Research And Application Of Flameless Blasting Weakening Technology For Hard Suspended Roof In High Gas Face

The problem of the roof collapse of the upper corner after the fully mechanized mining face is an important issue affecting the safety of underground coal production.Due to the increasing depth of coal seam exploitation in China,the in-situ stress of the coal seam is gradually increasing.Under the action of high-strength ground stress,the deep rock exhibits high hardness and strong integrality.It is difficult to form a free fall due to its own weight after mining.If the ceiling area is too large,it will cause serious hidden dangers to underground safety production.In addition,using the traditional emulsion explosive to crack roof is easy to cause safety problems such as underground gas explosion.The roof of the coal layer of the Geng Formation of Pingdingshan No.2 Mine is a hard roof.For the problem that the roof of Geng 20-2100 working face of Pingmei No.2 Mine is hard and it is difficult to directly fall off by its own weight during the mining process,a Non-Explosive Expansion Material(NEEM)is developed and a non-explosive expansion cracking method is proposed to achieve weakening and cracking of the hard coal roof.NEEM has the advantages of no pollution,no open flame,no gravel,and it has a strong application prospect.In this paper,the NEEM fracture-cracking unit and the fracture-induced primary rock analysis are carried out.The combination of laboratory analysis,field experiment and numerical simulation is used to determine the process parameters required for the flameless blasting in the underground.For example,the drilling distance of the top plate,the drilling arrangement,the charging link,etc.On this basis,the following results have been achieved:(1)The NEEM initial expansion stress is tested by NEEM expansion steel tube test.Then,the NEEM fractured primary rock test is carried out.The test shows that NEEM can completely crack the downhole roof and provide a reliable theoretical basis for the downhole flameless blasting weakening roof scheme.(2)By using COMSOL numerical simulation,the stress cloud diagram and stress distribution diagram of the two-hole central axis between the two holes are analyzed,and a reasonable distance suitable for the downhole flameless blasting drilling arrangement is proposed.By using FLAC3 D numerical simulation,the effect of cracking of the top plate by flameless blasting under different angles is analyzed.Combined with the relationship between the expansion stress and time after NEEM encounters water,following the principle of time-forspace,I creatively put forward the scheme of “weakening step by step-spatiotemporal coordination-overall weakening”.(3)In order to solve the problem of charging the underground upward hole,the way of packaging NEEM is developed,and a set of NEEM rapid charging device and charging process suitable for the downward hole package is designed.(4)On-site industrial application was carried out in the working face of Geng 20-21100 in Pingmei No.2 Mine.The application results show that the flameless blasting weakening technology can completely solve the problem that the hard roof of the Geng coal seam working face cannot be freely collapsed.During the application period,the gas concentration in the upper corner was within the normal range,the ceiling area of the upper corner was not exceeded,and the underground production operation was normally carried out.