Research On The Deformation And Failure Characteristics And The Stability Of Surrounding Rock Of Roadway With Large Hexagonal Section

With the building of productive and efficient mine and the developing of integrated mechanization mining technology, the mining technology, such as top coal caving of thick coal seam and overall mining of medium thick seam,have be used widely. The roadway section is required to become bigger with mining height increasing to reduce the coal loss in top of roadway, meet the installation requirements for large mining transport equipment, and meet the safety requirements for normal production, transport, ventilation and pedestrian. But the surrounding rock instability will increase significantly when roadway section become bigger. Currently, the research on stability of surrounding rock was mainly focused on surrounding rock stress and choice of supporting way.but the status about large deformation in roadway and difficulties in supporting was not changed effectively. So we should change the thinking to find a section morphology of roadway for particular state of surrounding rock by studying on the relation between section morphology of roadway and Stress distribution.Given these realities, this paper analyzes the necessity, basic features, current situation and existing problems of developing large section roadway; summaries the analytic methods used to study the stability of the roadway; describes the research status that section shapes influence on the stability of surrounding rock; puts forward hexagonal section roadway able to enhancing self-stability, and studies on its stability through similar material model test, numerical simulation test, and theoretical analysis. The study works which have been compiled are as follows:1. Through large-scale plane underground engineering simulation system, completing the large range of observations for model, applying high intensity loads of two-way to model for solving the technical problem of low intensity load, launching the similar material simulation test named "first load, after excavation" for large section roadway, and obtaining an applicable test data.2. Through similar material model test, analyzing the relationship between surface convergence rate of hexagonal roadway and lateral pressure coefficient; researching on the relation between roof vertical displacement and distance from roadway centerline, and relation between wall horizontal displacement and distance from roadway wall; analyzing the stress distribution of hexagonal surrounding rock; revealing the damage evolution of roadway at different depths; finding with depth increasing, the scope roof cracks gradually expanding form fissures ring to fracture network, the crack of wall gradually penetrating and extending to the roof, the original flap shape of wall becoming curved.3. Through comparing the test results of hexagonal roadway with the rectangular roadway, revealing the relation between the two type roadway’s displacement ratio and depth; analyzing the differences between two type roadway on fracture characteristics and damage extent of surrounding rock under different stress state; analyzing the different characteristics of stress distribution at key parts of surrounding rock of the two type roadway; confirming the factors that surrounding rock of hexagonal roadway has more smaller damage extent and stress concentration, and its flap-shaped wall has obvious effect about resisting the breakage.4. Through numerical simulation, studying on several rules that surrounding rock stability are influenced respectively by roadway width B, roadway aspect ratio K, roadway wall inclination a, roadway depth H, and lateral pressure coefficient λ; obtaining the optimal geometry and size of hexagonal section.The relational expression:Ei=a0+a1B+a2K+a3a+a4H+a5λ between five factors and surrounding rock stability, is obtained by multiple linear regression to quantitatively reveal the rule what five factors influence on surrounding rock stability together.5. Based on the optimal hexagonal section, the roadway classification model is established by SOM network with rock category evaluation which includes surrounding rock strength, mining depth, seam dip, and coal pillar width of13mines. The stability of hexagonal gateway of No.9coal seam in cao-village mine which is as engineering background is judged by roadway classification model, and the bolting program of the trial roadway is designed. The results show that roadway safety is improved, and support cost is saved after hexagonal section used.