The Bolting-grouting Support Application Of Gob-side Entry Retaining In Fully Mechanized Caving Face

In Tianchi Mine, two-entry-development is adopted for its longwall faces. With the retreating of longwall face, the gas dilution entry is maintained along the goaf and then reused as air return entry for the next longwall face. Due to the affect of abutment pressure caused by retreating longeall faces, it is very difficult to maintain the entry along goaf for its second use. Problems encountered include excessive coal pillar extrusion, roof rock breaking and caving in, floor heave, and excessive convergence of roadway section, resulting in necessity for repeatedly repairing, high labor intensity, high cost of roadway support and repairing, and disrupted longwall substitution.Setting out to three aspects namely rib side pillar deformation characteristics of roadways along goaf, the stability of the inclined beam structure and stress redistribution acting on surrounding rock of roadway maintained along goaf, this paper carries out its research work on the several major factors and their effects on the stability of roadway maintained along goaf. These factors include surrounding rock deformation features of roadways maintained along goaf, stress distribution and stress changing process, consumables property and parameter design of bolting & grouting. Based on case study, summary is made on support mechanism of bolting and grouting technology and its technological advantages.In connection with the special structure of strata surrounding a longwall entry maintained along goaf, in-situ stress measurement and stress change monitoring work has been undertaken so as to work out the stress acting on the inclined roof beam structure of the maintained longwall entry and its redistribution process, which leads to the identification of the elastic zone, yielding zone in the surrounding rock of the entry maintained along goaf as well as the influence arrange of front abutment pressure caused by longwall retreating. This identification provides a good engineering basis in designing the bolting and grouting reinforcement system for the No.103 gas dilution entry in Tianchi Mine.Hollow groutable cablebolts and rockbolts play a key role in the reinforcement system designed. The new type hollow groutable cablebolts and rock bolts feature innovative improvement in material properties, tendon configuration and the relevant grout packer. Cement-based grout material is chosen for its cost effectiveness and easy to source. Special additives is used for better pumpability, shorter gelling time and higher curing speed, so as to meet the demand of having a bolting and grouting system that features quickly load taking, rapid grout spreading, and high load bearing capacity after installation.In this paper, research work aims at increasing the stability of the special structure which consists of the narrow coal pillar rib side, the inclined roof beam and the solid coal rib side of the roadway maintained along goaf, with focus being on the co-function of the reinforcing system and the surrounding rock. The paper put forwards an approach of reinforcing the whole section of the roadway maintained along goaf by bolting and grouting. Specific measures of the proposed approach includes installation of hollow tendon groutable rockbolts in such a manner called "three high" bolting and grouting, namely high pretention, high cement-water ratio, and high grouting pressure, which aims to improve the integrity and load bearing capacity of the coal rib on both the narrow pillar side and the solid coal side so as to control rib side deformation. Another key part of the approach is the installation of hollow tendon groutable cablebolts in the roof of the roadway. The hollow tendon groutable cablebolts features longer length so as to build up mechanical linkage among the top coal, the immediate roof and the competent main roof. At the same time, grout fills up and seals off fractures and cracks in the roof, resulting in increased integrity and stability of the inclined roof beam. This approach leads to the required stability of the roadway maintained along goaf during its entire the service life.The designed bolting and grouting reinforcement system has shown its advantages in reinforcing roadway maintained along goaf as compared with using steel sets and hydraulic props. Roadway convergence and deformation rate have been dramatically reduced. The maintained roadway basically needs no repairing during its second service cycle, which leads to fundamental overcoming of the difficulty in keeping top coal caving longwall entry maintained along goaf in good condition. While labor intensity of workers is reduced and underground working environment improved, saving in labor and material cost is also obtained. The bolting and grouting reinforcement system plays a key role in making top coal caving longwall face’s pace of high production and high efficiency run safely with significant economic and social benefits being achieved.