Research On Dynamic Characteristics Of Expansive Soil Modified By Weathered Sand

With the continuous improvement of the level of China’s high-speed transportation system,the dynamic load generated by high-speed traffic and the impact of earthquakes on the roadbed should not be underestimated.Because of China’s vast territory,more and more highways,railways and other infrastructure will pass through the expansive soil area.The expansive soil will expand with water,and the characteristics of water shrinkage will have a destructive impact on the roadbed.In view of this,the paper will use the weathered sand to reduce the expansion of expansive soil,and through the cyclic load dynamic test,systematically studied the dynamic characteristics of the combined use of weathered sand modified expansive soil as the subgrade.Firstly,by conducting the GDS dynamic triaxial test,the effects of different confining pressure and sand content on the dynamic strength of expansive soil are studied.The results show that the dynamic strength of the modified expansive soil increases with the increase of confining pressure;when the content of weathered sand is small The influence on the dynamic strength of the mixed soil is small.When the content of the weathered sand exceeds 10%,the dynamic strength of the soil is accelerated and the instability is increased.Secondly,the influence law of different confining pressure and vibration frequency on dynamic characteristics such as dynamic strength,dynamic elastic modulus and equivalent damping ratio of weathered sand improved expansive soil is studied by GDS dynamic triaxial test.The results show that:The stress-strain backbone curve and the damping ratio and strain relationship of the modified expansive soil improved by weathered sand can be described by hyperbolic function;with the increase of dynamic strain,the dynamic elastic modulus of the modified expansive soil decreases,the damping ratio increases;Under the recycle action,the stress-strain relationship curve of the modified expansive soil in weathered sand is closed hysteresis loop.The axis of the hysteresis curve increases with the increase of the dynamic stress and the slope decreases.The soil sample exhibits typical strain softening characteristics.With the confining pressure and the loading frequency increases,the dynamic elastic modulus of the expansive soil is increased,and the damping ratio is decreased.The effect of the frequency on the dynamic elastic mode is concentrated in the range of strain εd<0.2%,and the influence on the damping ratio is concentrated in the range of εd<0.1%.Finally,The evolution law of hysteresis curve was studied under different confining pressure,loading frequency and dynamic stress amplitude by GDS dynamic triaxial test.The definded parameters,i.e.,the gradient k of the long axis,the area S of hysteretic curves,the ratio α of the long axis to the short axis of the hysteresis curve and the plastic deformation εp,were applied to analysis the hysteresis curve quantitatively.The results show that:the hysteresis curve of expansive soil is narrow and oblique,and k decreases with increasing dynamic strain,and increases with increasing confining pressure and loading frequency.The low frequency loading has less effect on the value of k.S and εp increae little in the early stage of the development of dynamic strain and increase exponentially later;The influence of confining pressure on S,εp is in the range of εd≥0.1%,while the influencce of frequency on S,εp is in the range of εd≥0.1%and εd≥0.2%respectively.There is a clear turning point in the relationship curve between α and dynamic strain,which firstly decreased and then increased,and the value of α decreases with the increasing confining pressure and frequency.Compared with the unmodified soil,k of the modified soil decrease while s,α,εp increase;The stiffness and the expansion of soil were reduced by improving the soil with sand,which has the advantage of reducing vibration when the modified soil was used as subgrade.