Research On The Dynamic Characteristics Of The Expansive Soil Improved By NaCl Solution In Southern Shaanxi

Expansive soil is a kind of high clay soil,its mineral composition has a strong hydrophilic,water absorption expansion,water loss contraction,the roadbed and structure damage is great.With the rapid development of public transportation system,the load and speed of vehicles have been greatly improved,and the influence of cyclic dynamic stress caused by high speed driving on expansive soil foundation and superstructure can not be ignored.At present,the research on the mechanical properties of expansive soil and improved expansive soil mainly focuses on the strength and deformation under static load,but it still fails to meet the requirements of engineering practice.In this paper,the dynamic characteristics of the improved expansive soil under different confining pressures and NaCl concentration were tested by GDS dynamic triaxial instrument.The dynamic strength,dynamic deformation characteristics and the evolution law of characteristic parameters of the hysteretic curve of the improved expansive soil under cyclic dynamic load with equivalent sinusoidal waveform were studied.The research results can provide some theoretical reference for engineering design related to ameliorate and vibration in the expansive soil area of southern Shaanxi.The research in this paper concludes:With the increase of the confining pressure,the dynamic strength of the NaCl solution modified expansive soil increased significantly.The greater the increase in the confining pressure,the greater the increase in the dynamic strength;As the concentration of NaCl solution increases,its dynamic strength increases,and the greater the concentration,the increase in cyclic dynamic load decreases;Compared with the unimproved expansive soil,the shear strength of the modified expansive soil is increased,which is manifested by the increase of the dynamic internal friction angle and dynamic cohesive force.The growth rate of the dynamic cohesive force gradually increases with the increase of the concentration.The growth rate gradually appeared to be flat with the increase of the concentration.The dynamic bone curve of the modified expansive soil can be described by a hyperbolic curve.With the increase of confining pressure and solution concentration,the dynamic bone curve has a different degree of upward trend,and the confining pressure has a greater influence on the dynamic bone curve of the sample;With the increase of dynamic strain,the dynamic elastic modulus of the modified expansive soil decreases,and the confining pressure has a significant influence on the dynamic elastic modulus of the modified expansive soil.The dynamic elastic modulus curve increases gradually with the increase of the solution concentration,of which lmol/L NaCl solution concentration is superior;The damping ratio is positively correlated with the dynamic strain.The damping ratio does not change significantly in the small strain stage.With the increase of the dynamic strain,the damping ratio changes significantly.Slope k of hysteretic curve is negatively correlated with dynamic strain under different confining pressures and solution concentrations,as the loading confining pressure and solution concentration increase,the value of k increases significantly,the maximum increase is 7.2%;when the dynamic strain is less than 0.1%,the hysteresis curve area S does not change significantly,with the increase of the dynamic strain,the S value gradually increases,among them,the S value increases relatively large when the confining pressure is small,compared with the unmodified expansive soil,the S value increases with the increase of the solution concentration,and the energy dissipation capacity of the modified expansive soil increases;the residual dynamic strain εp is negatively correlated with the change of the loading confining pressure and the solution concentration.Different loading confining pressure and solution concentration have a negative correlation.The effect of residual dynamic strain εp increases exponentially when the dynamic strain is greater than 0.1%;when the dynamic strain is greater than 0.1%,the fullness a of the hysteresis curve gradually increases.As the solution concentration increases,the improved expansive soil is better than the unimproved the fullness a of the hysteretic curve of expansive soil increases,reflecting the enhancement of the soil’s anti-vibration and energy dissipation capabilities.