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Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.


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Journal ArticleDOI
17 Nov 2006-Science
TL;DR: The volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions, but data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation, supporting a conceptual model in which ice segregation in near-surface permafrost leads progressively to rock fracture and heave.
Abstract: The volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions. Data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation. Fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model. The depth and geometry of fractures match those in Arctic permafrost and ice-age weathering profiles. This agreement supports a conceptual model in which ice segregation in near-surface permafrost leads progressively to rock fracture and heave, whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement.

319 citations

Journal ArticleDOI
TL;DR: In this paper, a variety of crystalline silicate rocks of low porosity (0·001-0·03) were fractured in triaxial experiments at strain rates from about 10−3 to 10−1 sec−1.

317 citations

Journal ArticleDOI
TL;DR: In this article, the water content (or void ratio or porosity) of any particular clay in the normally-consolidated condition is controlled by the effective overburden pressure p 0, given by Terzaghi9s law p 0 = σ − u, where σ is the total vertical pressure exerted by all the material (particles and water) above the point considered, and u is the pore water pressure at that point.
Abstract: Sedimentation compression curves, relating void ratio to effective overburden pressure, are presented for a wide lithological range of argillaceous deposits. These curves show the progressive changes from recently deposited muds on the sea floor, to Quaternary clays at depths of several tens of metres, and finally to hard clays and mudstones of Pliocene age at depths extending to about 3 000 m. Twelve localities are examined in some detail and information is also given from another eight previously published sites. In all cases the data are derived from ‘normally-consolidated’ deposits, strata which have never been under greater pressures than those existing at the present time. This procedure eliminates the difficulties of estimating the effect of pressure reduction by erosion. Clays containing high proportions of carbonates and organic matter are not included in this study. The water content (or void ratio or porosity) of any particular clay in the normally-consolidated condition is controlled by the effective overburden pressure p 0 , given by Terzaghi9s law p 0 = σ − u, where σ is the total vertical pressure exerted by all the material (particles and water) above the point considered, and u is the pore water pressure at that point. This law is shown to hold good even at porosities as low as 15 per cent. At any particular effective overburden pressure the water content of a normally-consolidated clay is directly related to the amount of clay minerals present and to their colloidal activity. The combined influence of these two factors can be indicated quantitatively by the Atterberg limits; and at a given value of p the water content is found to be a function of the Atterberg (liquid and plastic) limits for all inorganic non-calcareous clays except those with an extremely unstable microstructure, such as the so-called ‘quick clays’ of Scandinavia. Moreover, the water contents of muds on the sea bed or in tidal flats can also be expressed approximately by single-value parameters in terms of these limits. Thus if the water content, effective overburden pressure and Atterberg limits are known for an individual layer of normally-consolidated clay, it is possible to reconstruct the entire sedimentation compression curve for that clay with a reasonable degree of certainty; and hence an estimate can be made of the compaction which has occurred in the clay under its own weight and under the load of any overlying strata. At some of the sites, in addition to data relating to compaction, information is given on the increase in strength with depth and the rate of deposition as deduced from radiometric dating.

316 citations

Journal ArticleDOI
TL;DR: In this paper, two boreholes (EST204 and EST205) were drilled to a depth of 510 m for the purposes of scientific characterisation, and a semi-quantitative mineralogical study was conducted on the samples.
Abstract: Under the ANDRA Meuse/Haute Marne underground research laboratory scientific programme, two boreholes (EST204 and EST205) were drilled to a depth of 510 m for the purposes of scientific characterisation. Twenty-nine core samples were taken in borehole EST205 every 3 m between 422 and 504 m depth. Physical property measurements (water content, porosity, density, specific surface), geochemical analyses (major and trace elements, cation exchange capacity [CEC] and surface cation occupancy, leaching anions, redox state, organic matter concentration), and a semi-quantitative mineralogical study were conducted on the samples. As the rocks are in a reduced state, the core samples were stored under nitrogen immediately after drilling. All the steps of the sampling and of the characterisation are done with a research of limitation of the oxidation to obtain representative samples of the in situ conditions. The top of the formation is more carbonate-rich, with interbedded clayey layers and carbonate rock. The formation is more homogeneous in its central section with a clay mineral concentration of 45-50%, which corresponds to a maximum of flooding within the area. In the upper part of this section, micas and mixed-layer illite/smectite R0 dominate, whereas in the lower part of the section we find an abrupt transition to mixed-layer illite/smectite R1 associated with kaolinite. A statistical analysis, including the data of major and trace elements with the semi-quantitative mineralogy, enabled the identification of some mineralogical traps for trace elements. The values of cation occupancy at the surface of the clay minerals provided a good image of the pore water chemistry; pore water is in equilibrium with the clay surfaces. Leaching experiments revealed the pore water salinity and provided profiles of Cl and Br concentrations. Cl/Br values in the centre of the formation are close to the present-day seawater ratio, which could indicate a seawater origin of the pore water. Some measurements of total reduced capacity, provide quantified results of the reduced state of the rock. Processing the data on water content, helium and petroleum pycnometry enabled calculation of total rock porosity and gave an uncertainty range for this value. Finally, the high BET(N-2) specific surfaces are consistent with the clayey nature of the rock.

310 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluate the effect of a steady periodic variation of water level on the surface of a uniform porous elastic half-space using the fully coupled (Biot) equations of elastic deformation and pore fluid flow.
Abstract: The stress and pore pressure changes produced by a steady periodic variation of water level on the surface of a uniform porous elastic half-space are evaluated using the fully coupled (Biot) equations of elastic deformation and pore fluid flow. Diverse choices of material properties all give a coupled stress field differing from the elastic stress field by at most 0.035 po, where po is the water pressure at the bottom of the reservoir. Peak coupled pore pressure change can lag peak water level in the depth range 0 < (ω/2c)1/2z < π, where ω is frequency of the cyclic change in water level, c is diffusivity, and z is depth. The maximum lag increases as B decreases, where B is the ratio of pore pressure increase to mean compressive stress increase under undrained conditions. Directly beneath the reservoir, for example, peak pore pressure in an annual cycle can lag peak water level by at most 10 days if B = 0.80, but can lag by up to 122 days if B = 0.11. When cyclic water level changes are superimposed on the steady state reservoir level, the time during the cycle at which a fault is most destabilized depends on whether the weight of the reservoir stabilizes or destabilizes the fault, which, in turn, depends on its orientation and location relative to the reservoir. B and c also influence the timing of the greatest destabilization. If B and c are low, maximum destabilization at low water level is possible for faults that are stabilized by the weight of the reservoir; this mechanism may have operated at Lake Mead. The analysis suggests that induced seismic events should be separated into groups having a common focal mechanism and occurring in similar locations relative to the reservoir before studying the time at which the events occur relative to the water level. The fully coupled solution is compared with an uncoupled solution, with a solution that is coupled but which assumes incompressible solid and fluid constituents (consolidation) and with a decoupled solution in which the difference between the pore pressure field and B times the elastic mean compressive stress obeys a homogeneous diffusion equation. The uncoupled and consolidation solutions respectively underestimate and overestimate pore pressure during short-term reservoir level fluctuations as well as at times short compared to that required to achieve steady state. In contrast, the decoupled solution agrees closely with the fully coupled solution for the problem studied here.

300 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023552
2022995
2021572
2020564
2019566
2018566