Deformation response of roof in solid backfilling coal mining based on viscoelastic properties of waste gangue

Solid backfill mining(SBM)is a form of green mining,the core of which is to control and minimize the deformation and movement of strata above longwall coal mines.Establishing a mechanical model that can reliably describe roof deformation by considering the viscoelastic properties of waste gangue is important as it assists in improving mine designs and reducing the environmental impact on the surface.In this paper,the time-dependent deformation characteristics of gangue under different stress levels were obtained by using lateral confinement compression,that reliably represents the compaction of goaf.The viscoelastic foundation model for gangue mechanical response is different from the traditionally used elastic foundation model,as it considers the time factor and viscoelasticity.A mechanical model using a thin plate on a fractional viscoelastic foundation was established,and the roof deflection,bending moment,time-dependent,viscous and other characteristics of SBM were included and analyzed.Compared with the existing elastic foundation model,the proposed fractional order viscoelastic foundation model has higher accuracy with laboratory data.The plate deflection increases by 50.9%and the bending moment increases by 37.9%after 100 days,which the elastic model would not have been able to predict.

A state‑of‑the‑art review on rock seepage mechanism of water inrush disaster in coal mines

Water inrush is one of the most dangerous disasters in coal mining.Due to the large-scale mining and complicated hydrogeological conditions,thousands of deaths and huge economic losses have been caused by water inrush disasters in China.There are two main factors determining the occurrence of water inrush:water source and water-conducting pathway.Research on the formation mechanism of the water-conducting pathway is the main direction to prevent and control the water inrush,and the seepage mechanism of rock mass during the formation of the water-conducting pathway is the key for the research on the water inrush mechanism.This paper provides a state-of-the-art review of seepage mechanisms during water inrush from three aspects,i.e.,mechanisms of stress-seepage coupling,fow regime transformation and rock erosion.Through numerical methods and experimental analysis,the evolution law of stress and seepage felds in the process of water inrush is fully studied;the fuid movement characteristics under diferent fow regimes are clearly summarized;the law of particle initiation and migration in the process of water inrush is explored,and the efect of rock erosion on hydraulic and mechanical properties of the rock media is also studied.Finally,some limitations of current research are analyzed,and the suggestions for future research on water inrush are proposed in this review.

A Numerical Gas Fracturing Model of Coupled Thermal,Flowing and Mechanical Effects

Gas fracturing,which overcomes the limitation of hydraulic fracturing,is a potential alternative technology for the development of unconventional gas and oil resources.However,the mechanical principle of gas fracturing has not been learned comprehensively when the fluid is injected into the borehole.In this paper,a damage-based model of coupled thermal-flowing-mechanical effects was adopted to illustrate the mechanical principle of gas fracturing.Numerical simulation tools Comsol Multiphysics and Matlab were integrated to simulate the coupled process during the gas fracturing.Besides,the damage evolution of drilling areas under several conditions was fully analyzed.Simulation results indicate that the maximum tensile stress,which occurs in the upper and lower of the injection hole,decreases with the increase of the tectonic stress coefficient(TSC).As the TSC increases,shear fractures increase,a crushed area is gradually formed and the seepage area increases rapidly.The influence of TSC on fracture expansion is concluded as follows:with the decrease of TSC,the relative width of fractures decreases whilst the depth increases.It indicates that thermal stress and pore pressure promote the expansion of tensile fractures but restrain the expansion of shear fractures.Therefore,a relatively lower injection gas pressure is required to obtain the same degree of fracturing with a coupled thermal gradient.

Mechanical and hydraulic properties of fault rocks under multi‑stage cyclic loading and unloading

The rock mass in fault zones is frequently subjected to cyclic loading and unloading during deep resource exploitation and tunnel excavation.Research on the mechanical and hydraulic characteristics of fault rock during the cyclic loading and unloading is of great signifcance for revealing the formation mechanism of water-conducting pathways in fault and preventing water inrush disasters.In this study,the mechanical and seepage tests of fault rock under the multi-stage cyclic loading and unloading of axial compression were carried out by using the fuid–solid coupling triaxial experimental device.The hysteresis loop of the stress–strain curve,peak strain rate,secant Young's modulus,and permeability of fault rock were obtained,and the evolution law of the dissipated energy of fault rock with the cyclic number of load and unloading was discussed.The experimental results show that with an increase in the cyclic number of loading and unloading,several changes occur.The hysteresis loop of the stress–strain curve of the fault rock shifts towards higher levels of strain.Additionally,both the peak strain rate and the secant Young's modulus of the fault rock increase,resulting in an increase in the secant Young's modulus of the fault rock mass.However,the growth rate of the secant Young's modulus gradually slows down with the increase of cyclic number of loading and unloading.The permeability evolution of fault rock under the multi-stage cyclic loading and unloading of axial compression can be divided into three stages:steady increase stage,cyclic decrease stage,and rapid increase stage.Besides,the calculation model of dissipated energy of fault rock considering the efective stress was established.The calculation results show that the relationship between the dissipated energy of fault rock and the cyclic number of loading and unloading conforms to an exponential function.

Deformation and Failure Analysis of River Levee Induced by Coal Mining and Its Influence Factor

To study the influence of coal mining on the stability of river levees,a mechanical model of mining-induced river levee deformation was established.This was based on the mining-induced deformation characteristics of river levees and the application of a typical surface subsidence function.Meanwhile,a failure criterion was proposed for river levees.Using some examples,the deformation of,and stress distribution through,river levees under the influence of mining were obtained:the maximum tensile stress on the bottom of the river levee was less than the tensile strength,under which circumstance the river levee remained undamaged.Meanwhile,this research analyzed the influence of three factors including the maximum surface subsidence wmax,half-length of surface subsidence basin L,and foundation coefficient k on the stability of river levees.Results showed that reducing the mining height of the working face and the foundation co-efficient,and increasing the strike length of the working face could reduce the influence of mining on river levees.These results provided a theoretical basis for predicting the mining-induced deformation and failure of river levees.

深部充填开采岩层控制理论与方法研究进展

我国深部煤炭资源丰富,煤炭开发已逐步向深部转移,深部灾害防控和矸石等矿山固废排放问题日趋严峻。充填开采是实现灾变调控、地表沉陷控制和矿山固废处置的重要手段,已在我国煤矿绿色开采、矿压控制与岩层移动等领域广泛应用。然而,相对浅部,深部“三高一扰动”条件下充填开采岩层控制更为复杂,因此,构建深部绿色充填开采岩层控制理论与方法体系,对于深部煤炭资源安全高效开采具有重要意义。本文在系统分析深部充填开采岩层控制面临挑战基础上,提出了深部充填开采关键科学问题、研究目标与总体思路,并从多场耦合作用下充填体-围岩交互作用机理、强扰动条件下充填采场矿压分析模型、深部充填开采岩层控制方法、充填体与地下水环境互相影响四个方面阐述了相关研究进展。