Experimental Study On Dynamic Characteristics Of Saturated Expansive Soil Under Traffic Cyclic Loading

Expansive soil is widely distributed in China,which has the engineering characteristics of expansion and contraction,crack development,and has great harm to engineering construction,heavy loss and difficult prevention.With the acceleration of China ’ s traffic infrastructure,highways and railways will inevitably cross more expansive soil distribution areas,it is necessary to carry out more research on the dynamic characteristics of expansive soil.In view of this,the dynamic characteristics test of reinforced expansive soil and the static and dynamic strength characteristics test of unreinforced expansive soil were carried out for the expansive soil at 1.5–2.0 m depth of K59 +300 in Guangxi Qinchong Expressway,and the dynamic response law of three-dimensional subgrade under vehicle dynamic load was studied by MIDAS GTS NX software.The main research contents and results are as follows:(1)The dynamic stress-strain relationship,dynamic elastic modulus characteristics,dynamic shear modulus characteristics and damping ratio characteristics of reinforced expansive soil under graded cyclic loading were analyzed,and the normalized fitting formula of dynamic elastic modulus was obtained,and the dynamic elastic modulus attenuation model considering different confining pressures,compactness,reinforcement layers and frequencies was established.(2)Through the indoor static triaxial test of expansive soil,the stress-strain relationship of expansive soil,the development law of pore pressure,the static strength index parameters and the change law of Mohr circle area under different failure strains are studied,and the fitting relationship between the deviation stress and the development of axial cumulative strain is obtained.(3)The development law of axial cumulative strain,dynamic elastic modulus characteristics,evolution law of hysteresis curve and dynamic strength characteristics of expansive soil under long-term cyclic loading were studied,and the parameters of dynamic strength and static strength indexes were compared and analyzed.The correction formula of cumulative deformation of expansive soil,and the related formulas of dynamic cohesion and dynamic internal friction angle with the change of failure vibration semi-log coordinate were obtained.(4)Based on MIDAS GTS NX software,the dynamic response characteristics of threedimensional subgrade under vehicle dynamic load are discussed.The variation law of vertical dynamic displacement with the attenuation of subgrade depth under vehicle dynamic load at different action time is studied.The distribution law of vertical dynamic displacement,maximum principal stress and maximum shear stress at different structural layers with transverse distance and longitudinal distance is studied.The influence law of different vehicle loads on vertical dynamic displacement of subgrade is discussed.