Laboratory Simulation Of Flow Research Articles

Laboratory Simulation of Flow through Rough-Walled Microfractures under High Hydraulic Gradient

Laboratory experiments on fluid flow through fracture are important in solving the fluid-in-rush problems that happen during the tunnel excavation. In order to study the mechanism of fluid flow through a rough-walled microfracture, fluid flow experiments were carried out and the fiber Bragg grating (FBG) strain sensors were applied to monitor the deformation of the microfracture surface during the seepage process. Considering the difficulty of collection of undisturbed rock samples from the deep locations, a methodology to simulate fluid flow through a fractured rock mass using analog materials containing a single fracture was developed. This method is easy to simulate the fluid flow through a fracture of certain aperture. Experimental data showed that Forchheimer equation could provide an excellent description of the nonlinear relationship between hydraulic gradient and flow velocity, and the variations of Forchheimer coefficients with joint roughness coefficient (JRC) were studied. It was found that the deformation of the microfracture surface subjected to seepage could be accurately captured by the quasi-distributed FBG strain sensors. The test results also demonstrated that the surface strain is significantly affected by hydraulic pressure.

Effect of sample size on the fluid flow through a single fractured granitoid

Most of deep geological engineered structures, such as rock caverns, nuclear waste disposal repositories, metro rail tunnels, multi-layer underground parking, are constructed within hard crystalline rocks because of their high quality and low matrix permeability. In such rocks, fluid flows mainly through fractures. Quantification of fractures along with the behavior of the fluid flow through them, at different scales, becomes quite important. Earlier studies have revealed the influence of sample size on the confining stress–permeability relationship and it has been demonstrated that permeability of the fractured rock mass decreases with an increase in sample size. However, most of the researchers have employed numerical simulations to model fluid flow through the fracture/fracture network, or laboratory investigations on intact rock samples with diameter ranging between 38 mm and 45 cm and the diameter-to-length ratio of 1:2 using different experimental methods. Also, the confining stress, σ3, has been considered to be less than 30 MPa and the effect of fracture roughness has been ignored. In the present study, an extension of the previous studies on “laboratory simulation of flow through single fractured granite” was conducted, in which consistent fluid flow experiments were performed on cylindrical samples of granitoids of two different sizes (38 mm and 54 mm in diameters), containing a “rough walled single fracture”. These experiments were performed under varied confining pressure (σ3 = 5–40 MPa), fluid pressure (fp ≤ 25 MPa), and fracture roughness. The results indicate that a nonlinear relationship exists between the discharge, Q, and the effective confining pressure, σeff., and Q decreases with an increase in σeff.. Also, the effects of sample size and fracture roughness do not persist when σeff. ≥ 20 MPa. It is expected that such a study will be quite useful in correlating and extrapolating the laboratory scale investigations to in-situ scale and further improving theoretical/numerical models associated with fluid flow through rock masses.

Laboratory Simulation of Flow through Single Fractured Granite

Laboratory simulation on fluid flow through fractured rock is important in addressing the seepage/fluid-in-rush related problems that occur during the execution of any civil or geological engineering projects. To understand the mechanics and transport properties of fluid through a fractured rock in detail and to quantify the sources of non-linearity in the discharge and base pressure relationship, fluid flow experiments were carried out on a cylindrical sample of granite containing a ‘single rough walled fracture’. These experiments were performed under varied conditions of confining pressures, σ 3 (5–40 MPa), which can simulate the condition occurring about 1,000 m below in the earth crust, with elevated base pressure, b p (up to 25 MPa) and by changing fracture roughness. The details of the methodologies involved and the observations are discussed here. The obtained results indicate that most of the data in the Q verses b p plot, fall on the straight line and the flow through the single fracture in granite obeys Darcy’s law or the well-known “cubic law” even at high value of b p (=4 MPa) and σ 3 (=5 MPa) combination. The Reynolds number is quite sensitive to the b p, σ 3 and fracture roughness, and there is a critical b p, beyond which transition in flow occurs from laminar to turbulent. It is believed that such studies will be quite useful in identifying the limits of applicability of well know ‘cubic law’, which is required for precise calculation of discharge and/or aperture in any practical issues and in further improving theoretical/numerical models associated with fluid flow through a single fracture.

A three-dimensional spectral element model for the solution of the hydrostatic primitive equations

We present a spectral element model to solve the hydrostatic primitive equations governing large-scale geophysical flows. The highlights of this new model include unstructured grids, dual h– p paths to convergence, and good scalability characteristics on present day parallel computers including Beowulf-class systems. The behavior of the model is assessed on three process-oriented test problems involving wave propagation, gravitational adjustment, and nonlinear flow rectification, respectively. The first of these test problems is a study of the convergence properties of the model when simulating the linear propagation of baroclinic Kelvin waves. The second is an intercomparison of spectral element and finite-difference model solutions to the adjustment of a density front in a straight channel. Finally, the third problem considers the comparison of model results to measurements obtained from a laboratory simulation of flow around a submarine canyon. The aforementioned tests demonstrate the good performance of the model in the idealized/process-oriented limits.

Modeling stress-dependent permeability for anisotropic fractured porous rocks

Most of deep geological engineered structures, such as rock caverns, nuclear waste disposal repositories, metro rail tunnels, multi-layer underground parking, are constructed within hard crystalline rocks because of their high quality and low matrix permeability. In such rocks, fluid flows mainly through fractures. Quantification of fractures along with the behavior of the fluid flow through them, at different scales, becomes quite important. Earlier studies have revealed the influence of sample size on the confining stress–permeability relationship and it has been demonstrated that permeability of the fractured rock mass decreases with an increase in sample size. However, most of the researchers have employed numerical simulations to model fluid flow through the fracture/fracture network, or laboratory investigations on intact rock samples with diameter ranging between 38 mm and 45 cm and the diameter-to-length ratio of 1:2 using different experimental methods. Also, the confining stress, σ3, has been considered to be less than 30 MPa and the effect of fracture roughness has been ignored. In the present study, an extension of the previous studies on “laboratory simulation of flow through single fractured granite” was conducted, in which consistent fluid flow experiments were performed on cylindrical samples of granitoids of two different sizes (38 mm and 54 mm in diameters), containing a “rough walled single fracture”. These experiments were performed under varied confining pressure (σ3 = 5–40 MPa), fluid pressure (fp ≤ 25 MPa), and fracture roughness. The results indicate that a nonlinear relationship exists between the discharge, Q, and the effective confining pressure, σeff., and Q decreases with an increase in σeff.. Also, the effects of sample size and fracture roughness do not persist when σeff. ≥ 20 MPa. It is expected that such a study will be quite useful in correlating and extrapolating the laboratory scale investigations to in-situ scale and further improving theoretical/numerical models associated with fluid flow through rock masses.