| A certain amount of coal resources are left in the goaf by mechanized caving mining.The development of pores and fissures in the broken coal body left in the goaf has an important influence on the mobility of groundwater.Therefore,it is of great significance to study the coupling characteristics of creep and seepage of broken coal for safe and efficient mining.In the process of compressive creep of broken coal,the parameters such as strain,porosity,permeability and non-Darcy factor all have typical time-varying characteristics.Based on the combination of numerical simulation,laboratory test and theoretical analysis,the creep seepage characteristics of broken coal are systematically studied,and the following main research results are obtained.(1)The compression and creep tests of saturated and broken coal were carried out,and the changes of the strain and porosity of the broken coal with time under different loads(4 MPa,8 MPa,12 MPa)were obtained.Based on the strain-time change curve and the Kelvin-Volgt model,the correlation coefficients are analyzed.Based on the porosity-time change curve and the attenuation index model,the deformation characteristics are analyzed.The sample after compression creep is sieved to obtain the law of particle size change of broken coal.(2)A creep seepage test device for broken coal was designed to study the changes in permeability and non-Darcy factors of single-size and continuous-graded broken coal with time and axial pressure and hydraulic gradient under creep conditions.The nonlinear relationship with the flow rate,combined with existing theoretical formulas,analyzes the effect of porosity on permeability and non-Darcy factors.(3)Establish the numerical calculation model of creep seepage,and insert the fitted creep equation into the calculation model.The pore water pressure is used as the coupling term to realize the coupling between the seepage module and the solid mechanics module.The distribution characteristics of the broken coal sample under the influence of axial pressure and osmotic pressure for a long time,such as stress,strain and permeability characteristics of the sample,and their changes with time are analyzed.(4)On the basis of physical experiments and numerical simulation,combined with creep constitutive principle and fluid-solid coupling dynamics theory,a creep-seepage coupling model was established to explore the relationship between theporosity of the solid matrix of broken coal body and the osmotic pressure,The equilibrium equation of the seepage system of the broken coal in the steady state of creep is obtained.Combined with the numerical simulation calculation results,the validity of the theoretical model is verified.There are 59 figures,8 tables and 104 references. |
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