摘要:

This paper outlines the ultimate and serviceability limit states in geotechnical engineering analyses. The magnitude of customary total and suggested partial safety factors in earthworks, earth retaining structures, excavations, and foundations is discussed. On the basis of comparisons between these safety factors and using recommended load factors on various types of loading, including water pressures, common resistance factors on cohesion and friction of soils and performance factors can be established together with some additional modification factors for particular stability conditions. The serviceability limit states of foundations and structures are briefly discussed.

ISSN:0008-3674    

DOI:10.1139/t84-001

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A granite core containing a natural fracture, oriented parallel to the core axis, was collected, prepared, and its permeability measured in a hydrostatic test cell at different confining pressures. After the permeability hysteresis had been removed by several cycles of increasing and decreasing confining pressure, grout was placed within the fracture plane and allowed to cure for 40 days. Distilled water was forced through the sample until a significant flow rate developed. The influent solution for the sample was changed twice during the study to examine the effects of differing concentrations of Ca(HCO3)2solutions on calcite precipitation within the fracture plane. The interaction of the Ca(HCO3)2solution with the grout material resulted in a decrease in the permeability of the fracture plane over several months. At the close of the experiments, the sample was removed from the hydrostatic cell and opened along the fracture plane. The fracture exhibited two discrete braided channelways each with an average width of 2 mm. Precipitated calcite formed a rind along the walls of the channelways averaging 0.25 mm in thickness. The quantity of calcite precipitate determined from physical measurements was in reasonable agreement with that calculated using reaction rate expressions for calcite precipitation. The results of this study suggest the possibility that strategically located geochemical material could induce a geochemical evolution of groundwater within poorly grouted fractures, so as to decrease the permeability of the fractured rock system.Keywords: fracture permeability, grouted fractures, geochemistry, laboratory experiments, calcite precipitation.

ISSN:0008-3674    

DOI:10.1139/t84-002

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity Champlain clay. The clay structure is observed firstly on intact, remolded, and oven-dried soils and secondly on soils consolidated at various levels in one-dimensional compression. Both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra-aggregate porosity. Remolding affects interaggregate links but does not destroy aggregates.The observation of clay structure at various levels of one-dimensional compression shows that the collapse of the structure is progressive, the largest interaggregate pores being the first affected. As the consolidation proceeds, smaller and smaller pores are affected. For a given pressure increment, only the largest existing pores are affected. A structure anisotropy has been seen to develop with increasing compression.The scanning electron microscope and the mercury intrusion porosimeter used in conjunction with each other appear as a powerful approach for clay structure observation.Keywords: natural clay, microstructure, freeze-drying, porosimetry, microscopy, consolidation, aggregate.

ISSN:0008-3674    

DOI:10.1139/t84-003

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

As part of an urbanization scheme, artificial islands are being created on the swampy land around the Itaipu lagoon, close to Rio de Janeiro. The islands are being formed by hydraulic filling with sand and their periphery consists of retaining walls resting on sand cushions. The very soft local soils pose settlement and stability problems in execution and operation.A site and laboratory investigation program, involving several types of triaxial, consolidation, andin-situvane tests, has been carried out and is described. A full-scale instrumented settlement fill has been built and is mentioned. An instrumented 5 m deep trial trench has been carried out and monitored during the excavation stage which took 5 days and during a 45 day long repose stage. In both these stages failure was avoided by keeping water inside the trench at its original level. Finally, failure was induced by pumping water out of the trench. The observations at the trial trench are presented and discussed in some detail.Keywords: soft organic deposit, unretained excavation, field tests, laboratory tests, displacements, pore pressures, failure.

ISSN:0008-3674    

DOI:10.1139/t84-004

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A field, laboratory, and numerical modelling study was undertaken to determine the impact of groundwater on mining activities and underground space development in the Paleozoic rock units of the Niagara Escarpment near Milton, Ontario. Five holes were drilled at a site next to the Dufferin quarry, penetrating the Amabel dolostone, the Reynales dolostone, the Cabot Head shale, the Manitoulin limestone, the Whirlpool sandstone, and the top part of the Queenston shale. Results of hydrogeological field and laboratory tests indicate the presence of an unconfined aquifer with an average hydraulic conductivity of 2 × 10−5 m/s, and a confined sandstone aquifer with a conductivity of 5 × 10−7 m/s separated by a shale and limestone aquitard having a conductivity of less than 10−9 m/s.Numerical model simulations of the groundwater flow system indicate that, for a 2 km2underground mine located in the dolostone cap rock, the inflow rates range from 8 L/s to over 30 L/s with significant dewatering of the unconfined aquifer occurring within a distance of 1500 m of the mine boundaries. Calculations for a hypothetical mine located in the Whirlpool and Manitoulin Formations gave inflow rates of less than 3 L/s. It is concluded that groundwater conditions will not interfere with mining operations in either the dolostone unit or in the limestone–sandstone unit but could adversely affect subsequent space development in the dolostone unit.Keywords: hydrogeology, groundwater, underground space, aggregate, mining, sedimentary rocks, Niagara Escarpment.

ISSN:0008-3674    

DOI:10.1139/t84-005

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The EOL (Eastmain – Opinaca – La Grande) diversion scheme of the La Grande Complex (phase I) for the James Bay Hydroelectric development in northern Québec diverts the waters of the Eastmain, Opinaca, and Petite Opinaca Rivers into the LG 2 reservoir. The EOL diversion consists of four dams and seven dykes about half of which are founded for part of their length on overburden foundations of variable thickness and consisting of heterogeneous deposits of glacial till or sandy and silty alluvia. The till core of these zoned embankments is either placed directly on the till strata or extended through the alluvia to the underlying till by a core trench. The construction of these embankments was completed in 1979 and the maximum reservoir level achieved in November 1980.This paper deals with the seepage and pore pressure behaviour in the overburden foundations, namely, dams OA-10B and OA-11 and the dyke OA-8B, during and subsequent to the reservoir filling. The results of the parametric seepage analyses carried out by finite element methods are compared with the observations. Special attempts are made to resolve the long-existing speculations regarding the anisotropy of natural deposits. Comments are made regarding the effective anisotropy of such deposits in the James Bay region and its effect on exit gradients and uplift forces, which influence the design and safety of dams and dykes.Keywords: seepage, pore pressure, hydraulic conductivity, anisotropy, foundation treatment, cutoff.

ISSN:0008-3674    

DOI:10.1139/t84-006

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A drilling system is described for geotechnical exploration and soil sampling in the seabed, modelled after the concept of the marine riser pipe. The system derives its stability from a "tensioning weight," in the form of a cylindrical concrete block at the bottom, which keeps the conductor pipe in tension at all times. The axial tension from the tensioning weight and the self-weight of the conductor pipe substantially reduce the bending effects in the conductor pipe resulting from current and wave forces, as well as from the drift of the drilling vessel. The lateral reaction required to keep the pipe in place at the sea floor is provided by a concrete footblock. The bottom end of the conductor pipe slides into the footblock, which has a doughnut-shaped cross section that allows for the vertical movement or heave of the drilling vessel. The Hermitian equation is used to solve for the secondary effects due to the deformation of the flexible conductor under wave or current forces and the self-weight of the conductor pipe. The system has been used successfully on the Grand Banks in 122 m of water.Keywords: geotechnical exploration, sampling, deep water drilling, marine riser analogy, tensioning weight.

ISSN:0008-3674    

DOI:10.1139/t84-007

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Frost heave is an important consideration in the design of buried chilled pipelines. A procedure for calculating the amount of heave under a chilled gas pipeline is presented based on a finite-difference formulation of the heat and mass transfer in saturated soils. The frost heave of the soil is characterized in terms of the segregation potential concept developed in earlier papers by the authors. Good agreement is found between the predictions of heave obtained with this procedure and that observed in long-term full-scale experiments at a test site in Calgary, Canada. Additional calculations are presented to explore the influence of pipeline temperature, pipe insulation, and ground temperature on frost heave of buried pipelines.

ISSN:0008-3674    

DOI:10.1139/t84-008

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Hydraulic stabilization of soils using gravity drainage, pumped wells (dewatering), vacuum wells, and vacuum blankets has been applied with success in numerous field situations. References to the vacuum methods, however, are not abundant and the analytical developments with regard to these methods are limited. This paper provides methods for analytical evaluation of hydraulic stabilization and applies these methods to vacuum pretreatment of soft clay foundations and to temporary stabilization of slopes using vacuum wells. Both applications indicate that the vacuum methods are effective. Detailed analyses of various vacuum well placements and some discussion on the types of systems applicable to various problems are included in the paper. Other applications of the vacuum methods of hydraulic stabilization of soil masses are briefly discussed.Keywords: stabilization, slopes, foundations, vacuum wells, remedial measures.

ISSN:0008-3674    

DOI:10.1139/t84-009

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Two types of simple shear apparatus are in use — one developed at Cambridge, which is elaborately instrumented and accepts a cuboidal sample, and the other developed at the Norwegian Geotechnical Institute (NGI), which is attractively simple and accepts a cylindrical sample, and in which only shear and normal loads applied to the horizontal surface of the sample are measured.Results of drained monotonic and repeated shear straining tests in the Cambridge and an NGI type simple shear apparatus, both elaborately instrumented, show that nonuniformities of stress and strain develop in monotonic loading and grow with the number of cycles of shear straining. The rigid boundaries of the Cambridge type apparatus impose a definite simple shear configuration to the sample. The flexible boundary of the Norwegian Geotechnical Institute type apparatus provides less restraint allowing out-of-plane movements to occur. The characteristic responses of similarly prepared sand samples are different in the two apparatus because the conditions imposed are not exactly the same.The Cambridge apparatus can be expected to give an accurate estimate of the behavior of sand in monotonic loading if stress measurements are taken at the centre of the sample.Keywords: simple shear apparatus, NGI, Cambridge, monotonic and cyclic loading, dense sand, nonuniformities.

ISSN:0008-3674    

DOI:10.1139/t84-010

出版商:NRC Research Press    

年代:1984

数据来源: NRC