Pore water pressures under unsaturated conditions are measured with tensiometers, which operate by allowing the pore water to come into equilibrium with a reference pressure indicator through a permeable ceramic cup placed in contact with the soil. Pore water pressure is vital in calculating the stress state in the ground soil mechanics, from Terzaghi's expression for the effective stress of a soil.
|
|
Water then increases the pore-water pressure and reduces the shearing strength of the material.
|
|
Groundwater seepage and elevated pore water pressure can cause submarine landslides. Elevated pore water pressure causes reduced frictional resistance to sliding and can result from normal depositional processes, or can be coupled with other causes such as earthquakes, gas hydrate dissociation and glacial loading.
|
|
Peepers are passive diffusion samplers used for metals in freshwater and marine sediment pore water, so they can be used to find areas that may have metal-contaminated sediments. Peepers are plastic vessels filled with clean water and covered in a dialysis membrane, which allows metals in sediment pore water to enter the water inside the peeper. They are usually placed deep enough into sediment to be in an anoxic environment, in which metals will be soluble enough to sample. If the peepers are deployed long enough so the sediment pore water and contained peeper water reach equilibrium, they can accurately provide metal concentrations in sampled sediment pore water.
|
|
Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or rock, in gaps between particles (pores). Pore water pressures below the phreatic level of the groundwater are measured with piezometers. The vertical pore water pressure distribution in aquifers can generally be assumed to be close to hydrostatic. In the unsaturated ("vadose") zone, the pore pressure is determined by capillarity and is also referred to as tension, suction, or matric pressure.
|
|
At this stage, only the water resists the applied load. (Development of excess pore water pressure) # As soon as the hole is opened, water starts to drain out through the hole and the spring shortens. (Drainage of excess pore water pressure) # After some time, the drainage of water no longer occurs. Now, the spring alone resists the applied load.
|
|
Small to medium-sized blocks are forced out at or near the base of the river bank due to excessive pore water pressure and overburden.
|
|
In both cases a soil in a saturated loose state, and one which may generate significant pore water pressure on a change in load are the most likely to liquefy. This is because loose soil has the tendency to compress when sheared, generating large excess porewater pressure as load is transferred from the soil skeleton to adjacent pore water during undrained loading. As pore water pressure rises, a progressive loss of strength of the soil occurs as effective stress is reduced. Liquefaction is more likely to occur in sandy or non-plastic silty soils, but may in rare cases occur in gravels and clays (see quick clay).
|
|
Aliphatic, aromatic hydrocarbons and methane can be used as fuel in the humans' daily lives. In other words, these methanogens improve the coefficient of utilization. Moreover, these methanogens change the structure of the tailings pond and help the pore water efflux to be reused for processing oil sands. Because the archaea and bacteria metabolize and release bubbles within the tailings, the pore water can go through the soil easily.
|
|
The slab of material in the lower half of the bank will fall out, leaving an alcove shaped cavity. Failure is usually associated with steep banks and saturated finer grained cohesive bank materials that allow buildup of positive pore water pressure and strong seepage within structure. Popout failure is when small to medium-sized blocks are forced out at or near the base of the river bank due to excessive pore water pressure and overburden. The slab of material in the lower half of the bank will fall out, leaving an alcove shaped cavity. Failure is usually associated with steep banks and saturated finer grained cohesive bank materials that allow buildup of positive pore water pressure and strong seepage within structure. Small to medium-sized blocks are forced out at, or near the base of the river bank due to excessive pore water pressure and overburden. Slab failure is the sliding and forward toppling of deep-seated mass into the river channel.
|
|
The second major factor in the triggering of landslides is seismicity. Landslides occur during earthquakes as a result of two separate but interconnected processes: seismic shaking and pore water pressure generation.
|
|
97, SM-2, pp. 457-472. Most modern electronic CPT cones now also employ a pressure transducer with a filter to gather pore water pressure data. The filter is usually located either on the cone tip (the so-called U1 position), immediately behind the cone tip (the most common U2 position) or behind the friction sleeve (U3 position). Pore water pressure data aids determining stratigraphy and is primarily used to correct tip friction values for those effects.
|
|
Microtox Acute Toxicity Comparison & Inhibition Test. Azur Environmental. 1995. Retrieved 28 May 2014. These protocols are recommended for testing waste water treatment plant effluent, stormwater runoff, drinking water, pore water, and eluate.
|
|
Effects of acid-volatile sulfide on zinc bioavailability and toxicity to benthic macroinvertebrates: A spiked-sediment field experiment. Environmental Toxicology and Chemistry 15, 2113–2125 (1996). Spike studies that measured heavy metals concentrations in the pore water - that is, before extracting with HCl - found that, when [AVS] was greater than [SEM], pore water heavy metal concentrations were undetectable or nearly so.Casas, A. M. & Crecelius, E. A. Relationship between acid volatile sulfide and the toxicity of zinc, lead and copper in marine sediments.
|
|
The alkalinity can also be reduced by microbial sulphate reduction.SCOTT RITGER, BOBB CARSON and ERWIN SUESS, 1987. Methane- derived authigenic carbonates formed by subduction-induced pore-water expulsion along the Oregon/Washington margin. Geol. Soc.Am. Bull.
|
|
If particulate matter is in the sample that was collected, it may be necessary to centrifuge the sample for optimal clarity. Additionally, the pore water of sediments can be collected by centrifugation and tested without extraction.
|
|
The effective stress \sigma' is related to total stress \sigma and the pore pressure u by the relationship; :\sigma = \sigma' + u reading that total stress is equal to the sum of effective stress and pore water pressure.
|
|
Water is drawn into a small tube by surface tension. Water pressure, u, is negative above and positive below the free water surfaceIf there is no pore water flow occurring in the soil, the pore water pressures will be hydrostatic. The water table is located at the depth where the water pressure is equal to the atmospheric pressure. For hydrostatic conditions, the water pressure increases linearly with depth below the water table: :u = \rho_w g z_w where \rho_w is the density of water, and z_w is the depth below the water table.
|
|
Electronic tensiometer probe: (1) porous cup; (2) water-filled tube; (3) sensor-head; (4) pressure sensor At any point above the water table, in the vadose zone, the effective stress is approximately equal to the total stress, as proven by Terzaghi's principle. Realistically, the effective stress is greater than the total stress, as the pore water pressure in these partially saturated soils is actually negative. This is primarily due to the surface tension of pore water in voids throughout the vadose zone causing a suction effect on surrounding particles, i.e. matric suction.
|
|
A number of studies have indicated that gas hydrates lie beneath many submarine slopes and can contribute to the triggering of a landslide. Gas hydrates are ice-like substances consisting of water and natural gas, which are stable at the temperature and pressure conditions normally found on the seabed. When the temperature rises or the pressure drops the gas hydrate becomes unstable allowing some of the hydrate to dissociate and discharge bubble phase natural gas. If pore water flow is impeded then this gas charging leads to excess pore water pressure and decreased slope stability.
|
|
Instability of slopes in permafrost at elevated temperatures near freezing point in warming permafrost is related to effective stress and buildup of pore-water pressure in these soils. Kia and his co- inventors invented a new filter-less rigid piezometer (FRP) for measuring pore-water pressure in partially frozen soils such as warming permafrost soils. They extended the use of effective stress concept to partially frozen soils for use in slope stability analysis of warming permafrost slopes. The use of effective stress concept has many advantages such as ability to extend the concepts of "Critical State Soil Mechanics" into frozen ground engineering.
|
|
The physics refers to common types of physical processes, e.g., heat transfer (thermo-), pore water movement (hydro-), concentration field (concentro or diffuso/convecto/advecto), stress and strain (mechano-), dynamics (dyno-), chemical reactions (chemo- or chemico-), electrostatics (electro-), neutronics (neutro-), and magnetostatics (magneto-).
|
|
Ocean salinity has been stable for billions of years, most likely as a consequence of a chemical/tectonic system which removes as much salt as is deposited; for instance, sodium and chloride sinks include evaporite deposits, pore-water burial, and reactions with seafloor basalts.
|
|
Finally, landslides triggered by Hurricane Mitch in 1998 killed an estimated 18,000 people in Honduras, Nicaragua, Guatemala and El Salvador. So why does rainfall trigger so many landslides? Principally this is because the rainfall drives an increase in pore water pressures within the soil.
|
|
Earthquakes are a key factor which trigger most major submarine landslides. Earthquakes provide significant environmental stresses and can promote elevated pore water pressure which leads to failure. Earthquakes triggered the Grand Banks landslide of 1929, where a 20 km3 submarine landslide was initiated after an earthquake.
|
|
For example, bivalves (clams) in the family Lucinidae host symbiotic bacteria that oxidize sulfides. Lucinid bivalves' gills house the bacteria, and the siphon supplies the bacteria and surrounding pore water with oxygenated water from above the sediment. Bacterial oxidation of the sulfides results in sulfates, reducing toxicity.
|
|
45 As it is pushed into the soil, the resistance to penetration is measured, thereby providing an indication of soil strength.Das, p. 646 A sleeve behind the cone allows the independent determination of the frictional resistance. Some cones are also able to measure pore water pressure.
|
|
In dry soil, particles at this point experience a total overhead stress equal to the depth underground (5 meters), multiplied by the specific weight of the soil. However, when the local water table height is within said five meters, the total stress felt five meters below surface is decreased by the product of the height of the water table in to the five meter area, and the specific weight of water, 9.81 kN/m^3. This parameter is called the effective stress of the soil, basically equal to the difference in a soil's total stress and pore water pressure. The pore water pressure is essential in differentiating a soil's total stress from its effective stress.
|
|
R. H. Campbell did a study on shallow landslides on Santa Cruz Island, California. He notes that if permeability decreases with depth, a perched water table may develop in soils at intense precipitation. When pore water pressures are sufficient to reduce effective normal stress to a critical level, failure occurs.
|
|
The mechanism of ASR causing the deterioration of concrete can thus be described in four steps as follows: # The very basic solution (NaOH / KOH) attacks the siliceous aggregates (silicic acid dissolution at high pH), converting the poorly crystallised or amorphous silica to a soluble but very viscous alkali silicate gel (N-S-H, K-S-H). # The consumption of NaOH / KOH by the dissolution reaction of amorphous silica decreases the pH of the pore water of the hardened cement paste. This allows the dissolution of Ca(OH)2 (portandite) and increases the concentration of Ca2+ ions into the cement pore water. Calcium ions then react with the soluble sodium silicate gel to convert it into solid calcium silicate hydrates (C-S-H).
|
|
Simplot (13 March 2011). Retrieved on 24 November 2011. In areas of high pore water pressure, sand and salt water can form quicksand, which is a colloid hydrogel that behaves like a liquid. Quicksand produces a considerable barrier to escape for creatures caught within, who often die from exposure (not from submersion) as a result.
|
|
As mentioned above, much of the terrain is composed of pyroclastic materials with low permeability. Pore water pressure or pore air pressure are unable to dissipate fast enough; the subsequent strength loss triggers land sliding. This is especially true during seismic activity. See, for instance, the effects of landslides during the 2001 El Salvador earthquakes.
|
|
The bacteria and archaea associated with the SMTZ are very depleted in 13C, with archaea generally being more depleted than bacteria. Isotopes have also been the main tool to study ancient SMTZs. Paleo- SMTZ have been studied using a 34S isotopic signature. Extremely 34S depleted pyrite forms from the pore water sulfide, or the by product of AOM.
|
|
The topography of this interface is often dynamic, as it is affected by physical processes (e.g. currents causing rippling or resuspension) and biological processes (e.g. bioturbation generating mounds or trenches). Physical, biological, and chemical processes occur at the sediment-water interface as a result of a number of gradients such as chemical potential gradients, pore water gradients, and oxygen gradients.
|
|
Eroded unconsolidated sediment and ash is suspended and dissolved, increasing the density of the flow. Pore water pressure developed in unconsolidated soil and sediment causes liquefaction. Erosion increases as gravity drives mud flow through the drainage basin in confined channels. Mud flows mobilize woody debris and larger sedimentary particles as debris flow, which continues to accumulate as smaller channels combine with larger channels.
|
|
In order for toxic substances like heavy metals to cause effects in organisms, they must be bioavailable.Rand, G. M. Fundamentals Of Aquatic Toxicology: Effects, Environmental Fate And Risk Assessment. (CRC Press, 1995). For organisms residing in contaminated sediments, the contaminants are most bioavailable when dissolved in the pore water, as opposed to being precipitated as a solid or sorbed to a sediment particle.
|
|
The combination of natural processes giving rise to the formation of the carbonate-rich septaria remains unclear, but likely involves microbial activity and oxidation of the organic matter in the clay sediment as an internal source of carbonates. The calcium ions present in seawater, or in the pore water of the surrounding clay sediments, slowly diffuse towards the center of the initially soft concretion and progressively precipitate in contact with the carbonate anions present along their path and produced by the decaying organic matter. Indeed, when the pore water of the clay sediment becomes locally saturated with respect to calcium carbonate, this latter precipitates and progressively starts to cement the porosity of the initial medium (decaying marine organisms?). The cementation process seems to proceed from outside (harder) to inside (softer) along with the Ca2+ ions diffusion transport.
|
|
If the organic content of the sediment is too high the dissolved iron precipitates in the sediment and not in the carcass. Seawater sulfate ions diffusing toward animal carcasses enabled sulfate-reducing bacteria to oxidize the reactive organic matter of these remains, but the sulfide produced reacted promptly with the abundant Fe2+ ions of the pore water and pyrite precipitated right on the organic remains.
|
|
Mineralogical changes that occur during eogenesis are dependent on the environment in which that sediment has been deposited. For example, the formation of pyrite is characteristic of reducing conditions in marine environments. Pyrite can form as cement, or replace organic materials, such as wood fragments. Other important reactions include the formation of chlorite, glauconite, illite and iron oxide (if oxygenated pore water is present).
|
|
Failures are associated with steep, low height, fine grained cohesive banks and occur during low flow conditions. They are the result of a combination of scour at the bank toe, high pore water pressure in the bank material, and tension crack at the top of the bank. Cantilever failures occur when an overhanging blocks collapses into the channel. Failure often occurs after the bank has experienced undercutting.
|
|
Environmental Geology, Vol.35(4), 258–262 The following chemical formulae [Equations & ] will most likely be occurring, and [] responsible for the deposition of CaCO3 to create stalactites under concrete structures.Ishida, T and Maekawa, K, (2000). "Modeling of pH profile in pore water based on mass transport and chemical equilibrium theory". Translation from Proceedings of Japan Society of Civil Engineers (JSCE), No.648/Vol.47.
|
|
Bioreactor landfills are a relatively new technology. For the newly developed bioreactor landfills initial monitoring costs are higher to ensure that everything important is discovered and properly controlled. This includes gases, odours and seepage of leachate into the ground surface. The increased moisture content of bioreactor landfill may reduce the structural stability of the landfill by increasing the pore water pressure within the waste mass.
|
|
The term phreatic is used in hydrology and the earth sciences to refer to matters relating to ground water (an aquifer) below the water table (the word originates from the Greek phrear, phreat- meaning "well" or "spring"). The term 'phreatic surface' indicates the location where the pore water pressure is under atmospheric conditions (i.e. the pressure head is zero). This surface normally coincides with the water table.
|
|
Liquefaction is more likely to occur in loose to moderately saturated granular soils with poor drainage, such as silty sands or sands and gravels containing impermeable sediments. During wave loading, usually cyclic undrained loading, e.g. seismic loading, loose sands tend to decrease in volume, which produces an increase in their pore water pressures and consequently a decrease in shear strength, i.e. reduction in effective stress.
|
|
Triggering factors of a slope failure can be climatic events that can then make a slope actively unstable, leading to mass movements. Mass movements can be caused by increases in shear stress, such as loading, lateral pressure, and transient forces. Alternatively, shear strength may be decreased by weathering, changes in pore water pressure, and organic material. Several modes of failure for earth slopes include falls, topples, slides, and flows.
|
|
The increases in pore water pressure and in formation stress combine and affect weaknesses near the hydraulic fracture, like natural fractures, joints, and bedding planes. Different methods have different location errors and advantages. Accuracy of microseismic event mapping is dependent on the signal-to-noise ratio and the distribution of sensors. Accuracy of events located by seismic inversion is improved by sensors placed in multiple azimuths from the monitored borehole.
|
|
The standard method for measuring pore water pressure below the water table employs a piezometer, which measures the height to which a column of the liquid rises against gravity; i.e., the static pressure (or piezometric head) of groundwater at a specific depth. Piezometers often employ electronic pressure transducers to provide data. The United States Bureau of Reclamation has a standard for monitoring water pressure in a rock mass with piezometers.
|
|
The BIOMARUN model allows tracking of two substrates (or food), two microbial communities, and up to 8 solutes, and it was used to predict oil biodegradation under natural conditions (Geng et al. 2015) Geng, X., M. C. Boufadel, K. Lee, S. Abrams and M. Suidan (2015). "Biodegradation of subsurface oil in a tidally influenced sand beach: Impact of hydraulics and interaction with pore water chemistry." Water Resources Research.
|
|
The amount of water available in the system plays a major role in controlling the degree of melting at a given temperature. Low water availability will suppress melting. Furthermore, the degree of water saturation of a system will affect the composition of any melt generated. Water can be derived from a variety of sources, including from surrounding country rocks (pore water) or from the decomposition of hydrous minerals (e.g.
|
|
Cementation occurs as part of the diagenesis or lithification of sediments. Cementation occurs primarily below the water table regardless of sedimentary grain sizes present. Large volumes of pore water must pass through sediment pores for new mineral cements to crystallize and so millions of years are generally required to complete the cementation process. Common mineral cements include calcite, quartz or silica phases like cristobalite, iron oxides, and clay minerals, but other mineral cements also occur.
|
|
In terms of effective stresses, the shear strength is often approximated by: \tau = σ' tan(φ') + c' Where σ' = (σ - u), is defined as the effective stress. σ is the total stress applied normal to the shear plane, and u is the pore water pressure acting on the same plane. φ' = the effective stress friction angle, or the 'angle of internal friction' after Coulomb friction. The coefficient of friction \mu is equal to tan(φ').
|
|
Compared to the Basic Test it is more sensitive to operator technique, and as a result may be less precise. _Acute Toxicity Solid-Phase Test_ is a procedure that allows the test organism to come in direct contact with the solid sample as particulate in an aqueous suspension. Normally, this test provides results indicating equal or higher toxicity when compared to eluate or pore water tests of the same sample.Microtox Acute Toxicity Solid-Phase Test.
|
|
When coastal ecosystems do not have bioirrigating organisms, like lugworms, it results in a lot of sedimentary problems. Some of these problems include clogging of the sediment with organic-rich fine particles and a drastic decrease in sediment permeability. It also makes it so the oxygen cannot penetrate deeply into the sediment and there is accumulation of reduced mineralized products in pore water. These problems disrupt the foundations of a coastal ecosystem.
|
|
The carbon dioxide in the air reacts with the alkali in the cement and makes the pore water more acidic, thus lowering the pH. Carbon dioxide will start to carbonatate the cement in the concrete from the moment the object is made. This carbonatation process will start at the surface, then slowly move deeper and deeper into the concrete. The rate of carbonatation is dependent on the relative humidity of the concrete - a 50% relative humidity being optimal.
|
|
Geotechnical failure usually occurs due to stresses on the bank exceeding the forces the bank can accommodate. One example is oversaturation of the bank following a lowering of the water level from the floodplain to normal bank levels. Pore water pressure in the saturated bank reduces the frictional shear strength of the soil and increases sliding forces. This type of failure is most common in fine grained soils because they cannot drain as rapidly as coarse grained soils.
|
|
The hydroxyl groups on polysaccharide biopolymers allow them to form hydrogen bonds directly with charged clay particles (in dry soils), as well as with soil pore water itself (in moist soil). These interactions are promoted by the high surface area of both the biopolymers themselves and the clay particles they bond with. When ionized polymers (such as many biopolymers) with the same charge as clay particles adsorb to their surface, they increase the electrical double layer repulsion.
|
|
The advantages of the direct shear test over other shear tests are the simplicity of setup and equipment used, and the ability to test under differing saturation, drainage, and consolidation conditions. These advantages have to be weighed against the difficulty of measuring pore-water pressure when testing in undrained conditions, and possible spuriously high results from forcing the failure plane to occur in a specific location. The test equipment and procedures are slightly different for test on discontinuities.
|
|
The drained shear strength is the shear strength of the soil when pore fluid pressures, generated during the course of shearing the soil, are able to dissipate during shearing. It also applies where no pore water exists in the soil (the soil is dry) and hence pore fluid pressures are negligible. It is commonly approximated using the Mohr-Coulomb equation. (It was called "Coulomb's equation" by Karl von Terzaghi in 1942.) combined it with the principle of effective stress.
|
|
Localized stresses are often the result of moisture being confined in the active layer by the underlying permafrost and a semi-rigid carapace of dried surface mud, created by desiccation during the late summer. The moisture content of soils may increase during summer due to rain. Other stresses include the volumetric change of water during the freezing and thawing, and the flow of groundwater. The subsequent increase of hydrostatic, artesian, and/or pore water pressure pressures on slopes.
|
|
A study conducted by Guthrie et al. (2012) concluded that groundwater played a key role in the collapse. Prior to failure the flanks of Meager were subject to high pore water pressures indicated by extensive surface seepage observed throughout the failure surface and along lateral shears following the 2010 event. The largest visible bedrock spring occurred along the west lateral scarp and was the location of at least two previous landslides, occurring in 1998 and 2009.
|
|
Low molecular mass compounds account for much of the toxic nature of hydrocarbon spills. In particular, benzene, toluene, ethyl benzene and the xylenes (BTEX) are of great environmental interest due to their availability to organisms. This availability, also influenced by volatility and reactivity, impacts on biodegradation and bioremediation in water and soil environments, with even dissolved components within pore water considered bioavailable.Megharaj M, Ramakrishnan B, Venkateswarlu K, Sethunathan N, Naidu R. Bioremediation approaches for organic pollutants: A critical perspective.
|
|
Zinc phosphate slowly reacts with calcium cations and the hydroxyl anions present in the cement pore water and forms a stable hydroxyapatite layer. Penetrating sealants typically must be applied some time after curing. Sealants include paint, plastic foams, films and aluminum foil, felts or fabric mats sealed with tar, and layers of bentonite clay, sometimes used to seal roadbeds. Corrosion inhibitors, such as calcium nitrite [Ca(NO2)2], can also be added to the water mix before pouring concrete.
|
|
In 2009 a species of nematode, Halicephalobus mephisto, was discovered in rock fissures more than a kilometer down a South African gold mine. Nicknamed the "devil worm", it may have been forced down along with pore water by earthquakes. Other multicellular organisms have since been found, including fungi, Platyhelminthes (flatworms), Rotifera, Annelida (ringed worms) and Arthropoda. However, their range may be limited because sterols, needed to construct membranes in eukarya, are not easily made in anaerobic conditions.
|
|
The highest stress that it has been subjected to is termed the "preconsolidation stress". The "over-consolidation ratio" (OCR) is defined as the highest stress experienced divided by the current stress. A soil that is currently experiencing its highest stress is said to be "normally consolidated" and has an OCR of one. A soil could be considered "underconsolidated" or "unconsolidated" immediately after a new load is applied but before the excess pore water pressure has dissipated.
|
|
The primary nutrients determining seagrass growth are carbon (C), nitrogen (N), phosphorus (P), and light for photosynthesis. Nitrogen and phosphorus can be acquired from sediment pore water or from the water column, and sea grasses can uptake N in both ammonium (NH4+) and nitrate (NO3−) form. A number of studies from around the world have found that there is a wide range in the concentrations of C, N, and P in seagrasses depending on their species and environmental factors.
|
|
It was stronger than Portland cement but its poor water resistance (leaching) and corrosive properties (pitting corrosion due to the presence of leachable chloride anions and the low pH (8.5–9.5) of its pore water) limited its use as reinforced concrete for building construction. The next development in the manufacture of Portland cement was the introduction of the rotary kiln, which produced a stronger (more alite, C3S, formed at higher temperature, 1450 °C), more homogeneous clinker mixture and facilitated a continuous manufacturing process.
|
|
While remote sampling techniques often improve our point-sampling resolution, benthologists need to consider the real-world heterogeneity at small spatial scales and compare them to the noise inherent to most high-volume data collection methods (e.g. Rabouille et al. 2003 for microelectrode investigations of pore water). New developments in the field of SPI will provide tools for investigating dynamic sediment processes, but also challenge our ability to accurately interpolate point-data collected at spatial densities approaching continuous data sets.
|
|
In order to qualify for SQT assessment chemistry, toxicity, and in situ measurements must be collected synoptically using standardized methods of sediment quality. A control sample is necessary to evaluate impact of contaminated sites. An appropriate reference is a whole sediment sample (particles and associated pore water) collected near area of concern and is representative of background conditions in the absence of contaminants.Evidence of contaminant exposure and biological effect is required in order to assign a site as chemically impacted.
|
|
Corrections can be made by testing a sample of similar particle composition that is known to not be toxic. This test consists of two controls and 13 sample dilutions in duplicate. The Solid-Phase Test exposes the bacteria in such a way that is not always possible with pore water and elutriate. _Acute Toxicity Comparison & Inhibition Tests_ are the best procedures for testing samples with a low level of toxicity when an ECxx can not be determined using the Basic Test.
|
|
These flows usually begin when the pore pressures in a fine-grained mass increase until enough of the weight of the material is supported by pore water to significantly decrease the internal shearing strength of the material. This thereby creates a bulging lobe which advances with a slow, rolling motion. As these lobes spread out, drainage of the mass increases and the margins dry out, thereby lowering the overall velocity of the flow. This process causes the flow to thicken.
|
|
A kinetic model based on experimental data can capture most of the essential transformation in diagenesis, and a mathematical model in a compacting porous medium to model the dissolution-precipitation mechanism. These models have been intensively studied and applied in real geological applications. Diagenesis has been divided, based on hydrocarbon and coal genesis into: eodiagenesis (early), mesodiagenesis (middle) and telodiagenesis (late). During the early or eodiagenesis stage shales lose pore water, little to no hydrocarbons are formed and coal varies between lignite and sub-bituminous.
|
|
This is true because the chemical present in the interstitial water (or pore water) is the uncomplexed/free phase of the chemical that is bioavailable and toxic to benthic organisms. Other phases of the chemical are bound to sediment particles like organic carbon (OC) or acid volatile sulfides (AVS) and are not bioavailable. Thus the interstitial water concentration is important to consider for effects to benthic organisms. Equilibrium partitioning (EqP) predicts the bioavailable concentration of a chemical under given sediment conditions by using partition coefficients.
|
|
The sample is normally saturated before the test is run, but can be run at the in-situ moisture content. The rate of strain can be varied to create a test of undrained or drained conditions, depending on whether the strain is applied slowly enough for water in the sample to prevent pore-water pressure buildup. A direct shear test machine is required to perform the test. The test using the direct shear machine determines the consolidated drained shear strength of a soil material in direct shear.
|
|
The process of consolidation is often explained with an idealized system composed of a spring, a container with a hole in its cover, and water. In this system, the spring represents the compressibility or the structure of the soil itself, and the water which fills the container represents the pore water in the soil. Schematic diagram of spring analogy # The container is completely filled with water, and the hole is closed. (Fully saturated soil) # A load is applied onto the cover, while the hole is still unopened.
|
|
In addition to the friction and interlocking (dilatancy) components of strength, the structure and fabric also play a significant role in the soil behavior. The structure and fabric include factors such as the spacing and arrangement of the solid particles or the amount and spatial distribution of pore water; in some cases cementitious material accumulates at particle-particle contacts. Mechanical behavior of soil is affected by the density of the particles and their structure or arrangement of the particles as well as the amount and spatial distribution of fluids present (e.g., water and air voids).
|
|
There exist also other indirect sources of , all related to the presence of soluble Na and K salts in the pore water of hardened cement paste (HCP). The first category contains soluble Na and K salts whose corresponding anions can precipitate an insoluble calcium salts, e.g., , , , , , ... . Hereafter, an example for calcium sulfate (gypsum, anhydrite) precipitation releasing sodium hydroxide: : + → + 2 NaOH or, the reaction of sodium carbonate with portlandite, also important for the catalysis of the alkali–carbonate reaction as emphasized by Fournier and Bérubé (2000) and Bérubé et al.
|
|
Frost damage of early-age concrete is particularly harmful for the concrete mechanical resistance because the ice volume expansion causes micro-cracks in the concrete structures, and as a consequence it lowers the compressive strength of concrete. Therefore, when concreting at cold temperature cannot be avoided, it is essential to have a minimum curing time at a temperature sufficiently above the freezing point of the concrete pore water, so that the early strength of concrete is high enough to resist the inner tensile stress caused by water freezing.
|
|
Sediment Profile Imagery (SPI) is an underwater technique for photographing the interface between the seabed and the overlying water. The technique is used to measure or estimate biological, chemical, and physical processes occurring in the first few centimetres of sediment, pore water, and the important benthic boundary layer of water. Time-lapse imaging (tSPI) is used to examine biological activity over natural cycles, like tides and daylight or anthropogenic variables like feeding loads in aquaculture. SPI systems cost between tens and hundreds of thousands of dollars and weigh between 20 and 400 kilograms.
|
|
The column of water in a large and deep artificial lake alters in-situ stress along an existing fault or fracture. In these reservoirs, the weight of the water column can significantly change the stress on an underlying fault or fracture by increasing the total stress through direct loading, or decreasing the effective stress through the increased pore water pressure. This significant change in stress can lead to sudden movement along the fault or fracture, resulting in an earthquake. Reservoir-induced seismic events can be relatively large compared to other forms of induced seismicity.
|
|
Effect of pore water chemistry on the hydro-mechanical behaviour of Lianyungang soft marine clay Deng, Y.F. ; Yue, X.B. ; Cui, Y.J. ; Shao, G.H. ; Liu, S.Y. ; Zhang, D.W. Applied Clay Science, June 2014, Vol.95, pp. 167–175 Strength of High Water Content Marine Clay Stabilized by Low Amount of Cement Zhang, R ; Santoso, A ; Tan, T ; Phoon, K Journal of Geotechnical and Geoenvironmental Engineering, April 23, 2013 Structuration and Destructuration Behavior of Cement-Treated Singapore Marine Clay Kamruzzaman, A ; Chew, S ; Lee, F Journal of Geotechnical Engineering, Apr. 2009, Issue 4, pp.
|
|
This is because a loose sand has a tendency to compress when a load is applied. Dense sands, by contrast, tend to expand in volume or 'dilate'. If the soil is saturated by water, a condition that often exists when the soil is below the water table or sea level, then water fills the gaps between soil grains ('pore spaces'). In response to soil compressing, the pore water pressure increases and the water attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface).
|
|
When water is added to the soil, it functions as a softening agent on the soil particles, causing them to slide between one another more easily. At first, the dry unit weight after compaction increases as the moisture content (ω) increases, but after the optimum moisture content (ωopt) percentage is exceeded, any added water will result in a reduction in dry unit weight because the pore water pressure (pressure of water in-between each soil particle) will be pushing the soil particles apart, decreasing the friction between them.
|
|
From these concentrations, the [SEM]/[AVS] ratio can be obtained, summarizing the results in a single value. Based on the extremely low Ksp values for heavy metal sulfides, if [SEM]/[AVS] is less than 1 ([SEM < [AVS]), then all the extractable metals in the sediment should be in their solid sulfide form and non-bioavailable; above this value, the pool of sulfide is "exhausted" and heavy metals are more likely to be present in the sediment pore water, their bioavailable form. In theory, then, an [SEM]/[AVS] value of 1 represents a cutoff between a "no-effects" range and a "possible effects" range.
|
|
In many cold mountain areas, snowmelt can be a key mechanism by which landslide initiation can occur. This can be especially significant when sudden increases in temperature lead to rapid melting of the snow pack. This water can then infiltrate into the ground, which may have impermeable layers below the surface due to still-frozen soil or rock, leading to rapid increases in pore water pressure, and resultant landslide activity. This effect can be especially serious when the warmer weather is accompanied by precipitation, which both adds to the groundwater and accelerates the rate of thawing.
|
|
The high level of precipitation, which saturates the ground and adds water to the slope content, increases the pore- water pressure and reduces the shearing strength of the material. As the slope becomes wet, the earthflow may start as a creep downslope due to the clay or silt having less friction. As the material is increasingly more saturated, the slope will fail, which depends on slope stability. In earthflows, the slope does not fail along a clear shear plane and is instead more fluid as the material begins to move under the force of gravity as friction and slope stability is reduced.
|
|
Lithium aluminate solubility at high pH (12.5 – 13.5) is much lower than that of aluminium oxides. In the conditioning of low- and intermediate level radioactive waste (LILW), lithium nitrate is sometimes used as additive to cement to minimise aluminium corrosion at high pH and subsequent hydrogen production. Indeed, upon addition of lithium nitrate to cement, a passive layer of · 5 is formed onto the surface of metallic aluminium waste immobilised in mortar. The lithium aluminate layer is insoluble in cement pore water and protects the underlying aluminium oxide covering the metallic aluminium from dissolution at high pH.
|
|
The idealized chemical formula of chrysotile is Mg(SiO)(OH), although some of the magnesium ions may be replaced by iron or other cations. Substitution of the hydroxide ions for fluoride, oxide or chloride is also known, but rarer. A related, but much rarer, mineral is pecoraite, in which all the magnesium cations of chrysotile are substituted by nickel cations. Chrysotile is resistant to even strong bases (asbestos is thus stable in high pH pore water of Portland cement), but the fibres are attacked by acids: the magnesium ions are selectively dissolved, leaving a silica skeleton.
|
|
The theoretical formulation above assumes that time-dependent volume change of a soil unit only depends on changes in effective stress due to the gradual restoration of steady-state pore water pressure. This is the case for most types of sand and clay with low amounts of organic material. However, in soils with a high amount of organic material such as peat, the phenomenon of creep also occurs, whereby the soil changes volume gradually at constant effective stress. Soil creep is typically caused by viscous behavior of the clay-water system and compression of organic matter.
|
|
More recently slope stability radar technology has been employed, particularly in the mining industry, to gather real time data and assist in determining the likelihood of slope failure. Figure 2: Real life landslide on a slope Real life failures in naturally deposited mixed soils are not necessarily circular, but prior to computers, it was far easier to analyse such a simplified geometry. Nevertheless, failures in 'pure' clay can be quite close to circular. Such slips often occur after a period of heavy rain, when the pore water pressure at the slip surface increases, reducing the effective normal stress and thus diminishing the restraining friction along the slip line.
|
|
Diffusive gradients in thin films (DGT) samplers passively sample ionic trace metals, as well as antibiotics, oxyanions, bisphenols, and nanoparticles in different configurations. They are composed of plastic pistons and caps, with a window that exposes a binding gel, diffusive gel, and filter membrane to the sampling water. They can be used in both freshwater and marine environments, as well as in the water located between freshwater and marine sediment particles, called pore water or interstitial water. Once the mass of accumulated contaminants on the DGT sampler is known, the DGT equation (based on Fick's law) can be used to calculate the time averaged water concentration of contaminants.
|
|
Almost all karyorelictean species, except Loxodes, have been described from the marine interstitial habitat, where they live in the pore- water spaces between sediment grains. Animals from such habitats are known as meiofauna, and karyorelicteans have many morphological similarities to meiofaunal animals despite being protists: most karyorelicteans are relatively large (1 mm or more in length), have a worm-like (vermiform) body shape with an elongated tail, and exhibit thigmotactic behavior. Most karyorelicteans feed on bacteria or algae, and prefer microaerobic conditions. However, one genus, Kentrophoros, lacks an oral apparatus and feeds instead on symbiotic sulfur-oxidizing bacteria that are attached to one side of the cell.
|
|
Radiocarbon dating of the peat in which the axe head was discovered suggests that it was deposited in about 3200 BC. Wooden artefacts found at the site include paddles, a dish, arrow shafts, parts of four hazel bows, a throwing axe, yew pins, digging sticks, a mattock, a comb, toggles, and a spoon fragment. Finds made from other materials, such as flint flakes, arrowheads, and a chipped flint axe (in mint condition) have also been made. A geophysical survey of the area in 2008 showed unclear magnetometer data; the wood may be influencing the peat's hydrology, causing the loss or collection of minerals within the pore water and peat matrix.
|
|
SVFLUX is a finite element seepage analysis program developed by SoilVision Systems Ltd.. The software is designed to analyze both saturated and unsaturated flow through the ground through the solving of Richard's equation. The program is used in the fields of civil engineering and hydrology in order to analyze seepage and groundwater regional flow. The software is used for the calculation of flow rates, pore-water pressures, and pumping rates associated with regional groundwater flow. The software can be coupled with CHEMFLUX in order to calculate diffusion, advection, and decay rates or with SVHEAT in order to calculate thermal gradients and freeze/thaw fronts.
|
|
Two oedometers at the University of Cambridge Soil consolidation refers to the mechanical process by which soil changes volume gradually in response to a change in pressure. This happens because soil is a two-phase material, comprising soil grains and pore fluid, usually groundwater. When soil saturated with water is subjected to an increase in pressure, the high volumetric stiffness of water compared to the soil matrix means that the water initially absorbs all the change in pressure without changing volume, creating excess pore water pressure. As water diffuses away from regions of high pressure due to seepage, the soil matrix gradually takes up the pressure change and shrinks in volume.
|
|
During diagenesis, pore water is squeezed out of the sediments and, as burial continues and heat increases, water is liberated from clay minerals as the peripheral hydroxyl bonds are broken. As the rock enters the submetamorphic field, generally zeolite facies metamorphism, clay minerals begin to recrystallize into low-temperature metamorphic phyllite minerals such as chlorite, prehnite, pumpellyite, glauconite and so forth. This liberates not only water but incompatible elements attached to the mineral and trapped within crystal lattices. Metals liberated from clay and carbonate minerals as they are changed from clays and low-pressure disordered carbonate forms enters the remaining pore fluid which by this time has become concentrated into what is known as a deep formation brine.
|
|
Example applications are building and bridge foundations, retaining walls, dams, and buried pipeline systems. Principles of soil mechanics are also used in related disciplines such as geophysical engineering, coastal engineering, agricultural engineering, hydrology and soil physics. This article describes the genesis and composition of soil, the distinction between pore water pressure and inter-granular effective stress, capillary action of fluids in the soil pore spaces, soil classification, seepage and permeability, time dependent change of volume due to squeezing water out of tiny pore spaces, also known as consolidation, shear strength and stiffness of soils. The shear strength of soils is primarily derived from friction between the particles and interlocking, which are very sensitive to the effective stress.
|
|
When magma comes into contact with wet sediment several processes combine to produce the mixture of sedimentary and igneous clasts which is characteristic of a peperite. These processes are required to produce both the disintegration or fragmentation of magma to form juvenile clasts and the mingling of these clasts within the sediment. Mechanisms proposed for the fragmentation of the magma include; fracturing due to the stresses associated with quenching, autobrecciation due to continuing flow in the cooling magma, pore-water steam explosions and magma-sediment density contrasts. The main mechanism suggested for mingling of the igneous clasts with the sediment is fluidisation, in the sense of particle support and transport by a fluid.
|
|
A series of diagenetic processes act to enrich sediment pore water phosphorus concentrations, resulting in an appreciable benthic return flux of phosphorus to overlying bottom waters. These processes include (i) microbial respiration of organic matter in sediments, (ii) microbial reduction and dissolution of iron and manganese (oxyhydr)oxides with subsequent release of associated phosphorus, which connects the phosphorus cycle to the iron cycle, and (iii) abiotic reduction of iron (oxyhydr)oxides by hydrogen sulfide and liberation of iron-associated phosphorus. Additionally, (i) phosphate associated with calcium carbonate and (ii) transformation of iron oxide-bound phosphorus to vivianite play critical roles in phosphorus burial in marine sediments. These processes are similar to phosphorus cycling in lakes and rivers.
|
|
The slow but continuous production of hydrogen in deep low- permeability argillaceous formations could represent a problem for the long- term disposal of radioactive waste (Ortiz et al., 2001; Nagra, 2008; recent Nagra NTB reports). Indeed, a gas pressure build-up could occur if the rate of hydrogen production by the anaerobic corrosion of carbon-steel and by the subsequent transformation of green rust into magnetite should exceed the rate of diffusion of dissolved H2 in the pore water of the formation. The question is presently the object of many studies (King, 2008; King and Kolar, 2009; Nagra Technical Reports 2000–2009) in the countries (Belgium, Switzerland, France, Canada) envisaging the option of disposal in clay formation.
|
|
In the majority of cases the main trigger of landslides is heavy or prolonged rainfall. Generally this takes the form of either an exceptional short lived event, such as the passage of a tropical cyclone or even the rainfall associated with a particularly intense thunderstorm or of a long duration rainfall event with lower intensity, such as the cumulative effect of monsoon rainfall in South Asia. In the former case it is usually necessary to have very high rainfall intensities, whereas in the latter the intensity of rainfall may be only moderate - it is the duration and existing pore water pressure conditions that are important. The importance of rainfall as a trigger for landslides cannot be underestimated.
|
|
This capillary action is the "upward movement of water through the vadose zone" (Coduto, 266). Increased water infiltration, such as that caused by heavy rainfall, brings about a reduction in matric suction, following the relationship described by the soil water characteristic curve (SWCC), resulting in a reduction of the soil's shear strength, and reduced slope stability. Capillary effects in soil are more complex than in free water due to the randomly connected void space and particle interference through which to flow; regardless, the height of this zone of capillary rise, where negative pore water pressure is generally peaks, can be closely approximated by a simple equation. The height of capillary rise is inversely proportional to the diameter of void space in contact with water.
|
|
Surface water run off system by prefabricated channelsMicro-perforated flexible drainage tubes Drainage systems reduce the water level inside a potentially unstable hillside, which leads to reduction in pore water pressures in the ground and an increase in the shear strength within the slope. The reduction in pore pressure by drainage can be achieved by shallow and/or deep drains, depending on hillside morphology, the kinematics of movement predicted and the depth of creep surfaces. Usually, shallow drainage is adopted where the potential hillside movement is shallow, affecting a depth of 5-6m. Where there are deeper slippage surfaces, deep drainage must be introduced, but shallow drainage systems may also be installed, with the aim of running off surface water.
|
|
Creep and shrinkage of concrete are two physical properties of concrete. The creep of concrete, which originates from the calcium silicate hydrates (C-S-H) in the hardened Portland cement paste (which is the binder of mineral aggregates), is fundamentally different from the creep of metals and polymers. Unlike the creep of metals, it occurs at all stress levels and, within the service stress range, is linearly dependent on the stress if the pore water content is constant. Unlike the creep of polymers and metals, it exhibits multi-months aging, caused by chemical hardening due to hydration which stiffens the microstructure, and multi-year aging, caused by long-term relaxation of self-equilibrated micro-stresses in the nano-porous microstructure of the C-S-H.
|
|
For frost weathering to occur by volumetric expansion, the rock must have almost no air that can be compressed to compensate for the expansion of ice, which means it has to be water-saturated and frozen quickly from all sides so that the water does not migrate away and the pressure is exerted on the rock. These conditions are considered unusual, restricting it to a process of importance within a few centimeters of a rock's surface and on larger existing water- filled joints in a process called ice wedging. Not all volumetric expansion is caused by the pressure of the freezing water; it can be caused by stresses in water that remains unfrozen. When ice growth induces stresses in the pore water that breaks the rock, the result is called hydrofracture.
|
|
From their trace element contents and stable isotopic compositions it is inferred that the mud water is a mixture of sediment pore water (ancient seawater) and water released from dehydration of clay minerals. The 87Sr/86Sr of mud water (~0.7071) confirms the above inference and points out that altered oceanic crust plays a significant role in controlling the chemistry of water. The formation temperatures of mud ejecta, derived from mineralogical (smectite/illite), chemical (K+/Na+) and isotopic (δD/δ18O) geothermometers, lie in the range of 50 °C to 120 °C — which corresponds to a depth zone of 2 to 6 km within the Andaman forearc. It is believed that the mud volcano ejecta originate at the plate-boundary décollement zone, from the sediments and altered oceanic crust of the subducting Indian plate.
|
|
If the sedimentation rate is low (about 1 cm/yr), the organic carbon content is low (about 1% ), and oxygen is abundant, aerobic bacteria can use up all the organic matter in the sediments faster than oxygen is depleted, so lower-energy electron acceptors are not used. But where sedimentation rates and the organic carbon content are high, which is typically the case on continental shelves and beneath western boundary current upwelling zones, the pore water in the sediments becomes anoxic at depths of only a few centimeters or less. In such organic-rich marine sediments, sulfate then becomes the most important terminal electron acceptor due to its high concentration in seawater, although it too is depleted by a depth of centimeters to meters. Below this, methane is produced.
|
|
It was observed that the clay formed quickly, and using this amount of time and the known content of the sediment, concentration of potassium ions consumed by this process in rivers around the globe was estimated. Laboratory experiments can also include incubation experiments, in which sediment samples obtained from natural environments are enclosed in sealable containers with varied concentrations reverse weathering reactants (biogenic silica in the form of diatoms, cations, metals, etc.). 250x250px Using an inductively coupled plasma optical emission spectrometer (ICP-OES) also provides concentration and isotopic information for cation and silica concentrations in pore water and digested sediment samples. Utilization of a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) is also used as a means of obtaining isotopic data of metals and silica in solution.
|
|
Then in 1963, Mackenzie accepted a position as Staff Geochemist and Assistant Director at the Bermuda Biological Station for Research (BBSR, now the Bermuda Institute of Ocean Sciences). One of his tasks at BBSR was to manage Hydrostation S, the longest continuously occupied hydrostation in the world. In 1967 Mackenzie joined the faculty at Northwestern University becoming Full Professor and department Chair in 1971. Here between 1967 and 1981, he in association with colleagues Robert Garrels, Hal Helgeson, Abraham Lerman and his many graduate students and national and international colleagues published a number of classic papers involving an interdisciplinary range of scientific topics including early diagenetic processes of reverse weathering and controls on seawater composition, pore water geochemistry, kinetics and thermodynamics of mineral-water reactions, and modeling of Earth's surface environmental system over geological time.
|
|
In other words, as it is sometimes possible to fight fire with fire, it is also feasible to combat the ASR reaction by itself. A prompt reaction initiated at the early stage of concrete hardening on very fine silica particles will help to suppress a slow and delayed reaction with larger siliceous aggregates on the long term. Following the same principle, the fabrication of low-pH cement also implies the addition of finely divided pozzolanic materials rich in silicic acid to the concrete mix to decrease its alkalinity. Beside initially lowering the pH value of the concrete pore water, the main working mechanism of silica fume addition is to consume portlandite (the reservoir of hydroxyde (OH-) in the solid phase) and to decrease the porosity of the hardened cement paste by the formation of calcium silicate hydrates (C-S-H).
|
|
The creep of concrete, which originates from the calcium silicate hydrates (C-S-H) in the hardened Portland cement paste (which is the binder of mineral aggregates), is fundamentally different from the creep of metals as well as polymers. Unlike the creep of metals, it occurs at all stress levels and, within the service stress range, is linearly dependent on the stress if the pore water content is constant. Unlike the creep of polymers and metals, it exhibits multi-months aging, caused by chemical hardening due to hydration which stiffens the microstructure, and multi-year aging, caused by long-term relaxation of self-equilibrated micro-stresses in the nano-porous microstructure of the C-S-H. If concrete is fully dried it does not creep, though it is difficult to dry concrete fully without severe cracking.
|
|
Skempton worked on many high- profile projects through his life, notably the back analysis of the Chingford reservoir failure (July 1937) and other embankment dams, including that at Chew Valley Lake, for which he designed an array of sand-drains to accelerate consolidation of the weak alluvial foundations, the first such in the UK. In situ behaviour of natural clays was of great interest to Skempton, who wrote two papers published by the Geological Society on the geological compaction of natural clays. Among other academic writings, he formulated concepts such as that of A and B pore water pressure coefficient which is still widely used today. Many of his research documents and other writing are available in the Skempton and Bishop Archives at Imperial College. He was a founding member of the Institution of Civil Engineers' Soil Mechanics and Foundations committee (now the British Geotechnical Association).
|
|
The USGS also looked at how the land was historically used so that a correlation could be drawn between locations of high concentrations of chemicals and the source polluters. Scientists used passive-diffusion bag samplers to collect pore water from Cypress Creek and groundwater from other locations, which would provide data and concentration levels of the contaminants in the creek. Scientists also took tissue samples from trees that were growing along the Alabama River, Cypress Creek, and downtown Montgomery so that the analysis and data could give a better idea of the big picture and the true reach of the pollution. The tests concluded that the aquifer residing below the Capital City Plume site was contaminated with perchloroethylene (PCE) and trichloroethylene (TCE) and that the contamination was likely caused by the commercial printing industry that resided in downtown Montgomery in the late 1800s and early 1900s.
|
|
An anion-exchange reaction between chloride ions and the hydroxide anions contained in the lattice of some calcium aluminate hydrates (C-A-H), or related phases (C-A- S-H, AFm, AFt), is suspected to also contribute to the release of hydroxide anions into solution. The principle mechanism is schematically illustrated hereafter for C-A-H phases: : + (C-A-H)–OH → (C-A-H)–Cl + As a simple, but robust, conclusion, the presence of soluble Na and K salts can also cause, by precipitation of poorly soluble calcium salt (with portlandite, CH) or anion exchange reactions (with phases related to C-A-H), the release of anions into solution. Therefore, the presence of any salts of Na and K in cement pore water is undesirable and the measurements of Na and K elements is a good proxy (indicator) for the maximal concentration of in pore solution. This is why the total alkali equivalent content () of cement can simply rely on the measurements of Na and K (e.g.
|
|
The processes leading to landslides were accelerated by anthropogenic disturbances such as deforestation since the early 18th century, terracing and obstruction of ephemeral streams and cultivation of crops lacking capability to add root cohesion in steep slopes. The events have become more destructive given the increasing vulnerability of population and property. Majority of mass movements have occurred in hill slopes >20° along the Western Ghats scarps, the only exception being the coastal cliffs. Studies conducted in the state indicates that prolonged and intense rainfall or more particularly a combination of the two and the resultant persistence and variations of pore pressure are the most important trigger of landslides.Kuriakose SL, Jetten VG, van Westen CJ, Sankar G & van Beek LPH, 2008, Pore Water Pressure as a Trigger of Shallow Landslides in the Western Ghats of Kerala, India: Some Preliminary Observations from an Experimental Catchment, Physical Geography 29(4) 374–386 , Retrieved on 12 January 2009.
|
|
ISA also represents a major carbon source within a geological disposal facility (GDF) since it comprises >70% of cellulose degradation products as a result of alkaline hydrolysis. The high pH associated with the massive use of concrete in such a facility means that microbial activity may or may not occur within the alkaline disturbed zone depending on the local microbial consortia intruding upon or surrounding such a facility in the post closure phase. Initial studies have shown that both alpha and beta forms of ISA are readily available for microbial activity under the anaerobic conditions expected within the far field of a disposal facility or within ungrouted waste packages. Since the pH of pore water within the near field of a disposal facility is expected to fall from 13.5 to 12.5 − 10 over tens of thousands of years, the ability of micro-organisms to adapt to these alkaline pH values has also been investigated.
|
|
If concrete is fully dried, it does not creep, but it is next to impossible to dry concrete fully without severe cracking. Fig. 1 Changes of pore water content due to drying or wetting processes cause significant volume changes of concrete in load-free specimens. They are called the shrinkage (typically causing strains between 0.0002 and 0.0005, and in low strength concretes even 0.0012) or swelling (< 0.00005 in normal concretes, < 0.00020 in high strength concretes). To separate shrinkage from creep, the compliance function J(t, t'), defined as the stress-produced strain \epsilon (i.e., the total strain minus shrinkage) caused at time t by a unit sustained uniaxial stress \sigma = 1 applied at age t', is measured as the strain difference between the loaded and load-free specimens. The multi-year creep evolves logarithmically in time (with no final asymptotic value), and over the typical structural lifetimes it may attain values 3 to 6 times larger than the initial elastic strain.
|
|