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.

Mass physical properties, sliding and erodibility of experimentally deposited and differently consolidated clayey muds (Approach, equipment, and first results)

Abstract: On experimentally deposited kaolinite, illite, and Ca-bentonite consolidated under their own load or by additional vertical pressure, the progress of compaction in relation to excess pore water pressure, mass physical properties, gravitational mass movements in a tilted tank, and erodibility under running water in a flume were studied. The very low consolidated sediments near the mud/water interface do not obey the generally used theory in soil mechanics. They show a different, non-linear relationship between void ratio or water content and depth below the sedimentary surface on the one hand, or effective overburden pressure and shear strength on the other. The same is true of other physical properties such as permeability, which changes considerably with depth and time of consolidation. High sedimentation rates on slopes induce shallow sediment flow, whereas at low rates and critical slope angles different types of slope failures including the breaking up of water-rich sediment into sharp boundered blocks are observed. Flume studies on soft clay muds show three different types of erosion: continuously suspending, discontinuous erosion of crumbs or shreds, and wavy deformation of the clay surface with disintegration of particles from the crests. The critical tractive stress depends not only on clay type, void ratio, and shear strength, but significantly also on the ‘geologic history’of the clay (i.e. deposition from thin suspension or dense slurry, fabric, consolidation and swelling generating minute inhomogeneities etc.). The experiments may lead to a better understanding of all mechanical processe's including pore-water flow taking place near or not far below the sediment/ water interface.

Saturation, pore pressure and effective stress from sandstone acoustic properties

Abstract: [1] Acoustic velocity and Vp/Vs ratio show different responses in saturated and dry rocks under increasing differential pressures. Velocity is also shown to be sensitive to pore pressure, not just differential pressure. Under identical low differential pressure conditions, velocity is higher in sandstones when pore pressure is high during simulation of inflationary overpressure conditions. Vp/Vs ratios of sandstones with high fluid pressures are shown to lie between dry conditions and saturated conditions with constant and low pore pressure. Thus the velocity-differential pressure relationship is not unique. However, the use of the measured Biot effective stress coefficient results in a unique relationship. It is postulated that higher velocity and different Vp/Vs ratios are caused by loss of compliance in microfractures due to stiffening by increasing fluid pressure.

Sulphate Mobilization and Pore Water Chemistry in Relation to Groundwater Hydrology and Summer Drought in two Conifer Swamps on the Canadian Shield

Abstract: Variations in sulphate (SO42-) concentration of porewater and net SO42- mobilization were related to differences in water level fluctuations during wet and dry summers in two conifer swamps located in catchments which differed in till depth and seasonality of groundwater flow. Sulphate depletion at the surface and in 20 cm porewater coincided with anoxia and occurred mainly during the summer when water levels were near the peat surface and water flow rates were low in both catchments. There was an inverse relationship between net SO42- mobilization and water level elevation relative to the peat surface, explaining variation in SO42- dynamics between the swamps during summer drought periods. Aeration of peat to 40 cm and a large net SO42- mobilization (10–70 mg SO42- m-2 d-1) occurred during a dry summer in which the water level dropped to 60 cm below the surface in the swamp receiving ephemeral groundwater inputs from shallow tills within the catchment. This resulted in high SO42- concentrations in the surface water and porewater (30–50 mg L-1), and elevated SO42- concentrations remained through the fall and winter. In contrast, within the swamp located in the catchment with greater till depth (> 1 m), continuous groundwater inputs maintained surface saturation during the dry summer, and SO42- mobilization and concentrations of SO42- in the pore water during the following fall did not increase. Susceptibility to large water table drawdown and mobilization of accumulated SO42- is influenced by the occurrence of ephemeral vs. continuous groundwater inputs to valley swamps during dry summer periods in the Canadian Shield landscape. This study reveals that extrapolation of results of SO42- cycling from one wetland to another requires knowledge of the hydrogeology of the catchment in which the wetlands are located.

Tidally driven multiscale pore water flow in a creek-marsh system

Abstract: Intertidal wetlands are complex hydrological systems characterized by strong, dynamic interactions between coastal surface water and groundwater, driven particularly by tides. We simulated such interactions with a focus on three-dimensional, variably saturated pore water flow in a creek-marsh system that bordered a tidally dominated main channel. Simulated intra-tidal groundwater dynamics exhibited significant flow asymmetry with non-zero mean flow velocities over the tidal period. The tidally averaged flow led to pore water circulation with three dimensionality linked strongly to the marsh topography, over a range of spatial scales: near the creek bank, around the creek meander and over long marsh sections inclined towards the main channel. Particle tracking revealed that time scales associated with these circulations differed by orders of magnitude. Under the simulated conditions, the creek served as the main outlet of the pore water circulation paths, especially those linked with infiltration into the upper marsh surface areas away from the main channel. Local net efflux, influenced by the creek channel curvature, varied along the creek but produced a total discharge largely proportional to the creek length. Water infiltrating the soil in the lower marsh surface areas away from the creek tended to discharge directly to the main channel. However, the total discharge to the main channel was much less than that into the creek. This study highlights the hydrological complexity of intertidal marshes and the need for further research on interactions among marsh morphology, hydrology and ecology, which underpin the functionalities of these wetland systems.