Research On Deformation Characteristics Of Expansive Soil Modified By Phosphate Tailings

Expansive soil is a kind of multi-fractured,highly plastic clay formed during natural geological process,and the main components are clay minerals such as illite and montmorillonite.It is called catastrophic soil because of its special properties of water absorption and expansion,dewatering and contraction,and its engineering characteristics are unstable.Repeated expansion and contraction deformation of expansive soils lead to structural cracking,roadbed deformation and other problems,causing huge economic losses to the project.In this context,this paper simulates the force environment of modified expansive soil as foundation soil by mixing phosphorus tailings to improve expansive soil,and analyzes the dynamic properties of dynamic deformation and dynamic strength of improved soil under different conditions through cyclic loading test.In order to study the effect of phosphorus tailings incorporation on the shear strength index of the expanded soil,static triaxial tests were conducted to analyze the stress-strain relationship curves of the improved expanded soil under different phosphorus tailings incorporation and different envelope pressure conditions,and it was found that most of the stress-strain curves were continuously hardened,and a few curves had peaks.The strength envelope was determined for the same admixture,and the shear strength index of the improved soil under different admixtures was determined.The cohesive force c and internal friction angleφshowed a change pattern of increasing first and then decreasing with the increase of doping amount,and there was an obvious improvement effect compared with the plain soil,and the best effect of7%phosphorus tailings in the doping amount was selected for the test.Through GDS dynamic triaxial test,the deformation characteristics of phosphorus tailings improved swelling soil under different frequency and circumferential pressure were analyzed,and the variation of dynamic elastic modulus and damping ratio were obtained to study the influence of circumferential pressure and frequency on dynamic elastic modulus and damping ratio of phosphorus tailings improved swelling soil.The test results show that the stress-strain relationship of the improved soil is obviously affected by the surrounding pressure,and the difference is large under different surrounding pressure,and the curve shifts slightly upward with the increase of frequency.The backbone curve is denser when the strainε_d<0.1%,and the influence of the surrounding pressure is gradually significant as the stress increases.The dynamic elastic modulus E_dand damping ratioλare obviously influenced by the surrounding pressure,and the frequency is second,the greater the surrounding pressure the greater the dynamic elastic modulus and the smaller the damping ratio.When the dynamic strainε_d<0.2%,the dynamic modulus decreases rapidly and the damping ratio increases sharply.In order to study the effects of different surrounding pressure,consolidation stress ratio,dynamic stress amplitude and dynamic loading frequency on the hysteresis curve of the improved soil,a graded loading dynamic triaxial test was conducted,and parameters such as area s,residual strainε_p,form center distance d and slope k were introduced to quantitatively analyze the variation characteristics of the hysteresis curve.The test results show that the hysteresis curve gradually becomes wider and thicker from the initial elongated willow leaf shape with the increase of dynamic stress under adjacent dynamic stress loading conditions.With the increase of the surrounding pressure,consolidation ratio and frequency,the value of k gradually decreases and other characteristic parameters tend to increase.The hysteresis curve area k gradually becomes smaller with the increase of amplitude,and increases with the increase of surrounding pressure,frequency and consolidation ratio.The difference of k-value curve under low frequency and small consolidation ratio is small,and the influence of surrounding pressure on k-value is slightly larger.The hysteresis curves d,ε_p,and s are positively correlated with the surrounding pressure,frequency,and consolidation ratio.The curve growth rate has obvious inflection points,and the strainε_d<0.2%is less influenced by the variables,and the curves overlap,and the curve difference is obvious under different test conditions as the strain increases.Frequency and consolidation ratio have a slightly smaller effect on d and sThe above tests show that phosphorus tailings have certain effect on the improvement of swelling soil,which provides a reference basis for the rational development and utilization of resources.