短路径“疏干-回灌”水循环数值模拟及回灌研究
Numerical simulation of short-path “drainage-recharge” watercycle and recharge study
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摘要: 为保持露天煤矿区域地下水系统平衡,避免由疏干造成的水资源破坏及不良环境影响产生,缓解露天煤矿疏干和排水之间的矛盾,尝试在降落漏斗范围内同层回灌露天煤矿疏干水。在保障采矿安全的前提下,通过短路径“疏干-回灌”地下水循环,实现疏干水零排放。以水均衡为理论基础,依据短路径地下水循环疏干理论,以露天煤矿为研究对象,采用FEFLOW地下水数值模拟软件,构建疏干-回灌协同开采地质模型,对露天煤矿疏干和回灌同时运行条件下的地下水流进行模拟。分析疏干井和回灌井的井数、井距、流量与疏干效果的关系。对比分析降水孔疏干法和短路径地下水循环疏干法的疏干效果,验证短路径地下水循环疏干法。通过数学模型得出回灌完全补给疏干时,形成短路径地下水循环。给出疏干与回灌同步、疏干流量稳定、回灌量尽量接近疏干量、回灌井与疏干井距离短4个关键问题。模拟计算出形成短路径地下水循环的回灌井布设数量与疏干井为1∶1;回灌井距降水中心的最优距离段是2 000~3 000 m,并且距离越大疏干流量降幅越大,距离越短达到最大回灌流量的时间越短。突破地下水同层回灌以疏干降落漏斗为界限的限制条件,定义短路径地下水循环疏干;提出临时利用含水空间和水在含水层中循环的时间,换取采煤工作区安全开采的疏干思路,得出短路径地下水循环疏干理论。研究以露天煤矿地下水实现疏干目标为前提,模拟短路径“疏干-回灌”水循环疏干过程。得出单环型等距布设回灌井时,回灌与疏干井数相等;循环较好的回灌井与降水中心距离段;通过分析疏干流量、回灌流量、回灌井距离降水中心距离和疏干时间之间的关系,推算出距离降水中心最近的回灌井布设距离计算公式,并给出了该方法用于露天煤矿疏干排水的应用步骤。结合某矿疏干实例,在达到与降水孔疏干法相同的疏干效果时,短路径地下水循环疏干还具有保持疏干系统流量稳定、使疏干设备高效能稳定效率工作等优势,并可通过调整回灌井布设位置和调节回灌井井内水位,控制区域降落漏斗的范围和形态。通过实例模拟计算对比2种疏干方法,短路径“疏干-回灌”水循环使疏干井日出水量稳定在最大出水能力的82.5%以上,降低了疏干水外排量33%~98%。Abstract: In order to maintain the balance of the groundwater system in open-pit coal mines,avoid water resource destruction or adverse environmental impacts caused by drainage and alleviate the contradiction between dewatering and drainage,the method to recharge the water in open-pit coal mines at the same layer within depression cone is discussed.Under the premise of guaranteeing mine safety,the zero discharge of drained water can be achieved through a short-path “drain-recharge” groundwater circulation.Based on the theoretical analysis of water balance,according to the theory of short-path groundwater circulation drainage,this study constructs a drainage-recharge coordinated-mining geological model to simulate groundwater flow under the conditions of draining and recharging through the FEFLOW groundwater numerical simulation software.It analyzes the relationship among the numbers,well space,flow rate and drainage effect of drain wells and recharge wells,and comparatively analyzes the drainage effect of the precipitation hole drainage method and the short-path groundwater circulation drainage method to verify the short-path groundwater circulation drainage method.Using mathematical model,it shows that when the recharge well is completely complementary to the drain well,a short-path groundwater circulation is formed.The paper presents four key issues:the synchronization of draining and recharging,stable draining flow,recharging volume as close as possible to draining volume,and short distance between recharging wells and drain wells,then the simulation calculates that the number of recharge wells that form a short-path groundwater circulation is 1∶1 with the number of drain wells,and that the optimal distance between the recharge wells and the precipitation center is 2 000-3 000 m.The greater the distance,the greater the drain flow drops;the shorter the distance,the shorter the time to reach the maximum recharge flow rate.The limitation that the groundwater recharge in the same layer must be within the depression cone is broken through and the short-path groundwater circulation drainage theory is defined.It proposes an idea that the water-bearing space and the time for water to circulate in the aquifer can be temporarily used in exchange for a safety mining in coal mines,and develops the theory of short-path groundwater circulation drainage.Based on the premise that the groundwater in open-pit coal mines is drained,the study simulates the short-path “drain-recharge” water draining process.It is concluded that when recharge wells are arranged equidistantly in a single ring,the number of recharge wells is equal to the number of drain wells;the distance between recharge wells with better circulation and the dewatering center is given;and by analyzing the relationship among drain flow,recharge flow,the distance between recharge wells and dewatering center,the draining time the formula for the distance of recharge wells closest to the dewatering center is calculated,and the application steps of the drainage method in open-pit coal mines are given.Taking a mine drainage as an example,the result shows that when achieving the same drainage effect as the precipitation hole drainage method,the short-path groundwater circulation drainage method also has many advantages such as keeping the flow of the drainage system stable,making the drainage equipment efficient,and by adjusting location and water level of the recharge wells,it can control the scope and shape of the depression cone.Comparing the two drainage methods through simulations,the short-path “drainage-recharge” method stabilizes the water output of draining wells at 82.5% or more of the maximum water output capacity,and reduces the drainage volume by 33%-98%.