摘要:

A multiple regression analysis has been performed of the average annual number of avalanches and terrain factors. Observations were made at 36 paths at Rogers Pass over a period of 9 years. The average slope inclination measured from the starting point to the beginning of the run-out zone and exposure to wind proved to be the most significant variables. Slope angle at the starting point, variations over the track, and roughness of the ground surface were of secondary significance and their influence varied strongly from site to site. The analysis confirmed that avalanches need either a steep slope or a snow drift to start and a mimimum inclination of track to maintain their motion.

ISSN:0008-3674    

DOI:10.1139/t77-034

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Active landslides are occurring along the banks of the South Saskatchewan River at Saskatoon. A field investigation and stability analysis indicated that a multiple retrogressive mechanism is valid in explaining the failures at Beaver Creek, 28 km south of Saskatoon. Computations indicated that lateral pressures ranging from the active to something greater than the at-rest condition tend to support the successive blocks but are not high enough to stabilize the slides. It was assumed that the rate of movement of the blocks varies and probably increases downslope. Valuable information was obtained about the soil properties in the area and the mechanism of failure that seems to apply over a long section along the river bank south of Saskatoon.

ISSN:0008-3674    

DOI:10.1139/t77-035

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Results from laboratory and field tests on fractured rock systems have shown that changes in fluid pressure within a fracture can cause changes in the effective normal stress that result in significant normal displacements. These normal displacements change the fluid pressure distributions and hence the shear strength of the fracture system. The nature of the normal displacement (opening or closing of the fracture) can be detected by comparing the ratios of pressures measured at two points within the fracture plane. Other workers have shown in laboratory shear tests on rough fractures that movement along discontinuities, prior to failure, has both a normal and tangential component. Careful measurement of changes in fluid pressures in fractured rock slopes should be able to detect the effects of such normal displacements and thus give an indication of an approaching instability.

ISSN:0008-3674    

DOI:10.1139/t77-036

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The 27–45 m high bluffs along the north shore of Lake Erie in Ontario are retreating inland at a 150 year average rate of 0.5 to 3.0 m/year. The retreat mechanisms and rates are cyclic and consist of complex interrelationships of toe erosion by wave attack, cliff steepening, sheet sloughing, and landsliding associated with softening in response to changes in effective stress. Four cyclic failure types are presented.1. Slowly retreating (0.6 m/year) unvegetated cliff fronts of 27 m height and nearly constant profile associated with low energy wave attack (0.5 kW/m) at the toe and cyclic sheet sloughing caused by desiccation and wetting at monthly intervals. Landsliding very rare and surficial.2. Cliffs of 34 m height retreating at intermediate rates (1.4 m/year) showing cyclic changes in profile in response to major, cyclic landslides. Retreat mechanisms involve toe erosion by intermediate energy wave attack (1.0 kW/m) and large toe failures at 10–20 year intervals in response to softening and changes in effective stress.3. Cliffs of 42 m height retreating at 2.8 m/year showing cyclic changes in profile in response to major, high velocity, cyclic landslides that deposit offshore fans of slide debris that provide erosion protection but no counterbalancing moment protection. Toe sands play a significant role, enabling undercutting by high energy wave attack (~2 kW/m). Size and frequency of landslides too variable to quantify at present.4. Cliffs of 38–45 m height retreating at 2.0 m/year in response to toe erosion under high energy wave attack (2 kW/m). Thick water bearing surface sands cause sloughing and shallow failure of the upper slopes at 1.5 year intervals above near vertical wave cut toe cliffs. Huge, deep seated failures may develop during periods of cyclic low water level at roughly estimated intervals of 30 years.

ISSN:0008-3674    

DOI:10.1139/t77-037

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The stability of excavations adjacent to existing structures is an engineering problem and challenge. With the amount of construction increasing many such excavations are being planned and constructed. This paper documents the design, construction, and performance of a tied-back retaining system constructed by the slurry trench method. The system was necessary to retain the sides of a 30-ft (9.1-m) deep cut in glacial till immediately adjacent to the heavily loaded foundations of historically important and settlement sensitive structures. The main structures next to the excavation included the façade of the south transept and the 266-ft (81.1-m) high steeple of St. Jacques Church. Foundation loads imposed by these structures vary from 5.5 to 6.5 tons/ft2(527–622 kPa)at a depth of 5 ft (1.5 m) below ground level. The slurry trench, up to 50 ft (15.3 m) in depth, approached to within 8 ft (2.44 m) of these foundations. Excavation was in two stages with tiebacks holding the wall at each level. The slurry trench and surrounding structures were instrumented using settlement points, crack movement devices, horizontal measurement points, inclinometers, and load cells. The soil investigation and design methods adopted are described.

ISSN:0008-3674    

DOI:10.1139/t77-038

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

One year after the construction of a hospital in Saint-Jérôme, Lac Saint-Jean, a slide occurred in the slope behind the hospital building; that first slide was followed by three other small slides which took place during the following wet seasons. Some remedial works were carried out in order to drain the debris and decrease the pore pressures at the toe and behind the clay face by means of perforated drain pipes and drainage trenches, and to channel the runoff water from the plateau down into the river. The present paper gives a discussion on the causes and the mechanism of the slides, a description of the corrective works carried out, and an evaluation of their effectiveness based on different visual observations, on pore pressure and shear strength measurements, and on stability analysis.

ISSN:0008-3674    

DOI:10.1139/t77-039

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A comparison of bedrock joints with fractures in outcrops of fine-grained Quaternary glaciolacustrine deposits indicates that fractures in the lacustrine sediments are not related to underlying bedrock joints. Fractures in the silts are caused by an exfoliation type of weathering occurring at the outcrop face. They are not reliable indicators of a possible fracture fabric pervading the deposit away from the outcrop scarps.

ISSN:0008-3674    

DOI:10.1139/t77-040

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The performance, including a failure, of two embankments in New Liskeard, Ontario is analysed. The underlying medium-to-soft varved clay foundation is studied with respect to stability, undrained deformations, and excess pore pressure distribution.Total stress stability analyses were performed with undrained strengths based on measured and corrected field vane strengths, the average unconfined compression and unconsolidated undrained strength, and SHANSEP strength parameters with and without anisotropy. Several approaches yielded satisfactory factors of safety and reasonable critical arcs. Effective stress analyses using pore pressures predicted from finite element analyses showed that either the effective stress strength parameters were much lower than those measured in the laboratory or the predicted pore pressures at failure were much too low.Undrained deformations and excess pore pressures at end-of-construction were predicted with the finite element program FEECON. The values were generally consistent with field measurements for an embankment located 60 m from the failure area.

ISSN:0008-3674    

DOI:10.1139/t77-041

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The methods currently available to check the internal stability of reinforced earth retaining walls are reviewed and compared with two groups of experimental results obtained by model tests. The results do not agree with the theoretical predictions which generally underestimate the mechanical properties of this reinforced earth. After a reexamination of the mechanical behaviour of reinforced earth retaining walls, a new design method is suggested. It makes use of a cohesion term to represent the soil–ties interaction, and takes into consideration that reinforced earth is a composite material. This new method is in agreement with experimental results and shows the influence of such parameters as the length and spacing of the ties.

ISSN:0008-3674    

DOI:10.1139/t77-042

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

This paper discusses the design and performance of a tailings dam constructed over very loose, saturated sandy silt foundation soils. A major slide in an iron tailings disposal area in 1948 resulted in liquefied tailings flowing through a valley and depositing up to 6 m of very loose tailings over glacial till. The properties of the saturated tailings foundation soils were critical to the overall dam design. The new dam will eventually reach a height of 30 m.The paper discusses consolidation and strength parameters of the foundation tailings, design considerations including the potential for foundation and stored tailings liquefaction, and the result of monitoring programs during construction of the starter dam which reached a height of about 9 m. During construction the most critical stability conditions developed during placing of the initial 1.2 m lift of pit-run gravel. After foundation pore pressures dissipated additional fill was placed with no further problems. Contrary to experience with other fine grained angular soils having few clay sized particles, the iron tailings foundation soils consolidated significantly under applied load. It was computed that consolidation under the weight of the starter dam would be sufficient to increase the relative density to a value that would remain stable under maximum anticipated earthquake loadings.

ISSN:0008-3674    

DOI:10.1139/t77-043

出版商:NRC Research Press    

年代:1977

数据来源: NRC