Response of sediment to ice-sheet loading in northwestern Germany: effective stresses and glacier-bed stability

AbstractLaboratory tests on sediment over-ridden by the last ice sheet in north-western Germany reveal very low ice-induced pre-consolidation and high palaeo-pore-water pressures. Sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum. Generally low permeabilities of the bed caused sustained high pore-water pressure in over-ridden sediments close to the flotation point. This implies a serious possibility of hydraulic lifting of the ice sheet. It is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments, which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation. Ice motion was probably focused at the glacier sole by some combination of sliding and ploughing. However, isolated spots with deformation occur, so that the subglacial system in the study area can be characterized as a stable/deforming mosaic.

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Infiltration characteristics of two instrumented residual soil slopes

Canadian Geotechnical Journal ◽

10.1139/t03-049 ◽

2003 ◽

Vol 40 (5) ◽

pp. 1012-1032 ◽

Cited By ~ 35

Author(s):

Illias Tsaparas ◽

Harianto Rahardjo ◽

David G Toll ◽

Eng-Choon Leong

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Field Measurements ◽

Residual Soil ◽

Rainfall Runoff ◽

Rainfall Events ◽

Pore Water Pressures ◽

Soil Slopes ◽

Pressure Changes

This paper presents the analysis of a 12 month long field study of the infiltration characteristics of two residual soil slopes in Singapore. The field measurements consist of rainfall data, runoff data of natural and simulated rainfall events, and pore-water pressure changes during infiltration at several depths and at several locations on the two slopes. The analysis of the field measurements identifies the total rainfall and the initial pore-water pressures within the two slopes as the controlling parameters for the changes in the pore-water pressures within the slopes during infiltration.Key words: infiltration, rainfall, runoff, pore-water pressure, field measurements.

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Field measurement of anchor forces, ground temperatures, and pore-water pressures behind a retaining structure in northwestern Ontario

Canadian Geotechnical Journal ◽

10.1139/t92-012 ◽

1992 ◽

Vol 29 (1) ◽

pp. 112-116

Author(s):

K. D. Eigenbrod ◽

J. P. Burak

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Retaining Wall ◽

Field Measurements ◽

Strain Gauges ◽

Ground Temperatures ◽

Northwestern Ontario ◽

Pore Water Pressures ◽

Load Increase

Anchor forces, ground temperatures, and piezometric pressures were measured at a retaining wall in northwestern Ontario over a period of 2 years. The anchor forces were measured with strain gauges attached in pairs directly to the anchor rods. This method appeared practical in the field for time periods of less than 2 years as long as the strain gauges were carefully protected against moisture. The anchor forces increased from an average of 5 kN initially up to values of 50 kN during the winter periods and dropped during the summer periods back to the same values measured initially. The anchor forces were largely independent of pore-water pressure variations behind the wall. Rapid drawdown conditions, however, which were experienced during the second summer, were reflected in a load increase that was equivalent to the associated unloading effect in front of the wall. The pore-water pressures behind the wall were not noticeably affected by rapid drawdown, possibly due to the restraining effect of the anchors and the high rigidity of the low sheet pile wall. Ground temperatures at or below the groundwater table never dropped below 0 °C thus restricting the depth of frost penetration. Key words : anchor loads, freezing pressure, retaining walls, pore-water pressures, ground temperatures, field measurements.

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Experiment Study of Lateral Unloading Stress Path and Excess Pore Water Pressure on Creep Behavior of Soft Soil

Advances in Civil Engineering ◽

10.1155/2019/9898031 ◽

2019 ◽

Vol 2019 ◽

pp. 1-9 ◽

Cited By ~ 4

Author(s):

Wei Huang ◽

Kejun Wen ◽

Dongsheng Li ◽

Xiaojia Deng ◽

Lin Li ◽

...

Keyword(s):

Pore Water ◽

Creep Behavior ◽

Pore Water Pressure ◽

Water Pressure ◽

Soft Soil ◽

Stress Path ◽

Deviatoric Stress ◽

Excess Pore Water Pressure ◽

Pore Water Pressures ◽

Excess Pore

The unloading creep behavior of soft soil under lateral unloading stress path and excess pore water pressure is the core problem of time-dependent analysis of surrounding rock deformation under excavation of soft soil. The soft soil in Shenzhen, China, was selected in this study. The triaxial unloading creep tests of soft soil under different initial excess pore water pressures (0, 20, 40, and 60 kPa) were conducted with the K0 consolidation and lateral unloading stress paths. The results show that the unloading creep of soft soil was divided into three stages: attenuation creep, constant velocity creep, and accelerated creep. The duration of creep failure is approximately 5 to 30 mins. The unloading creep behavior of soft soil is significantly affected by the deviatoric stress and time. The nonlinearity of unloading creep of soft soil is gradually enhanced with the increase of the deviatoric stress and time. The initial excess pore water pressure has an obvious weakening effect on the unloading creep of soft soil. Under the same deviatoric stress, the unloading creep of soft soil is more significant with the increase of initial excess pore water pressure. Under undrained conditions, the excess pore water pressure generally decreases during the lateral unloading process and drops sharply at the moment of unloading creep damage. The pore water pressure coefficients during the unloading process were 0.73–1.16, 0.26–1.08, and 0.35–0.96, respectively, corresponding to the initial excess pore water pressures of 20, 40, and 60 kPa.

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Modelling unanticipated pore-water pressures in soft clays

Canadian Geotechnical Journal ◽

10.1139/t94-088 ◽

1994 ◽

Vol 31 (5) ◽

pp. 773-778 ◽

Cited By ~ 31

Author(s):

Jianhua Yin ◽

James Graham ◽

Jack I. Clark ◽

Longjun Gao

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Creep Behaviour ◽

Soft Clay ◽

Field Observations ◽

Soft Clays ◽

Secondary Compression ◽

Pore Water Pressures ◽

Clay Layers

Field observations in thin soft clay layers may show pore-water pressures that increase for some time after the loading is applied. Reasons for these observations are not well understood. The paper shows how an elastic viscoplastic constitutive model incorporated into the consolidation equation can predict these pore-water pressure increases in soils that exhibit significant creep behaviour (or secondary compression). The phenomenon has been related to relaxation in regions of the profile from which drainage has not yet begun. Key words : clay, consolidation, creep, secondary compression, viscous, relaxation, pore-water pressure, elastic–plastic.

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Formation of thrust-block moraines at the margins of dry-based glaciers, south Victoria Land, Antarctica

Annals of Glaciology ◽

10.1017/s0260305500015238 ◽

1996 ◽

Vol 22 ◽

pp. 68-74 ◽

Cited By ~ 24

Author(s):

Sean J. Fitzsimons

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Freezing Point ◽

Water Pressure ◽

Lacustrine Sediment ◽

Dry Valleys ◽

Bed Deformation ◽

Sedimentary Structures ◽

Victoria Land ◽

Subglacial Meltwater

Several dry-based alpine glaciers in the Dry Valleys of south Victoria Land, Antarctica, have prominent end moraines. Examination of their morphology, structure and sedimentology shows they consist of blocks of sand, gravel and organic silt within which sedimentary structures unrelated to entrainment and transportation by ice are well preserved. The nature and preservation of sedimentary structures, together with the presence of algae mats in the sediment, suggest formation by proglacial entrainment, transportation and deposition of frozen blocks of lacustrine sediment. Previous explanations of the formation of thrust-block moraines, including those that stress the importance of elevated pore-water pressure and Weertman’s ice-debris accretion hypothesis, depend on the presence of subglacial meltwater or the 0° C isotherm being situated close to the glacier bed. These models appear inappropriate for cold, dry-based glaciers because their basal temperatures are well below freezing point and they rest on deep permafrost. Three alternative models for the formation of thrust-block moraines at the margins of dry-based glaciers are examined in this paper: block entrainment of sediment associated with frozen-bed deformation; entrainment by overriding and accretion of marginal-ice and debris aprons; and transient wet-based conditions associated with glaciers flowing into ice-marginal lakes.

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Formation of thrust-block moraines at the margins of dry-based glaciers, south Victoria Land, Antarctica

Annals of Glaciology ◽

10.3189/1996aog22-1-68-74 ◽

1996 ◽

Vol 22 ◽

pp. 68-74 ◽

Cited By ~ 4

Author(s):

Sean J. Fitzsimons

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Freezing Point ◽

Water Pressure ◽

Lacustrine Sediment ◽

Dry Valleys ◽

Bed Deformation ◽

Sedimentary Structures ◽

Victoria Land ◽

Subglacial Meltwater

Several dry-based alpine glaciers in the Dry Valleys of south Victoria Land, Antarctica, have prominent end moraines. Examination of their morphology, structure and sedimentology shows they consist of blocks of sand, gravel and organic silt within which sedimentary structures unrelated to entrainment and transportation by ice are well preserved. The nature and preservation of sedimentary structures, together with the presence of algae mats in the sediment, suggest formation by proglacial entrainment, transportation and deposition of frozen blocks of lacustrine sediment. Previous explanations of the formation of thrust-block moraines, including those that stress the importance of elevated pore-water pressure and Weertman’s ice-debris accretion hypothesis, depend on the presence of subglacial meltwater or the 0° C isotherm being situated close to the glacier bed. These models appear inappropriate for cold, dry-based glaciers because their basal temperatures are well below freezing point and they rest on deep permafrost. Three alternative models for the formation of thrust-block moraines at the margins of dry-based glaciers are examined in this paper: block entrainment of sediment associated with frozen-bed deformation; entrainment by overriding and accretion of marginal-ice and debris aprons; and transient wet-based conditions associated with glaciers flowing into ice-marginal lakes.

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Three-dimensional numerical investigations of groundwater responses in an unsaturated slope subjected to various rainfall patterns

Canadian Geotechnical Journal ◽

10.1139/t01-057 ◽

2001 ◽

Vol 38 (5) ◽

pp. 1049-1062 ◽

Cited By ~ 48

Author(s):

C WW Ng ◽

B Wang ◽

Y K Tung

Keyword(s):

Pore Water ◽

Short Duration ◽

Pore Water Pressure ◽

Water Pressure ◽

Three Dimensional ◽

Ground Surface ◽

Rainfall Pattern ◽

Initial Water ◽

Pore Water Pressures ◽

Rainfall Patterns

Three-dimensional (3D) numerical analyses were conducted to investigate groundwater responses in an initially unsaturated cut slope at Lai Ping Road in Hong Kong subjected to rainfalls with various patterns, durations, and return periods. Initial and boundary conditions were established from field monitoring data. The computed results show that rainfall pattern has a significant influence on pore-water pressures in soil layers near the ground surface but its influence gradually diminishes with depth. Rainfall with an advanced storm pattern of 24 h duration was found to be the most critical because it results in the highest pore-water pressure in the slope. At a given depth, the influence of rainfall pattern on pore-water pressures depends on the initial groundwater conditions: the higher the initial water table, the smaller the influence of rainfall pattern on pore-water pressures. Under a given rainfall duration, the rise of pore-water pressure at the study site is significant only when the return period increases from 10 years to 100 years, but not from 100 years to 1000 years. Short-duration, intense rainfall causes larger variations in pore-water pressure at shallow depths, whereas long-duration rainfall has a greater influence on groundwater in deep soils because of the generally greater amount of rainfall. For prolonged rainfalls, the difference in pore-water pressure distribution resulting from different rainfall patterns is less significant than that from short-duration, intense rainfalls.Key words: Lai Ping Road, rainfall patterns, pore-water pressure distributions, suction, unsaturated slope.

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The Effects of Seismic Pore Water Pressure on Ground Surface Motion

Earthquake Spectra ◽

10.1193/1.1585780 ◽

1994 ◽

Vol 10 (2) ◽

pp. 403-438 ◽

Cited By ~ 15

Author(s):

George(Bebe)T. Zorapapel ◽

Mladen Vucetic

Keyword(s):

Pore Water ◽

Fourier Transforms ◽

Pore Water Pressure ◽

Water Pressure ◽

Ground Surface ◽

Surface Motion ◽

Surface Displacements ◽

Acceleration Time Histories ◽

Pore Water Pressures ◽

Time Histories

The effects of the gradual buildup of seismic pore water pressures and associated degradation of stiffness on the ground surface motion are examined for shallow saturated liquefiable deposits. Ground surface displacements and accelerations, the Fourier Transforms of the acceleration-time histories and layer gain factors are analyzed. The analysis is based on the ground surface and sub-surface accelerations and pore water pressures recorded at sites that either fully liquefied or built up considerable pore water pressures during strong earthquakes. The analysis shows that: (i) the seismic pore water pressures within the deposit and the ground surface motion are intimately related, (ii) relatively small seismic excess pore water pressures can cause a considerable lengthening of the predominant period of the ground surface motion, and (iii) these phenomena may lead to a limited maximum ground surface acceleration of approximately 0.2g, and a considerable increase of maximum ground displacements.

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Soft-bed experiments beneath Engabreen, Norway:regelation infiltration, basal slip and bed deformation

Journal of Glaciology ◽

10.3189/002214307783258431 ◽

2007 ◽

Vol 53 (182) ◽

pp. 323-340 ◽

Cited By ~ 42

Author(s):

N.R. Iverson ◽

T.S. Hooyer ◽

U.H. Fischer ◽

D. Cohen ◽

P.L. Moore ◽

...

Keyword(s):

Pore Water ◽

Surface Deformation ◽

Pore Water Pressure ◽

Water Pressure ◽

Water Layer ◽

Effective Pressure ◽

Bed Deformation ◽

Rock Bed ◽

Glacier Velocity ◽

Thickness Shear

AbstractTo avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m × 1.6 m × 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7–12 days, the glacier regelated downward into the prism to depths of 50–80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of sustained high pore-water pressure (70–100% of overburden), ice commonly slipped over the prism, due to a water layer at the prism surface. Deformation of the prism was activated when this layer thinned to a sub-millimeter thickness. Shear strain in the till was pervasive and decreased with depth. A model of slip by ploughing of ice-infiltrated till across the prism surface accounts for the slip that occurred when effective pressure was sufficiently low or high. Slip at low effective pressures resulted from water-layer thickening that increased non-linearly with decreasing effective pressure. If sufficiently widespread, such slip over soft glacier beds, which involves no viscous deformation resistance, may instigate abrupt increases in glacier velocity.

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