The Role of Pore-Water Pressures and Upward-Directed Seepage Forces in the Erosion of Cohesive Streambeds

2000 ◽  
Author(s):  
Andrew Simon ◽  
Andrea Curini ◽  
Gregory J. Hanson ◽  
Andrew J. Collison
Keyword(s):  
Pore Water ◽  
Pore Water Pressures

A new approach to the stability analysis of thawing slopes

1980 ◽  
Vol 17 (4) ◽  
pp. 607-612 ◽  
Author(s):  
Luis E. Vallejo
Keyword(s):  
Stability Analysis ◽  
Water Content ◽  
Pore Water ◽  
Active Layer ◽  
Necessary Conditions ◽  
Mass Movements ◽  
New Approach ◽  
Pore Water Pressures ◽  
The Stability ◽  
Excess Pore

A new approach to the stability analysis of thawing slopes at shallow depths, taking into consideration their structure (this being a mixture of hard crumbs of soil and a fluid matrix), is presented. The new approach explains shallow mass movements such as skin flows and tongues of bimodal flows, which usually take place on very low slope inclinations independently of excess pore water pressures or increased water content in the active layer, which are necessary conditions in the methods available to date to explain these movements.

An analysis of the stability of thawing slopes, Ellesmere Island, Nunavut, Canada

2000 ◽  
Vol 37 (2) ◽  
pp. 449-462 ◽  
Author(s):  
Charles Harris ◽  
Antoni G Lewkowicz
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Active Layer ◽  
Factor Of Safety ◽  
High Arctic ◽  
Ellesmere Island ◽  
Sensitivity Analyses ◽  
Pore Water Pressures ◽  
Hot Weather ◽  
The Stability

Active-layer detachment slides are locally common on Fosheim Peninsula, Ellesmere Island, where permafrost is continuous, the active layer is 0.5-0.75 m thick, and summer temperatures are unusually high in comparison with much of the Canadian High Arctic. In this paper we report pore-water pressures at the base of the active layer, recorded in situ on two slopes in late July and early August 1995. These data form the basis for slope stability analyses based on effective stress conditions. During fieldwork, the factor of safety within an old detachment slide on a slope at Hot Weather Creek was slightly greater than unity. At "Big Slide Creek," on a slope showing no evidence of earlier detachment failures, the factor of safety was less than unity on a steep basal slope section but greater than unity elsewhere. In the upper slope, pore-water pressures were only just subcritical. Sensitivity analyses demonstrate that the stability of the shallow active layer is strongly influenced by changes in soil shear strength. Possible mechanisms for reduction in shear strength through time include weathering of soils and gradual increases in basal active layer ice content. However, we suggest here that soil shearing during annual gelifluction movements is most likely to progressively reduce shear strengths at the base of the active layer from peak values to close to residual, facilitating the triggering of active-layer detachment failures.Key words: detachment slides, Ellesmere Island, pore-water pressures, gelifluction.

scholarly journals Subglacial Hydrology for an Ice Sheet Resting on a Deformable Aquifer

1986 ◽  
Vol 32 (110) ◽  
pp. 20-30 ◽  
Author(s):  
E. M. Shoemaker
Keyword(s):  
Pore Water ◽  
Coulomb Friction ◽  
Ice Sheet ◽  
Friction Angle ◽  
Water Channels ◽  
Water Drainage ◽  
Short Term ◽  
Overburden Pressure ◽  
Melt Water ◽  
Pore Water Pressures

AbstractSubglacial hydrology is investigated for an ice sheet where the substrate consists of a deformable aquifer resting on an aquitard. If sliding velocities are low or absent, subglacial melt-water drainage is dominated by drainage through the aquifer to water channels. Drainage along the bed is negligible. Efficient melt-water drainage requires that a system of subglacial water channels exists; otherwise, pore-water pressures will exceed the overburden pressure. In general, aquifer deformation near (away from) the terminus is most likely to occur during the winter (summer). The effect of short-term high channel pressures is, in general, not critical to aquifer deformation because the pressure pulse does not propagate far into the aquifer. (For aquifers of high permeability, short periods of high channel pressures constitute the most critical condition.) Aquifer deformation at the terminus is very likely to occur if the terminus ice slope exceeds tan ϕ, where ϕ is the Coulomb friction angle of the aquifer material. Upwelling of basal melt water near the terminus will normally cause soil dilation if the aquifer has a low permeability (e.g. till). Maximal profiles are computed corresponding to various aquifer materials using channel spacings which provide efficient drainage. (A maximal profile is the highest ice profile which the aquifer can sustain without deformation.) In general, maximal profiles lie well above observed profiles (such as h(x) = 3x1/2 (m)) except near the terminus. However, if channel spacings are sufficiently large, pore-water pressures are increased and maximal profiles can lie well below h(x) = 3x1/2.

Moisture Accumulation and Pore Water Pressures at Base of Pavements

1996 ◽  
Vol 1546 (1) ◽  
pp. 151-161 ◽  
Author(s):  
K. D. Eigenbrod ◽  
G. J. A. Kennepohl
Keyword(s):  
Pore Water ◽  
Base Material ◽  
The United States ◽  
Base Layer ◽  
Frozen Ground ◽  
Extensive Field ◽  
Pore Water Pressures ◽  
Excess Moisture ◽  
Pavement Base ◽  
Granular Base

A unique mechanism based on extensive field and laboratory studies is presented to account for certain premature failures of flexible pavements in cold areas like those in Scandinavia and in northern parts of Canada and the United States. Water condensing at the interface between pavement and granular base accumulates at subzero temperatures resulting in excess moisture in this zone. During the thaw period of the uppermost base layer, the excess water in the aggregate is trapped between impervious layers of frozen ground to the sides and below as well as an impervious layer of asphalt pavement above. Because of this containment, high pore water pressures can occur, leading to loss in shear strength of the base material and thus to failure of the pavement structure itself. It was found that under special conditions, excess moisture can accumulate in granular base with a silt content greater than 20 percent and very high pore water pressures can develop during initial thaw at the pavement-soil interface. With silt contents of less than 2 percent, excess pore water pressures can be avoided during thaw. It was also shown that when a clean open gravel is placed below the pavement on top of a silty base material, moisture accumulation near the pavement-base interface can be prevented, and thus also the development of high pore water pressures.

Sign in / Sign up

Export Citation Format

Share Document