摘要:

For soils exhibiting both cohesive and frictional components of strength, the natural variabilities of the components are compared for soil in the undisturbed state and as compacted in earth dams. The probability distributions of the components are shown to agree more closely with a theoretical beta distribution than with the commonly assumed normal distribution.The cohesive and frictional components can be regarded as independent variables and the design safety factor interpreted in terms of probabilities. Assuming equal probabilities for each component leads to the use of partial safety factors which are larger for the cohesive part than for the frictional part. For long-term stability problems limiting partial safety factors corresponding to zero probability can be obtained.The undrained strength of clays also agrees with a beta distribution but in this case there are no limiting safety factors, and some non-zero probability must be associated with the design.

ISSN:0008-3674    

DOI:10.1139/t70-032

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

An extensive confined aquifer, currently pumped at the rate of 3 billion gallons (13.6 billion l) per year, occurs in the fractured and jointed upper 50 ft (15 m) of the thick Paleozoic carbonate rock sequence underlying metropolitan Winnipeg. The karstic bedrock surface is mantled by 30 (9 m) to 200 ft (60 m) of glacial drift. The drift is composed of 20 ft (6 m) of till overlain by lacustrine sediments, mainly clays, that average 40 ft (12 m) in thickness. Two minor water-bearing zones occur in the drift, one in the silt deposits in the upper 5 to 15 ft (1.5 to 4.5 m) of the lacustrine unit and the other in the top few feet of the till. Moderately permeable sandstones interbedded with shales underlie the carbonate rock at depths between 250 and 800 ft (75 and 240 m). The sandstones are aquifers that contain saline water. A partially confined glaciofluvial aquifer covering 60 square miles (155 square km) occurs to the northeast of the city. The karstic bedrock surface, a controlling parameter of the groundwater flow systems, slopes towards the Red River Valley from recharge areas located in uplands along the borders of the Red River Basin.Groundwater has been a source of water supply in the Winnipeg area since the early 1800's. The Upper Carbonate aquifer, which during the first two decades of the twentieth century supplied all of the city's water requirements, has a transmissibility ranging between 2000 and 200 000 gallons (24.8 and 2480 m3/m/day)/ft/day. Total groundwater pumpage was 107gallons (4.5 × 107l)/day at the time groundwater usage was curtailed in 1919 following the completion of an aqueduct from the Lake of the Woods. The water in the aquifer is generally fresh to brackish; however, south of the Assiniboine River the water is brackish to saline and is not potable. The groundwater which in most places has a temperature of 39° to 43° F (3.9 to 6.1° C) is used mainly for commercial cooling purposes. Pumpage varies from 5 × 10° gallons (22.7 × 106 l)/day in the winter months to 107gallons (4.5 × 107 l)/day during the summer air-conditioning period.Groundwater withdrawals have created a major drawdown cone in the central industrial area of metropolitan Winnipeg. Elevations of the piezometric surface range between 800 and 1500 ft (240 and 450 m) in the recharge areas and are below 700 ft (210 m) in the drawdown cone. The Winnipeg drawdown cone is at the centre of a lateral radial flow system. The aquifer also loses water by natural discharge into the Assiniboine and Red Rivers and into the Red River Floodway.Under natural conditions the saline water-bearing Upper Sandstone aquifer is isolated hydraulically from the Lower Carbonate aquifer by the 10 to 20 ft (3 to 6 m) thick upper shale unit of the Winnipeg formation. However where open well bores penetrate the sandstone aquifers, higher hydraulic heads force saline water up into the carbonate aquifers.Hydrostatic pressure in the Upper Carbonate aquifer affects construction works that intercept the aquifer or initiate hydraulic fracturing by unloading the confining layers. Groundwater discharge from this aquifer has affected a number of excavation projects. The largest construction groundwater difficulties encountered in the metropolitan Winnipeg area occurred during the construction of the Red River Floodway. Groundwater flows from the aquifer interfered with the excavation of the lower sections of the channel and a number of structures. Groundwater seepage was first encountered on this project when artesian water discharged into a test pit that had been excavated to a depth of 20 ft (6 m) below the piezometric surface of the aquifer. Inflows commonly exceeded several hundred gallons/min. Groundwater control during construction of the floodway inlet control structure required a grout curtain 4000 ft (1220 m) long in the Upper Carbonate aquifer and the drift, and an extensive dewatering system. Knowledge of the groundwater regime prior to construction facilitated excavation and construction, and eliminated claims for unforeseen conditions.

ISSN:0008-3674    

DOI:10.1139/t70-033

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

Based on a finite difference technique, computer programs have been developed whereby temperature variations in layered systems as a function of position and time may be computed under conditions of both one- and two-dimensional heat flow by conduction. No limitations are imposed on the number of layers, or on the form of the initial and boundary temperature conditions. Variations in thermal properties of the materials with temperature and location, and the non-linear relation between amount of water frozen as a function of temperature, are directly taken into account. Comparison of predictions with actual measurements demonstrate that accurate forecasts of temperature distributions as a function of time can be made when prevailing ambient conditions are known. Even if the site conditions can be evaluated only approximately sufficiently reliable predictions can be made for design purposes.

ISSN:0008-3674    

DOI:10.1139/t70-034

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

An appraisal of the drained shear strength of Leda clay under low effective normal stresses has resulted in a new appreciation of its behavior in this stress range which can be applied to consideration of the stability of slopes. Closely spaced planes of weakness existing in the apparently intact clay give rise to dilatant behavior and predominantly frictional shearing resistance. This mode of failure is consistent with field observations that have been compiled from numerous landslides; three of these landslides are analyzed in this paper.

ISSN:0008-3674    

DOI:10.1139/t70-035

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

The pronounced yielding observed in laboratory tests on Leda clay has been associated with the destruction of cementation bonds in the clay. Triaxial test data presented in this paper show that a yield curve can be established for a Leda clay. The form of the yield curve deviates from that expected for an isotropic material and the pre-yield strains are shown to be different for vertically and horizontally orientated specimens.The shear strength of the clay is dependent on the mean normal stress at failure. A portion of the failure envelope is different for specimens orientated in different directions and this 'strength anisotropy' is associated with anisotropic yielding.

ISSN:0008-3674    

DOI:10.1139/t70-036

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

A failure of an unsupported section of a tunnel roof in till is described. The failure was preceded by the formation of longitudinal cracks in the tunnel roof and consisted of a series of falls of discrete blocks from the roof. The presence of sand lenses in the till appears to affect adversely the stability of the tunnel roof.

ISSN:0008-3674    

DOI:10.1139/t70-037

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

In case of foundations on thick layer of weak or medium quality, short tubes or sheet-pile mantles encompassing the footings and of small wall-thickness driven into the ground can increase considerably the bearing capacity of the soil. The footings are in this way artificially deepened and the horizontal displacements of the subsoil within the tube or mantle are confined. Thus, only vertical compression is possible within the "reinforcement" of the soil. The paper produces theoretical solution for the stress conditions and vertical settlement. Two illustrative examples with model tests are also included.

ISSN:0008-3674    

DOI:10.1139/t70-038

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

A mile-long line of piezometers were installed at various depths in a clay terrace system east of the City of Ottawa. Measurements indicated a significant downward piezometric gradient through the clay layer to the underlying bedrock. The downward flow of water through the clay affects both existing effective stresses and the stress history of the clay deposit.

ISSN:0008-3674    

DOI:10.1139/t70-039

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

A building founded on Billings Shale has suffered nearly 4 in. (10 cm) of heave to its basement floor slab. The heaved zone was thought to be associated with a fault zone in the shale, ear which the rock was fractured and contained extensive pyrite intrusions. Investigations have shown the heave to be due to the weathering of the pyrite in the presence of autotrophic bacteria. Factors creating a favorable environment for this complex weathering process are discussed.

ISSN:0008-3674    

DOI:10.1139/t70-040

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

A laboratory soil grinding mill capable of unattended pulverizing and sieving of soils for testing purposes, has been developed by the Materials and Research Branch of the Manitoba Department of Transportation. The cylindrical aluminum mills contain one or more steel rollers which are encased in heavy rubber tubing. A screened door on the mills allows crushed soils particles to escape when they have reached the required sieve size. The mills are driven by two rollers and the ground and sieved soil is collected in a pan beneath them. The mills can be operated unattended.

ISSN:0008-3674    

DOI:10.1139/t70-041

出版商:NRC Research Press    

年代:1970

数据来源: NRC