岩石粗糙裂隙非线性渗流特性试验研究

Laboratory Research on Nonlinear Flow Behavior of Rough Fractures

通过开展岩石单裂隙不同粗糙起伏、水力梯度及法向荷载作用下的非线性渗流特性室内试验,研究了裂隙非线性渗流特征与发生机制,建立了考虑裂隙几何形貌的临界雷诺数Rec模型。研究结果表明:随着裂隙试样两端的水力梯度逐渐增大,裂隙内水流流态从线性流向非线性流转变,过流流量(Q)与水力梯度(#P)的实测数据可以很好地用Forchheimer方程拟合;随着法向荷载的增大,Forchheimer方程线性项系数A增加了2~4个数量级,非线性项系数B增加了3~5个数量级;在建立的以水力开度eh为基本变量的非线性系数B参数化表达式基础上,首次提出了定量表征裂隙非线性渗流发生条件的临界雷诺数Rec模型。

This study experimentally investigated the nonlinear flow characteristics through rough-walled fractures subjected to a wide range of confining pressures. A large number of high-precision water flow tests were performed in the triaxial cell on mated axially-orientated fracture samples. The nonlinear fluid flow behaviours were examined and the causes that trigger the flow nonlinearity were elucidated. It is indicated that flow behaviours in the rough fractures become nonlinear as the hydraulic gradient increasing,and the measured pressure gradient（ #P） and volumetric flow rate（ Q） data points are fitted very well by the Forchheimer equation. Both the linear and nonlinear coefficients A and B in the Forchheimer＇s law experience a drastic increase in 2 ～ 4 and 3 ～ 5 orders of magnitude,respectively. For the first time,an empirical relationship between the nonlinear coefficient B and the hydraulic aperture ehunder varying confining pressure is developed based on the laboratory observations. A critical Reynolds number model was then proposed to quantify the onset of nonlinear flow through rough-walled fractures.