Pore Water Research Articles

Determining parameters of peat soil for finite-element analysis using the Cam Clay model

A practical procedure for determining soil parameters when analysing the deformation of peat by finite-element analysis (FEA) using the Cam Clay model is presented. FEA has not been frequently used to predict the deformation of peat soil, even though it can be a powerful prediction tool. The main reason for this is that a practical method for determining parameters has not been established. In this paper, the remarkable correlation between the soil parameters required for FEA using the Cam Clay model and the natural water content (wn) and ignition loss (Li) of peat and organic clay is presented. Then, based on this correlation, a flow chart for determining the soil parameters of peat and organic clay is proposed. Using this chart, it is possible to determine soil parameters directly from triaxial compression, oedometer and other detailed tests or to estimate them from wn, Li and other physical indexes. A trial embankment on peat soil in Hokkaido, Japan, was also created. FEA was performed on the trial embankment using the proposed procedure for determining the soil parameters. The results of the FEA corresponded to the measured settlement behaviour in the trial embankment with an accuracy in the range −4% to +8%. The FEA results also modelled the measured behaviour of pore water pressure and lateral and vertical displacements in the trial embankment very well.

Vallisneria spiralis Promotes P and Fe Retention via Radial Oxygen Loss in Contaminated Sediments

Microbial respiration determines the accumulation of reduced solutes and negative redox potential in organic sediments, favoring the mobilization of dissolved inorganic phosphorus (DIP), generally coprecipitated with Fe oxyhydroxides. Macrophytes releasing oxygen from the roots can contrast DIP mobility via the oxidation of anaerobic metabolism end-products. In this work, the submerged macrophyte Vallisneria spiralis was transplanted into laboratory microcosms containing sieved and homogenized organic sediments collected from a contaminated wetland. Sediments with and without plants were incubated under light and dark conditions for oxygen and DIP fluxes measurements and pore water characterization (pH, oxidation-reduction potential, DIP, dissolved Mn, and Fe). Bare sediments were net DIP sources whereas sediments with V. spiralis were weak DIP sources in the dark and large sinks in light. V. spiralis radial oxygen loss led to less negative redox potential and lower Fe, Mn, and DIP concentrations in pore water. Roots were coated by reddish plaques with large amounts of Fe, Mn, and P, exceeding internal content. The results demonstrated that at laboratory scale, the transplant of V. spiralis into polluted organic sediments, mitigates the mobility of DIP and metals through both direct and indirect effects. This, in turn, may favor sediment colonization by less-tolerant aquatic plants. Further in situ investigations, coupled with economic analyses, can evaluate this potential application as a nature-based solution to contrast eutrophication.

Effect of pore water pressure on mechanical performance of recycled aggregate concrete under triaxial compression

The pore water pressure in concrete can significantly increase due to volume compression. Recycled aggregate concrete (RAC) possesses a more complex microstructure compared to natural aggregate concrete (NAC). Understanding the porosity and micromechanical properties of RAC is crucial for analysing its failure mechanism under the influence of coupled confining pressure and pore water pressure. This study compares the constituent proportions and micromechanical properties of interfacial transition zones (ITZs) and the adjacent paste matrix in NAC and RAC. Compressive stress-strain curves were obtained for concrete under coupled confining pressure and pore water pressure. The results indicate that the newly formed ITZ, which bonds to old mortar, outperformed the one bonded to natural aggregate when considering the same water-cement ratio. Compressive strength, ductility, and maximum volumetric strain gradually increased with increasing confining pressure. However, when pore water pressure was removed, compressive strength decreased while elastic modulus improved. Due to the inferior microstructures of RAC compared to NAC, the supportive effect of pore water becomes more pronounced. This is evident in the gradual increase in peak strain with increased pore water pressure for the stress-strain curves of RAC (100 % replacement ratio). Finally, a failure criterion and stress-strain theoretical model considering pore water pressure are proposed, and satisfactory fitting results are obtained.

Salt transport dynamics across the sediment-underground brine interface driven by tidal hydrology and benthic crab burrowing in muddy tidal flats

Muddy coasts with burrows are widespread globally and most contain brine in underground aquifers. Salt evaporated on a tidal flat surface is an important source of shallow underground brine (phreatic brine and brine in the top layer). However, the salt accumulation/release process in shallow underground brine during tidal cycles remains unclear. To analyze the abovementioned process, sediment permeability and pore-water parameters are measured, and electrical resistivity tomography and ring electrode resistivity probe monitoring are conducted in a tidal flat on the south bank of Laizhou Bay, China, where underground brine occurs and biological activities are pronounced. The results show that evaporated salt on the surface of tidal flats and offshore high-salinity underground brine are the two salt sources of shallow underground brine in tidal flats. Dense burrows and large tidal ranges can accelerate the rate of salt cycling, and promoting the exchange of surface and deep salt through the top layer. During the flooding tide, shallow underground brine is primarily replenished by evaporated salt on the beach surface. In areas with dense burrows, some evaporated salt on the beach surface can pass through the top layer to recharge the phreatic brine. During the ebbing tide, the salt in layers U and B is released into seawater and phreatic brine, respectively. When seawater recedes from the beach surface, a trace amount of phreatic brine and salt in the top layer is released to the beach surface via an upward flow field. Layers U and B are the main areas of salt accumulation and release. The proportion of salt accumulation/release in layer M is the lowest; however, layer M is the most susceptible to salt accumulation and features the highest pore-water salinity among the top layers.

Stability Analysis of Surrounding Rock in Deep Underground Engineering Under Fluid-solid Interaction

The geological environment of deep rock masses is extreme and complex, characterized by typical deep geological features such as high geostress, high permeation water pressure, and high geotemperature. Geological disasters like water and mud inrush, high-intensity rock bursts, and large-volume collapses occur frequently in engineering construction, presenting more complex mechanisms of disaster than shallower rock masses and severely impacting the construction and operational safety of deep underground projects. Utilizing three-dimensional numerical simulation methods, this study investigated the deformation, stress, and plastic zone characteristics of surrounding rock under multi-field coupling conditions during the construction of deep caverns, revealing the stability influencing factors of deep caverns under multi-field coupling. A funnel-shaped precipitation area forms near the excavation surface of the cavern, gradually expanding as the initial pore water pressure increases. The concentration of seepage vectors in the sidewalls and arch feet continues to increase, with local seepage rates reaching 5.1×10^-6. The cavern's crown and sidewalls are particularly sensitive to changes in pore water pressure, with the maximum tensile stress appearing 1 m and 3 m axially along the sidewalls of the cavern. The plastic zone experiences its greatest increase at a water pressure of 4 MPa.

Dynamic thermo-mechanical responses of road-soft ground system under vehicle load and daily temperature variation

A complete road-soft ground model is established in this paper to study the dynamic responses caused by vehicle loads and/or daily temperature variation. A dynamic thermo-elastic model is applied to capturing the behavior of the rigid pavement, the base course, and the subgrade, while the soft ground is characterized using a dynamic thermo-poroelastic model. Solutions to the road-soft ground system are derived in the Laplace-Hankel transform domain. The time domain solutions are obtained using an integration approach. The temperature, thermal stress, pore water pressure, and displacement responses caused by the vehicle load and the daily temperature variation are presented. Results show that obvious temperature change mainly exists within 0.3 m of the road when subjected to the daily temperature variation, whereas the stress responses can still be found in deeper places because of the thermal swelling/shrinkage deformation within the upper road structures. Moreover, it is important to consider the coupling effects of the vehicle load and the daily temperature variation when calculating the dynamic responses inside the road-soft ground system.

The influence of cold seepage on the grain size and geochemistry of sediments from the Laptev Sea shelf

The East Siberian Arctic shelf is renowned for its active methane-rich fluid seeps, confirmed by numerous gas flares in the water column and direct observations of methane release from the seafloor. These cold-seep sites serve as natural laboratories for studying the impact of methane seepage on early diagenesis, authigenic mineral formation, and the geochemical cycles of carbon, sulfur, and other elements. This study examines the grain size and chemical composition of two sediment types from the Laptev Sea shelf: cold-seep sediments influenced by sulfate-driven anaerobic methane oxidation, and unaffected “seep-free” sediments (i.e., control site). High methane concentrations (up to 649 μM/L) in the surface layer of sediments indicate that the sulfate–methane transition zone is found close to the sediment–water interface approximately 5–6 cm below the seabed. At the cold-seep site, thin layers containing up to 40% sand fraction were discovered among the fine-grained sediments. We infer that upward-migrating fluids may contribute to the remobilization of the fine fraction, resulting in concentration of coarse particles. Cold-seep sediments are characterized by molybdenum (Mo) enrichment compared to the lithological background, although one “seep-free” core exhibits evidence of authigenic Mo deposition. The Mo concentration (up to 16.8 ppm) indicates that enrichment occurs under sulfidic conditions restricted to pore water, which are caused by anaerobic methane oxidation. The high Mo concentration in one “seep-free” core likely implies past cold-seep activity. A general Mo–U covariation indicates that the molybdenum enrichment in cold-seep sediments from the Laptev Sea outer shelf is controlled by a weak particulate shuttle process.

Dimension reduction for uncertainty propagation and global sensitivity analyses of a cesium adsorption model

This paper presents an efficient method to perform uncertainty and sensitivity analyses in a cesium adsorption model upstream chained with a pore water composition model. As the number of uncertain input parameters is about twenty for each of the two models, a dimension reduction technique is implemented to build a polynomial approximation of the cesium distribution coefficient in a reduced subspace. Two approaches are tested depending on the water composition and adsorption models are treated as a single block or two separate blocks. In view of assessing the robustness of the approaches, three initial cesium concentrations are considered to explore different regimes of the adsorption model. The interpretation of the linear transformations projecting the original inputs to the reduced coordinates is broadly consistent with the geochemical features of the model. Validation results show that the relative error levels of the surrogate models are around a few percent for both approaches with only one thousand realizations of the chained model. Global sensitivity analysis highlights that the variance of the cesium distribution coefficient is overwhelmingly governed by the adsorption model. Still, this conclusion is nuanced when considering the whole cumulative distribution function for which the interaction effects between the two models account for a fifth.

Stability analysis of loess slope combined with limit equilibrium method under different rainfall intensities

Abstract Due to the special characteristics of loess soil, once the stability of the slope is not detected in place, it is easy to cause serious loss of life and property, so this paper is based on the limit equilibrium method to analyze the stability of loess slopes under different rainfall intensities. The simplified Bishop’s method, the proposed static method, and the strength reduction method under the limit equilibrium method are studied to provide a reference basis for subsequent research. Explore the law of rainwater infiltration in loess under different rainfall conditions, construct a water-wetting model, investigate the seepage law of loess slope, and detect the degree of wetting and seepage of loess soil under different rainfall conditions. Combining the principle of effective stress of saturated soil, analyze the mechanical characteristics of the unsaturated soil on the loess slope. The stability of loess slopes under natural conditions and seismic conditions is analyzed, and the pore water pressure and shear strength of the sliding surface of loess slopes are analyzed under different rainfall conditions. The experimental data show that the slope safety coefficient of the simplified Bishop-limit equilibrium method under natural conditions is 1.118, and the difference with other algorithms is about 2.9%, which shows that the safety coefficient of the simplified Bishop-limit equilibrium method is more accurate to detect when combined with the slope stability model. When the rainfall intensity is 15, 30, 45, 60, and 75mm/h, the slope safety factor is 1.18, 1.14, 1.125, 1.12, and 0.98, respectively, the rainfall intensity is negatively correlated with the slope safety factor.

Lower nitrate leaching from dairy cattle slurry compared to synthetic fertilizer calcium ammonium nitrate applied to grassland

Nitrate leaching from agriculture can be reduced by the choice of fertilizer and a proper timing of its application. For permanent grassland grown under temperate conditions, nitrate leaching was hypothesized to be lower from dairy cattle slurry (CS) compared to synthetic fertilizer calcium ammonium nitrate (CAN), based on differences in chemical composition, consequential effects on nitrogen (N) conversion processes in soil, and resulting differences in synchronization of (nitrate) N availability and plant N uptake. We tested the hypothesis in a two-year field experiment on cut grassland on a leaching-sensitive sandy soil, fertilized each year with 320 kg ha−1 of plant-available N from either 100% top-dressed CAN or a combination of 40% from CAN and 60% from sod-injected CS, and measured effects on grass herbage yield, herbage N uptake, and nitrate concentration in pore water at 1.0 m depth. Our results show a comparable level of herbage N uptake for both treatments, allowing for a proper comparison of nitrate leaching at a similar level of plant-available N. Average nitrate concentration in pore water in the main leaching period (over winter) was after the first (dry) growing season 44% lower for CS + CAN (41 mg l−1) compared to CAN only (73 mg l−1), and after the second (wet) growing season 35% lower for CS + CAN (32 mg l−1) compared to CAN only (49 mg l−1). Nitrogen application increased nitrate concentration at 1.0 m depth not only in winter but also in the growing season. We conclude that for permanent grasslands in temperate regions, nitrate leaching from timely applied CS may be considerably lower than from CAN, which is different from previous assumptions.

Physical modelling of the seismic response of well casings in liquefiable soil

ABSTRACT Liquefaction is a catastrophic phenomenon that poses a serious threat to lifelines during an earthquake. To assess the seismic behaviour of a well casing buried in saturated sand, a series of 1-g shaking table model tests were performed. The present study aims to investigate the impacts of the relative density and groundwater level on the base case as well. The responses of the models, including accelerations, pore water pressure changes, settlements, and strains induced along the well casing at various locations, were measured during the shaking. The outcomes illustrated that the groundwater level has a significant effect on the position of maximum strain. A rise in relative density leads to a 40.7% reduction in strains and moments caused along the well casing, while the rate of strain permanence in denser soils is considerable compared to looser soils. Moreover, experimental results indicated that the maximum shear force caused at the bottom of the well casing grows about 67% with increasing groundwater table.

Semi-analytical solution for dynamic thermo-mechanical responses of multi-layered thermo-poroelastic media

Dynamic thermo-mechanical responses of multi-layered thermo-poroelastic media induced by internal thermal and mechanical loads are investigated utilizing a semi-analytical approach. To investigate the transient behavior of the thermo-poroelastic media, the governing equations that consider both the fluid inertia and the soil skeleton inertia are established. The Laplace–Hankel transform is then applied to derive solutions for a single thermo-poroelastic layer and a half-space in the transformed domain. The multi-layered thermo-poroelastic model is assembled using the layer and half-space elements with the continuity assumptions. Solutions for the multi-layered thermo-poroelastic model are obtained in the transformed domain using boundary conditions, while the final solutions are calculated using a numerical procedure. Comparisons with published results validate the accuracy of the multi-layered model. Finally, effects of the coupled internal dynamic thermo-mechanical load, as well as the influences of material stratification and permeability, on the dynamic responses, including vertical displacement, temperature, vertical stress, and pore water pressure, are graphically presented.

Experimental investigations on the effect of density, grain size, and fines content on ejecta-induced settlement

The occurrence of sand boils or ejecta following earthquakes can cause considerable ground settlement. This study aims to investigate how soil properties influence ejecta-induced settlement by conducting experimental tests that simulate the sand boil process. Three materials, namely coarse C306 sand, fine C778 sand, and non-plastic silt, were used to examine the effects of grain size, fines content, and density on the amount of sand boil and resulting settlement. The test results indicate that loose specimens with low density experience more ejecta-induced settlement, while specimens with higher amounts of coarse grains or fines exhibit less settlement even at similar void ratios or relative densities. However, the amount of ejecta produced is directly proportional to the duration of high pore water pressure (H-PWP), which is influenced by both PWP supplies and dissipation. The differences in permeability and one-dimensional stiffness among materials explain the varying H-PWP duration across the tests. Therefore, when estimating the ejecta amount, it is crucial to account for the varying stiffness and permeability during liquefaction and post-liquefaction consolidation to accurately assess the H-PWP duration.

Substantially excess uranium in the waters of an intertidal salt marsh: A case study of eastern Chongming Beach

Knowledge of the geochemical behavior of uranium is key to an accurate tracing of the decay chain of the uranium series nuclides for material transportation processes on different temporal scales. However, direct observations for understanding dissolved uranium input in tidal water are very limited. Therefore, dissolved uranium was measured in tidal creek water, overlying water, and pore water collected from the central cross section of eastern Chongming Beach, Changjiang Estuary, from November 2012 to October 2013, to observe the spatiotemporal distribution of uranium. The results indicated that the behavior of dissolved uranium is conservative in the tidal creek waters during the flooding process, and an excess of dissolved uranium is observed during the ebbing process; excess uranium phenomena are dominant in the overlying and pore waters throughout the year, particularly at the middle and high tidal flats. The element concentration profiles in pore water showed that uranium release follows Mn oxide reduction in the subsurface suboxic zone. Hence, the exchange process between tidal water and pore water, coupled with ebb tide, represents a potential path for uranium release into the estuary. The three-end-member (Changjiang River, seawater, and pore water) model estimates that 35% of the amount of uranium in ebbing water is derived from pore water. The exchange rate between tidal water and pore water is 196.4 nmol/(cm2·d), with an export flux of 2.34 × 104 mol/a. We suggest that the release of uranium from intertidal salt marshes is an important uranium source in estuarine and coastal regions.

Trace element characteristics of pore water from the deep-sea sediments of the Interoceanmetal exploration area in the Clarion-Clipperton Fracture Zone, NE Pacific

The concentrations of Fe, Mn, Co, Cd, Zn, Cu, Mo, and As were registered in broad intervals and are elevated compared to the mean values for the ocean water. Vertical distributions of the element concentrations in the pore waters along four sediment cores show distinct differences, mainly for the elements Fe, Mn, Cu, and Zn. Bioturbation activities developed in the depth interval 7–15 cm could be a probable reason for the variation trends. The distributions for the elements As, Cd, Co and Zn are conservative type and the patterns for the Mo and Ni – scavenged type. The obtained pore water profiles are similar to the distribution trends for areas in the Eastern Equatorial Pacific and show different patterns from the pore waters from the Western Pacific.

Autogenous Self‐healing of CTRC Repair Layers Exposed to Tensile Threshold Loading

AbstractThe experimental investigations presented in this paper contribute to fill the knowledge gaps on the subject of autogenous self‐healing of DURTEX layers for the surface repair of cracked or cyclic crack opening of concrete and reinforced concrete structures. Composite specimens, so‐called crack distribution specimens, were subjected to at least 1000 and up to 6900 cycles. Investigations show that neither the crack characteristics (e. g. crack width, crack geometry) change nor the mechanical properties (e. g. adhesive tensile strength or tensile load‐bearing behavior) are reduced compared to the reference specimens as a result of cyclic loading with both pore and crack water pressure. Also, the self‐healing potential of a selected material combination is demonstrated despite cyclic loading. It was observed that cracked DURTEX layers with wmax = 0.116 mm, under cyclic loading (Δwop = 0.6 mm) at a constant test speed set to 0.05 mm/min (piston controlled) with a 5 m pore and crack water pressure can self‐heal themselves leading to water tightness after 14 days. Chemical‐mineralogical analysis using X‐ray diffraction (XRD) on material taken from the cracked surface of the specimen evidenced the formation of CaCO3 as calcite.

Simultaneous immobilization of sediment internal phosphorus, arsenic and tungsten by lanthanum carbonate capping

In this study, lanthanum carbonate (LC) was selected as a capping agent to examine its effectiveness in immobilizing sediment internal phosphorus (P), arsenic (As) and tungsten (W). With a 180-day incubation experiment, it was determined that LC capping efficiently reduced the concentrations of soluble reactive P (SRP), soluble As and soluble W in pore water, with the highest reduction rate of 83.39%, 56.21% and 68.52%, respectively. The primary mechanisms involved in the adsorption of P, As and W by LC were precipitation reactions and ligand exchange. Additionally, P, As and W were immobilized by LC capping through the transformation of fractions from mobile and less stable forms to more stable forms. Furthermore, LC capping led to an increase in the Eh value, which promoted the oxidation of soluble Fe (Ⅱ) and soluble Mn. The significantly positive correlation and synchronized variations observed between SRP, soluble As, soluble W, and soluble Fe (II) indicated that the effects of LC on Fe redox played a crucial role in immobilizing sediment internal P, As and W. However, the oxidation of Mn, promoted by LC, played a more significant role in immobilizing sediment internal As than P and W. These effects resulted in LC capping achieving the highest reduction of SRP, soluble As and soluble W flux at 145.22, 22.19, and 0.58 μg m−2d−1. It is of note that LC capping did not lead to an elevated release hazard of Co, Ni, Cu, and Pb, barring Cd. Besides, LC capping did not modify the entire microbial communities in the sediment, but altered the proportional representation of specific microorganisms. Generally, LC has potential as a capping agent capable of simultaneously immobilizing sediment internal P, As and W.

Organic Matter in the Ocean: Indicators of Biogeochemical Processes

The article presents informative organogeochemical indicators used in oceanology to characterize biogeochemical processes. A classification based on data on suspended particulate matter, plankton, benthos, bottom sediments, and sea, river, and pore water has been developed. Clusters have been identified that include the elemental and isotopic composition of organic matter (OM), the group composition of lipids, aliphatic and alicyclic hydrocarbons, higher alcohols, macromolecular acids and ketones, isoprenoids, lignin and its structural monomers, and PAHs. The most informative indices are considered, which make it possible to assess the genesis of the original OM, the degree of its transformation, sources, and the ratio of aquatic and terrigenous components. These indices reflect the influx of riverine and aeolian material and permafrost thawing and make it possible to reconstruct the temperature of river waters and coastal upwellings. They significantly complement biooceanological, lithological, and geochemical studies and expand the biogeochemical methodology for studying the carbon cycle.

Evolution of kinetics and pore water composition during hydration of a CAC‐Calcite system by addition of Na5P3O10

AbstractIt was analysed how a low Na5P3O10 (STPP) concentration influences the hydration of a calcium aluminate cement. It is known that the hydration of a CAC‐Calcite system precipitates C2AHX as a precursor phase at 23°C during hydration before the formation of hemi‐ or monocarbonate and the additional formation of CAH10 and AH3. In our study the addition of 0.2 and 1.0 wt.% STPP (bwoc) to a CAC‐Calcite system at 23 °C and with a w/b of 0.33 was investigated and is compared with mixes without STPP addition. Heat flow calorimetry data showed that STPP accelerates the main reaction. Moreover, an additional heat flow event within the first 30 minutes was detected by STPP addition. However, from the results of QXRD analysis, crystalline hydrate phases are formed only during the main reaction. These are CAH10, C2AHX, AH3, hemicarbonate and monocarbonate. STPP shows an influence on the amount of crystalline C2AHX, otherwise, no difference in the qualitative phase content is observed. Gillmore‐Needle‐Testing (IMETER device) could observe an accelerated hardness development during the early heat flow event despite initially reduced viscosity. Pore water studies and thermodynamic modelling (PhreeqC) indicate the formation of an amorphous C‐P‐H phase during this early heat flow event.

Evaluating solute transport between soil particles and pore water considering intra-particle diffusion

Evaluating solute transport between soil particles and pore water considering intra-particle diffusion