Mechanical properties and failure characteristics of strengthening stratified cemented tailings backfill under triaxial compression

In order to solve the collapsible difficulties of primary stope in subsequent stoping backfilling method, the idea of strengthening stratified structure in primary stoping backfill is put forward. The effect of strengthening stratified height, cement-to- tailings ratio and confining pressure on the mechanical properties and failure rules of cemented tailings backfill (CTB) is investigated by the triaxial compressive testing. The difference of deviational-stress-strain curves and failure modes between CTB and strengthening stratified CTB is investigated. The results show that the yield phase and peak strength of CTB are enhanced by the strengthening stratified structure in CTB. When the strengthening stratified thickness keeps constant, the strengthening effect is raised as the cement-to-tailings ratio in the main layer become lower. Moreover, the cement-to-tailings ratio in the main layer remains unchanged, the strengthening effect is advanced by the increase of strengthening stratified thickness as well. The peak strength of CTB is logarithmically increased with confining pressures, and the apparent cohesion and friction angle are linearly increased with cement-to-tailings ratio in the main layer and strengthening stratified thickness. The failure mode of CTB without strengthening stratified structure is mainly dominated by an oblique shear crack, and the strengthening stratified CTB presents three failure modes: shear, tensile and mixed. When the cement-to-tailings ratio in the main layer is low, tensile cracks run through the strengthening stratified structure. The feasibility of 1:7-0 backfill replaced by 1:20-2/5 is verified, and the backfill cost of 1:20-2/5 can be saved by 6.85% cement cost, where 1:20 is cement-to-tailings ratio, and 2/5 is the proportion of strengthening stratified. The results can provide theoretical references for saving backfill cost and improving operation safety.