Study On Damage Degradation And Engineering Stability Analysis Of Weakly Cemented Soft Rock Under Hydro-Mechanical Coupling

With the development of the western region,the main coal producing areas in China have been gradually transferred from the east to the vast western regions such as Inner Mongolia,Shaanxi,Xinjiang,etc.Weakly cemented soft rock stratum widely exists in the western mining area of China.It has formed its unique engineering properties and mechanical properties under the action of special geographical and climatic environment,sedimentary process and geological conditions.In the natural state,the structure is relatively compact and complete.But it is easy to expand and dissolve when encountering water,and the mechanical properties are unstable.After the excavation of the rock stratum,the disturbance range is large and the deformation speed is fast.Under the action of water environment,the rock quality is rapidly deteriorated,resulting in the frequent occurrence of engineering accidents,which brings huge losses to the green mining of coal resources and engineering construction in western China.Therefore,revealing the mechanism of disasters in weakly cemented soft rock caused by water environment and excavation disturbances,proposing prevention and control measures have become urgent problems in energy development,geotechnical engineering construction and environmental governance in the western region.In this paper,according to the characteristics of excavation disaster of weakly cemented soft rock under the action of water environment,the deformation and failure characteristics of weakly cemented soft rock under the influence of water content and stress path are analyzed by means of indoor experiment,theoretical analysis and numerical simulation.The coupled damage constitutive equation of hydro-mechanical is constructed,and the evolution equation of surrounding rock stress and plastic zone of soft rock roadway under the action of water environment is deduced.Finally,the deformation and failure characteristics of the roadway are analyzed to provide guarantee for the stability control and safe mining of the weakly cemented soft rock roadway.The main work and conclusions are as follows:(1)Combined with acoustic emission and digital speckle,the uniaxial compression and splitting tests of weakly cemented soft rock with different water content were carried out.The damage characteristics of soft rock under the influence of different water content were obtained,and the influence of water content on the mechanical properties of weakly cemented soft rock was analyzed.The increase of water content intensifies the failure degree of micro fabric in soft rock,which leads to the deterioration of rock mechanical parameters,the failure mode of rock changes from brittleness to ductility.(2)Aiming at the unloading process of coal mine roadway excavation under the influence of water environment,triaxial compression tests of weakly cemented soft rocks with different water contents under complex stress paths were carried out.The fracture mechanism of weakly cemented soft rock under the coupling of hydro-mechanical was analyzed.The unloading path reduces the mechanical properties of rock,intensifies the post peak dilatancy deformation,and improves the critical value of confining pressure of rock specimen shear failure.(3)Based on the statistical damage theory,the statistical damage constitutive relation of weakly cemented soft rock was established.The model parameters were identified by the mechanical tests of weakly cemented soft rock with different water content.The hydro-mechanical coupled damage constitutive equation of weakly cemented rock mass was established.On this basis,the meso and macro mechanical properties of rock under different water-rock damage degree were studied by RFPA software.The results show that the hydro-mechanical coupled damage constitutive equation can better reflect the stress-strain state in the process of rock failure under the action of water-rock damage,and the RFPA simulation results can well reveal the macro strength deformation characteristics of rock under the water-rock damage from the meso point of view.(4)Based on the theory of humidity expansion stress field and elastoplasticity,the analytical solution of mechanical response of weakly cemented soft rock roadway under the action of water environment was derived,and the evolution law of stress field was analyzed.Combined with FLAC3D numerical simulation,the influence of stress release rate,formation water content and humidity stress field on the stability of surrounding rock was studied.The results show that the range of stress field and plastic zone of surrounding rock increases due to the diffusion of humidity,and the increase of stress release rate and formation water content will reduce the stability of roadway.