| The protection of water resources during the large-scale and high-production underground mining in Xinjiang with fragile ecological environment is currently becoming a very critical and urgent technical issue to be resolved.The application of water-preserving mining method is not only closely relevant to the achievement of advantageous resource transition but also the development of the regional social-economics in Xinjiang.The widely distributed weakly cemented overlying strata around the coal seams featured by the ultra-thickness results in the difficulty of using water-preserving technology.This Ph D thesis therefore starts with the investigation on the mechanical response of weakly cemented rock to either the stress or the moisture content based on the typical geological condition of Ili mining area,followed by the analysis on the deformation characteristics of the "Aquiclude-Barrier layer-Basic roof”(i.e.ABB)" and the establishment of the theoretical model to evaluate the stability of aquiclude.Then,the damage characteristics of aquiclude as well as the equivalent mining thickness were investigated.In the end of the thesis,the adaptive classification system for water-preserved mining in ultra-thick coal seams surrounded by weakly cemented strata were proposed based on these observations obtained from theoretical analysis,laboratory tests,numerical simulation as well as the field tests.The main findings presented in this thesis are listed in below for reference:(1)Revealing the different influences of stress condition and moisture content on the mechanical behavior of weakly cemented rock.The systematic tri-axial tests have been carried out to obtain the axial stress-axial strain behavior of typical rock samples(e.g.mudstone,sandstone,and sandy mudstone)with different moisture contents and confining pressures.Two sensitivity coefficient factors were proposed to evaluate the effects of confining pressure and moisture contents,respectively.It has been found that the stress response of weakly cemented rock mainly depends on the cementation state and the porosity,when the mineral components and the microstructures of these rock samples were compared.If the cementation state was very similar and the porosity was relatively low,the effect of the grain size would be obvious.For saturated rock samples,the mechanics response was sensitive to the type and content of the hydrophilic minerals.Whereas,it would be determined by the porosity of the rock,if there were only small content of hydrophilic minerals.(2)Developing a quantitative characterization method for the stability of aquiclude affected by mining based on the rock damage and deformation.The relationship between the stress-strain behavior and acoustic emission characteristics of rock samples during the test was set-up firstly,followed by the numerical modelling to parametrically investigate the type and distribution characteristics of micro fractures as well as the decreasing of strength.On the basis of these research,the comprehensive prediction method covering the density and penetration of micro-fractures of weakly cemented overlying strata was developed,achieving the quantitative characterization of the development and bridging of fractures and the stability of aquiclude.(3)Proposing a concept of equivalent mining thickness based on the deformation of aquiclude.Based on the geological condition of the weakly cemented overlying strata around the ultra-thick coal seams in Northern Ili mining area,the breakage of the “lower basic roof”,the movement of the “middle barrier layer” and well as the “overlying aquiclude” were investigated.Both the theoretical model and deformation criterion to evaluate the stability of the "overlying aquiclude" have been established.Moreover,the theoretical equation for the calculation of the equivalent mining thickness has been determined,in which the effect of the expansion due to the unloading of the “middle barrier layer” was accounted for.(4)Establishing the classification method and standard accounting for the geological conditions and mining methods for water-preserving mining in Ili mining area.There are two meaningful indicators being adopted to establish the geological classification for water-preserving mining.One is the parameter of Dm defined as the damage caused by mining activities,and the other one is its critical value(Dmin=0.12 and Dmax=0.20).According to the characteristics of stratum structure and sensitivity analysis of main control factors,the feasibility of the application water-preserving mining method was determined,which has been also verified by the field tests conducted in Northern Ili mining area.There are 101 pictures,23 tables and 189 references in this thesis. |
PDF Full Text Request