The assumption of cement grouts as 'Bingham fluids' has thus far facilitated the development of simplified analytical tools for rock grouting design. However, from a practical standpoint the use of the Bingham constitutive law throughout the design phase has several shortcomings that merit being more systematically addressed. For instance, the known key attributes of cementitious suspensions, e.g. wall-slip, thixotropy, shear rate and time dependency that influence the grout propagation especially at low shear rates are not considered when the Bingham model is used. As such, the consequences of overlooking such crucial phenomena whilst aiming for simplicity in design remain relatively unknown. In this work, we show how considering the shear rate aspects and stop criteria with the Bingham model can be better used for grouting design. Our design suggestions are based on fundamental analysis and theory of Bingham fluid radial flow and current knowledge on cement grout rheological behaviour, as reported from rheological experiments. Moreover, we contribute to the existing design procedure by presenting a nomogram that can readily be used for practical rock grouting design. The nomogram approach allows rapid computation of all key parameters, which in essence shows that unless wall slip is taken into account up to similar to 50% overestimation of grout travel results.

Measuring the radial flow velocity field of yield stress fluids (YSFs) between two parallel disks provides crucial data to understand the underlying flow phenomena. However, direct velocimetry of YSFs in the radial flow configuration remains a challenge, due to the complex fluid rheology and geometry constraints. In this paper, we present an experimental device for measuring YSF radial flow velocity profiles. Ultrasound Velocity Profiling (UVP) is used to non-intrusively measure the velocity profiles. The Tikhonov regularization method is implemented to obtain smooth velocity profiles, which are used to calculate the plug-flow region. Compared to our previous work on radial flow, the current contributions include: (i) additional structural frame members to maintain a constant aperture, (ii) wall slip reduction, and (iii) an improved velocity profile plug-detection algorithm. The results show that the experimental device and the measurement method are effective for further studying radial flow behavior of YSFs for industrial applications.

Measuring the radial flow velocity field of yield stress fluids (YSFs) between two parallel disks provides crucial data to understand the underlying flow phenomena. However, direct velocimetry of YSFs in the radial flow configuration remains a challenge, due to the complex fluid rheology and geometry constraints. In this paper, we present an experimental device for measuring YSF radial flow velocity profiles. Ultrasound Velocity Profiling (UVP) is used to non-intrusively measure the velocity profiles. The Tikhonov regularization method is implemented to obtain smooth velocity profiles, which are used to calculate the plug-flow region. Compared to our previous work on radial flow, the current contributions include: (i) additional structural frame members to maintain a constant aperture, (ii) wall slip reduction, and (iii) an improved velocity profile plug-detection algorithm. The results show that the experimental device and the measurement method are effective for further studying radial flow behavior of YSFs for industrial applications.

The present experimental study addresses the flow of a yield stress fluid with some elasticity (Carbopol gel) in a square duct. The behaviour of two fluids with lower and higher yield stress is investigated in terms of the friction factor and flow velocities at multiple Reynolds numbers Re* is an element of (1, 200) and, hence, Bingham numbers Bi is an element of (0.01, 0.35). Taking advantage of the symmetry planes in a square duct, we reconstruct the entire 3-component velocity field from two-dimensional particle image velocimetry (PIV). A secondary flow consisting of eight vortices is observed to recirculate the fluid from the core towards the wall centre and from the corners back to the core. The extent and intensity of these vortices grows with increasing Re* or, alternately, as the plug size decreases. The second objective of this study is to explore the change in flow in the presence of particles. To this end, almost neutrally buoyant finite-size spherical particles with a duct height, 2H, to particle diameter, d(p), ratio of 12 are used at two volume fractions phi = 5 and 10 %. Particle tracking velocimetry is used to measure the velocity of these refractive-index-matched spheres in the clear Carbopol gel, and PIV to extract the fluid velocity. Additionally, simple shadowgraphy is also used to qualitatively visualise the development of the particle distribution along the streamwise direction. The particle distribution pattern changes from being concentrated at the four corners, at low flow rates, to being focussed along a diffused ring between the centre and the corners, at high flow rates. The presence of particles induces streamwise and wall-normal velocity fluctuations in the fluid phase; however, the primary Reynolds shear stress is still very small compared to turbulent flows. The size of the plug in the particle-laden cases appears to be smaller than the corresponding single-phase cases. Similar to Newtonian fluids, the friction factor increases due to the presence of particles, almost independently of the suspending fluid matrix. Interestingly, predictions based on an increased effective suspension viscosity agrees quite well with the experimental friction factor for the concentrations used in this study.

During the design phase in rock grouting applications (e.g. for tunnels), analytical and numerical techniques based on inputs from the rock mass characterization and grout flow properties are used to estimate the grout spread. The design process is complicated by the fact that the exact geometry (network of fractures) within the rock mass is not completely known. In addition, the rheological flow properties of commonly used cement-based grouts are complex due to thixotropy and hydration. In such cases, simplified one-dimensional (1D) and two-dimensional 2D fracture geometries are used as a basis for the design solution. As for cement grouts, their rheological behavior is normally described by simplified constitutive laws e.g. the Bingham model.  Several  analytical solutions  for 1D channel flow and 2D radial flow of cement grouts have been presented in the literature describing the spread of grouts in fractures. Experimentally, only a limited amount of work has been carried out to study idealized yield stress fluid (YSF) flow between stationary parallel disks. The importance of such tests is that they facilitate the verification of analytical solutions and their limitations. Thus, in order to investigate in principle, the nature of 2D Bingham fluid  velocity profiles in radial  flow, we carried out  for apparently the first time  ultrasound velocimetry measurements  within the constraints of an experimental model. The  radial  flow region was formed by the gap (aperture) between two parallel acrylic glass (Plexiglas) disks, each with a diameter of 1 meter and a thickness of 25 mm. The disk separation was attained from a variable height metallic spacer configuration. Ultrasound velocity profiling (UVP) was used for flow visualization through the measurement of velocity profiles of a model yield stress fluid (Carbopol) at different radial positions. The results are a comparison of the measured velocity profiles with those from analytical solutions. Of particular interest is the plug-flow region of the radial velocity profiles along the radial length (diameter) of the parallel disks. The current observations show a distinct plug region, coupled with wall slip effects for the Carbopol model YSF fluid that was used. The theoretically predicted velocity profiles are lower than  the measured ones, however within a reasonably similar magnitude range. The main discrepancies between the theoretical predictions and measured data are then discussed. Future studies would then be targeted at improving the current experimental setup, for detailed measurements of the  plug-flow region along the radial length, which remains a generally challenging issue for studies on YSFs and more specifically for rock grouting design.  Moreover,  considering  roughened walls to significantly reduce wall slip  that was  present in the current study will also be part of the project’s continuation.

The rheological properties of cement grouts play a key role in determining the final spread in grouted rock formations. In terms of flow properties, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by the simple Bingham constitutive law. Due to their time dependent nature, the flow curves of cement grouts have been known to exhibit an unstable non-monotonic region, characterized by a negative slope below a critical shear rate. Within this paper, we focus on how this unstable region that is dominated by flow localization is affected by rheometer geometry and flow sweep measurement interval. We carried out controlled shear rate (CSR) flow sweeps on typical micro-cement grouts within different Couette geometries. Lastly, we discuss the effects of geometry and measurement interval on the resulting flow curves, with a focus on the critical shear rate that separates homogenous from non-homogeneous unstable flow.

The newly developed Flow-Viz rheometric system is capable of performing detailed non-invasive velocimetry measurements through industrial stainless steel pipes. However, in order to improve the current design for non-invasive measurements in industrial fluids, pulsed ultrasound sensors need to be acoustically characterized. In this paper, acoustic characterization tests were carried out, with the aim of measuring the ultrasound beam propagation through stainless steel (SS316L) pipes and into water. For these tests, a high-precision robotic XYZ-scanner and needle hydrophone setup was used. Several ultrasound sensor configurations were mounted onto stainless steel pipes, while using different coupling media between the transducer-to-wedge and sensor wedge-to-pipe boundaries. The ultrasound beam propagation after the wall interface was measured by using a planar measuring technique along the beam’s focal axis. By using this technique, the output for each test was a 2-D acoustic color map detailing the acoustic intensity of the ultrasound beam. Measured beam properties depicted critical parameters, such as the start distance of the focal zone, focal zone length, Doppler angle, and peak energy within the focal zone. Variations in the measured beam properties were highly dependent on the acoustic couplants used at the different interfaces within the sensor unit. Complete non-invasive Doppler ultrasound sensor technology was for the first time acoustically characterized through industrial grade stainless steel. This information will now be used to further optimize the non-invasive technology for advanced industrial applications.