Study On Expression Method Of Soil Structural Parameters Based On Strength Theory

The structural parameter of soil is an important physical property index of loess.At present,many scholars have established a variety of structural parameters based on the comprehensive structural potential.The structural parameters defined by various methods vary with test conditions,stress and strain states,so they are called structural variables in this paper and do not reflect the relationship between soil structure and strength.In this paper,the limit equilibrium theory of soil is applied to the mechanical deduction of loess structure index,and the evolution expression of soil structural parameters expressed by strength parameters is obtained.The strength parameters of remolded saturated soil are used to replace the strength parameters of saturated soil and remolded soil,and the structural stability and structural variability of soil are relieved at one time.The modified expression of soil structural parameters based on strength parameters is obtained.The new soil structural parameters based on strength parameters proposed in this paper can be obtained by conventional triaxial test and direct shear test.They reflect the essential properties of soil materials and do not change with the test parameters such as confining pressure,strain and stress,and belong to material constants.Through uniaxial,triaxial and direct shear tests of undisturbed and reconstituted soil under different water content,the stress-strain characteristics of soil samples under different test conditions were analyzed,and the differences and relationships among peak values of structural variables,structural evolution parameters and structural modification parameters were studied.The experimental results show that:(1)the peak values of structural variables and texture indexes decrease with the increase of water content,but the values of texture indexes are smaller than the peak values of structural variables.(2)With the increase of water content,the stress-strain curves of undisturbed soil and remolded soil gradually change from strain-softening type to strain-hardening type,and the peak strength of the stress-strain curves also increases with the increase of vertical pressure(confining pressure).The peak value of structural variable is a variable that changes with vertical pressure(confining pressure),and the larger the water content is,the smaller the peak value of structural variable is.(3)in this paper,by comparing the direct shear test,triaxial test)found that parameters of structural evolution and structural variables under peak is a structural variables change with the vertical pressure(confining pressure)variables,and the intensity of structural evolution parameters by theoretical derivation,is not a change with the vertical pressure,confining pressure parameters,with the increase of moisture content,Structural evolution parameters are also decreasing.Structural evolution parameters more directly,accurately and simply reflect the change of soil structure with water content.(4)compared to direct shear test,triaxial test)under the structural evolution and structural modification parameters found that structural modification parameters changing with the moisture content and structural evolution,and structural modification parameters slightly larger than the value of the structural evolution,but the difference is not big,proves the rationality of the structural modification parameter,Therefore,soil structure can be studied instead of structural evolution parameters.(5)by comparing the structural evolution of the direct shear test and triaxial test parameters and structural modification,found that under the two kinds of test parameters and structural modification of the value of the basic structural evolution,and changing with the moisture content is consistent,this paper puts forward the structural parameter is a material constant,does not change along with the change of the experimental conditions.The results show that the structural evolution parameters and structural modification parameters can accurately reflect the soil structure,and can be used to study the soil samples that are not easy to be tested by uniaxial test.However,the structural modification parameters have the advantages of less test workload,simpler formula and clearer physical significance.