increases,the top deflection value of the subbase decreases.The theoretical value of the top deflection of the subbase with low liquid limit silt used in the subbase is calculated by BISAR 3.0 software,and it is found that the maximum deflection lies in the load.The central area of action is 347.5(0.01mm),which needs to be improved.(3)In order to reduce the deflection of subbase,the indoor experiment of proportioning material was carried out.the low liquid limit silt is improved from two aspects.First,we choose bentonite as the only additive to improve the compactness.The results show that the maximum dry density and modulus of resilience of low liquid limit silt increase with the addition of bentonite.When the content of bentonite is 9%,the maximum dry density and modulus of resilience are obtained.Therefore,the optimum content of bentonite is 9%.(4)Secondly,cement,sodium silicate,anhydrous calcium chloride,lime and polypropylene fibers were selected for single-mixing test from the angle of increasing strength and reducing compressibility.It was found that the strength and compressibility of low liquid limit silt were improved to varying degrees by adding the other four materials except calcium chloride alone.On this basis,the experiment of mixing sodium silicate and calcium chloride in different proportions was carried out.The results show that adding a small amount of calcium chloride in sodium silicate can obviously improve the improvement effect.Therefore,four factors and three levels orthogonal test were carried out,The optimum combination of cement 4%,sodium silicate:calcium chloride 3:1,lime 4%and polypropylene fiber 0.4%(Material A)was determined by synthesizing multiple test indexes.The optimum proportion of low liquid limit silt material(Material B)was mixed with 9%bentonite.(5)ABAQUS software is used to study the deflection and tensile stress of subbase structure.The research is divided into two parts.First,the improved material A and B are used in the subbase respectively to evaluate the improvement effect.The results show that after the improvement,the deflection of the whole subbase structure and the tensile stress of the bottomof cushion are obviously reduced,and the tensile stress of the subbase is increased.Material B is used in the subbase to improve the deflection effect best.Second,the orthogonal simulation test of five factors and four levels is carried out.The results show that the sensitivity of the five factors to the deflection of the top wheel clearance center of the base course is:wheel pressure>subbase thickness>cushion thickness>subbase modulus>cushion modulus.The economic and reasonable parameters of the structure model of the subbase are determined as follows:subbase thickness is 0.5m,cushion thickness is 0.4m.subbase modulus is 1400 MPa and cushion modulus is 600 MPa;the sensitivity to the tensile stress of the bottom of subbase is as follows:Cushion modulus>wheel pressure>subbase modulus>subbase thickness>cushion thickness;the sensitivity to tensile stress of cusion is:cushion modulus>subbase thickness>wheel pressure>cushion thickness>subbase modulus.Combining indoor test and numerical simulation,this paper studies the material ratio of silt with low liquid limit based on deflection improvement,evaluates the deflection improvement effect of silt base with low liquid limit,and analyses the sensitivity of influencing factors of deflection and tensile stress of base structure,It provides references for the selection and analysis of reinforcement materials for subbase,numerical simulation of subbase structure and model parameters.