水沙混合物裂隙渗流特性分析

水沙在裂隙或破碎岩石中的渗透特性具有复杂性,研究水沙裂隙渗流特性对于揭示突水溃沙机理具有重要意义。利用自制的水沙裂隙渗流试验仪器,通过改变沙粒径、浓度等因素进行水沙渗透试验,获得水沙在裂隙中流动的滞后性特征。通过水沙裂隙渗流试验,得到了岩石裂隙中水沙渗流速度-压力梯度滞环曲线,分析了滞环曲线的特征,简单解释了滞后现象的原因。得到其渗透压力梯度与渗流速度在一个循环周期内形成了一条封闭滞后曲线,根据曲线的是否有交叉和往返曲线的距离分为4种变化类型;随沙粒径和沙浓度增大,曲线由Ⅰ型向Ⅳ型转化。滞后性指标用最大滞后量G_p和滞环面积S描述,随沙粒径和浓度增大,这两者均呈增大趋势,但增幅并不同步。进一步,利用ANSYS Fluent软件进行水沙裂隙渗流场的数值模拟,获得了在不同因素影响下渗流场的变化规律。数值模拟结果表明,粗糙裂隙流场物理量随时间波动;粗糙裂隙中水沙流动受壁面约束作用,表现出流场物理量空间分布的随机性。模拟结果显示裂隙中水沙渗流场不稳定,渗流场的压力损失与沙粒径呈反向变化。裂隙横截面上水沙流体时均速度和湍动能分布受沙粒径和沙体积浓度影响很大,表现为极值点的位置偏移。此研究可以为进一步研究浅埋煤层突水提供参考。

Analysis of water and sand seepage characteristics in fracture

The permeability characteristics of water-sand in cracks or broken rocks are complex.The study on the seepage characteristics of water-sand cracks is of great significance to reveal the mechanism of water inrush and sand rupture.Using a self-made instrument for water-sand fissure seepage test,the water-sand seepage test was carried out by changing sand particle size,concentration and other factors,and the hysteresis characteristics of water-sand flow in the fissure were obtained.Also,the hysteresis curve of velocity-pressure gradient of water and sand seepage in fractured rock was obtained from the test.A closed hysteresis curve of the seepage pressure gradient and the seepage velocity is formed in one cycle.With the increase of sand particle size and concentration,the curve changes from type I to type IV.The hysteresis parameters are described by the maximum hysteresis Gp and the hysteresis area S,both of which show an increasing trend with the increase of sand particle size and concentration,but the increase is not synchronous.Furthermore,the numerical simulation of water-sand fracture seepage field was carried out by using ANSYS Fluent software,and the variation rules of seepage field under the influence of different factors were obtained.Numerical simulation results show that the physical quantity of rough fracture flow field fluctuates with time.The flow of water and sand in rough cracks is restricted by the wall surface,which shows the randomness of the physical distribution of flow field.The simulation results show that the seepage field of water and sand is unstable,and the pressure loss of seepage field is inversely related to the particle size of sand.The average velocity and turbulent kinetic energy distribution of water-sand fluid on the fracture cross-section are greatly affected by the particle size and the concentration of the volume of sand.This study can provide a reference for further study of water inrush from shallow coal seam.