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.

Monitoring and modelling of pore water pressure changes and riverbank stability during flow events

Abstract: Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometerpiezometers at increasing depths in a riverbank of the Sieve River, Tuscany (central Italy), with the overall objective of investigating pore pressure changes in response to flow events and their effects on bank stability. The saturated/unsaturated flow was modelled using a finite element seepage analysis, for the main flow events occurring during the four-year monitoring period. Modelling results were validated by comparing measured with computed pore water pressure values for a series of representative events. Riverbank stability analysis was conducted by applying the limit equilibrium method (Morgenstern-Price), using pore water pressure distributions obtained by the seepage analysis. The simulation of the 14 December 1996 event, during which a bank failure occurred, is reported in detail to illustrate the relations between the water table and river stage during the various phases of the hydrograph and their effects on bank stability. The simulation, according to monitored data, shows that the failure occurred three hours after the peak stage, during the inversion of flow (from the bank towards the river). A relatively limited development of positive pore pressures, reducing the effective stress and annulling the shear strength term due to the matric suction, and the sudden loss of the confining pressure of the river during the initial drawdown were responsible for triggering the mass failure. Results deriving from the seepage and stability analysis of nine selected flow events were then used to investigate the role of the flow event characteristics (in terms of peak stages and hydrograph characteristics) and of changes in bank geometry. Besides the peak river stage, which mainly controls the occurrence of conditions of instability, an important role is played by the hydrograph characteristics, in particular by the presence of one or more minor peaks in the river stage preceding the main one. Copyright © 2004 John Wiley & Sons, Ltd.

Undrained anisotropy and rotational shear in granular soil

Abstract: The impact of fabric anisotropy on the behaviour of granular soil remains a subject of great interest. In particular, the effects of principal stress rotation on the undrained response of saturated sand are not fully understood. This paper describes an experimental investigation conducted in an automated hollow cylinder apparatus into the undrained anisotropic behaviour of saturated sand in rotational shear, which is defined as a class of non-proportional loading with a continuous rotation of the principal stress directions but a constant deviatoric stress. Special attention in this investigation was placed on the influence of the relative magnitude of the intermediate principal stress, characterised by the parameter b = (σ2 − σ3)/(σ1 − σ3), on the pore pressure response and deformation characteristics. The experimental observations indicate that soil specimens, even in very dense state, were weakened by the build-up of pore water pressure in rotational shear. The intermediate principal stress parameter b...

Consolidation around a point heat source

Abstract: When a heat source such as a canister of radioactive waste is buried in a saturated soil the temperature changes that occur will cause the pore water to expand a greater amount than the voids of the soil. The temperature change will thus usually be accompanied by an increase in pore pressure. If the soil is sufficiently permeable these pore pressures will dissipate. This paper develops an analytic solution for the fundamental problem of a point heat source buried deep in a saturated soil.

Triggering of Seismicity by Pore-pressure Perturbations: Permeability-related Signatures of the Phenomenon

Abstract: — We consider various cases of seismicity, induced by artificial fluid injections in boreholes. Like many other authors, we support the hypothesis that to a large extent the triggering of this seismicity is caused by a diffusive process of the pore pressure relaxation in porous (or fractured), saturated rocks. We show that if this hypothesis is correct, then the spatio-temporal distributions of the seismic events must have several specific features related to the effective permeability of the rock. As a rule the fluid injection-induced seismicity obeys such features. These features can be indications of the diffusive and even hydraulic nature of the seismicity triggering process.¶From this point of view we analyze the spatio-temporal distribution of the late aftershocks of the Antofagasta (northern Chile) 1995 earthquake. These aftershocks were concentrated in a plane, an approximately 3 km-thick spatial zone. This thin seismogenic layer is a part of the South American subduction zone. The time-distance distribution of the aftershocks along this layer indicates that they could be triggered by a diffusion-like process. Possibly, such a process is the relaxation of the pressure perturbation caused in the pore fluid by the main Antofagasta event. We estimated the permeability required to explain the spatio-temporal distribution of the aftershocks by such a triggering mechanism. The obtained value, 60 mD, is very large. However, it is realistic for a long-time existing and large-scale fault zone.