Stability Analysis And Key Technology Research Of Tunnel Formation In Extremely Soft Rock Of Jinshandian Iron Mine

The extremely soft ore rocks of Jinshandian Iron Mine include fine ore,skarn and fractured expansive rock.The roadway-forming problem of digging and mining quasi-roadway in extremely soft rock area has always been a key factor restricting production,safety and operation of mines.Based on the existing mine construction technology foundation and the research idea of strict control of construction quality,the key technology of roadway construction is studied.This paper carries out extensive on-site monitoring and testing work,and analyses the main factors affecting roadway formation.With the main influencing factors as the entry point,special research work was carried out and a series of valuable results were obtained.The main research results are as follows:(1)The main factors affecting the strength of shotcrete are the length of time the mixing material stays underground and the dosage of accelerator.The indoor test is carried out by means of orthogonal test.The results show that the mixing material of shotcrete should be controlled in one hour,and the dosage of accelerator should be controlled in about 2%,so the strength of shotcrete is high.(2)The pull-out force test of anchorage bolt shows that the relationship between pull-out force/deformation of anchorage bolt and support time is a step function.Combining with the convergence deformation characteristic curve of bolt support roadway with anchorage agent,the support safety factor can be reasonably determined,and the effect of support can be evaluated,which provides a basis for the optimization design of roadway support.(3)Convergence deformation of surrounding rock of expansive rock roadway shows that its deformation belongs to creep model;powdery expansive rock is not suitable for bolt-shotcrete net support;fractured expansive rock can be supported by bolt-shotcrete net in a short time,but it needs to increase the thickness of grouting,provide sufficient support reaction force,and long-term support with steel arch frame;massive expansive rock roadway needs to be supported by bolt-shotcrete net support in time.(4)By means of numerical simulation,it is determined that the grade III surrounding rock of the quasi-roadway in Jinshandian Iron Mine belongs to the middle loosening zone,and the thickness of the loosening zone is less than 1 m,so shotcrete bolt net is suitable for support.