Abstract:

When the mining method in the West No.2 mining area of Longshou mine was changed from down layered cemented filling mining method to sublevel caving mining method，it is necessary to form a loose overburden by caving or blasting the large area cemented filling.Using the traditional drilling and blasting method to form the loose overburden has a series of disadvantages，such as long period，large input and less output，which can not meet the production needs of the mine.A induced caving technical scheme of forming loose overburden by reserving ore bulk as safety cushion and uniformly expanding goaf was proposed，which combined the formation of overburden with the dual demand of stope productivity.Microseismic monitoring technology was used to monitor the caving process of cemented backfill.The monitoring results show that the caving mechanism of cemented backfill in West No.2 mining area can be divided into three types.The first type is the failure event of cemented backfill caused by the mining stress concentration within 20~45 m behind the goaf，which mainly occurs in the early to middle stage of drifts mining.The second type is that with the expansion of the goaf，the shear stress at the fulcrum of the suspended cemented backfill beam is also increasing，when the shear stress exceeds the shear strength of the cemented backfill，the beam will shear failure at the fulcrum at the rear edge of the goaf，this kind of failure event mainly occurs in the middle to end stage of drifts mining.The third is that when the exposed length of the cemented backfill beam increases to a certain extent，the cemented backfill beam bends and sinks under the ground pressure and its own gravity，resulting in tensile stress in the middle of the rock beam of the filling body，resulting in bending and tensile failure in the middle of the cemented backfill beam，this kind of failure event mainly occurs in the middle to end stage of drifts mining.Based on the comprehensive analysis of the results of microseismic monitoring，theoretical calculation and in-site ore drawing tracking，it can be seen that during 1 595 m sublevel mining，the caving of cemented backfill mainly occurs at the level of 1 610~1 630 m.Therefore，a loose overburden composed of residual ore and caving cemented backfill with a total thickness of about 30 m is formed on the floor of the first mining sublevel.This loose overburden thickness meets the safety requirements of mining and the requirements of relevant safety regulations，which shows that the preset goal of forming loose overburden safely，efficiently and at low cost has been successfully achieved by using induced caving technology in the West No.2 mining area.

Key words: non-pillar sublevel caving method, cementing backfill, induced caving, overburden, caving mechanism, micro-seismic monitoring