摘要:

Natural vegetation can be a useful indicator of terrain conditions and thus has significant geotechnical implications especially in identifying moisture, groundwater conditions, and strati-graphic changes. A pilot study was initiated to study physiographic, climatic, biotic, and compensating factors as they affect plant communities in the Langham area, near Saskatoon, Saskatchewan. The study area is located at the transition between the Dark Brown and Black Soil Zones, which are colour zones of the surface soil horizon as influenced by climate and vegetation. It is suggested that the findings at Langham can be extrapolated over a wide band across the province where the soil zones and geomorphic units are similar. It was found that trees or shrubs are more reliable indicators of soil moisture conditions than low-growing plants and that plant communities are better indicators than individual species. In some places, the recognition of changes in vegetation patterns could make a significant contribution to geotechnical projects. A direct correlation was found between the number of species occurring in a plant community and soil moisture conditions. Drier sites had fewer species.

ISSN:0008-3674    

DOI:10.1139/t77-048

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Slope stability analyses carried out in terms of effective stress require an understanding of the distribution of pore-water pressures in a slope. This understanding must be based on a knowledge of the groundwater flow system, which is in turn dependent on the regional geologic environment and the configuration of hydraulic conductivity contrasts. This paper presents several computer simulations of flow systems in a variety of hypothetical slopes. Results show that the presence of low-conductivity units at the surface or at depth can be extremely detrimental to stability, particularly if they confine units of higher conductivity. The contrast in conductivity need not be more than two orders of magnitude. Such situations are common in thrust blocks, interbedded sedimentary rocks, weathering profiles, and deformed metamorphic rocks. Groundwater conditions critical to stability arise in anisotropic formations, where the axis of maximum conductivity is parallel to the dip of the slope. Fluctuations in regional flow systems can be critical to the stability of unconsolidated, terraced sediments.

ISSN:0008-3674    

DOI:10.1139/t77-049

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

In view of the extensive open pit mining operation at Gaspé Copper Mines Limited, Murdochville, Quebec, a study of an optimum slope design was felt necessary. This paper describes the different steps of the slope stability project: origin and organization to achieve an optimum design. The various phases of the project were: survey of the ore body and topography, investigation of physico-mechanical properties of rocks, structural geological mapping, groundwater study, and detailed study of structural weaknesses. The results were subsequently used to analyse different modes of possible failure of rock mass. The information obtained is being used in redesigning the Copper Mountain pit.

ISSN:0008-3674    

DOI:10.1139/t77-050

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Unstable rock slopes along transportation routes in rocky terrain are hazards requiring carefully selected maintenance techniques if safety against rock falls is to be improved at reasonable cost. The paper reviews the causes of rock falls and methods of dealing with them in North American and European highway and railway practice. Methods are classified as those that: (a) stabilize slopes or prevent rocks from moving out of place, (b) protect the right-of-way by keeping rocks that do move out of place from reaching the roadway, and (c) warn or signal traffic when rocks arrive at the vicinity of the roadway. Methods of stabilization, protection, and warning are described and illustrated. Some of these methods can be combined for increased safety at a single site. Guidelines are suggested to organize an effective program to guard against rock falls. Steps in planning, deciding on the priority of sites to be treated, and choice of treatment methods at particular sites are all discussed. Desirable records and measurements are outlined. The paper is intended to be a practical reference for practising engineers.

ISSN:0008-3674    

DOI:10.1139/t77-051

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A regional study of the distribution and characteristics of landslides along four major rivers in southern Alberta was undertaken in order to relate landslide activity to geologic and physiographic factors such as bedrock outcrop, groundwater, river sinuosity, and the aspect of valley slope. This provides greater insight into the factors controlling slides in the study region, particularly in the Cretaceous bedrock.The study was based on an analysis of air photos, augmented by surficial and bedrock geologic maps and hydrogeologic and bedrock topographic maps. The area is underlain by a thick sequence of gently dipping sedimentary strata of Upper Cretaceous age. Late Pleistocene glaciation deranged the drainage to some extent and the rivers studied now occupy postglacial channels in some reaches and are re-excavating preglacial channels in other reaches.The results of the study indicate that the bedrock type is of considerable importance since there is marked difference in valley wall stability between relatively unstable marine formations and the relatively stable nonmarine formations. Areas of comparatively high groundwater exert an obvious influence on landsliding. The importance of buried valleys in locally drawing down the water table is clearly evident. More than 90% of the landslides occur in meander bends and are related to river erosion.Failures in the bedrock appear to be translational whereas those higher on the valley wall in Pleistocene sediments are largely rotational. The data have been assembled on a profile of the river and present a regional picture of landslide activity over a large area.

ISSN:0008-3674    

DOI:10.1139/t77-052

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Conventional stability analyses of a 47 ft (14.3 m) high embankment constructed of clayey silt fill indicated a satisfactory design with 2:1 slopes. However, cracking of the fill and movements of the embankment occurred when its height reached 32 ft (9.8 m). Investigation revealed that, in general terms, the geotechnical profile employed for the stability analysis was satisfactory. There was a localized layer of firm clayey soil at the interface between the fill and natural soil, which coincided with the observed cracks and the zone of high pore pressure.Construction scheduling was critical, and an initial wedge analysis showed that a 17 ft (5.2 m) high berm would ensure adequate safety during completion of the fill. A detailed investigation followed to determine the actual deformation mechanism responsible for the cracking. This included plane strain finite element runs using estimated moduli values. It was concluded that the cracking was caused by ‘spreading’ of plastic material at or near the base of the embankment. This case history illustrates that localized layers of weaker soil can be critical even when construction has been carefully controlled.

ISSN:0008-3674    

DOI:10.1139/t77-053

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Seventeen maps at a scale of 1:50 000 showing the distribution of sensitive clay deposits and associated landslides in Ottawa Valley have been compiled. The following map-units have been used: rock, till, and gravel older than the clay; sensitive clay associated with the Champlain Sea; sand and gravel overlying clay; and organic deposits overlying clay. Also shown on the maps are landslides that could be identified on aerial photographs and a line representing the maximum limit of marine transgression.From data collected from several test borings, the sensitive clay has been divided into four distinct stratigraphic units. Visual identification criteria have been developed and average index properties are given. These results show that ‘Leda’ clay is not a clay with unique properties, but displays considerable variability. The four stratigraphic units have been related to the history of transgression and regression of the Champlain Sea. Many of the large landslides occurred early in the history of the area during a period when a considerably larger Ottawa River cut several broad channels through the sediment.By combining the surficial geology and the stratigraphic profiles obtained by drilling it has been possible to classify sensitive clay slopes into two geologic settings. One setting consists of clay at the surface and the other has a thin layer of fine sand overlying the sensitive clay. The majority of the large retrogressive slides have occurred in slopes of the latter setting. A comparison study is being carried out on the two settings and some preliminary results are presented here.

ISSN:0008-3674    

DOI:10.1139/t77-054

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The problem of the prediction of stability or instability of natural clay slopes is examined in view of the random intrinsic nature of both soil properties and external actions. The probabilistic method of analysis appears to be a useful tool, which not only could account for these random properties but also could consider uncertainties derived from incomplete knowledge of pertinent model parameters and conditions of stability.Using the familiar method of slices, the different sources of error have been incorporated into a first-order probability analysis of the simplified Bishop model in order to arrive at quantitative information concerning the probability of failure. Field and laboratory data from an instrumented test valley slope in the Ottawa region have been considered to arrive at an instability risk prediction of the test slope. The mean functions of the strength parameters have been made explicitly dependent on a number of statistical parameters to emphasize dependence on available data. The analysis distinguishes between statistical uncertainty, which comes from insufficiency of available data, and probabilistic uncertainty, which is a measure of random heterogeneity of the soil.

ISSN:0008-3674    

DOI:10.1139/t77-055

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A borehole dilution method using fluoride in low concentrations as the tracer and an adapted, commercially available fluoride ion electrode to measure the tracer dilution has been developed and employed at two sites. The sites are shallow groundwater systems consisting of alluvial surficial gravels near Fort Macleod, Alberta, and glaciodeltaic sand deposits at the Chalk River Nuclear Laboratories, Ontario. Zones of relatively high groundwater velocities determined at Fort Macleod with the fluoride apparatus are also evident in the results of a large-scale tracer test that documented chloride profiles over the saturated gravel thickness from point samples at 0.3 m depth intervals. The performance of the fluoride electrode compared favorably with a radio tracer (131I) technique in a simultaneous dilution experiment at the Chalk River site. Other ion-selective electrodes such as the chloride electrode may provide an alternative sensor in areas where hydrochemical conditions may restrict the use of the fluoride electrode.

ISSN:0008-3674    

DOI:10.1139/t77-056

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Statistical techniques are used to forecast the compressibility of peaty ground. Based on data from more than 100 consolidation tests on undisturbed samples of peat and underlying clay, various regression equations are developed to estimate the compression index, in terms of more easily determined soil index properties. It is found that the compression index can be reasonably well approximated by the use of a simple linear regression model involving the natural water content and the natural void ratio. These regression equations are then compared with those that have been reported by other investigators. These regression equations may permit a preliminary estimation of the settlement of peaty ground. The obtained statistical relationships apply to the peaty ground in the Ishikari area, Hokkaido, Japan, and it should be emphasized that such relationships are approximate and caution should be used in their application.

ISSN:0008-3674    

DOI:10.1139/t77-057

出版商:NRC Research Press    

年代:1977

数据来源: NRC