Study On The Mechanism And Control Of Rockburst In Roadways Under Dynamic Loads

Underground activities like rock strata fracturing and caving,fault sliding and natural earthquake in the coal mines will produce stress waves,which may result in dynamic type of rockburst or some other serious dynamic disasters in the roadways.When mining the coal resources under conditions of large depth,hard roof or violent tectonic movements,these dynamic disasters increase greatly and cause great threat to the mining safety.In fact,this type of rockbutst is the sudden failure of coal and rock under dynamic and static loads.Nowadays,researches have conducted many experienments on the mechanical properties of coal,rock and their combined body,but the mechanical properties of coal in the combined body have not been studyed.And research on the dynamic type of rockburst is still in the primary stage,and the monitoring,early warning and control technologies can not meet the requirements of engineering practices.Therefore,using laboratory test,theoretical analysis,numerical simulation and field monitoring methods,researches on the mechanical properties and damage constitutive models of coal in the combined body,the energy evolution law and structural mechanics model of the surrounding rocks under dynamic loads,and the mechanism and control of rockburst induced by dynamic loads were conducted in the dissertation.The main research contents and achievements are as follows.Based on the strain measurement technique and the piezoelectric properties of PVDF,the test method for obtaining the mechanical properties of coal in coal-rock combined sample was proposed.A series of experiments on the coal specimens,rock specimens and their combined bodies were conducted using the AG-X250 Shimadzu Precision Universal Tester and the SHPB testing system,and the influences of loading mode,surrounding rock property,combination form,coal-rock height ratio and initial axial pressure on the mechanical properties of coal were obtained.Considering the compacted,elastic,plastic and viscous properties of coal,the compaction coefficient was defined and introduced to amend the classical damage constitutive model.Combined with the influences of rock property,combination form and coal-rock height ratio on the coal properties,the damage constitutive models of coal under static loads,dynamic loads and their combined loads were established.Compared with the test results,these models can well describe the mechanical behavior of coal under the corresponding loads and accurately reflect the influences of rock property,combination form and coal-rock height ratio.The three-dimensional differential forms of the new defined models were derived to load the models into FLAC3D software using C++.In view of the geological and mining conditions of no.2706 haulage way at no.14-3 coal seam in Xinzhouyao Mine,the new defined models were used to simulate the impact process of stress waves on the surrounding rocks,and the failure characteristics and energy evolutions of the surrounding rocks with different dynamic loads,initial static loads and rock properties were obtained.The structural mechanics model of surrounding rocks under dynamic loads was established,and the coal seam at roadway sides is divided into resistance zone,drive zone and no influence zone.The occurrence process and mechanism of dynamic type of rockburst in roadway induced by dynamic loads were revealed,and the energy criterion of bursting failure of the surrounding rocks was deduced.Considering the loading effect of surrounding rocks on the coal failure process and the time effect,a new bursting danger index,combined coal-rock impact energy speed index,was established.And based on the mechanical properties of coal under combined condition,the comprehensive evaluation method of coal seam bursting danger was proposed.The control technology system of dynamic type of rockburst was established including reduction of static stress concentration,control of dynamic load sources,increasing of stress wave attenuation,bearing capacity improvement of the surrounding rocks,increasing of failure depth of coal seam and increasing of anti-dynamic pressure ability of supporting system.A multi-stage pressure relief support system of surrounding rocks was invented by coupling the hydraulic and powerful spring control modes,which can significantly increase the anti-dynamic pressure ability of supporting system.According to the field practices in no.5302 coal face of-980 m level in Xinhe Mine,Shandong Province,the control technologies had obvious effect on preventing and controlling the rockburst.