Study On Bolt Support Of Loose Ribs In Roadway

Rock mass of two ribs of many coal roadways is broken and the broken zone is larger than bolting length. Because cohesion of the loose rock mass in ribs is very minimal, bolted mass in these ribs can bear only compression stress or shear stress and can not bear the stronger tensile stress.In the paper the support principle of the thick bolted mass has been presented because tensile stress will lead to failure when object has the shape characteristics of the thin plate and object failure will depend on compression stress or shear stress when object has the shape characteristics of thick plate in solid mechanics.Above on bolted mass in ribs is simplified into free beam and fixed beam. Stress distribution in the different thickness beams has been analyzed. The results reveals that tensile stress in beams is bigger and tensile stress will be reduced quickly as the thickness of beam is increase when the ratio between thickness and length of beam is less than 3:10. When the ratio is greater than 3:10, that tensile stress in beams are less and tensile stress will been reduced slowly as the thickness of beam increases. Numerical modeling analysis has been done in order to master further the correlation between thickness of bolted mass and its mechanical property. The uppermost results are as follows: 1. When bolted mass thickness is less than 1.2m, the level displacement of ribs is larger and the level displacement is reduced quickly as bolted mass thickness increases and tensile stress in bolted mass is reduced quickly. When the thickness is less than 0.55m, compression stress increased quickly when bolted mass is larger than 0.55m.2. When bolted mass thickness is larger than 1.2m, ribs displacement is less and the displacement is reduced slowly as bolted mass thickness increases, and compression stress in bolted mass increases slowly. So bolted mass thickness in ribs should reach 1.2m.Base on the mechanics and numerical modeling analysis, in the paper that the ratio between thickness and width of bolted mass is 3:10 is rational is presented.The deterministic principle and method of bolt length has been put forward according to those results and bolt mechanism of action.