Sensitivity analysis of factors affecting the phreatic water level recovery time caused by underground coal mining in wind-blown sand area
The phreatic micro-leakage caused by underground coal mining is prone to induce va-rying degrees of the phreatic level recovery in the wind-blown sand beach area of northwest,China.The sensitivity of factors affecting the recovery time is of great significance for the eco-geological environment protection of the mining area.Therefore,combined with the well flow model,a prediction model for the recovery time of phreatic water level under phreatic micro-leakage after coal mining was established.The factors influencing the recovery time of phreatic water level were analyzed.By combining the orthogonal experimental method,the evolution law of phreatic leakage during coal seam mining and post mining recovery process was simula-ted,and the time required for the post mining phreatic water level to 30％,50％,80％of the pre-mining phreatic water level buried depth was estimated.Furthermore,the sensitive factors influencing the recovery time of phreatic water level were determined using range analysis and matrix analysis.The results show that the main influencing factors for phreatic water recovery have been determined from the perspectives of stratigraphic structure,hydrogeologic and min-ing condition like bedrock thickness Tb,laterite thickness Tc,loess thickness T1,the buried depth of phreatic water level b,aquifer thickness Ta,aquifer permeability coefficient K,and coal seam mining thickness Tco.Under the condition of phreatic micro-leakage,the overall phreatic water leakage during the post mining recovery process shows a decreasing trend.In the initial stage of post-mining recovery,the leakage rate decreases rapidly,and after one to two months,the decline rate decreases and stabilizes to almost no leakage.When the phreatic water level is restored to 30％of the pre-mining phreatic water level buried depth,the sensitiv-ity order of each factor is Ta＞K＞Tc＞b＞T1＞Tb＞Tco.When the phreatic water level is re-stored to 50％and 80％of the pre-mining phreatic water level buried depth,the sensitivity or-der of each factor is Ta＞K＞b＞T1＞Tc＞Tb＞Tco.The two most sensitive influencing fac-tors are Ta and K,and the sensitivity of Tc is relatively large when the degree of phreatic wa-ter level recovery is less,and the sensitivity of b is relatively large when the degree of phreatic water level recovery exceeds 50％.The sensitivity of Tco and Tb is relatively small.The greater the permeability coefficient and thickness of the pre-mining phreatic water aquifer,the shorter the time required for the recovery of the phreatic water level.
orthogonal testcoal seam miningphreatic water level recovery timeinfluencing factorssensitivity
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