| Grout into overburden of isolated longwall panels(GOILP)is a surface subsidence control technology that is applied in coal mining areas to protect surface buildings.In response to the expansion effect of high-pressure injection,the mining-induced voids in the gob are compacted gradually;with such compaction,a compaction area forms.The conjunction support system of the compaction area and coal pillars is the mechanism by which GOILP reduces surface subsidence.Therefore,forming compaction area in the gob is the key to apply GOILP.However,there is a lack of a systematic research of the scientific problems associated with the formation mechanism of compaction area.For example,the mechanical model about formation of compaction area under grouting pressure,the dynamic evolutionary process of compacting area along with the advance of panel,the effects of geological and grouting factors on compacting area.With all this in mind,this dissertation adopted a comprehensive methodology that incorporates theoretical analysis,field trials,physical modelling and numerical simulation to reveal the formation mechanism of compaction area.The main research findings and conclusions are as follows:The mechanical model about formation of compaction area under grouting pressure was established.Based on mechanical model,the formula of subsidiary stress in the gob propagated from grouting pressure was given.Furthermore,the formulas of compression and compression ratio of fractured rock mass,stress and the width of compaction area in the gob were derivated.The mechanical model theoretically proves that compaction area can form in the gob,and the mechanism of GOILP reducing surface subsidence is true.The efficiencies of the model have been tested against the experiments and the field trials.The grouting pressure can be divided into 4 stages.Based on this characteristic the dynamic evolutionary process of compacting area along with the advance of panel was revealed;which establishes a foundation for the design of match scheme of injection-production ratio at different advance distance.The grouting pressure was divided into zero-pressure/ decrease-pressure stage,increase-pressure stage,stability-pressure stage and over-pressure stage.Then the dynamic evolutionary process of compacting area in different stage was revealed;which indicates that in the increase-pressure stage grouting pressure starts to compress fractured rock mass in the gob;in the stability-pressure stage the compression ratio of fractured rock mass in the gob increase along with the advance of panel and compaction area forms;in the over-pressure stage,the compression ratio of fractured rock mass and the width of compaction area can further increase.The effects of geological and mining parameters,grouting parameters on compacting area were revealed;based on which,the suggestions about design of GOILP were given.The increase of grouting pressure and panel width is conducive to the formation of compaction area while the increase of mining height,thickness and elasticity modulus of isolated layers goes against the formation of compaction area,.Besides,the effects of cover depth of coal,caving-mining ratio and uniaxial compressive strength of rock mass in caving zone on the formation of compaction area are small.Based on the effect of panel width on compacting area,the computational formula of minimum panel width conducive to the formation of compaction area is given.Based on above research results,field study of the technique of GOILP was carried out in Panel 7223 of Yuandian 2# coal mine operated by the Huaibei Mining Group Co.,Ltd.Firstly,the complexion of gob compaction was predicted by mechanical model,and the result shows that compaction area can form in the gob.Afterwards,the match scheme of injection-production ratio at different advance distance was given based on the dynamic evolutionary process of compacting area.GOILP was successfully operated according to the match scheme,no damage occurred to the surface structures. |
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