采动覆岩导水裂隙主通道分布模型及其水流动特性

Distribution model of water-conducted fracture main channel and its flow characteristics

  • 摘要: 含水层受采动破坏后其赋存水体并非均匀地由覆岩各区域漏失至采空区,其在导水裂隙带范围内应存在水体流动的主要通道;研究揭示导水裂隙主通道的分布规律及其水流动特性对于科学指导井下涌水量预计、顶板水害防治、保水采煤等具有重要意义。基于导水裂隙类型划分及其渗流/管流力学分析,就采动漏失水体的流动主通道分布模型进行了研究。结果表明:开采边界外侧岩体受超前支承压力作用易产生峰后压剪裂隙,裂隙导水属非达西渗流流态;而由岩层破断回转运动产生的拉剪裂隙,由于裂隙导水雷诺数相对偏大,其导水流态一般属于管流范畴,且受岩层破断位置相对开采区域的不同,又可将其划分为采区边界附近的上端张拉裂隙和下端张拉裂隙、以及中部压实区的贴合裂隙这3种。据此利用Forcheimer公式和伯努利方程对比揭示了上述2类4种裂隙导水流动特性的差异。研究得出开采边界附近的上端张拉裂隙在进流口开度、导水流量、出口流速等特征参数上均领先于其他裂隙;且由于其出口水压较小,其水流还会受到两侧邻近的压剪裂隙和下端张拉裂隙出口水流的水平径流补给。因而,含水层采动漏失水体多由上端张拉裂隙导流而来。由此基于岩层控制的关键层理论,构建形成了以关键层在开采边界处的破断尺寸参数为依据的导水裂隙带主通道分布模型。

     

    Abstract: Due to the underground coal mining,the water in the mining-destroyed aquifer will unevenly flow to the working face through the mining failure rock mass. There will be the main channel of water flow in the wa-ter-conduc- ted fracture zone. In this circumstance,it is necessary to reveal the distribution law of water-conducted fracture main channel and its flow characteristics,which is helpful for water inflow prediction,roof flood control,and water preserve mining. Based on the type partition of water-conducted fracture and the mechanical analysis of seepage flow or pipe flow model,the distribution model of water-conducted fracture main channel was studied. The results show that it is easy to occur post-peak compression shear fracture in the rock mass area out of the mining boundary due to the pre- support pressure. The flow pattern is non-Darcy flow while water flows through the fracture. Besides,another fracture type occurs during the strata breaking movement which is named as shear fracture. Due to the larger value of Reynolds number,the flow pattern belongs to pipe flow. Affected by the broken position against the mining area,the shear frac- ture can be divided into three types,which are upper stretch-draw fracture,lower stretch-draw fracture,and close frac- ture. According to the Forcheimer formula and Bernoulli equation,the difference of the four kinds of two types fracture was revealed. It can be concluded that the value of the characteristic parameters of upper stretch-draw fracture is the largest in terms of open degree of fracture inlet,water flowrate,and flow velocity in the fracture exit. In addition,the water flow from the nearby compression shear fracture and lower stretch-draw fracture can supply to the upper stretch- draw fracture due to its low hydraulic pressure in the fracture exit. Take the above analysis for consideration,the min- ing-lost water from the aquifer mostly flows through the upper stretch-draw fracture. Finally,the distribution model of water-conducted fracture main channel was built in the light of the breaking size of key strata (KS). The studies pro- vide a theoretical basis to the implementation of artificial control on the water flow in the main channel of water-con- ducted fractures.

     

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