Study On Strength And Deformation Characteristics Of Fiber-Cement Modified Iron Tailings

As one of the main components of industrial wastes,iron tailings have great potential hazards,such as the discharge and stockpiling of tailings will occupy land resources,pollute the environment,and threaten the safety of people’s lives and property.In order to deal with the tailings problem,we can combine the concept of saving mineral resources with the concept of ecological environment management,and improve the utilization rate of tailings by innovating a variety of secondary utilization methods of tailings.In addition,river sand,excavated earthwork and other materials cannot meet the development of public transport infrastructure in China.Therefore,promoting the use of tailings as road building materials and backfilling is an important way to reduce the loss of traditional building materials and utilize iron tailings resources.Based on the above,this paper mainly studies the strength and deformation properties of fiber cement iron tailings(FCIT)by using iron tailings with poor engineering properties of fiber and cement modification.The basic mechanical properties and strength of FCIT are studied by unconfined compressive strength test and static triaxial test,and the dynamic properties and deformation degree of FCIT are studied by dynamic triaxial test and hollow torsional shear test.The main research results of this paper are as follows:(1)Based on the unconfined compressive strength test and static triaxial test results,it is found that the fiber content and age are important factors affecting the strength performance.On the one hand,the age can improve the compressive strength of FCIT more effectively than the fiber content,and at the same time,improve the mechanical indicators of FCIT.The modification effect of fiber on FCIT focuses on the residual strength and shear resistance,which is conducive to improving the failure mode of FCIT.Furthermore,from the perspective of energy,it is explained that the increase of age and fiber content makes fibers become an important source of energy dissipation.In addition,through the stress path test,it is found that the strength of FCIT will increase with the decrease of the stress path slope,and the secant modulus will also increase accordingly.(2)Under different types of cyclic loads,the increase of dynamic static ratio will deepen the deformation of FCIT,while the addition of fibers will greatly reduce the deformation of FCIT and mitigate the damage of FCIT.Especially when the fiber content is 0.75%,the improvement effect of FCIT is the best and the damage degree is the lowest.Therefore,based on the cumulative strain variation law of FCIT after fiber addition,an empirical formula about cumulative strain,vibration times,dynamic stress amplitude and static strength is proposed.Furthermore,the plastic shakedown creep prediction model is established by using shakedown theory to evaluate the deformation behavior criterion,and the error is within ± 10%.(3)Through the comparison between FCIT under intermittent loading and continuous loading,it is found that the cumulative strain change amplitude under intermittent loading is generally smaller than that caused by continuous loading,and the resilience modulus of FCIT under intermittent loading is generally larger than that of FCIT under continuous loading.Moreover,through the step by step loading test,it is found that the modified translation addition method can modify the cumulative strain of FCIT under step by step loading,predict the cumulative strain under single-stage loading,and greatly reduce the test time and material consumption.(4)When the principal stress axis rotates,the strain and stress path of FCIT will increase with the increase of axial force and torsional shear,and the change of torsional shear strain is greater than the cumulative strain.As a result,the shear stiffness of FCIT changes more than the positive deflection stiffness,which makes FCIT non coaxial.At the same time,it is found that the non coaxial angle of FCIT will gradually decrease with the increase of axial force and torsional shear force,and the direction of strain increment will be closer to the stress direction,thus the non coaxial angle will become smaller.