Study On Mechanical Properties And Damage Evolution Mechanism Of Layered Cemented Backfill Under Different Loading Rates

With the proposal of the concept of green mining,filling mining has become an important technical means to control surface subsidence and ensure efficient resource mining.However,due to the limitations of subjective and objective factors such as backfill mining capacity,economic cost,settlement characteristics of filling slurry,and mismatching of backfill body strength leading to inadequate topping of the backfill wall,instability of roof and backfill wall,etc.Delamination of the cemented backfill inevitably occurs.Therefore,it is of scientific significance and engineering value to study the mechanical properties and damage evolution mechanism of layered cemented backfill for the safe implementation of filling and mining.In this thesis,MTS816Electro-hydraulic servo-controlled rock mechanics testing system and Micro-II Express digital AE system were used to conduct uniaxial compression test and acoustic emission monitoring test,and the mechanical properties and damage evolution mechanism of layered cemented backfill were systematically investigated by combining the experimental test and theoretical analysis,and the main results are as follows:(1)The effect of water-cement ratio on the microstructure of layered cemented backfill was studied by Scanning Electron Microscope,and the results showed that the backfill specimens had compact microstructure when the water-cement ratio was 3:4,while a larger water-cement ratio would deteriorate its microstructure.(2)The effects of height ratio and loading rate on the mechanical properties of layered cemented backfill were studied by uniaxial compression tests.The results showed that the compressive strength and elastic modulus of the specimens decreased exponentially with the increase of height ratio,and the specimens showed the critical loading rate effect with the increase of loading rate,and the mechanical properties of the specimens increased and then decreased with the loading rate;The macroscopic damage characteristics of the layered cemented backfill are consistent with the "Barrel Effect",the loading rate affected the failure mode of the sample.With the increase of loading rate,the degree of breakage of the sample increased and the failure mode changed.(3)The effects of height ratio and loading rate on the AE response characteristics of layered cemented backfill and it crack evolution were studied by acoustic emission test,and the results showed that: with the increase of height ratio,the accumulated value of acoustic emission ringing count increased exponentially as a function,and the acoustic emission b value increased greatly in the early stage and fluctuated sharply in the later stage;with the increase of loading rate,the accumulated value of acoustic emission ringing count increased logarithmically,and the emission b value did not fluctuate significantly in the later stage.The results of crack cracking mode of the specimen based on RA and AF values are basically consistent with the macroscopic damage characteristics.(4)Based on uniaxial compression test,the energy evolution of layered cemented backfill under different height ratios and loading rates was studied,and the results showed that the before the peak stress decreased with the increase of the height ratio,and the each energy value firstly increased and then decreased with the increase of the loading rate,and both the height ratio and the loading rate changed the dominant energy before the peak stress;the change law of the K value curve of the elastic energy consumption ratio under different conditions was consistent,and the rising abrupt change point of the K value could be used as the basis for the judgment of the specimen.The sudden change in K value can be used as the basis for judging the critical damage of the specimen.(5)Based on the relationship between acoustic emission parameters and damage variable,the characteristics of four damage stages of the layered cemented backfill were analyzed.Based on the strain equivalent damage theory and the Weibull statistical distribution,the damage intrinsic model of layered cemented backfill with initial damage was constructed by introducing the pressure density coefficient,and the theoretical curve calculated by the model was in high agreement with the test curve.