Instability Mechanism Of Weakly Cemented Roadway Surrounding Rock Under Force-Water Coupling

Weakly cemented strata are a type of special sedimentary sandstone strata widely distributed in the Jurassic and Cretaceous strata in the mining areas of western my country.The stratum has the characteristics of weak cementation,low strength,slushing and disintegration after encountering water,and sensitivity to disturbance,and its mechanical properties are extremely unstable.After excavation,the rock layer is easy to soften and swell under the action of the external water environment,and the rock quality deteriorates rapidly.Engineering disasters such as large roof fall,high slab,and severe bottom heave frequently occur.Therefore,revealing the mechanism of weakly cemented soft rock engineering disasters caused by water environment and excavation disturbances and proposing prevention and control measures have become urgent problems in energy development,geotechnical engineering construction and environmental governance in the western region.This thesis takes the weak cemented sandstone roof of No.3 coal in Chahasu Coal Mine as the research object,and uses rock mechanics test,theoretical analysis and numerical simulation to analyze the deformation and failure characteristics of weak cemented surrounding rock under different water content,as well as roadway failure and damage.The failure principle of the supporting structure provides a reference for the stability control of the surrounding rock of the weakly cemented soft rock roadway and the safe mining of coal.This subject has mainly achieved the following research results and progress:(1)Carry out mechanical tests such as conventional uniaxial compression under different water content,uniaxial compression under water environment,and triaxial compression under different confining pressures,and obtain the degradation and damage law of water content on weakly cemented rocks.The results show that the compressive strength,elastic modulus,triaxial strength,cohesion and internal friction angle of water-bearing weakly cemented sandstone all decrease with the increase of water content,and with the increase of water content,the failure mode of the sample gradually changes from Splitting failure transitions to shear failure,and the external water environment accelerates the damage and destruction of the rock.(2)Based on the PFC discrete element numerical simulation software,the effects of normal bond strength and tangential bond strength on peak strength and failure modes are respectively studied,and the correlation between microscopic parameters and macromechanical properties of weakly cemented sandstones under different water contents is revealed.The quantitative relationship between the water content and the peak strength of weakly cemented sandstone is established,and the water content threshold under different failure modes is defined.Based on the Lemaitre strain equivalence hypothesis and elastic damage mechanics,the segmental damage variable equations of weakly cemented sandstones with different water contents are derived.(3)Taking the 3-1 coal face roadway of Chahasu Coal Mine as the engineering background,the influence of water content on the stability of the roadway surrounding rock was studied by FLAC3 D simulation.The results showed that the roadway stress field and surrounding rock plasticity were increased with the increase of water content.The enlargement of the area has aggravated the deformation and destruction of the roadway.It also theoretically analyzes the failure mechanism of weak cemented roadway support structure under different water content,that is,under the long-term action of the external water environment,shear slip and fall of the anchoring agent-surrounding rock interface make it difficult for the anchor structure to perform effectively.effect.(4)According to the deformation and instability characteristics of weak cemented sandstone roadway surrounding rock under different water content,reasonable roadway surrounding rock stability control countermeasures are proposed,and reinforcement optimization support technology is proposed on the basis of the original support,and the optimized support technology Numerical simulation analysis was carried out on the supporting scheme of,and it was found that the active supporting scheme proposed in this thesis is more conducive to the control of the surrounding rock of the roadway,and it is feasible and effective.