Study On Dynamic And Static Mechanical Properties And Failure Law Of Cemented Backfill With Structural Plane Inclination

In recent years,production accidents caused by the quality of filling in underground mines have been frequent,and in the process of filling large scale mining areas,Due to the limited continuous slurry making capacity of the filling station,lead to the filling work of goaf cannot be completed at one time,And the filling slurry in the flow process there is a segregation phenomenon,Then multiple fillings will lead to structural phenomena after the filler is fully cured,That is,different inclination angles are formed at the Structural surface,And this structural phenomenon destroys the integrity of the filling body,Thus reducing the quality of filling,To ensure safe excavation and efficient construction of underground projects,This paper will address the structural phenomena of the filling body,Taking into account the parameters used for mining filling and the indoor test conditions,a filling specimen with a cement sand ratio of 1:4 and a slurry concentration of 75% is prepared,Exploring the dynamic and static mechanical properties and failure rules of cemented tailings backfill(CTB)with Structural surface inclination,To make further theoretical additions to the study of the structural phenomena of the filling body,and also to provide some theoretical references for the design of the strength of the filling body in the presence of Structural surface inclination in the well.The main conclusions were drawn as follows:(1)By conducting CTB uniaxial compressive strength tests at different curing ages and different Structural surface inclinations,This revealed that the Structural surface inclination was negatively correlated with the peak strength,peak strain,and elastic modulus of CTB,and positively correlated with the initial damage degree.When the inclination angle of the Structural surface is a fixed value,the increase in the curing age can effectively weaken the structural effect brought about by the inclination angle of the Structural surface.The presence of the inclination of the Structural surface shortens the pore compacting phase of the CTB specimen,resulting in some differences in the stress-strain curve characteristics from that of the intact specimen,However,with the increase of the maintenance age,the post-peak stages all show a change from “ductile damage” to “brittle damage”.The relationship between Structural surface inclination and CTB peak front elastic strain energy and dissipation energy follow a quadratic function and satisfies a linear relationship with the total energy.The evolution of the macroscopic damage mode of specimens with Structural surface inclination is mainly as follows: tensile damage at the Structural surface(0°,10°)→ tensile damage at the vertical Structural surface(20°)→ tensile-shear damage at the Structural surface(30°).Based on the SEM(Scanning electron microscopy)electron microscopy scanning results,the effect of Structural surface inclination on the strength and damage mode of CTB specimens was revealed from microscopic morphology.(2)Single impact test of CTB with different Structural surface inclination at different impact velocities,It is found that the existence of the inclination angle of the Structural surface can weaken the dynamic compressive strength of the filling body,but with the increase of impact velocity,it still exhibits a significant strain rate enhancement effect.Compared with the compressive strength under static load,the dynamic compressive strength of the specimen is 2-4.5 times higher than that under static load,while there is an inverse relationship between the magnitude of the Structural surface inclination and the dynamic compressive strength enhancement factor.At higher impact velocities,the dynamic stressstrain curve of CTB specimens with Structural surface inclination shows a "double-peak" phenomenon.It is shown that the CTB specimens containing the inclination of the Structural surface have dynamic strength hardening characteristics at low strain rates and exhibit rapid softening of dynamic strength at high strain rates.The energy reflection coefficient of CTB specimens containing the inclination angle of the Structural surface is proportional to the magnitude of the inclination angle,while the transmission coefficient is inversely proportional to the magnitude of the inclination angle.The energy dissipation rate is related to the impact velocity and the inclination angle of the Structural surface.When the specimen with the inclination angle of the Structural surface is destroyed,the whole specimen exhibits tensile shear composite failure.By using fractal theory,it is found that the fractal dimension of the specimen is proportional to the average strain rate and the inclination angle of the Structural surface,At the same time,combining with SEM analysis,it is verified from the microstructure that an increase in the inclination angle of the Structural surface will lead to an increase in the shear stress at the Structural surface,while causing changes in the failure mode.(3)By carrying out cyclic impact tests on CTB specimens with different Structural surface inclination angles,it was found that the size of the Structural surface inclination angle is proportional to the number of impact resistance of CTB specimens,and the larger the Structural surface inclination angle is,the weaker the impact resistance of the specimen is,Meanwhile the change pattern of dynamic compressive strength is consistent with that under single impact.As the number of cycles of impact increases,the dynamic stress-strain curve characteristics of CTB specimens with Structural surface inclination exhibit a “multi peak”phenomenon,which is different from the dynamic stress-strain curve stages of complete specimens and can be divided into 9 stages.Under the coupling effect of Structural surface inclination and impact times,the variation region of dynamic compressive strength of CTB specimens is obtained,When the Structural surface inclination is 0 ° and 10 °,the main damage mode is “tensile damage along the Structural surface”,20 ° and 30 ° specimens,the main damage mode is “tensile-shear composite damage along the Structural surface”,With a single impact are manifested as “tensile shear composite damage” is different.