| Drying up of coal resources in the central east area in our country,the coal resources mining step by step to the western region development,however,weak cementation strata are widely distributed in the western region in China,with such poor cementation of rock mass,the interlayer bonding strength is poor,water sand clay collapse,in this kind of rock excavation of roadway surrounding rock instability occur easily,roadway maintenance difficulties is an urgent problem in the coal mine safety production.This paper,taking a weak cementation in the western region the engineering background of soft rock tunnel supporting,comprehensively uses the field investigation,indoor test and theoretical analysis,numerical calculation,physical methods of analog simulation and field engineering practice,explores the weak cementation of the physical and mechanical properties of soft rock tunnel surrounding rock,deformation characteristics of roadway,weakly consolidated soft roof rock mass constitutive model,reveals the weak cementation of soft rock roadways roof unstability mechanism,based on the above-mentioned research results put forward roadway surrounding rock control countermeasures,weak cementation and on-site practice,effect is good.The main research results of this paper are as follows:(1)Through field investigation,the caving characteristics of the caving area of weakly consolidated roadway are obtained,and the reasons for roadway instability are clarified:Diagenesis time of Jurassic coal measure strata is short,cementation is poor,interlayer adhesion is weak,and fractures are well developed;Under the influence of weak aquifer and tunneling disturbance,the cementing ability between strata decreases with time.The section of the roadway is rectangular,which tends to lead to stress concentration of the roadway shoulder Angle.The tunnel span is large,and the roof structure is complex.In the roadway supported by bolting net and cable,the anchorage arch of surrounding rock is easy to be unstable as a whole,forming a loose roof outside the anchorage zone.(2)The mineral composition and microstructure were analyzed by XRD,SEM and rock cast thin sections.Mechanical parameters such as uniaxial compressive strength and tensile strength were determined by laboratory tests.The water-in-water disintegration and argillation characteristics of weakly consolidated rock were analyzed.The conventional triaxial test was carried out by using the MTS816 electro-hydraulic rock mechanics testing system,revealing the deformation and failure mechanism of weakly consolidated soft rock.The weakly consolidated soft rock presents obvious brittle failure.The peak strength,residual strength and elastic modulus of the rock increase with confining pressure,and poisson’s ratio decreases with confining pressure.(3)Based on conventional triaxial test results,a correction factor is introduced.Based on the Weibull distribution of the influence of mechanical damage on the strength of micro-element K of weakly consolidated soft rock,a constitutive model of mechanical damage of weakly consolidated soft rock is established,and its relationship is:(?)The stress-strain curves of rock samples with different confining pressures were calculated and compared with the experimental data to verify the accuracy of the damage constitutive model proposed in this paper.The relation between the parameter range of the constitutive model and the stress-strain curve is discussed.(4)The mechanical model of stress deformation of the composite roof was established,and the causes of separation instability were analyzed.The mechanical model of fracture development of roadway composite roof is constructed and the initiation Angle and critical stress of fracture development are deduced.The extended strain energy density factor was introduced to establish the criterion of fracture instability with crack crack Angle of 0.The mechanism of roof caving instability is clarified:the fracture is formed at the top Angle of roadway due to shear failure,and the fracture zone extends along the fracture Angle to the soft bedding surface which is easy to be separated and interconnects with it,leading to roof caving.(5)The numerical model is established,and explores the weak cementation and bedding,different sections of roadway surrounding rock plastic zone under the influence of single factor,stress field and displacement field evolution characteristics,reveals the weak cementation of soft rock tunnel surrounding rock deformation and failure law of dynamic response characteristics of the surrounding rock stability,provide important theoretical basis for the reasonable supporting technology.(6)Using the load test system both in all directions and through continuous increase load(excavation disturbance and mining influence),the regular supporting and supporting the two kinds of supporting conditions optimized simulation analysis,studied at various stages within the roadway surface displacement and stress change rule and the delamination crack evolution characteristics,won the support form change on the influence of the surrounding rock deformation of roadway damage evolution rule.Roadway roof instability.(7)Based on site investigation,combined with numerical simulation and physical simulation research,proposed the weak cementation roadway control countermeasures as follows:high strength and high pre-tightening force "inverted trapezoidal beam anchor net supporting structure for roadway cross section+cut straight wall arch section guniting coupling support forms,and determined by theoretical calculation,the length of anchor cable and anchor supporting density,determine its supporting parameters.The determined roadway support scheme is put into practice on site.The monitoring shows that there is no obvious deformation and no roof caving in the roadway,and the stability of surrounding rock of roadway roof is well controlled.Figure[109]table[14]references[161]... |
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