Instability Mechanism and Control of Cataclastic Structure in Compound Regenerated Roof
Author:Ma Wen Qiang
Supervisor:wang tong xu
The compound regenerated roof exists while mining the lower slice of ultra-close and thick coal seam,this kind of roof was formed by the falling rocks after compaction and cementing,it has cataclastic structure and is easy to break and fall when disturbed.In this paper,laboratory test,field observation,theoretical analysis and numerical simulation were used to study the bearing instability and control mechanism of the cataclastic structure in compound regenerated roof.The research thesis mainly includes the following aspects:mechanical properties of the roof rock,compression and shear strength features of the fragmentized rocks,cataclastic structure features of the compound regenerated roof,stability of compound regenerated roof and ground pressure manifestation in lower slice mining,bearing instability features and control design of the cataclastic structure of roadway regenerated roof.(1)Based on the mechanical parameters of roof obtained from indoor rock mechanics test,FISH programs were compiled in UDEC to build Trigon block model and monitor the fracture development length.Numerical specimens composed by a series of Trigon blocks were built to simulating the failure mode and fracture propagation and distribution law of cylinder specimens under different confining pressure.(2)Compression cylinder that can be opened and fixture of cylinder specimens under shear test were designed and developed.These devices were used to compress the fragmentized rocks and shear the specimens after demoulding,then this paper gave the compression and shear strength features of the fragmentized rocks with different block size under different compression ratio.(3)This paper established the cataclastic structure model of the compound regenerated roof in the gob,analyzed the vertical zoning and cataclastic features of the structure.Based on this model,a similar material simulation test model was built.Evolution law of caving arch rise in the regenerated roof was obtained under different compression time and span.This paper also studied the recementing mechanism of regenerated roof grouting,showed the roof movement law and ground pressure manifestation characteristics while mining the lower slice.(4)Based on the cataclastic structure model of the compound regenerated roof,this paper has constructed the modified natural arch and three hinged arch models of roadway roof structure in different layers,derived the arch curve and rise formulas of the former,gave the instability criterion of the latter arch.With the combination of UDEC simulation the bearing and instability mechanism of the roadway regenerated roof cataclastic structure were analyzed.(5)This paper constructed the mechanical model of"support-regenerated roof’ structure in lower slice stope,analyzed the mechanical characteristics of the support and gave the calculation expression of support stress.A calculation example was performed to verify the support applicability.This paper also gave the roof control scheme,which is applied in the numerical model,then an optimal support scheme was determined,it can control the roof well after field test and measurement.