Research On Dynammic Characteris Of Expansive Soil Modified By Phosphate Tailings

As China's economy continues to take off,a large number of infrastructure constructions have sprung up all over the motherland.China's expansive soil is widely distributed,and a large number of highways and railways cross its area.Expansive soil is a high plastic limit clay composed of strong hydrophilic minerals montmorillonite and illite.It has the engineering characteristics of swelling with water,shrinking with water loss and repeated deformation.Under the repeated action of dynamic load,the expansive soil will produce permanent deformation that cannot be recovered,causing excessive deformation and destruction of the soil.Phosphorus tailings are the solid waste of phosphate ore after beneficiation.Every 100,000 tons of phosphate ore will produce 30,000 to 40,000 tons of phosphorous tailings.Using it to replace lime,fly ash and other conventional materials to improve expansive soil can make full use of industry Waste,reduce the consumption of natural resources,and exert significant social and economic benefits.This paper takes phosphate tailings improved expansive soil as the research object,and uses the dynamic module of GDS true?_ddynamic triaxial instrument to carry out a series of improved soil dynamic strength characteristics tests under the action of dynamic load.The main conclusions are as follows:?1?The dynamic strength curve of the improved soil conforms to the power function relationship,and its dynamic strength increases with the increase of the confining pressure,and increases with the amount of phosphorus tailings and then decreases.Compared with pure expansive soil,the maximum improvement of the dynamic strength of the improved soil is about 40k Pa The increase is about 30%.The dynamic cohesive force cd of the improved soil increases first and then decreases with the amount of phosphorous tailings.Compared with pure expansive soil,the maximum increase is about 9k Pa,and the increase is up to 36%.However,the amount of phosphorous tailings affects the dynamic internal friction angle?_dSmaller.By nonlinearly fitting the relationship between dynamic strength parameters and the amount of phosphorous tailings,the formula for calculating dynamic strength is given.?2?The?_d-?_dcurve moves upwards with the increase of the amount of phosphorus tailings.When the incorporation mass ratio reaches 7%,the strength reaches the highest level,and then the curve moves down.The optimum amount of phosphorus tailings-modified expansive soil is 7%.?3?The dynamic modulus E_dof phosphorus tailings-modified expansive soil decreases as the dynamic strain increases.When?_d?2%,the E_d-?_dcurve tends to be steep,and the dynamic elastic modulus decreases rapidly with the increase of the dynamic strain;?_dWhen>2%,the soil enters the stage of plastic development,and the dynamic elastic modulus decreases slowly.The relationship between the dynamic elastic modulus E_dand the dynamic strain?_dconforms to the Hardin-Drnevich modified linear curve model,and the fitting correlation coefficient R²values are all above 0.9.?4?The damping ratio of phosphate tailings-modified expansive soil shows an upward trend as the dynamic strain increases.When the dynamic strain is less than0.1%,the damping ratio increases slowly.When the dynamic strain increases to 0.1%-1%,the damping ratio increases sharply,And then tended to be flat.Under the same conditions,the confining pressure and the amount of phosphorus tailings can effectively reduce the damping ratio of the mixed soil.?5?Under different confining pressures and phosphorus tailings content,the changes of k,d,s,and?_pof the hysteresis loop are similarly divided into two stages,which increase slowly and almost overlap in the early stage of loading,and increase exponentially in the later stage of loading.