Study On Mechanical Properties Of High Concentration Cemented Tailings Backfill Under Dynamic Impact

Backfill mining method can effectively control the ground stress,improve the stability of mined-out area,and ensure the safe and effective mining of deep mineral resources.In recent ten years,cemented tailings backfill（CTB）materials have developed rapidly as a kind of green and economic backfill materials.However,the backfill materials are often subjected to external dynamic disturbances such as blasting and drilling during the support process,which seriously harms the mining safety.Therefore,it is very important to study the mechanical properties of CTB materials of different ages.In this paper,the dynamic characteristics of the CTB samples with strain rates ranging from 40.2s^-1 to 238.4 s^-1 were mainly studied.At the same time,LS-DYNA finite element software was used to further analyze the stress-strain characteristics of the samples under dynamic impact.The main conclusions are as follows:（1）Under dynamic impact,with the increase of curing time and cement content,the overall dynamic compressive strength（DCS）of the high concentration CTB samples also increases.The overall DCS of the CTB samples increases with the increase of the average strain rate（ASR）,especially in the samples with curing time of 14d and 28d and cement-sand ratio of 1:3,the strain rate effect are more obvious.（2）There are mainly three crack propagation modes and two failure types for samples under dynamic impact.When the curing time is short（3d and 7d）and the cement content is low（1:8）,the failure of the samples is mainly shear failure;when the curing time is long（14d and 28d）and the cement content is high（1:5 and 1:8）,the main failure mode is tensile split failure.（3）The energy changes of samples under dynamic impact can be obtained by energy calculation formula.The results show that the absorption energy（E_A）of cemented tailings backfill samples with different curing time and different proportion increases with the increase of incident energy（E_I）.When the cement-tailings ratio（C/T）is 1:3,the sensitivity of E_A to strain rate increases with the increase of curing time.When C/T is1:5 or 1:8,the E_A is not sensitive to the change of strain rate,but the overall trend is still positively correlated.（4）LS-DYNA finite element software was used to simulate the samples under dynamic impact.The results showed that the CTB samples with curing time of 3d had a large stress concentration area and strain near the transmission end face,and the samples always failed from the transmission end to the incident end.The stress concentration zone and strain of the CTB samples with curing time of 28d mainly appear in the lateral axial direction and run through the whole CTB samples.