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.

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 tanϕ, whereϕis 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 ash(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 belowh(x) = 3x1/2.

Effect of drainage and sequential filling on the behavior of backfill in mine stopes

2014 ◽  
Vol 51 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Nawfal El Mkadmi ◽  
Michel Aubertin ◽  
Li Li
Keyword(s):  
Pore Water ◽  
Numerical Study ◽  
Water Drainage ◽  
Filling Rate ◽  
Mining Operations ◽  
Overburden Pressure ◽  
Filling Sequence ◽  
Pore Water Pressures ◽  
Backfilled Stopes ◽  
Excess Pore

Underground backfilling offers significant economic and environmental advantages to mining operations. There is however a limited knowledge and understanding of how the backfill behaves within mine stopes, which creates some concern regarding the risk of accidents with potentially serious consequences. It is thus important to investigate further the response of backfill to ensure safe working conditions and optimize the filling sequence. This paper presents key results from a numerical study aimed at analyzing the hydrogeotechnical response of backfill in a narrow vertical stope. The simulations illustrate how stresses are influenced by stope geometry, water drainage, and filling rate. Three main cases are presented here to illustrate these effects; namely, (i) simulation of dry (or drained) backfill, (ii) a rapidly filled stope with progressive drainage and consolidation, and (iii) sequential backfill placement with different filling rates. The third case includes a simulation with evolving properties due to the binder added to the backfill. The results from the numerical analyses show that arching effects develop within narrow backfilled stopes because of the stiffness contrast between the rock and the fill material. This can produce a significant reduction of the stresses (horizontal and vertical) in comparison with the overburden pressure. The simulation results also show the development of excess pore-water pressures after the placement of the saturated backfill within the stope. Drainage tends to reduce these pressures and increase the frictional stresses along the rock walls. The sequentially filled stope simulations show that a rapid filling rate produces much higher total stresses and excess pore-water pressures, compared to slower rates. The simulation of the cemented backfill, with evolving properties, indicates that the progressive changes can have a significant effect on the total and effective stresses in the stope. A discussion follows on the implications of these results.

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

1997 ◽  
Vol 43 (145) ◽  
pp. 495-502 ◽  
Author(s):  
Jan A. Piotrowski ◽  
Anna M. Kraus
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Ice Sheet ◽  
Bed Deformation ◽  
Pore Water Pressures ◽  
Sediment Consolidation ◽  
Western Germany ◽  
Bed Stability ◽  
North Western

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.

Effects of freeze–thaw and softening on a natural clay at low stresses

1985 ◽  
Vol 22 (1) ◽  
pp. 69-78 ◽  
Author(s):  
J. Graham ◽  
V. C. S. Au
Keyword(s):  
Pore Water ◽  
Compacted Clay ◽  
Lake Agassiz ◽  
Overburden Pressure ◽  
Freeze Thaw ◽  
Weathering Processes ◽  
Preconsolidation Pressure ◽  
Pore Water Pressures ◽  
Access To Water

Weathering processes such as softening and freeze–thaw cycling affect the properties of clays. Care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes, compacted clay embankments, and trench excavations in which significant proportions of the cross section can be affected by climatic weathering.Samples of plastic Lake Agassiz clay from Winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure. They were therefore all overconsolidated with respect to the field preconsolidation pressure. The samples were then loaded under drained or undrained conditions along steeply rising stress paths in p′, q stress space. One group of samples was tested immediately to identify the "undisturbed" behavior, a second group was subjected to freeze–thaw cycles, and a third group allowed to swell freely before testing.The freeze–thaw cycling produced increased compressibility and pore-water pressures, and reduced strengths at low stresses compared with the behavior of undisturbed clay. Freezing also caused the development of a clearly defined fissure structure. Softening at low stresses with access to water produced less marked effects. Key words: clay, undisturbed, freeze–thaw, softening, strength, yielding, pore-water pressures.

Physical and numerical modelling of drainage and consolidation of tailings near a vertical waste rock inclusion

2020 ◽  
Author(s):  
Faustin Saleh-Mbemba ◽  
Michel Aubertin
Keyword(s):  
Pore Water ◽  
Fine Particles ◽  
Numerical Models ◽  
Physical Modelling ◽  
Waste Rock ◽  
Coupled Processes ◽  
Water Drainage ◽  
Fine Grained ◽  
Pore Water Pressures ◽  
Tailings Impoundments

The use of waste rock inclusions in tailings impoundments is a recent technique that offers many advantages, but it also raises a few technical issues that must be addressed to optimize their design. A laboratory physical modelling study was conducted to assess the effect of waste rock inclusion on the behavior of initially saturated tailings in terms of drainage and consolidation. The evolution of pore water pressures and settlements after hydraulic deposition of the fine-grained tailings (slurry), with and without a drainage inclusion, has been monitored and analyzed. This investigation also focused on the evolution of the tailings void ratio and volumetric water content, the amount of water transferred to the waste rock, and the movement of fine particles at the interface between the two materials. The experimental results are used to demonstrate how such waste rock inclusion can affect tailings consolidation by reducing pore water pressures with accelerated water drainage, for various imposed conditions. The experimental data are also analysed with numerical models to better understand the coupled processes involved. A discussion follows on practical implications of the use of waste rock inclusions in tailings impoundments.

scholarly journals Soil disturbance from pile driving in sensitive clay

1978 ◽  
Vol 15 (3) ◽  
pp. 346-361 ◽  
Author(s):  
M. Bozozuk ◽  
B. H. Fellenius ◽  
L. Samson
Keyword(s):  
Pore Water ◽  
Ground Surface ◽  
Soil Disturbance ◽  
Pile Driving ◽  
Horizontal Distance ◽  
Lateral Movement ◽  
Marine Clay ◽  
Eastern Canada ◽  
Overburden Pressure ◽  
Pore Water Pressures

Soil disturbance due to the driving of two groups of 116 concrete piles each in sensitive marine clay was studied on a construction project in eastern Canada. Pore-water pressures, heave, and lateral movement of soil and piles, and tests of strength, compressibility, and consistency limits of the soil were observed prior to and up to 3 months after pile driving whereas observations of pore-water pressures were continued for an additional 5 months. Driving of the piles had little effect on the compressibility and consistency limits of the marine clay, but the in situ shear strength and cone penetration resistance were reduced by about 15 and 30%, respectively. Soil heave within the group of piles decreased linearly with depth from a maximum of 450 mm (18 in.) at the ground surface to about zero at the pile tips, and in volume amounted to approximately 55% of the soil displaced by the piles. The vertical heave outside the pile group was confined to a horizontal distance of 12 m (39 pile diameters). During pile driving, the lateral movement of previously driven piles was as much as 175 mm (7 in.). Horizontal soil movements measured by inclinometers varied up to 125 mm (5 in.). Pore-water pressures generated during piling exceeded the total overburden pressure by 35–40%. The excess pore pressures dissipated in about 8 months after the piling was completed.

Postfailure analysis: Tramping Lake causeway, Saskatchewan, Canada

1989 ◽  
Vol 26 (4) ◽  
pp. 687-704
Author(s):  
J. L. Labossiere ◽  
E. K. Sauer ◽  
E. A. Christiansen
Keyword(s):  
Pore Water ◽  
Slip Surface ◽  
Friction Angle ◽  
Triaxial Tests ◽  
Lake Basin ◽  
Pore Water Pressures ◽  
Back Calculation ◽  
Vertical Subsidence ◽  
Sand And Gravel ◽  
Effective Friction

A traffic causeway placed on the sediments of saline Tramping Lake failed during construction in the summer of 1982. Vertical subsidence has continued until present (1988). The failure mechanism was controlled by sedimentary structure and artesian groundwater conditions. The shear zone is in a soft, near normally consolidated lacustrine sandy silt unit 22 m thick. The lake basin contains lacustrine, deltaic, and fluvial deposits of postglacial origin. Artesian conditions in the Upper Cretaceous Judith River Formation and postglacial fluvial sand and gravel dominate the hydrogeology at the site. The failure took place along a composite slip surface when excess pore-water pressures developed during loading [Formula: see text]. The estimated effective friction angle from triaxial tests and back calculation was 27° assuming c′ = 0. However, a parametric analysis showed that at very high pore-water pressures the effective friction angle required for equilibrium is very sensitive to small variations in ru. The calculated cohesion at [Formula: see text] required for equilibrium was 3.9 kPa, whereas the remolded vane strength measured in the field was 5.0 kPa. Key words: Foundation failure, artesian, saline environment, groundwater discharge, silty clays, postglacial fluvial and lacustrine deposits.

scholarly journals Effect of Drainage and Consolidation on the Pore Water Pressures and Total Stresses within Backfilled Stopes and on Barricades

2019 ◽  
Vol 2019 ◽  
pp. 1-19 ◽  
Author(s):  
El Mustapha Jaouhar ◽  
Li Li
Keyword(s):  
Hydraulic Conductivity ◽  
Numerical Simulations ◽  
Young’S Modulus ◽  
Pore Water ◽  
Hydraulic Properties ◽  
Underground Mine ◽  
Filling Rate ◽  
Short Term ◽  
Pore Water Pressures ◽  
Backfilled Stopes

The pore water pressures (PWPs) and total stresses during the placement of a slurried backfill in underground mine stopes are the key parameters for the design of barricades, built to retain the backfill in the stopes. They can be affected by the drainage and consolidation of the backfill. Over the years, several studies have been reported on the pressure and stresses in backfilled stopes by accounting for the drainage and consolidation. Most of them focused on the pressure and stresses in the stopes, few specifically on the barricades. The effect of the number of draining holes commonly installed through the barricade has never been studied. In this paper, the influence of hydraulic properties and filling rate of the backfill, stope size, barricade location, and number of draining holes is systematically investigated with numerical simulations. The results show that the stresses in the backfilled stope and on the barricade largely depend on the filling rate, hydraulic conductivity, and Young’s modulus of the backfill. The draining holes can significantly decrease the PWP, but only slightly the total stresses on the barricades in short term.

scholarly journals In situ equilibrium pore-water pressures derived from partial piezoprobe dissipation tests in marine sediments

2013 ◽  
Vol 50 (12) ◽  
pp. 1294-1305 ◽  
Author(s):  
Nabil Sultan ◽  
Sara Lafuerza
Keyword(s):  
Slope Stability ◽  
Pore Pressure ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Design Parameters ◽  
Short Term ◽  
Pore Water Pressures ◽  
Time Required

Excess pore-water pressure has a significant effect on submarine slope stability and sediment deformation, and therefore its in situ equilibrium measurement is crucial in carrying out accurate slope stability assessments and accurately deriving geotechnical design parameters. In situ equilibrium pore-water pressure is usually obtained from pore pressure decay during piezocone tests. However, submarine shelves and slopes are often characterized by the existence of low-permeability (fine-grained) sediments involving long dissipation tests that are an important issue for offshore operational costs. Consequently, short-term and (or) partial dissipation tests are usually performed and in situ equilibrium pore-water pressures are predicted from partial measurements. Using a modified cavity expansion approach, this paper aims to predict for four different sites the in situ equilibrium pore-water pressures. Comparisons between predicted and observed in situ equilibrium pore-water pressures allowed the development of a guide to evaluate the minimum time required to perform short-term dissipation tests for a given marine sediment. The main finding of this Note is that the second derivative of the pore pressure, u, versus the logarithm of time, t, ∂2u/∂ln(t)2 must be positive to calculate accurately the in situ equilibrium pore-water pressures from partial measurements.

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

1997 ◽  
Vol 43 (145) ◽  
pp. 495-502 ◽  
Author(s):  
Jan A. Piotrowski ◽  
Anna M. Kraus
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Ice Sheet ◽  
Bed Deformation ◽  
Pore Water Pressures ◽  
Sediment Consolidation ◽  
Western Germany ◽  
Bed Stability ◽  
North Western

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.

Sign in / Sign up

Export Citation Format

Share Document