高应力和高渗压下粗糙单裂隙非线性渗透行为试验研究

Experimental study on nonlinear flow behavior of rough single fracture under high geostress and high seepage pressure

为研究高地应力和高渗压下深部裂隙岩石的渗透演化特征,文章采用RockTop-50HT全应力多场耦合三轴试验系统,开展一系列高围压和高渗压作用下不同粗糙度系数(JRC)单裂隙砂岩渗透试验。基于试验获得不同水力梯度下单裂隙砂岩的非线性渗透特性以及其表征方法;建立Forchheimer方程中参数A、B与JRC之间的定量关系;探究不同JRC单裂隙砂岩非线性渗流过程中雷诺数Re、非达西渗流因子E和表观透过率Ta等渗透参数的演化规律。结果表明:①随着水力梯度逐渐增大,单裂隙砂岩的渗流量呈现出明显的非线性渗流特性;随着JRC值增大,单裂隙砂岩的非线性渗流特征逐渐增强;②高围压和高渗压作用下裂隙的非线性渗流成因机制为渗透失稳和固液界面效应。采用Forchheimer方程定量分析时其非达西惯性系数为负值,表征单裂隙的渗流成因机制为渗透失稳;采用Izbash方程定量分析时发现单裂隙砂岩的非线性渗流特征是由显著的固液界面效应导致;③随着水力梯度增加,雷诺数Re呈非线性增大;非达西渗流因子E为负值且呈非线性降低变化;表观透过率Ta呈现出先振荡,后平稳发展,再迅速增大的发展趋势。研究成果对高地应力和高渗压下的深部裂隙岩体非线性渗流规律、稳定性分析和防灾减灾工程认识具有较重要的意义。

To study the seepage evolution characteristics of deep fractured rock under high geostress and high seepage pressure,a series of seepage tests on single fractured sandstone with different roughness coefficients(JRC)under high confining pressure and high seepage pressure were carried out by using Rock Top-50HT full-stress multi-field coupling triaxial test system.Based on the experiment,the nonlinear seepage characteristics and the characterization method of single fractured sandstone under different hydraulic gradients were obtained.The quantitative relationship between parameters A,B and JRC in Forchheimer equation was established.The evolution of seepage parameters,such as Reynolds number Re,non-Darcy seepage factor E and apparent transmittance Ta,of single fractured sandstone with different JRC in the nonlinear seepage process,were investigated.The results show that:(1)With the increase of hydraulic gradient,the flow of single fractured sandstone presents obvious nonlinear flow characteristics.With the increase of the JRC value,the nonlinear flow characteristics of single fractured sandstone gradually increase.(2)The nonlinear seepage causal mechanism of fracture under high confining pressure and high seepage pressure is seepage instability and solid-liquid interface effect.When the Forchheimer formula is used for quantitative analysis,its non-Darcy inertia coefficient is negative,indicating that the seepage mechanism of single fracture is seepage instability.When the Izbash formula is used for quantitative analysis,it is found that the nonlinear seepage characteristics of single fractured sandstone are caused by the significant solid-liquid interface effect.(3)With the increase of hydraulic gradient,Reynolds number Re increases nonlinearly,the non-Darcy flow factor E is negative and decreases nonlinearly.The apparent transmittance Ta presents a trend of first oscillation,then steady development,and final rapid increase.The research results are of great significance to understanding of nonlinear flow law,stability analysis and disaster prevention of deep fractured rock mass under high geostress and high seepage pressure.