摘要:

An extensive programme of vane testing has been carried out in a peat bog at Escuminac, N.B. to assess the applicability of vane testing to peat. The variables involved in the programme were depth, size of vane, method of insertion, rate of rotation of the vane, and state of peat tested. Vane strength profiles were obtained in a 7 m thick deposit consisting of sphagnum peat (0–4 m), sphagnum carex peat (4–6 m), and carex sphagnum peat (6–7 m). Vane tests were also carried out in the sphagnum peat under anchored Plexiglas sheets to observe the mode of deformation and failure and to measure the movement of markers inserted into the face of the peat. Additional tests were carried out with field vanes in confined sphagnum peat samples in the laboratory.The observed failure surface was essentially cylindrical for all sizes of vane used, but its diameter was consistently 7–10 mm greater than that of the vane for all vane sizes. The sphagnum peat failed at true angles of rotation of between 17 and 40°, leaving a void behind each blade. At maximum torque the peat within each sector started to move monolithically.The moderately decomposed sphagnum moss peat tested is typically neither fibrous nor amorphous, although some fibres and amorphous material are generally present as a result of varying growth and degradation processes. This type of peat could be considered representative of most moss peats with respect to geotechnical behaviour. It is not, however, representative of the less common, truly fibrous sedge peats or of any purely amorphous peat deposits.Analyses of the mode of deformation of the sphagnum peat in vane shear and comparisons with modes of deformation in other types of shear have led the author to conclude that the vane test, in spite of its practical advantages, does not serve any useful purpose in the testing of peat.

ISSN:0008-3674    

DOI:10.1139/t80-001

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Observations of the deformation of the temporary lining of two tunnels are presented. The Whitemud Creek tunnel was 6.05 m in diameter and was bored through Upper Cretaceous clay shale. The 170 Street tunnel was bored through till and had a diameter of 2.56 m.In the Whitemud Creek tunnel, the vertical diameter decreased by 10–15 mm and the horizontal diameter decreased by 6 mm. Movement was essentially complete in about 3 months. There was a rigid body movement upward of the lining system probably due to unloading of the soil in the invert area. Deformation moduli indicate a softening of the soil around the tunnel, which is consistent with the deformation observations. A finite-element analysis suggests that this softened zone is as important with regard to lining deformation as increasingK0from 0.67 to 1.0In the 170 Street tunnel, the ground surface showed significant movement despite the small diameter and considerable overburden thickness. The vertical and horizontal diameter decreases were about one half of those of the Whitemud Creek tunnel and were essentially complete in 4–5 weeks. Soil pressures calculated from the observations showed a wide variation. Values derived from lagging deflection yielded a maximum of 63% of overburden pressure whereas pressure cell readings were 3.3% of overburden.It appears that the space between the lagging and the moled surface of the soil is an important factor affecting the magnitude of stresses in the temporary lining. Diameter changes are considered to be the easiest and most reliable observation of tunnel linings. The deflection of the lagging is also simple to observe but may not satisfy simple beam theory. Pressure cell results were disappointing and their use is debatable.

ISSN:0008-3674    

DOI:10.1139/t80-002

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Geotechnical investigations revealed the presence of high hydraulic conductivity zones with high grout takes in the left abutment of King Talal Dam. Control measures were needed to protect the foundations against the anticipated high leakage losses as well as against the probability of piping erosion, which may develop along the weakness and high hydraulic conductivity zones. The porosity, hydraulic conductivity, and groutability characteristics of the geological formations of the left abutment were investigated in detail. The data were analyzed and conclusions were made concerning the heterogeneity of the geotechnical properties of the different geological formations, the effectiveness of cement–bentonite grouting in improving the hydraulic conductivity and groutability characteristics of the foundation materials, and the measures taken to safeguard the foundations of the dam against the potential dangers of piping erosion.

ISSN:0008-3674    

DOI:10.1139/t80-003

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Slope stability analyses in terms of effective stresses are most often based on hypothetical conditions of pore pressure. It is generally assumed that the flow occurs parallel to the slope or even that the conditions are hydrostatic. In fact,insitumeasurements tend to show that the real situation could significantly deviate from these approximations due to geologic conditions. The influence of various geometric and stratigraphic factors on the groundwater regime and on the stability of slopes was studied with the finite-element method. To illustrate the parametric study, experimental evaluations of the flow patterns are presented at four sites. The stratigraphy and permeability measurements combined with the finite-element method enabled a complete flow net to be drawn and although some hypotheses had to be formulated with regards to the underlying aquifer recharge or permeability anisotropy, reasonable agreement was found between simulated and measured piezometric heads.

ISSN:0008-3674    

DOI:10.1139/t80-004

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Artificially prepared, previously frozen specimens of a clayey silt have been subjected to thermal gradients under both closed and open systems. Direct observation of moisture content changes reveals that substantial amounts of water are imbibed by frozen soil under an open system. If an ice lens exists within the system, the increase in water content on the cold side of the lens is small compared with that on the warm side. Heave rate is governed primarily by the frozen fringe of soil between the warmest ice lens and the frozen–unfrozen interface.

ISSN:0008-3674    

DOI:10.1139/t80-005

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

This paper presents a critical review of the analytical methods of slope stability analysis.The effective stress methods of analysis surfer from four fundamental weaknesses related to the magnitude of the effective stresses, the assumed stress path, the indiscriminate use of a Mohr–Coulomb criterion, and the definition of the factor of safety. As a result the quality of the computed factors of safety must be questioned.Practical consequences as well as alternative solutions for the analysis of stability of slopes or foundations are discussed.

ISSN:0008-3674    

DOI:10.1139/t80-006

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Uniaxial unconfined compression tests were carried out on frozen saturated Ottawa sand containing about 20% by weight of water, at temperatures between −2 and − 15°C, and at strain rates varying between 10−7and 10−2 s−1. The compressive strength and the initial tangent modulus increased with increasing strain rate and with decreasing temperature. At −2°C, values of strength and modulus were considerably lower than those predicted by linear extrapolation of the values observed at lower temperatures, on a log–log scale. This could be due to the presence of unfrozen water in the samples at −2°C.

ISSN:0008-3674    

DOI:10.1139/t80-007

出版商:NRC Research Press    

年代:1980

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t80-008

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Successful use of artificial islands as exploration drilling platforms in the southern Beaufort Sea requires an understanding of the interactions of ice sheets with wide structures. Ice forces exerted on wide structures arise from the mechanical processes inherent in particular ice failure modes as environmental stresses move an ice sheet past a structure. Four primary ice failure modes occur against wide structures: flexure, rubble formation, buckling, and crushing. The horizontal forces associated with these modes differ by more than two orders of magnitude depending on structure geometry, ice sheet properties, and ice movement rates. Structure width influences the occurrence of ice failure modes, the ice failure stresses, and the total forces that can be exerted on a structure by an ice sheet. The relative inability to clear failed ice around wide structures (compared with narrow structures) leads to rubble formation when ice movement is continuous. After consolidation, the resulting rubble field can amplify forces exerted on the structure. Increased structure width generally results in decreased expected forces per unit width of structure. For crushing, the most serious ice failure mode for island design, increased structure width generates the possibility of nonsimultaneous failure. The resulting averaging of statistical variations across the width leads to reduced expected stresses for wide compared to narrow structures.

ISSN:0008-3674    

DOI:10.1139/t80-009

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

This note presents an experimental study of the plane strain – contact stress distribution beneath a rigid footing resting on a compacted soft cohesive soil medium. The immediate contact stress distribution was found to be highly dependent on the magnitude of the applied stress relative to the ultimate bearing capacity of the foundation. At low levels of applied stress the contact stresses were substantially higher at regions adjacent to the footing edges. As the applied stresses were increased, the contact stresses achieved a more uniform configuration.

ISSN:0008-3674    

DOI:10.1139/t80-010

出版商:NRC Research Press    

年代:1980

数据来源: NRC