Sustainability of Water Resources in Karst Undermined by Tunneling: A Case Example

Water resources in karsts are scarce due to the high cavernosity in the otherwise low-permeability limestone rock mass. The highly variable porosity and transmissivity of karst aquifers are caused by a network of channels, caverns, and caves that typically act as water-bearing, connected vessels. Tunneling in a karst environment can severely deplete an aquifer and undermine the sustainability of water resources over the long term. A research study was carried out to elaborate and develop measures for the sustainable preservation of the water resources in a Slovenian karst, in which two approximately 7 km-long tunnels will be driven as part of the construction of the new Divača–Koper railway line. Hydrogeological site investigations were carried out with an aim to evaluate the transmissivity and spatial spreading of the karst aquifer along the route of the tunnels, including the observation of the long-term variation of the groundwater levels and trace experiments. The main findings, which are presented in this paper, were used to develop a methodology for the selection of adequate measures for tunnel construction with an aim of ensuring the sustainability of water resources in karst aquifers. The construction measures comprise limiting the inflows using injection grouting, obscuring the groundwater intake by undrained sections of the tunnel, and constructing bypasses around the tunnel to preserve the current groundwater flow regime. The presented methodology of dynamically accommodating the preventive measures to the actual hydrogeological conditions onsite is generally applicable for common cases in which the state of the karst aquifer could not be pre-determined with a sufficient accuracy of tens of meters to a meter. The spatially and temporally continuous hydrogeological investigations and decision-making charts to reduce the tunnelling’s impact on the karst aquifer are explained in detail in this paper.

Flow Control in Passive 3D Paper-Based Microfluidic Pump by Variable Porosity

Active pumps are often used in microfluidic devices for programmable fluid flowrate in a microchannel. Active pumps have some drawbacks due to their large size and requirement of external power. To overcome them, a new class of passive pumps based on capillary action in cellulose material, known as paper-based microfluidic pumps, has recently been explored. In this study, fluid flow in 3D paper-based pumps was investigated using flowrate measurements in microchannels. In order to develop 3D cylindrical pumps, Whatman filter paper grade 1 was shredded, mixed with water, molded and dried. The patterned serpentine channel was created using a CO2 Laser Cutting/Engraving machine. The 3D paper-based pump was integrated with microfluidic channel. The effect of paper pumps of different porosities on the fluid flowrate through a serpentine microchannel was investigated. It was found that flowrate of the fluid flowing through the channel increases with an increase in the pump’s porosity. Moreover, these pumps have the ability to transport larger volumes of liquid with improved flowrate, programmability and control, in addition to being inexpensive and simple to design and fabricate. These 3D pumps will help researchers move closer to developing an effective miniaturized diagnostic platform for point-of-care (POC) diagnostic applications.

The Influence of Hyper-Alkaline Leachate on a Generic Host Rock Composition for a Nuclear Waste Repository: Experimental Assessment and Modelling of Novel Variable Porosity and Surface Area

Deep geological disposal is the preferred solution for long-term storage of radioactive waste in many countries. In a deep repository, cementitious materials are widely used in the structure and buffer/backfill of the repository for the stabilisation of the hazardous materials. The cement acts as a physical barrier and also contributes chemically to waste containment by buffering the groundwater to a high pH, limiting the solubility of many radionuclides. This paper describes an experimental and modelling study which evaluates the geochemical interaction between young cement leachate (YCL, pH = 13) and a generic hard rock (in this case Hollington sandstone, representing a ‘hard’ host rock) during permeation with the leachate, as it drives mineralogical changes in the system. One-dimensional reactive transport was modelled using a mixing cell approach within the PHREEQC geochemical code to identify the essential parameters and understand and scale up the effect of variations in these parameters on the observed geochemical processes. This study also focused on the effects of variable porosity, reactive surface area and pore volume on improving the modelling of rock alteration in the system compared to conventional models that assume constant values for these properties. The numerical results showed that the interaction between the injected hyper-alkaline leachate and the sandstone sample results in a series of mineralogical reactions. The main processes were the dissolution of quartz, kaolinite and k-feldspar which was coupled with the precipitation of calcium silicate hydrate gel and tobermorite-14A (C–S–H), prehnite (hydrated silicate), saponite-Mg (smectite clay) and mesolite (Na–Ca zeolite). The simulation showed that the overall porosity of the system increased as primary minerals dissolve and no stable precipitation of the secondary C–S–H /C–A–S–H phases was predicted. The variable porosity scenario provides a better fitting to experimental data and more detailed trends of chemistry change within the column. The time and the number of moles of precipitated secondary phases were also improved which was related to greater exposure surface area of the minerals in the sandstone sample to the YCL. Article Highlights The drop in calcium, aluminium and silicate concentrations is mainly due to the formation of calcium silicate hydrate and zeolite minerals as secondary phases. The simulation showed that the overall porosity of the system increased as primary minerals dissolve and no stable precipitation of the secondary C–S–H /C–A–S–H phases was predicted. The dissolution of primary minerals and the precipitation of secondary C–S–H phases had a minimal effect on the pH values, and this was controlled mainly by the initial fluid chemistry. The variable porosity scenario provides a better fitting to experimental data and more detailed trends of chemistry change within the column.

Rock Physics Diagnostics as a prerequisite for optimal Petrophysics

One of the key outputs from petrophysical evaluation is porosity. Sonic log is considered as one of the logs for deriving petrophysical volumes including porosity. However, the sonic data might not be always suitable to be included in the petrophysical model even if the quality of the log is quite good. One of the key reasons lies behind the variable porosity-velocity relationship for different types of formations attributed to post depositional processes. Without performing proper rock physics diagnostics before petrophysics model building can create inconsistencies in the petrophysical volumes as well as force the petrophysicist to use unreasonable endpoints for matrix or fluid. In this paper, an attempt is made to perform rock physics diagnostics using Wyllie-time-average and Raymer-Hunt-Gardner relations, drawing conclusion on the consolidation state of the rock, followed by computation of porosity from sonic using these relations. Later, rock physics diagnostic using theoretical rock physics models is carried out to confirm and complement this understanding of rock’s consolidation state. The results show that even though these empirical relations in their original form are useful and widely used but it is not quite suitable for unconsolidated and weakly cemented (poorly consolidated) formations or at least cannot justify the porosity-velocity trend in the data. Here computed sonic porosity is compared with field calibrated density porosity. It could be seen from this study that, in order to match sonic porosity with density porosity, an unreasonable matrix/fluid endpoints or non-theoretical empirical fitting coefficient is required. Since, this might not always be the case, a proper assessment using rock physics diagnostic should be carried out before incorporating sonic data into the petrophysical model.

Verification of a chamberless HLFC design with an outer skin of variable porosity

A chamberless HLFC leading edge segment featuring an outer skin with variable porosity has been designed, manufactured and wind tunnel tested under flight Reynolds-number conditions. The aerodynamic design involved the extention of current HLFC design routines to variable pressure loss characteristics of the outer skin. Advanced options for structural design and manufacturing solutions with focus on industrialization, arising from the avoidance of aerodynamically driven chambering, are explored. The leading edge segment has been installed on an existing vertical tail-plane model and tested at the large low-speed wind-tunnel facility DNW-LLF. The design process and some results of the successful verification of the chamberless design are presented herein.

Hybrid nanofluid flow through a spinning Darcy–Forchheimer porous space with thermal radiation

This work investigates numerically the solution of Darcy–Forchheimer flow for hybrid nanofluid by employing the slip conditions. Basically, the fluid flow is produced by a swirling disk and is exposed to thermal stratification along with non-linear thermal radiation for controlling the heat transfer of the flow system. In this investigation, the nanoparticles of titanium dioxide and aluminum oxide have been suspended in water as base fluid. Moreover, the Darcy–Forchheimer expression is used to characterize the porous spaces with variable porosity and permeability. The resulting expressions of motion, energy and mass transfer in dimensionless form have been solved by HAM (Homotopy analysis method). In addition, the influence of different emerging factors upon flow system has been disputed both theoretically in graphical form and numerically in the tabular form. During this effort, it has been recognized that velocities profiles augment with growing values of mixed convection parameter while thermal characteristics enhance with augmenting values of radiation parameters. According to the findings, heat is transmitted more quickly in hybrid nanofluid than in traditional nanofluid. Furthermore, it is estimated that the velocities of fluid $$f^{\prime}\left( \xi \right),g\left( \xi \right)$$ f ′ ξ , g ξ are decayed for high values of $$\phi_{1} ,\phi_{2} ,\,Fr$$ ϕ 1 , ϕ 2 , F r and $$k_{1}$$ k 1 factors.