Study On Anchoring And Bearing Mechanical Properties Of Surrounding Rock Containing Weak Interlayer In Deep Roadway And Application

The weak interlayer widely exists in the sedimentary strata of coal mine,which induces significant structural effect and increases difficulty in the mechanical properties evaluation and the stability control of the surrounding rocks.The weak interlayer is well known as one of the most important factors influencing the stability of the surrounding rock and causing hazards in deep underground roadway.What's more,there is a lack of complete and effective understanding about this rock structure.Therefore,it is of great significance to study the bearing characteristics and strength failure behavior of rock mass containing weak layers,and its further influence on the stability control of deep underground roadways.The research was funded by the National Natural Science Foundation Key Projects of China?Grant No.51734009?,the National key R&D project?Grant No.2017YFC0603001?and the National Natural Science Foundation for Young Scientists of China?Grant No.51504247?.It is based on the background of one-kilometer depth roadway engineering in Fourth Coal Mine of Pingdingshan coal mine group.The rock mass stabilization around the roadway engineering is significantly dependent to the containing weak interlayer in the roof.The anchorage unit test,geomechanical model test,numerical simulation,theoretical analysis and other method were systematically carried out to study the bearing characteristics of surrounding rock with weak interlayer in deep roadway.The main achievements and conclusions are as follows:As many as 120 specimens?with size of 200×200×200 mm?containing weak interlayer made with artificial similar materials were prepared and their bearing properties were studied.Law of the thickness,strength,dip angle of the weak interlayer and the density and pretension of bolt influencing on the bearing capacity of the anchorage was systematically obtained for the first time.The quantitative relation between the peak strength and the elastic modulus of the anchorage and the aforementioned five factors is established.The mechanism of the weak interlayer promoting the failure mode of anchorage was investigated,and the structural effect of the anchorage was revealed.It was found that,at the post-peak stage of the anchorage,approximately 70⁸0%normal displacement of the free surface of the anchorage caused by the cracking and slipping of the fractures is the structural deformation.Based on the bearing capacity test of the anchorage with weak interlayer,geo-mechanical model test was adopted to investigate the bearing capacity of surrounding rock with weak interlayer.The results showed that the weak interlayer is formed by unloading zone and weak bearing zone of tangential stress of the surrounding rock.With the deformation and failure of the roadway,the bearing structure of the rectangular tunnel roof with weak interlayer was changed from composite beam to pressure arch,and the stability of composite beam is the precondition and guarantee of roadway stability.The arching criterion of pressure arch(s_q/s_q0?28?1.1)was put forward based on the test results.By embedding the criterion into the FLAC³DD software package,the influence of weak interlayer on the pressure arch of the surrounding rock was numerically simulated.The numerical simulation results showed that the influence of the weak interlayer on the pressure arch tends to be stable when it was 3 m far away from the surface roof.The equivalent homogeneous mechanical model of rock mass with weak intercalated layer was established based on homogenization theory,and the law of weak interlayer influencing on cohesive and internal friction angle of the equivalent homogeneous was revealed.The composite beam mechanical model of the roof with weak interlayer was proposed.The influencing mechanism of the weak interlayer on the ultimate bearing capacity of the composite beam with the failure model of cutting failure and tensile failure at the mid-span was illuminated and the influencing law was obtained.The failure criterions of the composite beam for the failure models were established.The pressure arch mechanical model of the roof with weak interlayer was put forward,and the influence of weak interlayer on the compressive failure of arch vault and the ultimate bearing capacity of arch foot shear failure were discussed.The concept of“synergy and coupling”for stability control of surrounding rock with weak interlayer was put forward according to the bearing characteristics of the anchorage and surrounding rock with weak interlayer.The stability control technology based on the combination of“high strength constant resistance bolt and composite grouting”was built.The key technical system of synergy and coupling for stability control of deep roadway with weak interlayer was formed.Aiming at solving the stability control problem of the surrounding rock in deep underground with weak interlayer,the research findings were successfully applied to Four Coal Mine of Pingdingshan coal mine group.The field industrial test illustrated that the research results of the paper was reasonable and practical.