Pore Water Research Articles

Numerical simulation of fracking and gas production in shale gas reservoirs

AbstractIn this work, different stages of gas production in shale reservoirs are modelled. First, hydraulic fracturing is considered by injecting water at high pressures to crack the formation and increase the flow capacity of the reservoir. During the fluid injection, rock properties are modified and water appears in the stimulated area. Then, these changes can be detected through seismic monitoring. Finally, once the fracking stage is completed, the simulation of gas production begins. The simultaneous gas–water flow in the injection and production stages is modelled using the Black‐Oil formulation. Furthermore, a fracture criterion is applied under the hypothesis of constant temperature and constant stress field in this first analysis of the problem. The numerical simulations allow us to analyse the propagation of the fracture and the behaviour of the pore pressure and water saturation in the stimulated area. The advance of the fracturing fluid is delayed in relation to the breakdown of the rock. Besides, the presence of new fractures is detected by applying a poroviscoelastic wave propagation simulator that considers mesoscopic losses induced by heterogeneities in rock and fluids. After the fracture network is created, the injection well becomes a producer, allowing the extraction of gas and the flowback of the injected fluid. The simulated gas flow rates are compared with those obtained by a simplified single‐phase analytical solution used for practical applications, achieving optimum matching results.

Influence of Imbibition Fracturing Fluid on the Original Water and Methane Occurrence in Actual Coalbed Methane Reservoirs Using the Integrated Device of Displacement and Low-Field Nuclear Magnetic Resonance.

The original water in the coal rock pores plays a controlling role in the occurrence of gas. Furthermore, during the hydraulic fracturing process, pressurized fracturing fluid with a higher pressure than the original pore pressure in the fractures drives the fracturing fluid to infiltrate into the coal rock pores, thereby altering the occurrence pattern of gas and water in the original pores. However, due to the limitations of the indoor simulation device, a systematic conclusion on the impact of the original pore water and imbibition fracturing fluid on coalbed methane reservoirs has not yet been formed. In this paper, an integrated device combining displacement and low-field nuclear magnetic resonance was employed using underground cylindrical coal rock samples as experimental subjects. Experimental conditions were maintained at a temperature of 30 °C, a confining pressure of 23 MPa, and an approximate reservoir pressure of 15 MPa. The initial water saturation levels were altered to 0, 27.88, and 42.18% to replicate the conditions of a coalbed methane reservoir at a depth of approximately 1200 m. Fracturing fluid with a pressure of 18 MPa was injected into the experimental samples to simulate the impact of the fracturing fluid on the original reservoir during hydraulic fracturing. This allowed for a realistic assessment of the influence of initial water saturation and fracturing fluid absorption on the coalbed methane recovery rate in the reservoir. The experimental results indicate that the imbibition process promotes the desorption of adsorbed gas, and the desorption amount of adsorbed gas increases with the increase in the original water saturation. This will result in an increase in the gas pressure within the pore system. The conditions of this experiment, in comparison to the previous ones, more closely resemble real reservoir conditions. This enables a realistic assessment of how the presence of the original water content and the absorption of the fracturing fluid affect gas occurrence within the reservoir.

Water properties and bottom water patterns in hadal trench environments

Abstract. We examine baseline water properties and bottom water patterns in hadal trench environments across the Southern Ocean, Indian Ocean, and western Pacific. Significant differences are identified in the South Fiji Basin and surrounding the Philippine Sea, primarily due to the movement of cold Lower Circumpolar Deep Water along topographic features, highlighting the importance of a trench's geospatial position. We present the first hydrographic profiles in the Java Trench, warranting further research. Salinity increases with increasing depth for profiles over 10 000 dbar, with potential causes including instrumentation error, internal mixing, and saline pore water expulsion. These hadopelagic variations are crucial for assessing climate change impacts, especially regarding Antarctic Bottom Water. The study underscores the importance of incorporating these adiabatic conditions to gain insights into ecological biodiversity, alongside the indispensable baseline conditions presented, which are crucial for future oceanographic research across multiple disciplines.

Quantitative characterization of the effect of compaction rate on ammonium release from clayey sediments

Ammonium-rich pore water will release from clayey sediments into adjacent aquifers during aquitards compaction, which can adversely affect groundwater quality. Differences in the rate of groundwater exploitation can lead to differences in the rate of compaction of aquitards, which may, to some extent, affect the release of chemical components of the pore water from the aquitard. However, the effect of the compaction rate of aquitards on the process of ammonium release from clayey sediments is poorly understood. Three groups of indoor compaction experiments were conducted to identify the effect of compaction rate on ammonium release from clayey sediments during compaction. The results showed that the compaction rate and sediment liquid limit exert a clear controlling effect on the release rate and internal change process of ammonium in clayey sediments. The increase in the ammonium release rate was approximately proportional to the increase in the compaction rate. When the moisture content of the clayey sediments exceeds the liquid limit, the ammonium concentration in pore water increases mainly due to the mineralization of organic matter containing nitrogen and the dissolution of the carbonate-bound ammonium. When the moisture content drops to the liquid limit, the ammonium concentration in pore water begins to decrease. Because the increase in the compaction rate weakened sediment mineralization and accelerated pore water release, the main forms of ammonium released from the sediment change from organic sulfide-bound ammonium and carbonate-bound ammonium to carbonate-bound ammonium and ion-exchanged ammonium. The results of this study have important significance for the management of groundwater quality in groundwater exploitation areas.

The Fundamental Flaws of the Waxman-Smits and Dual Water Formulations, Attempted Remedies, and New Revelations from Historical Laboratory Complex Conductivity Measurements

The Waxman-Smits formula was introduced in 1968 as a parallel conductance model to improve previous models. A careful inspection of the Waxman and Smits model reveals it is not a parallel conduction model by the conventional definition. First, Waxman-Smits assumed that “the electrical current transported by the counterions associated with the clay travels along the same tortuous path as the current attributed to the ions in the pore water” (Waxman and Smits, 1968), removing an essential feature of a parallel conduction model, that there be two separate conductors. Based on this assumption, they assign the same geometrical factor to both current paths. The geometrical factor is defined as the reciprocal of the formation resistivity factor (1/F or σm). Waxman-Smits found experimentally that a shaly sand appeared to have an F that was larger than a clean sand and introduced F* to account for this. Therefore, the tortuosity of the current paths through the clay and the pore water were deemed to be equivalent, with both tortuosities increasing equally as the clay content increased. Second, a parallel model requires the bulk conductivity of a volume to be weighted by the fractional volumes of the separate clay and interstitial water current paths. Clavier et al. (1977) discovered during the field testing of the new 1.1-GHz electromagnetic propagation tool that there existed a volume of clay water of near-constant salinity in shales. These two concepts are not accounted for in the Waxman-Smits model. A re-evaluation of the Waxman-Smits database by Clavier et al. (1977, 1984) revealed the F* increase was primarily due to the Waxman-Smits model not accounting for the physical presence of the volume of the clay water. The inclusion of the clay water volume in the dual water model produces a true parallel conductivity model. However, like Waxman-Smits, it assigns the same tortuosity to both the clay and pore water current paths. This assumption seems dubious based on observations of scanning electron microscope (SEM) photos showing actual clay morphologies. Laboratory measurements of pure clay and glass beads would allow one to quantify tortuosity changes due to the introduction of clay into an otherwise pure glass bead environment. Theoretically and experimentally, the value of the clay water conductivity (Ccw) at room temperature was found to be 6.8 S/m. Therefore, for a pore water conductivity (Cw) less than 6.8, the clay adds to the rock conductivity relative to an Archie rock, as written in the Waxman-Smits model. However, when Cw is greater than 6.8, the clay water subtracts from the rock conductivity relative to an Archie rock. This cannot be accommodated by the Waxman-Smits formulation. To correct for this model deficiency, B was made a function of salinity and temperature when, theoretically, it is a function of temperature only. Thirdly, neither model accurately predicts the rock conductivity at pore water salinities below approximately 0.5 to 1 S/m. Having a proper model at these lower salinities is important for geothermal evaluations, waterflooded reservoirs, and naturally occurring freshwater reservoirs. We propose a correction method based on our knowledge gained from the study of the quadrature conductivity measurement from cores and recent laboratory measurements.

Early Diagenetic Controls on Sedimentary Iodine Release and Iodine‐To‐Organic Carbon Ratios in the Paleo‐Record

AbstractIodine cycling in the ocean is closely linked to productivity, organic carbon export, and oxygenation. However, iodine sources and sinks at the seafloor are poorly constrained, which limits the applicability of iodine as a biogeochemical tracer. We present pore water and solid phase iodine data for sediment cores from the Peruvian continental margin, which cover a range of bottom water oxygen concentrations, organic carbon rain rates and sedimentation rates. By applying a numerical reaction‐transport model, we evaluate how these parameters determine benthic iodine fluxes and sedimentary iodine‐to‐organic carbon ratios (I:Corg) in the paleo‐record. Iodine is delivered to the sediment with organic material and released into the pore water as iodide (I−) during early diagenesis. Under anoxic conditions in the bottom water, most of the iodine delivered is recycled, which can explain the presence of excess dissolved iodine in near‐shore anoxic seawater. According to our model, the benthic I− efflux in anoxic areas is mainly determined by the organic carbon rain rate. Under oxic conditions, pore water dissolved I− is oxidized and precipitated at the sediment surface. Much of the precipitated iodine re‐dissolves during early diagenesis and only a fraction is buried. Particulate iodine burial efficiency and I:Corg burial ratios do increase with bottom water oxygen. However, multiple combinations of bottom water oxygen, organic carbon rain rate and sedimentation rate can lead to identical I:Corg, which limits the utility of I:Corg as a quantitative oxygenation proxy. Our findings may help to better constrain the ocean's iodine mass balance, both today and in the geological past.

Diagenesis Decreasing the Mo Isotopic Composition in Estuarine Systems: Implications for Constraining Its Riverine Input to Ocean

AbstractUnderstanding the geochemical behavior of the Mo isotopes in estuarine systems is essential for determining the isotopic composition of riverine inputs to the ocean and for assessing the historical oxidation state of Earth’s ancient oceans. However, the extent and mechanisms of Mo isotope fractionation during estuarine processes are not yet fully understood. This study systematically investigated the seasonal and spatial variations in aqueous and particulate δ98Mo values within the Pearl River Estuary (PRE). Our research found that aqueous δ98Moaque. values in both summer and winter deviated significantly from the theoretical mixing line for the PRE. Based on the geochemical characteristics of the water column, particulate matter, and pore water in the PRE, we first propose that diagenesis release from sediments is the predominant factor resulting in lower than anticipated aqueous δ98Moaque. values. Given the prevalence of suboxic and anoxic sediments in estuarine and coastal areas, such diagenetic release may substantially decrease the global riverine influx of aqueous Mo isotopes to the ocean. Additionally, particulate δ98MoSPM values exhibit an increasing trend (from 0.02 to 1.62‰) with increasing salinity in both seasons, suggesting that the terrestrial input particulate δ98MoSPM value would be heavier than the mean value for UCC. We hypothesize that the adsorption and desorption processes involving Fe (hydro) oxides predominantly influence this trend. This study advances our understanding of the mechanisms of aqueous and particulate Mo isotopic fractionation in estuarine systems and would be helpful in constraining Mo isotopic compositions of rivers and oceans.

Mercury Mobility in Epibenthic Waters of a Deltaic Environment

AbstractMercury (Hg) cycling at the sediment‐water interfaces (SWI) encompasses multiple homogeneous and heterogeneous biogeochemical reactions whose result is not yet elucidated. Estuarine SWIs, where the organic matter mineralization is active, constitute experimental sites particularly suitable for scrutinizing Hg speciation and mobilization. Here, we present high‐resolution vertical concentration profiles of Hg species, including inorganic divalent Hg () and monomethyl Hg (MMHg) in solid and dissolved (<0.22 μm) phases, on both sides of the SWI of the proximal part of the Rhône prodelta (northwestern Mediterranean Sea) using sediment cores and dialyzers implemented for a 67‐day‐long period. Concentrations of the dissolved species were <0.10 nM in the sediment pore waters but reached up to 0.58 nM in the epibenthic water zone, a concentration level that is ∼200 times higher than that of the water column. Conversely, MMHg concentrations were low (<0.5 pM) above the SWI and increased to up to 4.6 pM in the sulfate‐reducing zones of the sediment. The dynamic of the Hg species interconversions was explored using one‐dimensional transport‐reaction equations. This model allowed us to constrain the depth intervals where various species are produced or consumed and to approximate the reaction rates. We conclude that the epibenthic zone of the Rhône prodelta is a location of intense mobilization of inorganic HgII associated with organic matter mineralization and MMHg distribution in pore water is controlled by microbiological in situ reactions, but sedimentary MMHg does not diffuse in the overlying water column.

Combining dredging with modified zeolite thin-layer capping to control nitrogen release from eutrophic lake sediment

Dredging is widely used to control internal sediment nitrogen (N) pollution during eutrophic lake restoration. However, the effectiveness of dredging cannot be maintained for long periods during seasonal temperature variations. This study used modified zeolite (MZ) as a thin-layer capping material to enhance dredging efficiency during a year-long field sediment core incubation period. Our results showed that dredging alone more effectively reduced pore water N, N flux, and sediment N content than MZ capping but showed more dramatic changes during the warm seasons. The N flux in dredged sediment in summer was 1.8 and 2.5 times that in spring and autumn, respectively, indicating a drastic N regeneration process in the short term. In contrast, the combination method reduced the extra 10% pore water N, 22% N flux, and 8% sediment organic N content compared with dredging alone and maintained high stability during seasonal changes. The results indicated that the addition of MZ to the surface of dredged sediment not only enhanced the control effect of dredging by its adsorption capacity but may also smooth the N regeneration process via successive accumulation (in the channel of the material) and activation of bacteria for months, which was evidenced by the variation in microbial diversity in the MZ treatment. As a result, the combination of dredging with modified zeolite simultaneously enhanced the efficiency and stability of the single dredging method in controlling sediment N content and its release, exhibiting great prospects for long-term application in eutrophic lakes with severe pollution from internal N loading.

Research on dynamic stress and excess pore water pressure of asphalt pavement under hydraulic-mechanical coupling

The impact of the initial static stress field on dynamic calculation results was considered, a three-dimensional refined coupling system model was constructed using finite element software, and the time domain and space domain distribution laws of dynamic stress and excess pore water pressure of saturated asphalt pavement under moving load were investigated. The findings show that the influence of the initial static stress field on the pavement dynamic calculation results will increase as the pavement depth increases. On the bottom surface of the upper layer, when the initial static stress field is not considered, the errors in vertical dynamic stress and excess pore water pressure are 29.6% and 30.8% respectively. As compared to dry pavement, the tensile stress on saturated asphalt pavement increases, and the stress attenuation rate slows when the load passes, putting the pavement structure in an undesirable situation. The negative peak value of the hydrodynamic pressure in the higher layer drops linearly as the permeability coefficient of the upper layer increases. In contrast, the negative peaking of the vertical dynamic stress grows linearly. Under the situation of potholes, the dynamic stress components in six directions of the saturated asphalt pavement all rise dramatically. Among the three shear stress components, τyz increases the most under the condition of pavement pothole, which is 345% higher than that without pothole. Among the three normal stress components, the vertical dynamic stress has the largest increase, which is 156% higher than that without potholes, and the increase in shear failure of the pavement is greater than that of tensile failure. The research findings will be helpful in determining the degradation process of saturated asphalt pavement and in designing asphalt pavement structures in rainy areas.

Elemental interactions between pore water and lake sediments with their environmental significance: a case as Holocene sediments in Guozha Co, northwestern Tibetan Plateau

Elemental interactions between pore water and lake sediments with their environmental significance: a case as Holocene sediments in Guozha Co, northwestern Tibetan Plateau

Fabrication and characterization of low-cost kaolin based tubular ceramic membrane for microalgal harvesting

Tubular membranes with natural kaolin as a key precursor were fabricated in this study. Membranes with five different compositions were prepared, and the optimized membrane (77% kaolin, 2% boric acid, 2% sodium metasilicate, 4% sodium carbonate, and 15% calcium carbonate) was used to harvest microalgal culture. The pore size, porosity, water permeability, chemical and mechanical strength of the membranes were investigated. An assessment of the cost related to the membrane fabrication was also conducted. The fabricated membranes had porosity of ∼26–47%, a pore diameter of 0.123–0.182 µm, water permeability of 4.2 × 10−8 – 17.1 × 10−8 m3 m−2 s−1 kPa−1, along with good mechanical and chemical strength. The optimized membrane was tested for microfiltration of microalgae Monoraphidium sp. KMC4 with 1.5 g L−1 of initial concentration at a persistent cross-flow rate (1.11 × 10−5 m3 s−1) and various transmembrane pressures (69 kPa - 345 kPa). The separation results yielded an average permeate flux of 1.85 × 10−5 m3 m−2 s−1 at 276 kPa transmembrane pressure. Complete algal cell recovery and substantial nutrient passage (>88%) were observed within the pressure range of 69 kPa to 345 kPa. Fouling mechanism was explained by fitting four distinct pore-blocking models, of which the cake filtration model provided the most accurate fit as compared to the complete, intermediate and standard pore-blocking models. Additionally, the total organic carbon varied in the range of 31.6–63.2 mg L−1. This essentially explained the source of pore blocking.

Penetration Characteristics of Suction Caisson for Offshore Wind Power: A Field Study

Suction caisson is a new offshore wind power foundation structure developed in recent years. Understanding its penetration characteristics is crucial to the successful application. A field test was conducted in the eastern waters of Rudong, Jiangsu Province, China, to investigate the penetration process of suction caisson. The test results demonstrate that suction caisson can penetrate smoothly to a predetermined elevation of seabed soil under the complex environmental loads, such as natural wind and wave currents. The inclination of the caisson is only 0.018° once the penetration process is complete. The pore water pressure at the outer skirt is primarily influenced by the tide level and drainage conditions of the contact soil layer during penetration, and the peak effective interface pressure at the skirt-soil interface decreases by about 46.7% due to negative pressure inside the skirt. Frictional fatigue effects are found at the skirt-soil interfaces. Meanwhile, the seepage reduction and squeezing induced resistance effects at the skirt-soil interface are the leading causes for the different distributions of effective interface pressure between the inner and outer skirts of the caisson. The findings of this study can guide the future penetration of suction caisson under challenging geological circumstances.

Low soil Moisture Slows Uptake and Elimination Rates of Phenanthrene in Springtails

This study investigated the influence of soil water status on the toxicokinetics of phenanthrene in the springtail Folsomia candida allowing estimation of uptake and elimination rates at two contrasting soil water potentials. Fitting a three-phase model to the observations showed that uptake rate (ku) was almost two times higher in moist soil (-2 kPa) than in dry soil (-360 kPa). During the first days of the exposure, elimination rate (ke) was not significantly different in moist and dry soil, but after eight days ke had increased significantly more in moist soil than in dry soil. Our results confirm the general notion that the exposure route via soil pore water is important. Understanding the significance of soil moisture in exposure and effects of contaminants on soil invertebrates is crucial for assessing the ecological risks associated with soil pollution in a changing climate.

A fully coupled thermo-hydro-mechanical elastoplastic damage model for fractured rock

A detailed and fully coupled thermo-hydro-mechanical (THM) model for fractured rock is presented. This model distinguishes itself by harmoniously integrating elastoplastic material behaviour with a continuum damage mechanics framework. Solid matrix displacement, pore and fissure water pressures and temperature of the solid are introduced as the primary nodal variables. The ingenuity of this research is embedded in the intricate coupling of THM processes with plastic deformation and damage mechanics in a double porous medium, a venture that significantly broadens the remit of existing methodologies. The model is implemented using finite element method (FEM) and validation is achieved by comparing the FEM results against existing literature numerical outcomes describing linear and elastoplastic continuum damage behaviour of fractured rock. The model also exhibits an extraordinary proficiency in reproducing experimental triaxial test results, using THM components conjoined with elastoplastic bounding surface aspects and inherent hardening effects. It is imperative, nonetheless, to underscore the model's sensitivity to certain material properties, inclusive of strength parameters, leakage coefficients, and permeability attributes. This fully coupled THM model provides a comprehensive and sophisticated tool for investigating the behaviour of fractured rock under various loading conditions. It can help us better understand the physics of fractured rock behaviour and contribute to the development of more accurate and reliable models for engineering applications, such as CO2 injection.

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Effect of collated fly ash, GGBS and silica fume on index and engineering properties of expansive clays as a sustainable landfill liner

The effect of supplementary cementitious materials (SCMs) such as fly ash (FA), GGBS and silica fume (SF) on the geotechnical index and engineering properties of expansive clays (EC) are studied in this research work. This manuscript aims to determine the workability (consistency limits (CL)), swellability (free swell index (FSI)), compaction properties, strength characteristics (UCS) and hydraulic conductivity (HC) of varied eighteen mix proportions of FA-EC (P-series), FA-GGBS-EC (Q-series) and FA-GGBS-SF-EC (R-series) are experimentally studied as a bottom liner in landfills. From the test results, CL and FSI significantly decreased in P, Q and R series, this is due to the effect of flocculation, a process that increases the average particle size of mix blends and also depletion of the double-diffusive layer thickness of EC by promoting the Ca2+ ions in the pore water from SCMs. The compaction parameters such as optimum moisture content decreased in all the series, due to the higher flocculation of mixes. However, maximum dry unit weight increased in Q and R and decreased in the P series. The UCS values increased with an increase in optimum SCMs quantities and with curing intervals tested at 0, 7, 14 and 28 days. The higher UCS value is attained at 40 %FA with EC (i.e. P2), 60 %FA-GGBS with EC (i.e. Q3) and 60 %FA-GGBS-SF with EC (i.e. R3) in R-series which confirmed to be optimum due to the loss of cementation action/reduced cohesion in the matrix. In the case of HC, P2, Q3 and R3 mixes are confirmed to be optimum and fall under the criterion standards of landfill liner as per USEPA recommendation. Overall, this work proves to be a novelty and shows the feasibility of various collated SCMs blended with EC as landfill liner material, furthermore, these mixes are optimized to combine with EC to create a sustainable landfill liner that fits with the United Nations sustainable goals of 2030

Unveiling the role of pore characteristics in sludge dewatering: Visualization by Nano-CT and micromodel study

The solid-liquid separation is an indispensable and primary link in the process of sludge treatment and disposal. The past research was focused primarily on the technique explorations of sludge dewatering and always disregarded the internal pore structure and water migration behavior in sludge. In this work, the real three-dimensional pore structure of sludge was obtained by Nano-CT. Based on this, a pore-scale heterogeneous sludge micromodel was firstly presented, and the water flooding experiment was carried out to visualize the water migration behavior. The results showed that the sludge structure transformed from sheet-like floc to microsphere particles, and then agglomerated into large globular granules during anaerobic ammonia oxidation. And the equivalent pore size increases from 342 μm to 617 μm, improving the sludge dewaterability characterized by capillary suction time (CST). The most significant implication of this work was revealing the critical role of invalid connected pore in sludge dewatering. Such pore was not contributed to fluid flow but the circulating vortex in it even induced energy dissipation, thus deteriorated the sludge dewaterability. This work may be helpful to understand the critical role of pore characteristic in water migration and shed light on the new dewatering techniques from the perspective of regulating sludge structure.

Macropore flow in relation to the geometry and topology of soil macropore networks: Re-visiting the kinematic wave equation

The rapid flow of water through soil macropores significantly affects the partitioning of precipitation between surface runoff and infiltration and also the rate of solute transport in soil, both of which have an impact on the risk of contamination of surface water and groundwater. The kinematic wave equation is often employed as a model of gravity-driven water flow through soil macropores. The exponent in this simple model influences the pore water velocity attained in the macropores at any given input rate and is usually estimated by inverse modelling against measured flow rates or water contents. In theory, the exponent in the kinematic wave equation should depend on the geometry and topology of the conducting macropore networks, although these relationships have not so far been investigated. In this study, we related metrics of soil structure derived from X-ray images to values of the kinematic exponent estimated from drainage experiments on twenty-two columns sampled at three different field sites under two contrasting land uses and at three different depths.We found that smaller values of the exponent in the kinematic wave equation, which would equate to more rapid flow of water through soil macropores, were found in plough pan and subsoil columns of smaller macroporosity, for which biopores comprised a significant fraction. The macroporosity in these columns was more vertically oriented and poorly inter-connected, though still continuous across the sample. In contrast, topsoil columns from both arable land and grassland had better connected, denser and more isotropically-distributed macropore networks and larger values of the kinematic exponent. Our results suggest that for predictive modelling at large scales, it may be feasible to estimate the kinematic exponent using class pedotransfer functions based on pedological information such as land use and horizon type.

Investigating Pore Water Pressure Development in Paste Backfill Under Conditions Mimicking Field Loading

Investigating Pore Water Pressure Development in Paste Backfill Under Conditions Mimicking Field Loading