In response to the hazard problems such as collapse impact and surface subsidence caused by the composite goaf during shallow hole shrinkage mining in a certain mine,a combination of theoretical analysis and numerical simulation was used to study the mechanism of overlying strata caving and the treatment method of goaf.Through mechanical analysis of rock mass ultimate caving span,it is calculated that the ultimate caving span of the goaf roof is 46.4 meters,which is smaller than the length of the goaf,indicating a risk of caving in the goaf.The results of RFPA2D numerical simulation show that the size of exposed space in goaf,the existence of dominant joint group and stress balance arch under the influence of mining stress are the main influencing factors that lead to the rapid-slow caving mechanism of overlying strata.For the mining of ore bodies under the condition of composite goaf,the remaining top pillars can't effectively support the goaf.Therefore,a composite goaf treatment method of caving middle stage top pillars in sequence and surface collaborative filling was proposed.This method can eliminate the hazards of the goaf and effectively recover 40％ore of the top pillars,generating an economic benefit of 13.5 million yuan.The research can provide a reference for the treatment of composite goaf in mines.
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