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.

Klinkenberg effect for gas permeability and its comparison to water permeability for porous sedimentary rocks

Abstract: . The difference between gas and water permeabilities is significant not only for solving gas-water two-phase flow problems, but also for quick measurements of permeability using gas as pore fluid. We have measured intrinsic permeability of sedimentary rocks from the Western Foothills of Taiwan, using nitrogen gas and distilled water as pore fluids, during several effective-pressure cycling tests at room temperature. The observed difference in gas and water permeabilities has been analyzed in view of the Klinkenberg effect. This effect is due to slip flow of gas at pore walls which enhances gas flow when pore sizes are very small. Experimental results show (1) that gas permeability is larger than water permeability by several times to one order of magnitude, (2) that gas permeability increases with increasing pore pressure, and (3) that water permeability slightly increases with increasing pore-pressure gradient across the specimen. The results (1) and (2) can be explained by Klinkenberg effect quantitatively with an empirical power law for Klinkenberg constant. Thus water permeability can be estimated from gas permeability. The Klinkenberg effect is important when permeability is lower than 10−18 m2 and at low differential pore pressures, and its correction is essential for estimating water permeability from the measurement of gas permeability. A simple Bingham-flow model of pore water can explain the overall trend of the result (3) above. More sophisticated models with a pore-size distribution and with realistic rheology of water film is needed to account for the observed deviation from Darcy's law.

Observations and modelling of soil slip-debris flow initiation processes in pyroclastic deposits: the Sarno 1998 event

Abstract: . Pyroclastic soils mantling a wide area of the Campanian Apennines are subjected to recurrent instability phenomena. This study analyses the 5 and 6 May 1998 event which affected the Pizzo d’Alvano (Campania, southern Italy). More than 400 slides affecting shallow pyroclastic deposits were triggered by intense and prolonged but not extreme rainfall. Landslides affected the pyroclastic deposits that cover the steep calcareous ridges and are soil slip-debris flows and rapid mudflows. About 30 main channels were deeply scoured by flows which reached the alluvial fans depositing up to 400 000 m3 of material in the piedmont areas. About 75% of the landslides are associated with morphological discontinuities such as limestone cliffs and roads. The sliding surface is located within the pyroclastic cover, generally at the base of a pumice layer. Geotechnical characterisation of pyroclastic deposits has been accomplished by laboratory and in situ tests. Numerical modelling of seepage processes and stability analyses have been run on four simplified models representing different settings observed at the source areas. Seepage modelling showed the formation of pore pressure pulses in pumice layers and the localised increase of pore pressure in correspondence of stratigraphic discontinuities as response to the rainfall event registered between 28 April and 5 May. Numerical modelling provided pore pressure values for stability analyses and pointed out critical conditions where stratigraphic or morphological discontinuities occur. This study excludes the need of a groundwater flow from the underlying bedrock toward the pyroclastic cover for instabilities to occur.

Implications of the distribution of δD in pore waters for groundwater flow and the timing of geologic events in a thick aquitard system

Abstract: A detailed vertical profile of the stable isotope δD in pore water was measured through a thick aquitard system consisting of surficial Quaternary clay-rich till (80 m thick) and an underlying Cretaceous marine clay (76 m thick). Numerical modeling was used to simulate one-dimensional (vertical) groundwater flow and transport of δD. Best fit simulations to the data provided an independent estimate of long-term groundwater velocity through the aquitard and estimates of the timing of late Pleistocene and Holocene events. Best fit simulations to the measured isotope profile across the till-clay interface yielded a groundwater velocity of 0.75–1.0 m per 10 ka for a transport time of between 20 ka and 30 ka. The estimate of velocity agreed well with that calculated from hydraulic data and suggested that hydraulic conductivities of these aquitards are independent of volume tested. The 20–30 ka time frame required for the δD profile to develop across the till-clay interface reflects the timing of till deposition and shows that the till is the Battleford Formation, a younger till than previously believed. Numerical transport modeling of δD in the upper 30 m of the profile yielded a nonunique fit. Assuming a similar groundwater velocity to that determined across the till-clay interface, a best fit was obtained for a transport times of 7.5–10 ka. This range compared favorably with that reported for the start of the Holocene (about 10 ka B.P.). This study shows that the application of δD, and by analogy δ18O, to the study of thick aquitard systems not only can provide independent, long-term estimates of very low groundwater velocities but can also provide insight into the timing of major geologic events such as glaciations.