| In Jinfeng gold mine,the rock mass is not only soft but fractured,the engineering geological conditions are complex,and the ground support is difficult.Disasters such as roof falling and rib spalling often occur.In recent years,with the increase of mining depth,the roadway support failure caused by large deformation due to squeezing is more frequent.Bolts + mesh + shotcrete is the most important support method in the mine,but the shotcrete support is mainly designed based on empirical methods,which is inadequate to fit complex and variable engineering conditions.In this thesis,the mechanical performance of polypropylene fiber reinforced concrete(PFRC)and its supporting characteristics for fractured soft rock roadway are systematically studied by means of field investigation and testing,physical tests,theoretical analysis,and numerical simulation.The main research work and achievements are as follows:(1)Based on large sets of geological drilling data from Jinfeng gold mine,a threedimensional RQD block model is established with the Surpac software.On this basis,the quality and integrity of the rock mass are classified.Based on the summary and analysis of previous engineering geological survey works,the rock mass quality of the mining area is also classified by the RMR and Q systems.(2)The physical and mechanical properties of polypropylene fiber and the compressive strength,flexural strength and bending toughness of PFRC were tested in laboratory.The destruction of the shotcrete is investigated on site and summarized into three modes: at the early age,due to insufficient strength,it’s destroyed by loose rock;When supported together with higher support stiffness bolts,bending and tensile failure will occur due to pressure formed by ground deformation;The squeezing ground undergoes large deformation,resulting in structural compression,shear,bending,or composite failure.(3)Based on block theory,the loosening pressure of blocky structure rock mass is calculated with the Unwedge software.Based on Platts theory,the loosening pressure generated by disintergrated structure rock mass is calculated with the Ansys software.The support strength requirements of fresh shotcrete under two load conditions are calculated respectively.The early strength test of the fresh shotcrete was conducted on site,and the safe re-entry time to the working face after spraying was specified.(4)Based on the elastic mechanics solution of fixed-end beam,the stress and displacement of shotcrete coupling support with bolts are analyzed.The relationship between the resistance of PFRC in crack propagation stage and the test results of C-1550 panel was established.Taking the actual support scheme of Jinfeng Gold Mine as an example,the whole process support characteristic curve of PFRC is constructed.(5)Through numerical simulation,the squeezing potential of ground is estimated,and the stress and failure mechanism of PFRC under squeezing conditions are studied.The ground reaction curves and the roadway longitudinal deformation profiles are calculated and drawn.Combined with the mining construction technology,the installation time of support is determined.On this basis,the stress and failure mechanism of PFRC under the condition of extrusion deformation are studied by numerical simulation.(6)A portable laser scanner was used to measure the roadway.A three-dimensional geometric model of the roadway was established and its geometric characteristics were analyzed.On this basis,the influence of the irregular surface of the surrounding rock on the shotcrete support characteristics was analyzed by numerical simulation. |
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