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.

Regulation of landslide motion by dilatancy and pore pressure feedback

Abstract: [1] A new mathematical model clarifies how diverse styles and rates of landslide motion can result from regulation of Coulomb friction by dilation or contraction of water-saturated basal shear zones. Normalization of the model equations shows that feedback due to coupling between landslide motion, shear zone volume change, and pore pressure change depends on a single dimensionless parameter α, which, in turn, depends on the dilatancy angle ψ and the intrinsic timescales for pore pressure generation and dissipation. If shear zone soil contracts during slope failure, then α 0, and negative feedback permits slow, steady landslide motion to occur while positive pore pressure is supplied by rain infiltration. Steady state slip velocities v0 obey v0 = −(K/ψ) p*e, where K is the hydraulic conductivity and p*e is the normalized (dimensionless) negative pore pressure generated by dilation. If rain infiltration and attendant pore pressure growth continue unabated, however, their influence ultimately overwhelms the stabilizing influence of negative p*e. Then, unbounded landslide acceleration occurs, accentuated by an instability that develops if ψ diminishes as landslide motion proceeds. Nonetheless, numerical solutions of the model equations show that slow, nearly steady motion of a clay-rich landslide may persist for many months as a result of negative pore pressure feedback that regulates basal Coulomb friction. Similarly stabilized motion is less likely to occur in sand-rich landslides that are characterized by weaker negative feedback.

Wave Velocities in Rocks as a Function of Changes in Overburden Pressure and Pore Fluid Saturants

Abstract: A system is described for determining precisely the dilatational and shear-wave group velocities in rock samples subjected to hydrostatic confining and internal pore pressures independently to 10,000 psi. Both velocities have been measured on three dry sandstones in directions perpendicular and parallel to the bedding plane. Two exhibited transverse isotropy with the bedding plane as the plane of symmetry, decreasing in degree as confining pressure increased. If effects of mechanical hysteresis of the rock were avoided, the velocities in sandstones depended on the simple difference between the hydrostatic confining pressure and internal pore pressure.

Electrical resistivity changes in saturated rocks during fracture and frictional sliding

Abstract: Changes in electrical resistivity were observed as a function of compressive stress in a variety of crystalline rocks that were subjected to confining pressure of up to 5 kb and to pore pressure of water of 500 bars In the majority of the rocks, resistivity increased slightly up to about half the fracture stress; just the reverse effect has been noted elsewhere for rocks that were apparently partially saturated Beyond half and particularly within about 20 per cent of the fracture stress, resistivity dropped typically by an order of magnitude This sharp decrease corresponded closely to an increase in porosity, or dilatancy, which took place under compressive stress Detailed study of one rock, Westerly granite, showed that changes in resistivity and, hence, porosity with stress were insensitive to effective pressure, when stress was normalized with respect to fracture stress This suggests that fracture occurred at a critical crack porosity that was pressure independent The changes in resistivity with stress that accompany frictional sliding on a fault are insignificant when the measurement volume contains the fault, even though faulted rock under pressure can support high stress

Organic carbon dynamics and preservation in deep-sea sediments

Abstract: Three methods of estimating the particulate organic carbon fluxes to the sediment-water interface of the deep Pacific Ocean agree to within the error of the measurements at MANOP sites M, H, and C. Sediment trap experiments, pore water results, and surface sediment organic carbon data suggest that a major fraction of the particulate organic carbon raining to abyssal depths at these locations is degraded within the surface sediments rather than at the sediment-water interface or in the nephloid layer. Organic carbon rain rates at the three sites are similar—within a factor of two; however, the preservation rate of organic carbon and the chemistry of sediment pore waters are very different. A model developed to describe the pore water oxygen and sedimentary carbon distributions indicates model developed to describe the pore water oxygen and sedimentary carbon distributions indicates that changes in the rate constant for organic matter degradation and the bioturbation rate may contribute significantly to the observed differences in character of both pore water and sediment chemistry at these locations. The implication with respect to interpreting the sedimentary record is that cycles of organic carbon and redox sensitive metals (i.e., manganese) are not simply related to particulate organic carbon flux or surface water primary productivity. The residence time of organic carbon with respect to degradation in the surface sediments is on the order of 15 to 150 y.