Pore Water Pressure Research Papers (original) (raw)

Gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion. The interaction of these forces control streambank mechanics. Hydraulic forces exerted by... more

Gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion. The interaction of these forces control streambank mechanics. Hydraulic forces exerted by flowing water on in situ bank-toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower-bank profiles. Seepage forces exerted on in situ bank material by groundwater, downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength. Data from a study site on Goodwin Creek, MS, USA clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore-water pressures. Negative pore-water pressures (matric suction) have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear. A stable bank can be transformed into an unstable bank during periods of prolonged rainfall through:increase in soil bulk unit (specific) weight,decrease or complete loss of matric suction, and, therefore, apparent cohesion,generation of positive pore-water pressures, and, therefore, reduction or loss of frictional strength,entrainment of in situ and failed material at the bank toe, andloss of confining pressure during recession of stormflow hydrographs.

Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometer-piezometers at increasing depths in a riverbank of the Sieve River, Tuscany (central Italy), with the overall objective... more

Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometer-piezometers 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.

In the Argentera massif (French Southern Alps), large active landslides develop along strike of an active corridor of dextral strike-slip faults revealed by shallow ongoing seismicity. Glacially polished bedrock outcrops are offset by... more

In the Argentera massif (French Southern Alps), large active landslides develop along strike of an active corridor of dextral strike-slip faults revealed by shallow ongoing seismicity. Glacially polished bedrock outcrops are offset by right-lateral strike-slip faults. Gravitational structures appear to be spatially connected to these active faults. Dating using the in situ-produced 10Be cosmogenic nuclide performed on glacial, tectonic and gravity surfaces. The late glacial–interglacial Holocene transition is constrained by 10Be ages between 12 and 15 ka obtained on glacially polished surfaces. The main tectonic activity closely post-dates the main deglaciation event and is constrained by 10Be ages of 11 and 7–8 ka obtained on fault scarps. Three successive periods of landsliding are recognized, at 11–12, 7–9 and 2.5–5.5 ka. These Holocene ages were obtained on right-lateral strike-slip fault scarps indicating that recent Alpine tectonics are expressed by transcurrent movements. The discussed close age relationship between deglaciation and a tectonic pulse may suggest that post-glacial rebound and enhanced pore water pressure do influence seismogenic tectonic activity. Gravitational destabilizations at 11–12 and 7–9 ka are coincidental with the main tectonic activity, and suggest tectonic shaking as a landslide trigger. The third gravitational destabilization at 2.5–5.5 ka could be attributed either to slope weakness resulting from multiple low-magnitude earthquake events, as currently revealed by the seismic activity or to climatic causes during the wetter optimum climatic period. These early and middle Holocene ages coincide with a phase of large landslide throughout the Alps scale which suggests that these large gravitational mass movements could be related to combined effects of intense tectonic activity and transitions form cold and dry period to warm and wetter phase.

A full-scale field study was conducted to investigate the effects of rainfall infiltration on a natural grassed expansive soil slope in China. A 16 m wide × 28 m long area was selected for instrumentation. The instrumentation included... more

A full-scale field study was conducted to investigate the effects of rainfall infiltration on a natural grassed expansive soil slope in China. A 16 m wide × 28 m long area was selected for instrumentation. The instrumentation included jet-filled tensiometers, moisture probes, a tipping bucket rain gauge, and a vee-notch flow meter. One artificial rainfall event amounting to about 370

Among the various laboratory studies to investigate the Thermo-Hydro-Mechanical (THM) behaviour of Boom clay, relatively few were devoted to the time dependent behaviour, limiting any relevant analysis of the long-term behaviour of the... more

Among the various laboratory studies to investigate the Thermo-Hydro-Mechanical (THM) behaviour of Boom clay, relatively few were devoted to the time dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were