Study On The Dynamic Characteristics Of Loess Modifiedby Red Mud Under Cyclic Loading

In order to explore the method of disposal of solid waste-red mud,red mud is proposed as a subgrade material.On the basis of previous studies,cyclic loading test of red mud improved loess was carried out by GDS dynamic three axis instrument.On the basis of a large number of indoor experiments,the dynamic characteristics of the modified loess with different moisture content,different confining pressure,different dynamic stress amplitude and different frequencies were studied.The influence of various factors on dynamic stress strain relation,cumulative plastic strain and critical dynamic stress,dynamic modulus of elasticity and damping ratio and dynamic strength curve were analyzed.Considering the leaching toxicity of modified soil and comparing with the unmodified loess,the mechanism of the modified loess of red mud was discussed.It provides theoretical basis for the application of red mud in roadbed engineering and has certain academic value.It reduces the use of cement,lime and other traditional curing materials,thus effectively reducing the cost of the project,and has good economic benefits.The main conclusions are as follows:(1)The dynamic stress-strain curve of loess improved by red mud is nonlinear,hysteresis and cumulative deformation,and the dynamic constitutive relationship accords with the hyperbolic model of Hardin-Drnevich.The modified soil has the characteristics of the sudden brittle failure of concrete.The hysteresis curve of the improved soil includes three stages:elastic deformation stage,plastic strain accumulation stage and failure stage.The higher the water content is,the greater the cumulative plastic deformation is,and the brittleness of the soil is improved.(2)The cumulative plastic strain increases with the number of load cycles and the dynamic stress amplitude,yet decreases with the increase of confining pressure.When the water content is near the optimum water content,the cumulative plastic deformation is the smallest.That water content is too low or too high will reduce the ability of resisting to deformation,and it is especially significant when the water content is too high.The?_p-N curve of loess improved by red mud basically conforms to the Monismith model.Based on the long-term stability factor,the power exponent b can easily determine the stability of soil under cyclic vibration,which provides an important reference for long-term dynamic stability evaluation of soil and subgrade design based on cumulative dynamic deformation control.(3)The dynamic elastic modulus increases first and then decreases with the increase of the dynamic strain amplitude,and the fitting results are greatly obtained by using quadratic function.The damping ratio increases slightly with the increase of the amplitude of the dynamic strain,and then increases,as a check mark.The dynamic modulus reaches the maximum at its optimal moisture content,and the higher water content makes the modified soil elastic modulus decrease obviously.The dynamic modulus decreases with the increase of the frequency at small strain amplitude,and increases with the increase of the frequency when the amplitude is larger.The damping ratio is larger when the loading frequency is high.(4)Compared with the unmodified loess,the improved soil has the characteristics of sudden brittle failure,but the plasticity deformation of loess is larger and there are obvious signs.The incorporation of red mud can effectively improve the state of wet loess,and the dynamic elastic modulus is more than four times higher than that of loess,improving its carrying capacity and resistance to deformation.The critical dynamic stress of improved loess reaches 600-650 kPa,far above the actual dynamic load level of subgrade soil.The concentration of harmful elements in the improved soil leaching solution is much lower than the relevant standards,and has no leaching toxicity characteristics,which has good environmental effects.