Basic theory of constructional backfill mining and the underground space utilization concept

In order to cope with the challenges of increasing cost,relatively low efficiency and waste of underground mining space faced in backfill coal mining,the thought of constructional backfill mining ( CBM) is put forward. The CBM is a kind of backfill mining with low backfill rate,strong structural stability and good backfill effect. The targets of CBM include the efficient usage of solid waste resources in mining areas to reduce the backfill cost,the improvement of backfill materials and backfill technology to increase the backfill efficiency,and the rational planning for backfill and mining scheme to reuse of underground mining space. The design principles of CBM are that the immediate roof does not break and the deformation of it is within the allowable range,the strength of backfill body is large enough and the backfill body has long term stable bearing capacity. Based on the design principles,the key positions of CBM are deter- mined as follows: special geological structure area, the stress concentration area of surrounding rock, the maximum stress point and maximum deformation point of immediate roof,and the weak point of backfill body,etc. The key tech- nologies of CBM should include:① the development of new solid waste backfill materials by optimizing the shape and particle size distribution of gangue aggregate;② the development of low-cost new cementitious materials;③ the devel- opment of new additives and various alternative raw materials,etc. ;④ the construction of the composite bearing struc- ture of “backfill body-immediate roof” through the construction of high strength backfill structure with different shapes and self-supporting structure of immediate roof;and ⑤ the development of the underground integrated system including intelligent preparation system, visual delivery system, independent construction system, mobile pouring system, and three-dimensional monitoring system. Based on the thought of CBM and the mining demand of “three-under” coal re- sources,the concepts of constructing underground complex under city,constructing underground agricultural base un- der village and farmland and constructing underground storage under railway (highway) and water body are put for- ward.