摘要:

The one-dimensional form of Skempton'sBequation is inadequate to describe the behavior of cohesionless materials with pore fluids that contain large quantities of free and dissolved gas. Fredlund derived the compressibility of an air–water pore fluid in terms of the ideal gas laws, gas solubilities, and saturations. This paper extends the derivation of the compressibility of pore fluids, and couples the compressibility with that of the soil skeleton (e– σ′ relationship) to extend Skempton's equation to the most general one-dimensional undrained case. The differential equation derived is studied for the specific case of unloading behavior of oil sands: a very dense relatively incompressible quartzose sand, which contains sufficient volumes of interstitial bitumen to result in undrained behavior. The behavior of these materials, which have stiffnesses approaching that of water, can be qualitatively understood by means of a spring model: the stiffest spring (either pore fluid or soil skeleton) absorbs most of the stress change, and the stiffness of the springs change with changing total stress level.Practical application of the concepts herein should not be difficult for soils having very compressible skeletons, but for very dense sands, the derivation of the appropriatee– σ′ relationship is very difficult. Other system parameters that have a great effect on the behavior are the gas saturation, the gas solubility coefficients, and the initial stress conditions.

ISSN:0008-3674    

DOI:10.1139/t79-073

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Landsliding has been a major problem to property owners and developers along the Ottawa River and its tributaries. A study of aerial photographs of a section of the Ottawa River near Ottawa, taken over a period of nearly 50 years, has identified a cyclic relationship between the processes of erosion, landsliding, and riverbank recession. Using detailed measurements of topographic maps and of contours plotted from the aerial photographs, a physical model has been proposed to describe the erosion–landsliding cycle. For the area under study the average cycle return period is estimated to be about 60 years, and the long-term rate of riverbank recession is about 0.4 m/year.

ISSN:0008-3674    

DOI:10.1139/t79-074

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

During the extension of the Hamilton Mountain trunk sewer, instantaneous and long-term movements were monitored in the rock strata containing the excavated trench. Movements as far as 150 m from the trench axis were observed over a period of more than 1 year.Although the movements seem to be continuous and decreasing with time, their spatial distribution and dissipation are not entirely predictable, suggesting the important role of local geological features.Interpretations of the results and recommendations for other work in the region are submitted.

ISSN:0008-3674    

DOI:10.1139/t79-075

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

When submitted to cyclic shearing, loose dry sand densifies, and undrained saturated sand may liquefy. Based on energy considerations, a unified theory for densification and liquefaction of a homogeneous sample of cohesionless sand is proposed. It is observed that these phenomena involve rearrangement of grains in microscale, requiring an expenditure of a certain amount of energy, which increases as the void ratio approaches its minimum value and decreases as the excess pore water pressure increases. On the basis of rough estimates, explicit relations are developed for both the densification and liquefaction phenomena, and the results are applied to predict relevant available experimental data.

ISSN:0008-3674    

DOI:10.1139/t79-076

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A survey of the slope protection on 62 dams in the Prairie Provinces was undertaken to relate the field performance to design and construction practices. The slope protection included riprap, gravel, and glacial clay. The dams were earthfill embankments, which varied from 5 to 65 m in height, and impounded reservoirs with fetches of 1–35 km.The study involved the measurement of slopes and profiles, rock and particle sizes, voids, layer thicknesses, and the rating of the riprap condition. It also required the calculation of reservoir straight line and effective fetches, the application of existing wind data, and the estimation of significant wave heights.The observations indicated that 75% of the rock riprap was in good to excellent condition, 20% in fair condition, and 5% in poor condition. Unsatisfactory performance was due to thin riprap layers and uniform rock size, which did not provide a sufficiently dense cover for the bedding gravel. Also, some of the earlier designs, which utilized a straight line fetch criterion, had resulted in the underdesign of riprap for wide or circular reservoirs. Effective fetch calculations provided a more accurate measure of the exposure of the dam. Gravel and glacial clay slopes were found to provide economical slope protection where allowances had been made for flat slopes, adequate layer thickness, and periodic maintenance.Empirical procedures have been developed for the design and construction control of slope protection for small dams. A more rational design procedure, based on effective fetch and regional wind conditions, is proposed for riprap on large dams.

ISSN:0008-3674    

DOI:10.1139/t79-077

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A laboratory testing program for predicting undrained excess pore pressures beneath embankments constructed on sensitive clays is reported. A study of the pore pressure response, based on Henkel's equation applied to triaxial and plane strain tests performed on marine clay from South Gloucester, Ontario, provides a basis for comparing behaviour under conditions of axisymmetry and plane strain. Comparison shows that (1) pore pressure is smaller in plane strain than in axisymmetric conditions; (2) a below-elastic response prevails at the prepeak stage of the stress–strain curve; and (3) there is an elastic response at the peak.Finite element and modified elastic methods are developed for estimating undrained excess pore-water pressures from laboratory test results. The estimated values are used to evaluate the effect of consolidation under the center of an embankment during construction. The procedure is illustrated with case records.

ISSN:0008-3674    

DOI:10.1139/t79-078

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

In 1973 the Saskatchewan Department of Highways began construction of a crossing over the North Saskatchewan River at Maymont, Saskatchewan. The south approach to the river required a cut some 20 m in depth at the top edge of the valley and when the excavation reached the design elevation a massive failure occurred on one of the backslopes. The major portion of the slip surface followed a slickensided clay shale zone. An analysis of the failure indicates residual angles of shearing resistance were being mobilized. The reason for mobilizing only the residual strength is attributed to previous shearing arising from glacial ice-thrusting.The sliding occurred entirely within the sediments of the nonmarine Upper Cretaceous Judith River Formation, but the strengths mobilized were essentially the same as those mobilized by slides in the marine Upper Cretaceous Bearpaw and Lea Park Formations. Negative water pressures arising from the stress change due to excavating did not appear to influence the stability. Direct shear box tests on natural slickensided surfaces gave strengths higher than required for a safety factor of unity. The testing of precut surfaces gave results that seem to correlate more closely with the field residual strengths. Furthermore, the Maymont case history clearly illustrates the need for identifying geological details and demonstrates the engineering significance of glacial ice-thrusting.

ISSN:0008-3674    

DOI:10.1139/t79-079

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Two case histories are discussed where groundwater lowering was used to permit completion of excavations that experienced problems because of the lack of groundwater control.The first case involved a 4.1 m diameter tunnel, some 26 m below grade, within a clay stratum sandwiched between two water-bearing, granular deposits. Several collapses of the tunnel roof occurred because of a local depression in the surface of the clay stratum, allowing the upper, water-charged granular material to flow into the tunnel. Subsequent investigations indicated the feasibility of lowering the groundwater level by means of an eductor well system, allowing completion of the tunnel in relatively dry conditions.The second case describes groundwater problems associated with the sinking of a 21 m deep exploratory mine shaft through water-bearing silts and sands. Three attempts at sinking the shaft without groundwater control had failed. Therefore, based on the results of a pumping test, eductor wells were installed around a steel sheet pile cofferdam to permit the successful sinking of the shaft to bedrock.

ISSN:0008-3674    

DOI:10.1139/t79-080

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A method of stabilizing or inhibiting the occurrence of planar landslides in regions of permafrost, utilizing an insulative material and a free-draining surcharge load, is presented. A measure of the pore pressures considered in the effective stress analysis is determined by assuming steady state seepage parallel to the surface and pore water pressures generated during thaw consolidated due to self-weight and surcharge load. The insulation reduces the rate of thaw and thus the rate of generation of excess pore water pressures, and the surcharge increases the effective normal stress disproportionate to any increase in shearing stress.Different design methods are outlined and a series of design charts is proposed for rapid computation of the required combination of insulation thickness and surcharge load for a range of typical soil and climatic conditions encountered in arctic and subarctic regions.

ISSN:0008-3674    

DOI:10.1139/t79-081

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

In 1973 and again in 1975 the town of Port Alice on Northern Vancouver Island was damaged by debris flows from the steep mountain slopes behind the town. The flows were triggered during heavy rains by small earth slumps that flowed down steep narrow gullies in bedrock and scoured additional debris from the channel. The debris flowed rapidly while confined to the gully and slowed down and came to rest on the fan on which the town is built. Dykes to protect the town from future debris flows were designed and built. Model studies were used to assist in designing the system of dykes.

ISSN:0008-3674    

DOI:10.1139/t79-082

出版商:NRC Research Press    

年代:1979

数据来源: NRC