Study On Strata Deformation Mechanism And Control Technology Of Composite Roof In Qujiang Mining

With the increasing of mining depth, surrounding rock control of roadway with thickcomposite roof is more and more difficult, and becoming the focus of the field. Therefore thedeformation and failure of this roadway and control technology research is necessary. Thepaper based on project of " Research on supporting technology of coal and soft rock roadwayunder thick composite roof in deep mine" with Qujiang company in Fengcheng, thedeformation and failure mechanism of composite roof was studied with theoretical analysisand numerical calculation, supporting scheme is put forward which applied well in theengineering practice.Combined with the characteristics of the thick composite roof, the mechanical modelwas established, which simplified to hierarchical rock beam that parallel in transverse andserial in vertical. Result shows that flexural rigidity is the key of roof deformation,deformation and bed separation is mainly caused by the horizontal stress; Based on Verticaland Horizontal Bending Theory, different hierarchical lithology and thickness lead toincoordinated deformation, weak interlayer with lower maximum deflection easily bedseparate. Analyzed the thick composite roof’s bed separation cause by different deflectionwith the model of two ends hinged beam. Analyzed the force and bending deformation ofdriving roadway along goaf by cantilever beam,the key block B rotational angle of thickcomposite immediate roof is smaller than normal roof, driving roadway along goaf isadvantageous right now, and the deformation of driving roadway along goaf might be lessthan entity coal roadway.Through theoretical analysis concluded that the failure types of coal roadway under thickcomposite roof and its characteristics of deformation and failure under different support forms.Analyzed the influence factors of the roof deformation and failure. Combined with internaldetection and separation monitoring, concluded the internal characteristics of surroundingrock of coal roadway under thick composite roof and the control function of new supportform for the weak damage and bed separation.Analyzed the support principle of thick composite roof, established simple mechanicalmodel, discussed the mechanism of surrounding rock control, analyzed the influence ofsupport to moment and shear of coal rock beam. The results show that support resistance could reduce the plastic and broken zone, and the greater support resistance, the bettersurrounding rock support effect. Discussed and analyzed the potential key parts of coalroadway under thick composite roof, and corresponding reinforcement technology was taken.Analyzed the anchor combination effect model with composite and superposed beam,concluded that fine anchoraged composite beam significantly improved the flexural rigidityand flexural strength of composite roof, and reduced the maximum deflection, moreover themore combination of stratification, the better effect. Analyzed the anchor and anchor cablesupporting mechanism of roof and side, concluded the " reducing span " effect both, discussedthe way to coupling on time and space of anchor and anchor cable, analyzed the truss andanchor cable supporting mechanism of sides and roof.Analyzed the forms of failure and the reason of602air return way in Qujiang mineoriginal support scheme,"cable anchor+truss and anchor cable" combined support was putforward and applied in field. FLAC2Dsimulation was used to analyze the truss and anchorcable’s effect on roadway with thick composite roof, combined with the field observation data,and compared with the original scheme, showed that the truss and anchor cable has taken fulladvantage of the interior rock’s bearing effect, the stability of surrounding rock was controlledwell. Using orthogonal experiment, FLAC3Dwas used to simulate schemes, and select thebest anchor cable support parameters. The orthogonal experiment results and field practiceshow that the anchor cable not the longer the better. The potential reason as follow: the deepercable hole, the harder to push anchor agent, the more possibility for broken on the way; Thelonger anchor cable, which hanging more composite roof layers by its end anchoring,burdened more rock weight, that increased the failure possibility. Interlayer slipping is morefrequent occurred in composite roof, which also increased the burden of anchor cable.Therefore, the best length of anchor cable which combined supporting well and costreasonable is7m for the roof.