Experimental Study On Reasonable Supporting Stress Of Rockbolt For Coal Roadway

In this paper,the studies were carried out in Hejita coal mine 50105 air return roadway.Based on the in-situ stress distribution of the coal mine,the depth of the earth was deepened into 200m,600m and 1000m,which represented the shallow,middle and deep mine.To study the reasonable supporting stress of rockbolt for coal roadway,the combination of physical simulation,numerical simulation and true triaxial test methods were adopted.The research results were obtained as follows:(1)The physical simulation method was used to monitor the internal stress field of the concrete samples under axial loading and surrounding constraints.The concrete sample was composed of soft and hard layers with different elastic modulus.The experimental results showed that the stress field distribution was proportional to the elastic modulus,and according to this relationship,the in-situ stress of the coal seam was deduced from the assumption of in-situ stress of the rock seam under above different buried depth.(2)To study the evolution law of the main stress of surrounding rock in coal roadway under different burial depth,the numerical simulation method was used.The numerical simulation showed that the trends of the maximum,intermediate and minimum principal stress for the different burial coal roadway were similar.The maximum principal stress decreased first and then increased to be stable,and the intermediate and minimum principal stress also decreased first and then decreased to be stable.(3)To study the reasonable supporting stress of rockbolt for roadway,the coal sample of which size was 150mm × 150mm ×150mm subjected to loading + pressure unloading + pressure reloading true-triaxial test,which simulating unexcavating-excavating-supporting process of the coal roadway.The initial confining pressure of the test was determined by the physical simulation test,and the stress path was determined by the numerical simulation.The Experiments showed that the confining pressure was restored immediately when the coal sample was destroyed,the internal rupture was obviously inhibited,and the coal sample was stable.But when the confining pressure was lower,the coal was immediately broken,the project could explain there was a reasonable supporting stress for the coal roadway,when the reasonable supporting stress was higher,the roadway would be stable,otherwise,roadway would be broken.(4)The peak strength of the coal sample at the time of failure could be regarded as the concentrated stress caused by the excavation activity,and the stress concentration coefficient a was the ratio of the stress to the gravity stress.For the 200m depth,the stress concentration factor a was 6.14,the reasonable support stress was 0-0.1 MPa;for 600m depth,stress concentration factor a was 3.13,and the reasonable supporting stress of the rockbolt was about 0.1 MPa.For the 1000m depth,the stress concentration factor a was 2,and the reasonable supporting stress of the rockbolt was 0.1-0.2MPa.(5)The supporting suggestions of rockbolt for the coal roadway were made.For the coal roadway under 200m depth,supporting stress of rockbolt was 0-0.1 MPa;For the coal roadway under 600m depth,supporting stress of rockbolt was about 0.1 MPa;For the coal roadway under 1000m depth,supporting stress of rockbolt was 0.1-0.2MPa...