Study On Stability Analysis And Control Of Surrounding Rock In Washout Zone In Coal Seam Of Large Section Coal Roadway

The geological conditions of underground coal mines are complex and changeable.In the process of tunneling,the roadway will inevitably encounter some difficult and unmanageable conditions,such as faults,folds,back-tilt,coal seam wash belts and other special geological structures.Due to the influence of geological structure,the plastic zone of the surrounding rock increases and the stability decreases.The roof and and the two gangs often exhibit weak and broken characteristics.It is difficult to ensure the roadway if conventional bolt support is still used in this special structural section.The section width of the 1301 roadway of the Licun Coal Mine of Shanxi Lu'an Group has reached 6m and the height has reached 4.2m.It is a conventional large section roadway in terms of section size.In this paper,the roadway over-soil scouring section is selected as the engineering research background.Through the theoretical analysis method,laboratory test method,numerical simulation method and on-site monitoring method,the surrounding rock stability of the large-section coal roadway through the coal seam scouring zone is carried out.Based on the analysis,the control technology and scheme of the large section roadway under the influence of specific geological conditions(coal washout belt)are put forward,and the control technology and scheme are finally applied to the site for on-site application and data measurement.The following main research results have been obtained:(1)Through theoretical analysis,the effect of the size effect of the roadway section on the stability of surrounding rock when passing through the coal seam scouring zone is analyzed:the analysis shows the maximum sinking amount of the roadway roof ?max=-ql4/384EI.It can be concluded that under the premise that other conditions are consistent,the maximum sinking amount of the roadway is positively correlated with the width of the roadway.The greater the roadway span.the worse the stability of the roadway roof.It can be transformed into the problem of solving the plastic zone range of the roadway.According to the analysis,the plastic zone range of the roadway(?)under the premise that other conditions remain unchanged,the greater the height of the roadway,the larger the plastic zone of the two lanes of the roadway,which means that the stability of the roadway is worse.Therefore,when the roadway passes through the coal seam washing belt,the size of the roadway should be appropriately reduced to ensure the stability of the roadway.(2)By using FLAC3D numerical simulation software to simulate the influence of the position of the scouring belt on the stability of the roadway,it can be known that whether the scouring belt is located in the roof of the roadway,the floor of the roadway or the roadway passes through the scouring belt,due to the influence of the scouring belt,the amount of the top and bottom of the roadway is approached.Both are larger,reaching more than 260mm.When the scouring zone exposed by the roadway and the exposed coal seam area account for half of each,the plastic zone range and the top floor of the roadway are the largest,reaching 297.58mm,indicating that the roadway layout of the semi-coal rock roadway has the worst stability.Secondly,it can be seen from the simulation that the instability of the roadway occurs mostly at the junction of the scouring zone and the coal seam of the coal seam.(3)Through the analysis of the surrounding rock stability of the large-section coal roadway over-scouring zone,a joint support method of full-section long-stay anchor cable+mesh spray is proposed.The analysis of the support mechanism of the anchor and the anchor cable,combined with the range of the plastic zone in the numerical simulation,found that the length of the bolt is not enough to be anchored outside the plastic zone of the roadway,and the use of short anchor cable instead of the anchor rod is proposed.The combination of long and short anchors and the combination of long and short anchors were analyzed and compared,and the reasonable combination of length and length of anchors was 6.3m long anchor cable and 4.3m short anchor cable.In addition,due to the surrounding rock fragmentation on the roadway surface,the auxiliary mesh support method of metal mesh+shotcrete is used.(4)In the large section coal roadway through the coal seam scouring zone,the on-site industrial test was carried out by using the optimized support scheme,and the surface displacement,internal displacement and the length and anchorage of the roadway were measured.Pressure data:The instability and damage of the roadway are substantially controlled,and the roofing slab is reduced.The deformation of the roadway is basically stable after 30 days of deformation.The displacement of the top and bottom plates is only 115mm;the long anchorage of the roof is 340KN,short anchor cable.The force is 241 KN,and the force of the two sets of short anchor cables are 134KN and 137KN,respectively,which can also provide a large anchoring force.