Secondary Development Of Bolt Tensile And Shear Broken Mechanical Models In FLAC^3D And Its Application

In order to compensate for defects of tensile broken original model in FLAC~3DD which takes plastic tensile strain of each bolt element node as the broken criterion and solve the problem that the shear broken failure of bolts cannot also be simulated with this program,the new tensile and shear broken criterions were thus proposed based on the PILE structural elements according to the laboratory data.The tensile and shear broken modified mechanical models were established and embedded into FLAC~3DD with Fish programming language.The rationalities of tensile and shear broken modified mechanical models were verified by the direct tensile and shear tests of bolts respectively and the engineering applicability and reliability of the two modified models were analyzed.The main research achievements were as follows:(1)To further improve the tensile broken original mechanical model,the tensile broken modified mechanical model taking the whole elongation rate of the bolt free section as the broken criterion was established,and the structural element with the largest elongation of the bolt free section broke while the elongation rate of the bolt free section exceeded the bolt broken elongation rate.The shear broken modified mechanical model taking the bolt shear force as the broken criterion was established,and the bolts were broken while their shear force exceeded the bolt ultimate shear force.(2)In the direct tensile tests,the bolt with tensile broken original model broke prematurely while its elongation rate was 51.5%of the preset broken elongation rate,and the one with tensile broken modified model broke while its elongation rate was equal to the preset broken elongation rate,therefore the result of modified model was more realistic.In the direct shear tests,the shear force of bolt with shear original model increased with the increasing shear displacement while it exceeded the ultimate shear force,which was not consistent with the reality.The shear load-displacement curve with the shear broken modified model presented the shear broken failure characteristics,and the quantitative broken effect was achieved through the shear force judgment.(3)A numerical calculation model was established in which the bolts were mainly subjected to tension and the tensile breakage phenomenon of the elements composing of the free section at the end of the free sections and the interface between free and anchor sections was implemented.There were only four bolts broken with the tensile broken modified model at the side roadway while the whole bolts broke with the tensile broken original model,and the result of modified model was more realistic.The maximum horizontal and vertical displacement of roadway surrounding rock with modified model were 395mm and 298mm respectively while they were428mm and 332mm respectively with original model,and the tensile broken failure of the whole bolts led to the serious deformation of surrounding rock with original model.(4)A numerical calculation model was established in which the bolts through the interface were mainly subjected to shear force,and a mining roadway model with large coal-rock interface slippage was given in this paper.The shear breakage phenomenon of the shoulder bolts with shear broken modified model through the interface was implemented.The greatest calculated sliding displacement at the coal-rock interface with the modified model was 13.1 mm larger than that with the original model,and the result was more realistic.(5)Finally,the tensile broken modified model was applied to analyze the broken failure phenomenon of GFRP bolts in 11 mining area of XiaoJiawa coal mine.It is pointed out that the bolts were little affected by the excavation and the side abutment pressure caused by the mining of an adjacent panel,and they were greatly affected by the front abutment pressure caused by the mining activity of the current panel,which led to the rapid increase of the elongation rate of free section,causing the broken failure phenomenon of GFRP bolts while its elongation rate exceeded the broken elongation rate.The GFRP bolts of original support scheme was 1600mm long,whose diameter was 16mm,which led to a small ultimate elongation and axial force of the free section,and they were unable to provide adequate support reaction to surrounding rock.Therefore the size of GFRP bolts was optimized and the final determination diameter was 22mm and the length was 2200mm.At this point,the GFRP bolts could bear the influence of the front abutment pressure,and there were no broken failure characteristics.