Evolution Of Surrounding Rock Structure And Its Control Of Roadways With Pre-backfill Instead Of The Pillar In Top Caving Working Faces

At present, non-chain-pillar entry protection is mainly achieved through thegob-side entry retaining and gob-side entry driving. Generally speaking, gob-sideentry retaining has to suffer the mining influences twice. So it’s harmful to roadwaymaintenance. As to gob-side entry driving, it always requires to set a coal pillar about5~7m wide, which cannot be called the real mining without coal pillar.In this study, we mainly talked about a new technology——pre-backfill insteadof the pillar in top caving working faces. In other words, we can build the backfill inthe lane of upper working face which close to the side of the non-cutting roadway inadvance, then we excavate the roadway along the backfill, finally we can minewithout coal pillar. With the help of theoretical analysis, numerical simulation, sitemonitoring and industrial test, and combined with evolution characteristics of theroadway surrounding rock structure of pre-backfill instead of the pillar in top cavingworking faces, it can be divided into three stages, they are upper working face mining,working face driving and working face mining. We systematically studied on the"three-stages" by focusing on the influences large structure of surrounding rock havemade on the backfill and the stability of gob-side entry and the interaction betweenbackfill and structures. Main results are as follows:(1) First of all, we built a Winkler elastic foundation model for the basic roof,immediate roof, coal seam, backfill and other related rock structure, we analyzed whatimpacts may made on backfill by different fracture positions and mining geologicalconditions of basic roof arc triangles. And then, we drawn a criterion aboutpre-backfill instead of the pillar which can be applied into any mining geologicalconditions.(2) Pre-backfill instead of the pillar is different from gob-side entry driving witha narrow coal pillar. Owing to the backfill is always in a high stressful state among the"three-stages", gob-side entry will be driven in a high stress environment, whichmeans it has higher requirements for strength, width of the backfill and supportstrength in the roadway.(3) According to the research, width and strength of the backfill can make anotable influence on stress and plastic zone distribution of the small structures.Besides, it also effects fracture position and initial subsidence of the basic roof.Finally, we find out the interactions between the backfill and the surrounding rocks. (4) Based on the analysis of the mechanism and the mechanical characteristicsfor the "three-stages" process of the backfill, we can determine essential parameters ofthe backfill reasonably.(5) By analyzing the deformation characteristics of roadways for pre-backfillinstead of the pillar, we can divide all roadways into immediate roof interlayer glidingseparation zone, backfill side roadway shoulder angle top coal shear subsidence area,roof shallow tensile fracture area, and buttock shear compression failure area.Therefore,"non-symmetrical supporting aimed at different zones" system was putforward.All the results above mentioned were applied successfully to the S510workingface in Changcun Coal Mine. The parameters of backfill meet the requirements ofsafety production, and it can control the deformation of the surrounding rockseffectively.