| In underground metal mines,open stoping with subsequent backfill mining method is a beneficial combination of mining with backfill and open stoping,which represents the direction of green and mass mining method in the future.However,the costs of the cemented backfill(binder dosage)in primary stopes cover more than seventy percent of the overall filling costs.How to balance the costs and stability of the exposed cemented backfill optimally is one of the key issues that restrict the sustainable development of safe and economical mining with backfill.In this study,integrated research methods including theoretical analysis,analytical calculation,numerical modelling,lab samples test,physical model tests,and results validation in practical mining application have been employed for breaking through some bottleneck problems of the arching mechanism and its influential factors,analytical solutions of stress distributions,strength requirement calculation and stability investigation within the backfill in stopes.The achievements could provide theoretical basis and methodological references for the optimization of strength requirement design of the cemented backfill in open stoping with subsequent backfill mining method.(1)A kind of non-planar interface elements idealized by saw teeth has been constructed to quantify the characteristics of practical rock wall surfaces in mine stopes.The influential laws on backfill arching mechanism after considering planar smooth or non-planar rough interface elements between backfill and rock walls have been investigated.Responding mechanism on the stress distributions from the interface contact properties(roughness indexes,shear strength)and dimensional,physical and mechanical properties of backfill has been studied.A more general numerical modelling method for arching stresses calculation with consideration of practical characteristics of rock walls in stopes has been obtained.(2)The classic Mitchell method to evaluate required strength and stability of exposed cemented backfill has been revisited.Combined with FLAC3D codes,the physical model tests for validating the Mitchell method have been numerically regenerated to compare and investigate the relationships between the strength requirement and stability of the exposed cemented backfill under different sizes.The limitations and applicable conditions of the classic Mitchell method have been discussed.And the potential sliding failure modes and related descriptions of vertically exposed cemented backfill have been obtained.(3)Three dimensional arching stress distribution modes for uncemented backfill,cemented backfill before and after vertical exposure under consolidated and drained long-term strength properties have been studied.Then three dimensional analytical models and formulations for stress calculations of these backfill have been constructed.The stress transfer laws and mechanical boundary conditions along the contact interfaces among the uncemented backfill,cemented backfill and rocks after considering arching effect in backfill have been obtained.(4)Lateral pressure mechanism from uncemented backfill to adjacent cemented backfill under different conditions among the excavating and filling sequences of open stoping with subsequent backfill mining method has been investigated.Then three dimensional analytical models for the calculation of strength requirement of the exposed cemented backfill in primary stopes have been constructed.After comprehensive comparisons between the analytical and numerical solutions about the required strength simulated with FLAC3D,an optimal analytical model and its formulations have been recommended for the evaluation of theoretical solution of backfill strength requirement.(5)Combined with the tested strength results of the core samples by drilling the backfill in field stopes of an engineering based mine,mathematical statistical probability analyses have been carried out to investigate the non-uniform distribution properties of backfill strength in practical mine stopes.Based on the statistical results,a kind of method to select reasonable floating factor of safety(FS)has been defined which can be used to quantitatively evaluate the overall filling technical level and practical quality control effect of the mine.And then,a model used for floating optimization of cemented backfill strength requirement has been constructed following the sequences of "Theoretical solution of strength requirement ? Evaluation and feed-back from the practical filling strength quality control statistics ? Selection of a reasonable floating factor of safety ?Practical required strength design for exposed cemented backfill". |
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