Showing papers on "Pore water pressure published in 1998"
TL;DR: In this article, a new theoretical model for calculating pore volume compressibility and permeability in coals as a function of effective stress and matrix shrinkage, using a single equation is presented.
Abstract: In naturally fractured formations, such as coal, permeability is sensitive to changes in stress or pore pressure (i.e., effective stress). This paper presents a new theoretical model for calculating pore volume compressibility and permeability in coals as a function of effective stress and matrix shrinkage, using a single equation. The equation is appropriate for uniaxial strain conditions, as expected in a reservoir. The model predicts how permeability changes as pressure is decreased (i.e., drawdown). Pore volume compressibility is derived in this theory from fundamental reservoir parameters. It is not constant, as often assumed. Pore volume compressibility is high in coals because porosity is so small. A rebound in permeability can occur at lower drawdown pressures for the highest modulus and matrix shrinkage values. We have also history matched rates from a {open_quotes}boomer{close_quotes} well in the fairway of the San Juan basin using various stress-dependent permeability functions. The best fit stress-permeability function is then compared with the new theory.
682 citations
TL;DR: In this article, a robust numerical procedure for biogeochemical interpretation and analysis of measured concentration profiles of solutes in sediment pore water has been developed, which involves finding a series of least square fits to the measured concentration profile, followed by comparisons of these fits through statistical F-testing.
Abstract: A robust numerical procedure for biogeochemical interpretation and analysis of measured concentration profiles of solutes in sediment pore water has been developed. Assuming that the concentration-depth profile represents a steady state, the rate of net production or consumption as a function of depth can be calculated, together with the flux across the sediment-water interface. Three kinds of vertical transport can be included in the analysis: molecular diffusion, bioturbation, and irrigation. The procedure involves finding a series of least square fits to the measured concentration profile, followed by comparisons of these fits through statistical F-testing. This approach leads to an objective selection of the simplest production-consumption profile that reproduces the concentration profile. Because the numerical procedure is optimized with respect to speed, one prediction can typically be done in a few minutes or less on a personal computer. The technique has been tested successfully against analytical solutions describing the transport and consumption of 0, in sediment pore water. In other tests, measured concentration profiles of O,, NO;, , NH:, and ZCO, have been interpreted using the new procedure.
572 citations
TL;DR: In this paper, the authors developed a new electrical conductivity equation based on Bussian's model and accounting for the different behavior of ions in the pore space, which is applied to in situ salinity determination in the Gulf Coast, and it provides realistic salinity profiles in agreement with sampled pore water.
Abstract: We develop a new electrical conductivity equation based on Bussian's model and accounting for the different behavior of ions in the pore space. The tortuosity of the transport of anions is independent of the salinity and corresponds to the bulk tortuosity of the pore space which is given by the product of the electrical formation factor F and the porosity ϕ. For the cations, the situation is different. At high salinities, the dominant paths for the electromigration of the cations are located in the interconnected pore space, and the tortuosity for the transport of cations is therefore the bulk tortuosity. As the salinity decreases, the dominant paths for transport of the cations shift from the pore space to the mineral water interface and consequently are subject to different tortuosities. This shift occurs at salinities corresponding to ξ/t(+)f ∼ 1, where ξ is the ratio between the surface conductivity of the grains and the electrolyte conductivity, and t(+)f is the Hittorf transport number for cations in the electrolyte. The electrical conductivity of granular porous media is determined as a function of pore fluid salinity, temperature, water and gas saturations, shale content, and porosity. The model provides a very good explanation for the variation of electrical conductivity with these parameters. Surface conduction at the mineral water interface is described with the Stern theory of the electrical double layer and is shown to be independent of the salinity in shaly sands above 10−3 mol L−1. The model is applied to in situ salinity determination in the Gulf Coast, and it provides realistic salinity profiles in agreement with sampled pore water. The results clearly demonstrate the applicability of the equations to well log interpretation of shaly sands.
440 citations
TL;DR: In this article, a parametric study has been conducted using the finite element method to investigate the influence of various rainfall events and initial ground conditions on transient seepage and hence slope stability.
389 citations
TL;DR: In this paper, the authors show that the least horizontal stress decreases with decreasing reservoir pressure, as predicted by poroelasticity, and that dilatant fracturing and normal faulting are always promoted, in extensional environments, near the edge of the reservoir or in regions of high pore-pressure gradient.
342 citations
TL;DR: Coseismic water level rises in the 30m deep Bourdieu Valley (BV) well near Parkfield, California, have occurred in response to three local and five distant earthquakes as mentioned in this paper.
Abstract: Coseismic water level rises in the 30-m deep Bourdieu Valley (BV) well near Parkfield, California, have occurred in response to three local and five distant earthquakes. Coseismic changes in static strain cannot explain these water level rises because (1) the well is insensitive to strain at tidal periods; (2) for the distant earthquakes, the expected coseismic static strain is extremely small; and (3) the water level response is of the incorrect sign for the local earthquakes. These water level changes must therefore be caused by seismic waves, but unlike seismic water level oscillations, they are monotonic, persist for days or weeks, and seem to be caused by waves with periods of several seconds rather than long-period surface waves. Other investigators have reported a similar phenomenon in Japan. Certain wells consistently exhibit this type of coseismic water level change, which is always in the same direction, regardless of the earthquake's azimuth or focal mechanism, and approximately proportional to the inverse square of hypocentral distance. To date, the coseismic water level rises in the B V well have never exceeded the seasonal water level maximum, although their sizes are relatively well correlated with earthquake magnitude and distance. The frequency independence of the well's response to barometric pressure in the frequency band 0.1 to 0.7 cpd implies that the aquifer is fairly well confined. High aquifer compressibility, probably due to a gas phase in the pore space, is the most likely reason why the well does not respond to Earth tides. The phase and amplitude relationships between the seasonal water level and precipitation cycles constrain the horizontal hydraulic diffusivity to within a factor of 4.5, bounding hypothetical earthquake-induced changes in aquifer hydraulic properties. Moreover, changes of hydraulic conductivity and/or diffusivity throughout the aquifer would not be expected to change the water level in the same direction at every time of the year. The first 2.5 days of a typical coseismic water level rise could be caused by a small coseismic discharge decrease at a point several tens of meters from the well. Alternatively, the entire coseismic water level signal could represent diffusion of an abrupt coseismic pore pressure increase within several meters of the well, produced by a mechanism akin to that of liquefaction. The coseismic water level changes in the BV well resemble, and may share a mechanism with, coseismic water level, stream discharge, and groundwater temperature changes at other locations where preearthquake changes have also been reported. No preearthquake changes have been observed at the BV well site, however.
338 citations
TL;DR: In this article, the real and imaginary parts of the relative dielectric permittivity values of four silt and clay soils were measured at different densities and moisture contents ranging from oven dry material to the plastic state.
337 citations
TL;DR: In this paper, anisotropic elastic properties of drained, saturated shales were measured as a function of confining pressure and the strongest anisotropy was seen in the Kimmeridge Clay shale.
Abstract: The ultrasonic anisotropic elastic properties of drained, saturated shales were measured as a function of confining pressure. Two shales were characterized in this study: a Jurassic outcrop shale retrieved under the sea in a saturated state and a Kimmeridge Clay shale cut from a North Sea borehole. Both shales were highly anisotropic, both texturally, as revealed by scanning electron microscopy analysis, and elastically, as measured ultrasonically in the laboratory. The strongest anisotropy was seen in the Kimmeridge Clay shale, where up to 38% compressional wave anisotropy (Thomsen's parameter e) and up to 58% shear wave anisotropy (Thomsen's parameter γ) were observed. In addition, for both shales, e and γ were found to decrease as a function of increasing confining pressure, with the pore pressure drained to atmosphere, while the anellipticity (deviation of the slowness surfaces from ellipses) was found to be positive and decreased as a function of increasing confining pressure. Accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure, from 10.5 to 8.5% for the Jurassic shale. The decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid-filled porosity.
276 citations
TL;DR: In this article, the authors investigate how rainfall signals propagate through an unsaturated soil profile, leading to a rapid pore pressure response and slope instability, and propose that the rain spike produced a slight pressure wave that traveled relatively rapidly through the unsaturated zone, where it caused a large change in hydraulic conductivity and the rapid effusion of stored soil water.
Abstract: As part of a larger, collaborative study, we conducted field experiments to investigate how rainfall signals propagate through an unsaturated soil profile, leading to a rapid pore pressure response and slope instability. We sprinkler-irrigated an entire, unchanneled headwater basin in the steep, humid Oregon Coast Range, and we drove the system to quasi steady state as indicated by tensiometers, piezometers, and discharge. During initial wetting some of the deeper tensiometers responded before the arrival of an advancing head gradient front. With continued irrigation most tensiometers attained near- zero pressure heads before most piezometers responded fully, and a stable unsaturated flow field preceded the development of a stable saturated flow field. Steady discharge occurred after the last piezometer reached steady state. With the onset of steady discharge the unsaturated zone, saturated zone, and discharge became delicately linked, and a spike increase in rain intensity led to a response in the saturated zone and discharge much faster than could have happened through advection alone. We propose that the rain spike produced a slight pressure wave that traveled relatively rapidly through the unsaturated zone, where it caused a large change in hydraulic conductivity and the rapid effusion of stored soil water. An important control on the hydrologic response of this catchment lies with the soil-water retention curve. In general, below pressure heads of about 20.05 m, soil-water contents change slightly with changes in pressure head, but above 20.05 m the soil-water content is highly variable. Minor rainstorms upon a wet soil can produce slight changes in pressure head and corresponding large changes in soil-water content, giving rise to the passage of pressure waves in response to increased rain intensity and a relatively rapid response in the unsaturated zone. This rapid unsaturated zone response led to a rapid rise in the saturated zone, and it may be the underlying mechanism enabling short bursts of rain to cause slope instability.
268 citations
TL;DR: The most common technique for estimating seismic velocities in rocks with mixed pore fluid saturations is to use Gassmann's relations with an effective fluid whose density and compressibility are averages of the individual pore fluids properties as discussed by the authors.
Abstract: The most common technique for estimating seismic velocities in rocks with mixed pore fluid saturations is to use Gassmann’s relations with an effective fluid whose density and compressibility are averages of the individual pore fluid properties. This approach is applicable only if the gas, oil, and brine phases are mixed uniformly at a very small scale, so the different wave‐induced increments of pore pressure in each phase have time to diffuse and equilibrate during a seismic period. In contrast, saturations that are heterogeneous over scales larger than the characteristic diffusion length, i.e., patchy saturation, will always lead to higher seismic velocities than if the same fluids are mixed uniformly at a fine scale. Critical saturation scales separating uniform from patchy behavior are typically of the order 0.1–1 cm for laboratory measurements and tens of centimeters for field seismic frequencies. For low seismic frequencies, velocities corresponding to patchy and homogeneous saturations represent a...
259 citations
TL;DR: In this article, high-resolution crosswell seismic imaging surveys were conducted before and after CO2 flooding to monitor the CO2 flood process and map the flooded zones, and the velocity changes observed by these time-lapse surveys are typically on the order of −6%, with maximum values of −10% in the vicinity of the injection well.
Abstract: A carbon dioxide (CO2) injection pilot project is underway in Section 205 of the McElroy field, West Texas. High‐resolution crosswell seismic imaging surveys were conducted before and after CO2 flooding to monitor the CO2 flood process and map the flooded zones. The velocity changes observed by these time‐lapse surveys are typically on the order of −6%, with maximum values on the order of −10% in the vicinity of the injection well. These values generally agree with laboratory measurements if the effects of changing pore pressure are included. The observed dramatic compressional (VP) and shear (VS) velocity changes are considerably greater than we had initially predicted using the Gassmann (1951) fluid substitution analysis (Nolen‐Hoeksema et al., 1995) because we had assumed reservoir pressure would not change from survey to survey. However, the post‐CO2 reservoir pore fluid pressure was substantially higher than the original pore pressure. In addition, our original petrophysical data for dry and brine‐sa...
TL;DR: Time-domain reflectometry (TDR) has been used for in situ, non-destructive measurement of water, ionic solutes and air within the soil profile as discussed by the authors.
Abstract: Soil water exerts a strong influence on the transfer and storage of solutes, heat, air, and even water itself, within the soil profile. Soil water also dominates the mass and energy balance of the soil–atmosphere interface. Over the last decade or so, the development and continuing refinement of the time-domain reflectometry (TDR) technique for in situ, nondestructive measurement of water, ionic solutes and air has revolutionized the study and management of the transfer and storage of mass and energy within the soil profile. TDR-measured water content has been applied successfully to water balance studies ranging from the km scales of small watersheds to the mm scale of the root–soil interface. TDR-measured ionic solute status, which applies to the same sample volume as the water content measurement, has been used successfully on soil column, field plot and whole field scales for in situ determination of solute transport parameters, such as pore water velocity and dispersivity. TDR-measurement of air-filled porosity in space and time has given new insights into the mechanisms controlling aeration and gaseous exchange in the crop root zone. The combined water content – solute mass measurement capability of TDR has made this technique a very powerful tool for characterizing solute leaching characteristics, as well as for evaluating solute transport theories and solute transport models. The portability of TDR instrumentation coupled with the simplicity and flexibility of TDR soil probes has allowed the separation of water and solute content measurement error from soil variability, resulting in the capability for determining the mechanisms behind the spatial and temporal variability in field-based soil water content distributions and solute leaching patterns. The usefulness and power of the TDR technique for characterizing mass and energy in soil is increasing rapidly through continuing improvements in operating range, probe design, multiplexing and automated data collection.
TL;DR: In this article, during a pause in cone penetration in fine-grained soils, pore-water pressure dissipation tests are performed to evaluate the coefficient of consolidation for standard piezocones with shoulder fil...
Abstract: During a pause in cone penetration in fine-grained soils, pore-water pressure dissipation tests are performed to evaluate the coefficient of consolidation. For standard piezocones with shoulder fil...
TL;DR: In this paper, the molecular weight distribution of dissolved organic carbon (DOC) in pore waters from estuarine and continental margin sediments was examined using ultrafiltration techniques and it was found that the majority of the pore water DOC (∼60-90%) had a molecular weight less than 3 kDa.
TL;DR: Pressures higher than the vascular pressure cannot be sustained in the vascular porosity due to the swift pressure relaxation in this porosity (unless the fluid drainage through the boundary is obstructed); the model predicts a slight hydraulic stiffening of the bulk modulus due to longer draining time of the lacunar-canalicular porosity.
Abstract: The maximum pore fluid pressures due to uniaxial compression are determined for both the vascular porosity (Haversian and Volkmann's canals) and the lacunar-canalicular porosity of live cortical bone. It is estimated that the peak pore water pressure will be 19 percent of the applied axial stress in the vascular porosity and 12 percent of the applied axial stress in the lacunar-canalicular porosity for an impulsive step loading. However, the estimated relaxation time for the vascular porosity (1.36 microseconds) is three orders of magnitude faster than that estimated for the lacunar-canalicular porosity (4.9 ms). Thus, under physiological loading, which has a stress rise time generally larger than 1 ms, pressures higher than the vascular pressure cannot be sustained in the vascular porosity due to the swift pressure relaxation in this porosity (unless the fluid drainage through the boundary is obstructed). The model also predicts a slight hydraulic stiffening of the bulk modulus due to longer draining time of the lacunar-canalicular porosity. The undrained bulk modulus is 6 percent higher than the drained bulk modulus in this case.
TL;DR: In this article, the Nauset Marsh estuary (Eastham, Massachusetts) was studied and it was found that groundwater discharge into the Nomeset Marsh (EASTHAM, MA) occurred in high-velocity seeps immediately seaward of the upland-fringing salt marsh.
Abstract: As residential development, on-site wastewater disposal, and groundwater contamination increase in the coastal zone, assessment of nutrient removal by soil and sedimentary processes becomes increasingly important. Nitrogen removal efficiency depends largely on the specific flow paths taken by groundwater as it discharges into nitrogen-limited estuarine waters. Shoreline salinity surveys, hydraulic studies, and thermal infrared imagery indicated that groundwater discharge into the Nauset Marsh estuary (Eastham, Massachusetts) occurred in high-velocity seeps immediately seaward of the upland-fringing salt marsh. Discharge was highly variable spatially and occurred through permeable, sandy sediments during low tide. Seepage chamber monitoring showed that dissolved inorganic nitrogen (principally nitrate) traversed nearly conservatively from the aquifer through shallow estuarine sediments to coastal waters at flux rates of 1–3 mmol m−2 h−1. A significant relationship between pore water NO3-N concentrations and NO3-N flux rates may provide a rapid method of estimating nitrogen loading from groundwater to the water column.
TL;DR: In this paper, the authors derived time-dependent and self-similar solutions for the growth of buoyant dikes fed by porous flow in partially molten rock, and showed that the dikes are thin, about 6 mm wide when they are a few kilometers tall, for an ambient melt pressure that exceeds the least compressive stress by 1 MPa.
Abstract: Field observations indicate that dikes form and grow in magma source regions, but the mechanics of this process are poorly understood. I derive time-dependent and self-similar solutions for the growth of buoyant dikes fed by porous flow in partially molten rock. The host rock is treated as poroelastic; for basaltic (but not rhyolitic) dikes, large-scale viscous deformation of the rock is insignificant for dikes large enough to meet the classical Griffith fracture criterion. Observed wetting angles in partially molten peridotite suggest that subcritical crack growth may be important in crack initiation and render viscous deformation insignificant for dikes that are shorter still. Melt is driven into the dike by the difference between the ambient pore pressure and the least compressive stress and driven up the dike by magma buoyancy. The volume increase of the melting reaction, driven by the local drop in pore pressure, may be more important than elastic compressibility of the pore volume and pore fluid in driving melt into the dike. Because channel flow is very efficient relative to porous flow, the dikes are thin, about 6 mm wide when they are a few kilometers tall, for an ambient melt pressure that exceeds the least compressive stress by 1 MPa. This thickness is relatively insensitive to all relevant parameters (including the dike height) because the channel flux increases as the cube of the channel thickness. One implication appears to be that dikes that traverse the lithosphere must drain large segregations of magma, rather than partially molten rock. If dikes feed compliant sills at a depth where the source region is conductively cooled, crystallization onto the dike walls could increase the observable thickness while mass balance maintains a narrow aperture for flow.
TL;DR: In this paper, an alternative solution of hydroxypropyl methylcellulose (HPMC) in water has been used to solve the scaling laws relating to movement of pore fluid through the soil during dynamic loading events.
Abstract: In geotechnical modeling, the use of a pore fluid having viscosity greater than that of water is a well-established method of satisfying the scaling laws relating to movement of pore fluid through the soil during dynamic loading events. This has often been achieved with either silicone oil or mixtures of water and glycerol. However, there are a number of inherent drawbacks and difficulties in using silicone oil in particular, and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has been used recently with success. This paper presents test data documenting the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration. The relative performance of the fluid is illustrated with data from two centrifuge model tests, one with pure water as the pore fluid and one with an HPMC solution having viscosity ten times that of water.
Journal Article•
TL;DR: In this paper, an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has recently come into use has been described and the relative performance of the fluid is illustrated with pore pressure dissipation data from two centrifuge model tests involving earthquake simulations.
Abstract: Pore fluids having viscosity greater than water are sometimes used in geotechnical centrifuge model tests to more accurately satisfy the scaling laws relating to movement of pore fluid through the soil when modeling dynamic loading events This is frequently done using either silicone oil or mixtures of water and glycerol There are some drawbacks in using silicone oil and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has recently come into use The authors present test data showing the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration The relative performance of the fluid is illustrated with pore pressure dissipation data from two centrifuge model tests involving earthquake simulations One test was done with pure water as the pore fluid and the other test was done with an HPMC solution having viscosity ten times that of water
TL;DR: In this article, the qualitative and quantitative effects of macropore flow and transport in an agricultural subsurface-drained glacial till soil in eastern Denmark have been investigated.
TL;DR: In this article, the behavior of a fine-grained clayey soil at Moss Landing during the 1989 Loma Prieta earthquake was investigated, and it was shown that a deposit of this soil underlies portions of the Mo...
Abstract: Results of an investigation into the behavior of a fine-grained clayey soil at Moss Landing during the 1989 Loma Prieta earthquake are presented. A deposit of this soil underlies portions of the Mo...
TL;DR: In this article, a finite element parametric study was carried out to investigate the influence of different rainfall events and ground conditions on transient pore water distributions in unsaturated soils, and it was found that the factor of safety not only depended on the intensity of rainfall and the initial groundwater table, but also on rainfall duration.
Abstract: Rain-induced landslides are major geotechnical hazards. The influence of infiltration under various rainfall, ground conditions on slope stability is still poorly understood. In this paper, a finite element parametric study was carried out to investigate the influence of different rainfall events and ground conditions on transient pore water distributions in unsaturated soils. A steep, unsaturated colluvium hillside in Hong Kong was chosen: the initial water table, rainfall intensity and rainfall duration were variables. Pore water pressures predicted during the transient seepage analyses were used as input groundwater conditions for subsequent limit equilibrium analyses of the stability of the slope. Shear strength variation due to the presence of matrix suction was also taken into account. It was found that the factor of safety not only depended on the intensity of rainfall and the initial groundwater table, but also on rainfall duration. A critical rainfall duration was identified, when the factor of safety was the lowest.
TL;DR: In this paper, the vertical profiles of virus-like particles (VLPs) and bacteria were determined by near-synoptic sampling through the water column and 15 to 25 cm into the sediment at 5 stations across the mouth of Chesapeake Bay, USA.
Abstract: Vertical profiles of virus-like particles (VLPs] and bacteria were determined by near-synoptic sampling through the water column and 15 to 25 cm into the sediment at 5 stations across the mouth of Chesapeake Bay, USA. VLPs were about 10 times more abundant in the pore water (grand mean = 3.6 X 10' VLPs ml-l) than in the water column (grand mean = 3.8 X 107 VLPs ml-l). Similarly, bacteria counts were about 3 tmes higher in the pore water (grand mean = 6.5 X 10' bacteria ml-l) than in the water column (grand mean = 2.4 X 106 bacteria ml-l). The virus to bacteria ratio (VBR) was greater in the pore water (range = 29 to 85) than in the water column (range = 12 to 17). The VBR was lowest in the water-over-boxcore samples and variable in the pore water. Counts of VLPs and bacteria were positively correlated in the water column, although neither was correlated to chlorophyll a. In the water column, VLP and bacteria counts exhibited significant differences among stations, with the highest values on the southern side of the Bay mouth. In the pore water, VLP abundance varied with depth and was negatively correlated to grain size. Bacteria abundance was highest at the sediment-water interface, decreased in the first cm of sediment, was uniform in the deeper horizons, and showed no significant relationship with grain size. Bacteria counts in pore water were not significantly different among stations. In contrast, VLP abundances in pore water were significantly different among stations, although they did not increase in abundance from north to south across the Bay mouth, as did counts of water-column VLPs. These are the first data ind~cating the abundance of VLPs below the surface layer of sediment In aquatic systems and demonstrate that VLPs are components of the sedimentary microbial community to at least 25 cm depth.
TL;DR: In this article, a mini drivepoint solution sampling (MINIPOINT) technique was developed to collect pore-water samples at 2.5-cm vertical resolution in gravel streambeds.
Abstract: A new method for collecting pore-water samples in gravel streambeds is presented. We developed a mini drivepoint solution sampling (MINIPOINT) technique to collect pore-water samples at 2.5-cm vertical resolution. The sampler consisted of six small-diameter stainless steel drivepoints arranged in a 10-cm-diameter circular array. In a simple procedure, the sampler was installed in the streambed to preset drivepoint depths of 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 cm. Sampler performance was evaluated in the Shingobee River, Minnesota, and Pinal Creek, Arizona, by measuring the vertical gradient of chloride concentration in pore water beneath the streambed that was established by the uninterrupted injection to the stream for 3 d. Pore-water samples were withdrawn from all drivepoints simultaneously. In the first evaluation, the vertical chloride gradient was unchanged at withdrawal rates between 0.3 and 4.0 ml min− but was disturbed at higher rates. In the second evaluation, up to 70 ml of pore water was withdrawn from each drivepoint at a withdrawal rate of 2.5 ml min−1 without disturbing the vertical chloride gradient. Background concentrations of other solutes were also determined with MINIPOINT sampling. Steep vertical gradients were present for biologically reactive solutes such as DO, NH4+, NO3−, and dissolved organic C in the top 20 cm of the streambed. These detailed solute profiles in the hyporheic zone could not have been determined without a method for close interval vertical sampling that does not disturb natural logic mixing between stream water and groundwater.
TL;DR: In this paper, the pore pressure data are presented for experimental tests in which saturated cement mortar specimens were subjected to high temperature radiant heating conditions and a numerical modeling technique is used to numerically simulate the experimental work.
Abstract: Evaluation of airfield pavement degradation and fire safety evaluation of concrete structures are examples of situations that involve moist porous media (concrete) subjected to severe thermal loadings. When a saturated (or partially saturated) porous medium is subjected to a high temperature heating source, pore pressures large enough to initiate explosive spalling can be developed within the pore spaces of the material. The level to which these pore pressures ultimately rise depends on the saturation and permeability of the medium as well as the rate at which heat flows into the material. In this paper, experimental and numerical studies involving the measurement and prediction of pore pressures in porous media are presented. Pore pressure data are presented for experimental tests in which saturated cement mortar specimens were subjected to high temperature radiant heating conditions. A numerical modeling technique is then presented and is used to numerically simulate the experimental work. Close agreement is shown between the pore pressures and temperatures recorded experimentally and those predicted through simulation.
TL;DR: In this paper, the authors examined the solute exchange between sediments and the water column induced by the interaction of a current and a half-buried spherical obstruction, where the interaction results in pressure perturbations on the sediment surface, which in turn drive flows through the sediment.
Abstract: Laboratory experiments are used to examine solute exchange between sediments and the water column induced by the interaction of a current and a half-buried spherical obstruction The sphere is a model of a stone half buried in the bed of a stream or coastal sea The interaction results in pressure perturbations on the sediment surface, which in turn drive flows through the sediment This interaction can significantly enhance solute exchange Using an experimentally derived surface pressure field and a numerical transport model, the measured mass of effused solutes is accurately predicted, providing quantitative validity of the exchange mechanism To assess the biochemical significance of this exchange process, the behavior of a relative solute was simulated An example of a reactive solute of major significance to water quality in rivers is oxygen, which is consumed within sediments by oxidizing organic matter Depending on the water flow velocity, specific solute consumption rate, and properties of the s
TL;DR: In this paper, an extension of Terzaghi's model of the mechanical consolidation to incorporate chemical loading of soil is proposed, and a linearized model is used to solve analytically two one-dimensional problems of consolidation of a homogeneous layer simulating a landfill liner with drained or undrained boundaries.
Abstract: Consolidation (and swelling) of clayey soils caused by change in chemistry of pore fluid is addressed. Such phenomena are caused by changes in the concentration of various species in the solution and result primarily from a stress-independent deformation of individual clusters, and from a mechanical weakening or strengthening of the clay solid matrix in the presence of stress. Second, transport of chemicals that involves concentration gradients induces additional driving forces of osmotic consolidation due to semipermeable membrane nature of clay. In this paper an extension of Terzaghi's model of the mechanical consolidation to incorporate chemical loading of soil is proposed. A linearized model is used to solve analytically two one-dimensional problems of consolidation of a homogeneous layer simulating a landfill liner with drained or undrained boundaries. The numerical results show a strong dependence of distribution of pore pressure on the chemical load and chemically induced settlements of soil to be comparable to the mechanical ones.
TL;DR: In this article, the numerical implementation of the coupled formulation for the theory of unsaturated soils is described, and the developed computer code is verified using the Mandel-Cry algorithm.
Abstract: This paper first describes the numerical implementation of the coupled formulation for the theory of consolidation of unsaturated soils. The developed computer code is verified using the Mandel-Cry...
TL;DR: Here it is shown that one-dimensional compaction can be described in its simplest form by a nonlinear diffusion equation, controlled principally by a dimensionless parameter $\lambda$, which is the ratio of the hydraulic conductivity to the sedimentation rate.
Abstract: A mathematical model of compaction in sedimentary basins is presented and analyzed. Compaction occurs when accumulating sediments compact under their own weight, expelling pore water in the process. If sedimentation is rapid or the permeability is low, then high pore pressures can result, a phenomenon which is of importance in oil drilling operations. Here we show that one-dimensional compaction can be described in its simplest form by a nonlinear diffusion equation, controlled principally by a dimensionless parameter $\lambda$, which is the ratio of the hydraulic conductivity to the sedimentation rate. Large $\lambda$ corresponds to very permeable sediments, or slow sedimentation, a situation which we term "fast compaction," since the rapid pore water expulsion allows the pore water pressure to equilibrate to a hydrostatic value. On the other hand, small $\lambda$ corresponds to "slow compaction," and the pore pressure is in excess above the hydrostatic value and more nearly equal to the overburden value...
01 Feb 1998
TL;DR: In this paper, pore water concentration profiles and calculations of the corresponding diffusive fluxes were used to characterize single biogeochemical provinces within the study area. But the results of the study were limited to the eastern South Atlantic.
Abstract: From pore water concentration profiles and calculations of the corresponding diffusive fluxes, regional distribution patterns of benthic phosphate and silicate release rates were studied in the eastern South Atlantic. Comparisons among nutrient recycling rates and their control parameters, such as primary production and water depth, give evidence for significant differences in the benthic environment. Varying influences of these control parameters to decomposition and dissolution within surficial sediments are used to characterize single biogeochemical provinces within the study area. Maximum pore water concentrations (>0.4 mmol/l H 4 SiO 4 and >10 μmol/l) and diffusive release rates (>400 mmol/m 2 a H 4 SiO 4 and >4 mmol/m 2 a PO 3- 4 were observed in sediments off Namibia. Compared to benthic recycling rates in this upwelling regime, those in other regions of intensified primary production seem to be minor. While early diagenetic phosphate release is related to water depth and organic carbon flux to the sea floor, the benthic silicate flux is influenced by the general primary production and other parameters, such as the chemistry and rain rate of biogenic opal. These, again, depend on the oceanographic situation. With respect to the oceanic nutrient cycling and the role of marine deposits as geochemical sink, the presented data confirm the importance of degradation and dissolution processes at the sediment–water interface. At approximately 6.2×10 11 mol/a the benthic silicate re-flux is about three times greater than the dissolved silicate discharge of the Zaire River, which is the dominant terrestrial source in this region.