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.

Experience with the use of methylcellulose as a viscous pore fluid in centrifuge models. technical note

Abstract: Pore fluids having viscosity greater than water are sometimes used in geotechnical centrifuge model tests to more accurately satisfy the scaling laws relating to movement of pore fluid through the soil when modeling dynamic loading events This is frequently done using either silicone oil or mixtures of water and glycerol There are some drawbacks in using silicone oil and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has recently come into use The authors present test data showing the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration The relative performance of the fluid is illustrated with pore pressure dissipation data from two centrifuge model tests involving earthquake simulations One test was done with pure water as the pore fluid and the other test was done with an HPMC solution having viscosity ten times that of water

An evaluation of factors influencing pore pressure in accretionary complexes : Implications for taper angle and wedge mechanics

Abstract: [1] At many subduction zones, accretionary complexes form as sediment is off-scraped from the subducting plate. Mechanical models that treat accretionary complexes as critically tapered wedges of sediment demonstrate that pore pressure controls their taper angle by modifying basal and internal shear strength. Here, we combine a numerical model of groundwater flow with critical taper theory to quantify the effects of sediment and decollement permeability, sediment thickness, sediment partitioning between accretion and underthrusting, and plate convergence rate on steady state pore pressure. Our results show that pore pressure in accretionary wedges can be viewed as a dynamically maintained response to factors which drive pore pressure (source terms) and those that limit flow (permeability and drainage path length). We find that sediment permeability and incoming sediment thickness are the most important factors, whereas fault permeability and the partitioning of sediment have a small effect. For our base case model scenario, as sediment permeability is increased, pore pressure decreases from near-lithostatic to hydrostatic values and allows stable taper angles to increase from ∼2.5° to 8°–12.5°. With increased sediment thickness in our models (from 100 to 8000 m), increased pore pressure drives a decrease in stable taper angle from 8.4°–12.5° to 15° to <4°) with increased sediment thickness (from <1 to 7 km). One key implication is that hydrologic properties may strongly influence the strength of the crust in a wide range of geologic settings.

An Experimental Study of Tectonic Overpressure in Franciscan Rocks

Abstract: Approximately 4 kb tectonic overpressure was required, according to one theory, for the formation of jadeite-aragonite-bearing rocks of the Franciscan. Strength of two common Franciscan rocks—massive graywacke, and thin-bedded shale and graywacke—was determined to see if this tectonic overpressure could have been generated under the conditions of metamorphism; that is, 4 kb confining pressure, 200 to 300° C, in the presence of aqueous pore fluid. The strength was found to depend markedly on both pore and total pressures. The required tectonic overpressure could only have been generated in massive graywacke, and only when pore pressure was less than hydrostatic. With even moderate amounts of interbedded shale, tectonic overpressure could not have exceeded 1 kb.

Experimental Validation of a Mathematical Model For Seabed Liquefaction Under Waves

Abstract: This paper summarizes the results of an experimental study directed towards the validation of a mathematical model for the buildup of pore water pressure and resulting liquefaction of marine soils under progressive waves. Experiments were conducted under controlled conditions with silt (d50 D 00070 mm) in a wave flume with a soil pit. Waves with wave heights in the range of 7.7‐18 cm, 55-cm water depth and 1.6-s wave period enabled us to study both the liquefaction and no-liquefaction regime pore water pressure buildup. The experimental data were used to validate the model. A numerical example is also included in the paper to demonstrate the implementation of the model for real-life scenarios.

Depositional processes and gas pore pressure in pyroclastic flows: an experimental perspective

Abstract: The depositional processes and gas pore pressure in pyroclastic flows are investigated through scaled experiments on transient, initially fluidized granular flows. The flow structure consists of a sliding head whose basal velocity decreases backwards from the front velocity (U f) until onset of deposition occurs, which marks transition to the flow body where the basal deposit grows continuously. The flows propagate in a fluid-inertial regime despite formation of the deposit. Their head generates underpressure proportional to U f 2 whereas their body generates overpressure whose values suggest that pore pressure diffuses during emplacement. Complementary experiments on defluidizing static columns prove that the concept of pore pressure diffusion is relevant for gas-particle mixtures and allow characterization of the diffusion timescale (t d) as a function of the material properties. Initial material expansion increases the diffusion time compared with the nonexpanded state, suggesting that pore pressure is self-generated during compaction. Application to pyroclastic flows gives minimum diffusion timescales of seconds to tens of minutes, depending principally on the flow height and permeability. This study also helps to reconcile the concepts of en masse and progressive deposition of pyroclastic flow units or discrete pulses. Onset of deposition, whose causes deserve further investigation, is the most critical parameter for determining the structure of the deposits. Even if sedimentation is fundamentally continuous, it is proposed that late onset of deposition and rapid aggradation in relatively thin flows can generate deposits that are almost snapshots of the flow structure. In this context, deposition can be considered as occurring en masse, though not strictly instantaneously.