Constant Water Research Articles

Influence of eco-friendly dispersants on the properties of a lateritic soil-based mortar

Tropical regions like French Guiana need local building materials to cope with high population growth and the high cost of imported cementitious materials. Poured earthen construction could represent a local, cost-effective, and ecologically friendly alternative. To ensure good workability and facilitate pouring, the use of dispersants to deflocculate clay particles is an effective strategy that reduces water demand and increases the material's density and strength. Natural organic dispersants can replace industrial ones while reducing costs and carbon footprint. It is currently unknown how organic dispersants could improve the workability, physical and mechanical properties of the iron-rich lateritic soils present in French Guiana. Here, different potential dispersants were evaluated at constant water content on a lateritic soil-based mortar: citric acid, sodium carbonate, tannins, tannins+sodium hydroxide (tannins+NaOH), tannins+sodium carbonate (tannins+Na2CO3). These dispersants were compared to industrial sodium hexametaphosphate (NaHMP). Three types of tannins were tested: hydrolyzable tannins from oak and chestnut, and condensed tannins from acacia. This study shows that all formulations improved workability and mechanical strength but only tannins+NaOH or Na2CO3 had a strong dispersant effect comparable to NaHMP. Furthermore, tannins+NaOH or Na2CO3 decreased the mortar's density without impacting strength, which may result from reactions between the soil's iron oxides and tannins, as observed by infrared spectroscopy (FTIR). Altogether, these results show that the addition of organic dispersant is an appropriate strategy to improve the fresh and hardened properties of lateritic soils. Particularly, tannins combined with sodium carbonate may represent an eco-friendly dispersant for poured earth in regions with iron-rich lateritic soils.

Investigation on natural to ventilated cavitation considering the air-vapor interactions by Merging theory with insight on air jet location/rate effect

Cavitation is of significant practical importance since unstable flow characteristics can have noticeable consequences on objects nearby. An essential approach for controlling the cavitation flow field's instability is air injection. This work aims to conduct a numerical and experimental investigation on the natural to ventilated cavitation around a Clark Y hydrofoil. Having three phases: water, vapor, and air, the cavitation model is adjusted based on the Merging theory to consider the impact of dissolved air on cavitation. Furthermore, the Density Corrected-based Method (DCM) is used to alter the turbulence model. The experimental tests are carried out in the water tunnel, which can maintain the constant water flow rate (Qwater=490 m3⁄h) and regulate the pressure level (105–180 kPa). The Clark Y hydrofoil is fixed at an angle of attack of 8° and includes injection and pressure taps. Two holes, called Tap1-injection and Tap5-injection, are alternatively used for air injection purposes.Two cavitation numbers (σ=1.1, 1.6) and three air injection rates (Q = 0, 0.5, 1 l/min) are considered current case studies. The results demonstrate the meaningful impact of location and rate of aeration on the dynamic/average characteristics of cavitation. Increasing the air injection rate results in an increase in the pressure coefficient values, a decrease in the shedding frequency, and an elongation of the cavity with an M-shaped structure. Also, during a cycle of cavity development, air injection may take place in the reversed jet, perpendicular jet, or direct jet configurations. In addition, a close agreement between numerical and experimental results is recorded.

Phytodiversity and sustainable Management status of Reforested Sites of the Soudano-Sahelian Zone of Cameroon

A study was carried out on the phytodiversity and the sustainable management situation of reforested sites in order to ameliorate the living conditions of the local population of three villages (Kilguim, Going I and Going II) of Kaélé in the Mayo-Kani division. The semi-structured and structured maintenance beside the 200 persons and the registration of the vegetation was done in three villages. Findings revealed higher bushfires practice in sites. Data analysis proved that the practice of bushfires in forbidden or restricted sites (83.50 ± 16.01), the lack of plausibility studies of reforestation projects associating local populations (78.50 ± 13.99), insufficiency of bore holes for constant water supply for the follow up of the reforestation (76.00 ± 19.10), lack of specialized structures in the reforestation domain (72.83 ± 13.03), the insufficiency of sensitization on the importance of reforestation (71.67 ± 27.55) and the cutting of wood (68.00 ± 12.17) are real problems that the reforestation sites faces. The confiscation of land for reforestation without any alternative measure taken for the assurance of alimentary security and firewood of the population is the major cause of the dissatisfaction of the riverine population. The death rate is pretty elevated in the Kilguim site (15%) because of the lack of maintenance in reforested sites. The Shannon index is very high in the Going I site (2.71bits) because it is less perturbed by anthropic activities. Vegetation presents a structure in the form of a bell or cloche in prohibited sites translate a heterogeneity of the milieu because of anthropic perturbations. The durable management plan was opted for the management of reforestation sites.

Experimental Investigation on the Utilization of Marble and Scoria Powder as Partial Replacement of Cement in Concrete Production

This paper explores how marble and scoria powder can be used as partial substitutes for ordinary Portland cement in creating C-25 concrete. Both materials contain over 50% of the major oxides found in cement, with marble high in CaO and scoria high in SiO2. Experimental investigations were conducted to study the chemical, physical, mechanical, and fresh properties of concrete containing marble and scoria powder. For the investigation, 13 different mixes, including the control mix, were used with a constant water–cement ratio of 0.5 and a slump range of 25–50 mm for concrete with a compressive strength (CS) of 25 MPa. Marble-to-scoria ratio of 2 : 1, 1 : 1, and 1 : 2 was used, and then the combined fraction of both marble waste and scoria in concrete was increased from 0% to 20% in 5% range. Including the control test specimens, a total of 117 (150 × 150 × 150 mm) concrete cubes for CS test, 39 (100 × 100 × 500 mm) concrete beam specimens for flexural strength test, 39 (100 × 200 mm) cylinder specimens for splitting tensile strength (STS) test and, 39 (100 × 100 × 100 mm) cube specimens for water absorption test were cast and tested at 3, 7, 28, and 56 days. The test results indicate that marble and volcanic scoria powders with marble-to-scoria ratio of 1 : 1 could replace cement up to 15% without compromising the CS and up to 10% without compromising the flexural and STS; also, the water absorption decreases up to 10% replacement; however, the workability of the fresh mix decreases as the combined replacement level of marble and scoria increases. Generally, a 10% replacement with marble-to-scoria ratio of 1 : 1 produces concrete with higher compressive, flexural, tensile strength, and water absorption manifestations when compared to conventional concrete.

Wave statistics and energy dissipation of shallow-water breaking waves in a tank with a level bottom

The present study focuses on two-dimensional direct numerical simulations of shallow-water breaking waves, specifically those generated by a wave plate at constant water depths. The primary objective is to quantitatively analyse the dynamics, kinematics and energy dissipation associated with wave breaking. The numerical results exhibit good agreement with experimental data in terms of free-surface profiles during wave breaking. A parametric study was conducted to examine the influence of various wave properties and initial conditions on breaking characteristics. According to research on the Bond number ( $Bo$ , the ratio of gravitational to surface tension forces), an increased surface tension leads to the formation of more prominent parasitic capillaries at the forwards face of the wave profile and a thicker plunging jet, which causes a delayed breaking time and is tightly correlated with the main cavity size. A close relationship between wave statistics and the initial conditions of the wave plate is discovered, allowing for the classification of breaker types based on the ratio of wave height to water depth, $H/d$ . Moreover, an analysis based on inertial scaling arguments reveals that the energy dissipation rate due to breaking can be linked to the local geometry of the breaking crest $H_b/d$ , and exhibits a threshold behaviour, where the energy dissipation approaches zero at a critical value of $H_b/d$ . An empirical scaling of the breaking parameter is proposed as $b = a(H_b/d - \chi _0)^n$ , where $\chi _0 = 0.65$ represents the breaking threshold and $n = 1.5$ is a power law determined through the best fit to the numerical results.

Experimental study on energy and exergy assessments of a new PV system with a concave cover for active cooling and self-cleaning

Sandstorms and the spread of dust are problems in semi-arid and arid desert regions. The performance of the photovoltaic cells is lowered as a result of dust buildup on their front side and overheating. Through the use of a combined cooling and self-cleaning technique, the overall performance of a solar panel is improved in this experimental study. As a result, the solar panel receives four upgrades: a concave cover, mirrors, constant flow water cooling, and natural flow air cooling. For this purpose, a transparent concave cover is applied to the front side of the photovoltaic cells to allow the greatest amount of solar radiation to pass through while preventing the accumulation of dust on this face. The front face is cooled with water at a constant flow of 0.0042 kg/s and cooled by air to pass between the front face of the solar cell and the concave cover with a natural flow. Mirrors are positioned on the right and left sides to increase solar radiation. The modified PV solar panel module (PV-M) and conventional solar panel module (PV-C) are contrasted in terms of their operating temperature, current, and output voltage. According to the experimental findings, PV-M had a 24.11% increase in electrical efficiency over PV-C under the same operating conditions and at maximum solar radiation. With a 76.51% improvement, the overall average energy efficiency of PV-C and PV-M was calculated to be 23.63 and 41.71%, respectively. in comparison, the average exergy efficiency was about 25.04%.

Performance investigation of a hybrid PV/T collector with a novel trapezoidal fluid channel

The photovoltaic-thermal collector (PV/T) is an innovative technology that combines PV cells and solar thermal collectors into a co-generation unit, enabling full-spectrum solar utilization. This research proposes and examines a hybrid PV/T system with novel trapezoidal fluid channels embedded in graphite, arranged in a parallel S-shaped structure under outdoor conditions of Beijing. Parametric discussions and daily performance analysis are conducted to assess its effectiveness and stability. A daily average of 12.7 °C reduction in cell temperature compared to PV modules results in a relative 5.20 % improvement in electrical output under the intensity of solar radiation is 597 W/m2. Similarly, the peak temperature of the water tank reaches 56.9 °C, and thermal efficiency is enhanced by 7.86 % over conventional sheet-tube PV/T collectors. For further optimization, a constrained adaptive particle swarm optimization algorithm (EPF-APSO) is constructed based on the experimental data, implementing a variable water flow rate (VWV) strategy. Compared to a constant water flow rate (CWV), the overall energy collected varies from 2.755 to 2.828 kWh per day, potentially reducing pump energy consumption by 17.93 %. The contribution of this paper provides references on structural and operational parameters optimization of PV/T collectors applying machine learning algorithms for better comprehensive efficiency.

HOTFLOOR: A benthic chamber system to simulate warming on the seafloor

AbstractThe frequency of abnormally warm water events is increasing not only in surface waters, but also in subsurface layers, with major impacts on benthic ecosystems. Previous insights on heatwave effects have been obtained through field observations or manipulative laboratory experiments. Here, we introduce a system capable of inducing elevated water temperatures in benthic habitats in situ over several days. The system consists of a commercially available electric boiler, usually applied in domestic underfloor heating, and custom‐designed benthic acrylic glass chambers connected to individual thermostats. Furthermore, the chambers are semi‐open, allowing constant water exchange, maintaining otherwise near‐natural conditions, including oxygen concentrations, while the temperature is elevated. The water exchange can be stopped to facilitate incubations measuring changes in benthic fluxes. We conducted a 15‐d trial study in July 2021 on a bare‐sediment habitat at 2.5 m depth, exposing five chambers to water temperatures 5°C above ambient temperatures for 6 d and comparing with five control chambers. In this assessment, we demonstrate that the temperature control and stability were reliable while maintaining natural oxygen conditions. The modular character of the system permits adaptations for various benthic habitats, facilitating the investigation of elevated temperatures in situ for future climate change scenarios.

A comparative study of the cutting efficiency of diamond rotary instruments with different grit sizes with a low-speed electric handpiece against zirconia specimens

The use of zirconia in dentistry has increased. However, little attention has been given to the difficulty experienced by clinicians when cutting zirconia restorations intraorally. Evidence for which grit size and type of rotary instrument is best for cutting zirconia intraorally is lacking. The purpose of this in vitro study was to identify the most efficient diamond rotary instrument grit size for cutting zirconia intraorally. Efficiency was measured by comparing the cutting depth of each rotary instrument into zirconia, analyzing zirconia specimens for surface damage after cutting, and measuring instrument deterioration. Thirty zirconia specimens of the same measurements were used as test specimens and cut with 30 diamond rotary instruments with different grit sizes. An electric handpiece was used with constant force (1.7N), speed (40 000rpm), time (1min), and water flow rate (25mL/min) to produce comparative data. The mean cutting efficiency values were compared by analysis, and the median values were compared by the nonparametric Kruskal-Wallis test (α=.05). Each test was followed up with pair wise comparisons of the mean or median values if significance was indicated. The greatest cutting depth was achieved with a fine-grit instrument with a mean cutting depth of 5.79mm compared with 4.54mm for the coarse-grit instrument (P=.032). The greatest damage to zirconia was done by the coarse- and supercoarse-grit instruments (both 33%), with no substrate damage by the superfine-, fine-, and medium-grit instruments. The greatest instrument deterioration was found on the supercoarse rotary instruments (9.05%). With only 3 exceptions, the power calculations were all sufficient and above 83%. The fine grit rotary instrument (between 40 and 50µm) was the most efficient, achieving the greatest cutting depth, with no detectable macroscopic damage to the zirconia and minimal instrument deterioration.

Suitability of Torricelli’s Theorem Formulation in Cases of Leaking Reservoirs with Video Analysis Tracker

This study aims to empirically prove the Torricelli equation formula in the case of leaky reservoirs with the help of video tracker analysis. The method used in this research is quantitative descriptive. The experiment was carried out with a simple tool: a 19-liter gallon of water filled with water and dyed, and then three holes were made vertically with different heights. The gallon is filled with water with a constant water level. Next, take a video of each leaking hole. Video is analyzed with Tracker software. Variables observed were the velocity of water exiting from the leak point (v), the time it took for water to gush from the leak point to the bottom (t), and the horizontal distance from the leak point position to the bottom (x). The results obtained based on video analysis with the tracker are that the farther the distance from the surface of the water to the leak point, the farther the horizontal distance of the resulting jet of water will be. This study concludes that theoretical data and experimental data have significant value, so the video analysis tracker software is feasible to use in dynamic and static fluid learning.

Iron-carbon micro-electrolysis material enhanced high-solid anaerobic digestion: Performance and microbial mechanism

Iron-carbon micro-electrolysis (ICME) materials are widely used as composite conductive materials for wastewater treatment to promote the degradation of volatile solids (VS), but there is virtually no research on their effect on high-solid anaerobic digestion (HSAD). This study aimed to investigate the effect of 10–50 g/L ICME dosages on HSAD and to reveal the microbial enhancement mechanism. The batch experiments (working volume of 400 mL) were conducted in a constant temperature water bath shaker. The results showed that the ICME materials promoted methane production by HSAD. The highest methane production rate was 297.79 mL/ g VS at a dosage of 50 g/L, which was 28% higher than that of the control. Scanning electron microscopy results showed that the ICME materials increased the attachment area of microorganisms. Further analyses of microbial community indicated that ICME materials facilitate symbiotic metabolism of syntrophic acetate-oxidizing bacteria (Synergistaceae) and hydrogenotrophic methanogens (Methanospirillum). This potentially promotes the conversion of the acetoacetic methanogenesis pathway to the syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathways. This study revealed ICME material enhancement in HSAD as well as new insights into the microbial mechanisms.

Impact of Blade and Solidity on the Performance of H-Darrieus Hydrokinetic Turbines by CFD Simulation

Purpose: In the present work, the 2D design of H-Darrieus turbines with a diameter of 900 mm and NACA blades 0018, 0025, 2415, and 4415 has been carried out for the solidity values of 0,5; 1 and 1,5. In order to know its maximum performance. Method/design/approach: The 2D simulations were developed with the ANSYS® FLUENT package in the transient state, varying the angular velocity (ω) for a peak velocity ratio (TSR) of 1 to 7 and the SST K-ω turbulence model, for a constant water flow rate of 1 m/s. This in order to know the results of the torque (Nm) generated and thus calculate the power coefficient (Cp). Results and conclusion: The NACA 0018 blade reached a power coefficient of 0,604 for a solidity of 0,5, followed by NACA 2415 blade at the same solidity with a maximum Cp of 0,594. On the other hand, the NACA 0025 blade for solidity of 1 reached a maximum Cp value of 0,570, while the NACA 4415 profile with a solidity of 1,5 obtained a maximum value of 0.495. Research implications: These results of maximum Cp values were given in a TSR range of 2 to 4 with a mean value of 3,5 for NACA profiles 0018 and 2415. Thus, evidencing the behavior of this type of turbine reaching maximum values to then begin to decrease. Originality/value: The present work contributes to the understanding of the impact of geometrical parameters on the operating coefficient of H-Darrieus.

Effect of submerged curing on properties of cemented paste backfill

ABSTRACT Mine stopes are often characterised by near-saturate conditions from constant water inflow from the ore body. Although significant research has been conducted on mechanical properties of cemented paste backfill, there are limited studies on curing practices that reflect saturate conditions. This study examines the effects of submerged curing to simulate saturate conditions. The results indicate that observed dark grey colouration associated with submerged curing is similar to ‘greening effect’ observed in concrete material containing Ground Granulated Blast-furnace Slag. Our study indicates that submerged curing has limited adverse material effects and is effective in simulating near-saturated conditions.

Investigation on the surface hardness and durability-related properties of concrete containing coconut shell as partial substitute to coarse aggregates

Purpose Using coconut shell aggregates (CSA) in concrete benefits agricultural waste management and reduces the demand for mineral resources. Several studies have found that concrete containing CSA can achieve strengths that are comparable to regular concrete. The purpose of the present work is to evaluate the concrete’s durability-related properties to supplement these earlier findings. Design/methodology/approach Cylindrical specimens were prepared with a constant water–cement ratio of 0.50 and CSA content ranging from 0% to 50% (at 10% increment) by volume of the total coarse aggregates. The specimens were cured for 28 days and then tested for density, surface hardness, electrical resistivity and water sorptivity. The surface hardness was measured to describe the concrete resistance to surface wearing, while the resistivity and sorptivity were evaluated to describe the material’s resistance to fluid penetration. Findings The results showed that the surface hardness of concrete remained on average at 325 Leeb and did not change significantly with CSA addition. The distribution of surface hardness was also similar across all CSA groups, with the interquartile range averaging 59 Leeb. These results suggest that the cement paste and gravel stiffness had a more pronounced influence on the surface hardness than CSA. On the other hand, concrete became lighter by about 9%, had lower resistivity by 80% and had significantly higher initial sorptivity by up to 110%, when 50% of its natural gravel was replaced with CSA. Future work may be done to improve the durability of CSA when used as coarse aggregate. Originality/value The present study is the first to show the lack of correlation between CSA content and surface hardness. It would mean that the surface hardness test may not completely capture the porous nature of CSA-added concrete. The paper concludes that without additional treatment prior to mixing, CSA may be limited only to applications where concrete is not in constant contact with water or deleterious substances.

Application of Opposition-Based Learning Jumping Spider Optimization Algorithm in Gas Turbine Coupled Cooling System

A gas turbine cooling system is a typical multivariable, strongly coupled, nonlinear system; however, the randomness and large disturbances make it difficult to control the variables precisely. In order to solve the problem of precise process control for multi-input and multi-output coupled systems with flow, pressure, and temperature, this article conducts the following research: (1) Designing a secondary circuit for waste hot water and establishing a water-circulating gas turbine cooling system to improve the efficiency of waste heat utilization. (2) Identifying the coupled system model and establishing a mathematical model of the coupling relationship based on the characteristic data of input and output signals in the gas turbine cooling system. (3) Designing a coupled-system decoupling compensator to weaken the relationships between variables, realizing the decoupling between coupled variables. (4) An Opposition-based Learning Jumping Spider Optimization Algorithm is proposed to be combined with the PID control algorithm, and the parameters of the PID controller are adjusted to solve the intelligent control problems of heat exchanger water inlet flow rate, pressure, and temperature in the gas turbine cooling system. After simulation verification, the gas turbine cooling system based on an Opposition-based Learning Jumping Spider Optimization Algorithm can realize the constant inlet flow rate, with an error of no more than 1 m3/h, constant inlet water temperature, with an error of no more than 0.2 °C, and constant main-pipe pressure, with an error of no more than 0.01 MPa. Experimental results show that a gas turbine cooling system based on the Opposition-based Learning Jumping Spider Optimization Algorithm can accurately realize the internal variable controls. At the same time, it can provide a reference for decoupling problems in strongly coupled systems, the controller parameter optimization problems, and process control problems in complex systems.

Improving the performance of recycled concrete by biodeposition of biogenic silica as a surface coating

This study addresses the challenges of sustainability and the implementation of a circular economy in the construction and maintenance of concrete structures used in clean-water applications. Specifically, it examines the use of an innovative surface treatment based on a biofilm comprising diatom biosilica deposition as a waterproofing agent and surface pore sealant to improve the longevity of recycled concrete. To this end biofilm-treated and untreated (control) samples of a concrete mix containing 50% recycled aggregates were subject to four performance tests directed at assessing the durability of concrete structures under environmental conditions: resistance to carbonation, freeze–thaw durability, resistance to water penetration, and electrical resistivity as an indicator of the corrosion resistance of concrete. In addition, the protective biofilm was characterised using SEM. Results suggest that the biogenic silica surface treatment significantly improves the durability of recycled concrete, in particular, for treated compared to untreated samples there was a 56 % reduction of the carbonation front, 26% lower mass loss in freeze–thaw cycles, 57% reduction in the water penetration front under pressure, and 44% higher electrical resistivity. Together these findings confirm that the biofilm used in this study constitutes an effective treatment to improve the properties of recycled concrete and ensure its durability, particularly when used in the construction of structures in contact with constant water fluctuations.

A novel nanogold sol SERS/RRS dual-mode assay for trace imidacloprid with Ti3C2Tx@Ti-MOFs/peptide bifunctional nanoprobe

The development of rapid, simple, and highly sensitive analytical methods for detecting pesticide residues is crucial for safeguarding the environment and human health. In this study, MXeneTi3C2Tx nanosheets are used to load a titanium-based metal-organic framework (Ti-MOFs) and imidacloprid peptide (PTIMI), and a novel bifunctional nanoprobe (TN@Ti-MOFs/PT) is prepared by irradiation in a domestic microwave oven and stirring at room temperature. Powder X-ray diffraction, transmission electron microscope and Fourier transform infrared spectrometer are used to characterize the prepared nanomaterials. It is found that TN@Ti-MOFs/PT not only specifically recognizes imidacloprid (IMI), but also catalyzes the nanogold indicator reaction to generate gold nanoparticles (AuNP) in an 80 ℃ constant temperature water bath. The generated AuNP can be directly used as an optical probe for resonance Rayleigh scattering (RRS) at wavelength of 370 nm. In the presence of the Victoria blue 4 R molecule probe, it shows a robust surface enhanced Raman scattering (SERS) signal at wavelength number of 1617 cm−1. When the target molecule IMI is added, it can interact with the PTIMI specific base sequence, resulting in PT chain shedding from the TN@Ti-MOFs/PT nanoprobe surface, exposing abundant redox sites and accelerating the redox charge transfer, resulting in AuNP increase and SERS/RRS signal enhancement. As a result, a highly sensitive and specific PT-based dual-mode biosensing platform is developed for the detection of trace IMI, with a linear range of 0.01–0.25 ng/mL and a detection limit of 0.0011 and 0.0039 ng/mL by SERS and RRS assays, respectively. To demonstrate its practical application, the platform is used to detect IMI in vegetable samples, with relative deviations of 1.36–5.86% and recoveries of 95.0–107%. Additionally, the mechanism of nanocatalysis enhancement is also investigated.

Expected stiffness changes during compaction in laboratory and field

The use of stiffness indexes to assess soil compaction has the potential to revolutionise the earthworks industry. However, conventional Proctor based compaction methodology fails to adequately explain the relationship between soil modulus and density. To address this issue, this paper presents recent laboratory and field trial results and analysis demonstrating the importance of soil degree of saturation when evaluating the effectiveness of using stiffness indexes to monitor and assess compaction.During a recent compaction study of silty sand samples, it has been found that the small-strain shear modulus (G0) and dry density (ρd) can be simply related provided changes in degree of saturation (Sr) are monitored. Multi-staged, one-dimensional compaction tests have been conducted at varying moisture contents, and first arrival shear wave velocity measured via Bender Elements (BE). Results presented in this paper show that G0 increases with increasing ρd at a constant Sr rather than constant water content (w). Further analysis indicates that additional compaction past a critical Sr reduces the stiffness response G0 at a constant w, and that when compacting across the typical range of Sr of 40–70%, G0 appears to be largely independent of ρd and is instead indexed by moisture content.At a construction phase field compaction trial in Australia, field dry density was measured against Intelligent Compaction (IC) unit Compaction Meter Value (CMV). Two outcomes of the field trial are discussed. As in the laboratory G0 trial, CMV, a stiffness related parameter, and field dry density were found to be practically independent. Drawing upon the common results of these two trials, a practical framework is proposed involving a method-based specification with respect to the compacted state and stiffness indexes, one in which adequate compaction and strength could be achieved while reducing the requirement for regular nuclear densometer gauge testing.

Effective Relative Permeabilities Based on Momentum Equations with Brinkman Terms and Viscous Coupling

Summary The relative permeability expresses the mobility reduction factor when a fluid flows through a porous medium in the presence of another fluid and appears in Darcy’s law for multiphase flow. In this work, we replace Darcy’s law with more general momentum equations accounting for fluid-rock interaction (flow resistance), fluid-fluid interaction (drag), and Brinkman terms responding to gradients in fluid interstitial velocities. By coupling the momentum equations with phase transport equations, we study two important flow processes—forced imbibition (coreflooding) and countercurrent spontaneous imbibition. In the former, a constant water injection rate is applied and capillary forces are neglected, while in the latter, capillary forces drive the process and the total flux is zero. Our aim is to understand what relative permeabilities result from these systems and flow configurations. From previous work, when using momentum equations without Brinkman terms, unique saturation-dependent relative permeabilities are obtained for the two flow modes that depend on the flow mode. Now, with Brinkman terms included, the relative permeabilities depend on local spatial derivatives of interstitial velocity and pressure. Local relative permeabilities are calculated for both phases utilizing the ratio of phase Darcy velocity and phase pressure gradient. In addition, we use the Johnson-Bossler-Naumann (JBN) method for forced imbibition (with data simulated under the assumption of negligible capillary end effects) to calculate interpreted relative permeabilities from pressure drop and average saturation. Both flow setups are parameterized with literature data, and sensitivity analysis is performed. During coreflooding, Brinkman terms give a flatter saturation profile and higher front saturation. The saturation profile shape changes with time. Local water relative permeabilities are reduced, while they are slightly raised for oil. The saturation range where relative permeabilities can be evaluated locally is raised and made narrower with increased Brinkman terms. JBN relative permeabilities deviate from the local values: The trends in curves and saturation range are the same but more pronounced as they incorporate average measurements, including the strong impact at the inlet. Brinkman effects vanish after sufficient distance traveled, resulting in the unique saturation functions as a limit. Unsteady state (USS) relative permeabilities (based on transient data from single-phase injection) differ from steady-state (SS) relative permeabilities (based on SS data from coinjection of two fluids) because the Brinkman terms are zero at SS. During spontaneous imbibition, the higher effect from the Brinkman terms caused oil relative permeabilities to decrease at low water saturations and slightly increase at high saturations, while water relative permeability was only slightly reduced. The net effect was a delay in the imbibition profile. Local relative permeabilities approached the unique saturation functions without Brinkman terms deeper in the system because phase velocities (involved in the Brinkman terms) decreased with distance. In both systems, scaling and simulations demonstrate that the relative change in relative permeabilities due to Brinkman terms increases with the Brinkman coefficient, permeability, and inverse squared distance from the inlet.

Thermo-hydro-mechanical behaviour of a deep plastic clay formation

Several applications which are framed in the energy geotechnics field, particularly the design of energy geo-structures, energy geo-storage, enhanced geothermal energy systems and radioactive waste disposal, require a thorough thermo-hydro-mechanical (THM) characterisation of their host soil/rock formation. The present study comes up from the need to investigate the THM behaviour of deep Ypresian clays (Ycs, 300 to 400 m below ground) since they are one of Belgium’s potential host rock formations for deep geological disposal of heat-emitting and long-lived radioactive waste.
 The impact of temperature on the hydro-mechanical response of deep clays has been extensively tackled for the last four decades. Nevertheless, to the authors’ knowledge, the study of the evolution of radial stresses during drained thermal paths under oedometer conditions has never been addressed. Such information would allow for drawing a better-defined stress state while accurately measuring volume changes. To this aim, the present study used a newly designed and fully instrumented temperature-controlled oedometer cell [3] combined with well-planned test protocols. The local instrumentation consisted of a pore pressure transducer embedded in the soil 3 mm from the bottom boundary, thermocouples at various positions and radial displacement transducers with a localised thin-wall system to estimate radial stress.
 Two well-preserved Ycs core samples retrieved at different depths at Kallo (Belgium) and belonging to distinct lithological units were tested (see Table 1). Both slightly overconsolidated samples (Yield Stress Ratios of Ycs between 1.2 and 1.8, [1, 2, 3]) presented high initial matric suctions induced on deep water-undrained sampling. Consequently, the first stage of the well-planned test protocol consisted of loading at constant water content to bring the samples to the large in situ stresses and diminish the induced matric suction. The remaining matric suction was then reduced by soaking with synthetic water equivalent to in situ. Afterwards, drained loading and unloading paths were followed to attain different vertical effective stresses at varying overconsolidation ratios (OCRs) before performing the main research goal of drained thermal paths. The heating-cooling (H-C) cycles consisted of slowly stepwise increase/decrease in temperature (steps of 10ºC) with intermediate stabilising periods of around 15 hours controlled by the embedded pore pressure transducer.
 Figure 1 depicts the vertical deformation in terms of the mean effective stress (p’) beyond in situ stress. Changes in radial stresses ruled the variations in p’ during heating-cooling cycles since the vertical effective stress was kept constant during non-isothermal paths. At a slightly overconsolidated (OC) state (Core-48), the drained ‘1st H-C’ cycle showed a quasi-reversible response in volume changes and radial stresses. At OC state (OCR=2) on Core-103 (‘2nd H-C’), the response was reversible. However, the induced volume change in normally consolidated (NC) states was not reversible with a contractive response dependent on the stress level. Therefore, the nature of the thermal-induced volume changes aligned with the behaviour observed on other plastic clays. Nevertheless, the stress dependence of the contractive response at NC state differed from the observations made by [4] on NC Boom Clay -the other poorly indurated clay considered as potential host rock in Belgium. As observed in ‘2nd H-C’ (NC conditions) on Core-48, a reduction of the radial effective stress was only recorded at temperatures higher than 70°C. In contrast, the radial effective stress systematically increased on heating at values < 70°C, tending the sample to lower deviatoric stress. This phenomenon might be
 associated with some change in the soil structure on heating that tends to a more isotropic stress state despite the oedometer condition. A clear transition between the elastic and elastoplastic domains was detected during the subsequent loading after each H-C cycle at NC states.
 Finally, the study included a thermo-mechanical elastoplastic interpretation: thermal expansion coefficients dependent on temperature and mean effective stress in the elastic domain and thermal softening function on post-yield drained heating.