摘要:

The results of full-displacement pressuremeter tests in beds of sand, clay, and layered soil have been used to estimate the lateral soil pressures, ultimate capacity, and displacements of instrumented rigid model piles under eccentric and inclined loads. Comparisons of these estimates with observations on the piles under horizontal load and pure moment have been made and reasonable agreement is found. The analyses are also compared with some field case records.Key words: bearing capacity, clay, displacements, horizontal load, lateral pressure, layered soil, model test, moment, pile, pressuremeter, sand.

ISSN:0008-3674    

DOI:10.1139/t87-063

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Field examination of highwall slope failures occurring in some coal strip mines in Alberta in association with bentonite has led to the concept of a multiple-block plane shear failure mode in which a series of individual block failures regresses back into the slope for distances up to five times the slope height. These failures cause a rapid deterioration of the bench from which the dragline operates, reduce productivity, and necessitate bench maintenance to provide a safe, stable bench prior to the next pass of the dragline.A probabilistic limiting equilibrium analysis was developed to predict the positions of successive failure blocks and its predictions were compared with slope geometry and laboratory strength data from a producing coal strip mine in which a failure was active.Two slope failures reported in the literature (Folkestone Warren landslips and an Oxford Clay brick pit, both in England) were reanalysed using the multiple-block plane shear failure mode, and it is suggested that this mode of failure offers an alternative explanation for the slope kinematics observed.Finally, the most effective means of reducing the probability of failure or controlling the extent of slope failure retrogression is by dewatering.Key words: slopes, failure, coal mining, bentonite, clay bands, plane shear, case history, probabilistic analysis.

ISSN:0008-3674    

DOI:10.1139/t87-064

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Research has been carried out atUniversité deSherbrooke since 1975 on the behaviour of agricultural tower silos built in the St. Lawrence Lowlands in the Province of Quebec. The structures considered are built over soft sensitive Champlain Sea clays. The current foundation designs usually rely heavily on qualitative estimations of the performance of previously built silos. Settlement surveys are now available for a 10 year period for 19 silos out of an original group of 28. Sampling and laboratory testing have been carried out at 11 of these locations, while Nilcon vane shear testing has been performed at each site. Settlement and stability calculations have been made. It is thus possible to compare the observed and predicted behaviours of each silo over a substantial period of time. Foundation design recommendations are proposed as a result of these observations. It is shown that the factor of safety against failure can be used as an indicator of settlement behaviour.Key words: case history, settlement, sensitive clays, tower silos.

ISSN:0008-3674    

DOI:10.1139/t87-065

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Borehole television survey and acoustic televiewer logging provide rapid, cost-effective, and accurate methods of surveying fractures and their characteristics within boreholes varying in diameter from 7.6 to 15.3 cm. In the television survey, a camera probe is used to inspect the borehole walls. Measurements of location, orientation, infilling width, and aperture of fractures are made on the television screen and recorded on computer data record sheets. All observations are recorded on video cassette tapes. With the acoustic televiewer, oriented images of fractures in the borehole walls are recorded on a strip–chart log and also on video cassette tapes. The images are displayed as if the walls were split vertically along magnetic north and spread out horizontally. Measurements of fracture characteristics are made on the strip–chart log, using a digitizing table and a microcomputer, and the data recorded on floppy diskettes. In both surveys, an inclined fracture is displayed as a sinusoidal curve, from which the apparent orientation of the fracture can be measured. Once the borehole orientation is known, the true orientation of the fracture can be computed from its apparent orientation. Computer analysis of the fracture data, provides a rapid assessment of fracture occurrence, fracture aperture, and statistically significant concentrations of fracture orientations.Key words: borehole, television survey, acoustic televiewer logging, fractures, distribution, orientation, aperture.

ISSN:0008-3674    

DOI:10.1139/t87-066

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

For an economic design of side slopes lined with geomembranes or protected with geotextiles, the frictional resistance at the soil–geosynthetic interface has to be known. Direct shear testing appears to be an appropriate method by which to determine these frictional resistances. As low normal stresses apply for most typical conditions along side slopes, two simple direct shear box devices were designed for tests at low normal stresses. Soil–geosynthetic interaction was tested for 4 soil types (2 clay and 2 sand types), 19 geotextiles, and 2 geomembranes. It was found that the friction between soils and geosynthetics is less than the angle of shearing resistance for the soil. The nonwoven geotextiles mobilized more than 90% of the sand friction, whereas woven geotextiles had efficiencies between 86 and 76%. For the clays, the efficiencies recorded were approximately 60% for woven geotextiles and 70% for nonwoven geotextiles. It was further observed that for granular materials the shear strength reached after repeated loading and unloading is independent of the degree of compaction. Based on the results obtained in this study and data reported in the literature, design recommendations are suggested for side slopes protected by geotextiles or lined by geomembranes.Key words: geosynthetics, frictional resistance, relative efficiency, soil–geosynthetic interface, low stress levels, direct shear test, side slopes.

ISSN:0008-3674    

DOI:10.1139/t87-067

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

This paper discusses some improvements on the first-order second-moment (FOSM) probabilistic approach to slope design. The stability model by Morgenstern and Price is used for the formulation of the performance function, thus enabling the FOSM method to be applied to the probabilistic assessment of a general slip surface. A new solution scheme is also used herein for Morgenstern and Price's method. It does not require iterations for the calculation of the interslice forces and the derivatives of the performance function can be evaluated analytically. The reliability index βHLdefined by Hasofer and Lind is used as an index of safety measure. It has the advantage of being "invariant," that is, its value does not depend on the format of the performance function, a property considered lacking in the conventional reliability index. Reference is also made to the probabilistic modelling of soil profiles. The importance of the correlation structure of soil properties is highlighted and its effect on the reliability index βHLis discussed.Key words: slope stability, safety factors, reliability index, probability of failure, general slip surface, rigorous stability model.

ISSN:0008-3674    

DOI:10.1139/t87-068

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Cores from two deep-sea sites from the Labrador Sea have been extensively studied using various analyses. X-ray techniques provided a continuous profile of bulk densities and an accurate description of the bedding. The soil structure was analyzed by scanning electron microscopy. Detailed identification, laboratory shear strength, and compressibility tests have been used to determine the geotechnical properties of the soils, both in their intact and remolded states. Geological data and fabric observations are compared with geotechnical properties in order to explain the observed overconsolidation of the surficial sediments. Characterization of the seabed materials is further improved by using existing empirical correlations with soils of onshore and offshore origin.Key words: marine sediments, deep-sea investigation, overconsolidation, laboratory testing, offshore.

ISSN:0008-3674    

DOI:10.1139/t87-069

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A method of interpreting conventional oedometer test data using work per unit volume as a criterion for determining bothin situeffective and yield stresses in clay is presented. This technique was applied to the results of oedometer tests carried out on samples of natural clay deposits and on specimens consolidated anisotropically from a slurry to a known effective stress state. The work per unit volume – effective stress relationship, using arithmetic scales, can be approximated or fitted using linear relationships. The intersections of these fitted lines are demonstrated to provide accurate values forin situcurrent and yield (preconsolidation) stresses. The yield stress is defined as the intersection of the initial fitted line and the linear relationship observed at higher stresses. The current effective stress is indicated by the first significant divergence of the data from the initial fitted line. These relationships apply to both conventionally (horizontally) trimmed specimens and to vertically trimmed oedometer samples. It is hypothesized that thein situeffective and yield stresses (in both the vertical and horizontal directions) in a natural clay can be determined by the work per unit volume interpretation of oedometer tests carried out on horizontally and vertically trimmed specimens.Key words:in situ, stress, yield, oedometer, interpretation, clays, work, state,K0, preconsolidation pressure.

ISSN:0008-3674    

DOI:10.1139/t87-070

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A two-dimensional finite element model is proposed to simulate transient seepage for complex groundwater flow systems. The complete soil system is treated as a continuum encompassing flow in both saturated and unsaturated zones. In the unsaturated zone, the air phase is assumed to be continuous and open to atmospheric pressure. The coefficient of permeability of the unsaturated soil is assumed to be a function of pore-water pressure.The governing differential equation is derived within a framework familiar to geotechnical engineers. The stress state variables and the constitutive relationships for an unsaturated soil are used in the derivation. The finite element solution to the governing differential equation is based on the Galerkin weighted-residual method. The nonlinearity of the equation is solved by iterative procedures.The finite element formulation is implemented into a computer model named TRASEE. The model can be applied to a wide variety of problems involving complex boundary conditions and geometries with arbitrary degrees of heterogeneity and anisotropy. Example problems are presented to demonstrate the capabilities of the model. The results indicate that the quantity of water flow in the unsaturated zone may be substantial, and that the phreatic line is not a flow line. It has been found that the traditional "saturated-only" flow-net technique can be approximated as a special case to the proposed saturated–unsaturated model.Key words: unsaturated flow, finite element model, phreatic line, permeability function, transient seepage.

ISSN:0008-3674    

DOI:10.1139/t87-071

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

This paper discusses methods for evaluating the coefficient of permeabilitykof the weathered and fissured Champlain clay crust. This parameter is important because losses due to seepage from fluid-retaining structures are directly porportional to the value ofk. The presence of fissures complicates its evaluation, and conventional techniques produce questionable results for two reasons: Clogging of fissures by the smearing of the clay on the walls of test holes during drilling and insertion of a probe leads to anunderestimationofk, and conversely, hydraulic fracturing caused by the application of excessive heads leads to anoverestimationofk. A new technique is presented that prevents the smearing of the clay by reaming the walls of a prebored auger hole. Falling head and constant head tests were performed with feeding devices using a large range of heads including low values. Results confirm that hydraulic fracturing occurs when a critical value of head is reached. As a result, the use of the low-head reaming permeameter described in this paper appears suitable for evaluating the coefficient of permeability of weathered Champlain clay crust.Key words: permeability, field test, hydraulic fracturing, fissured clay, smearing effect.

ISSN:0008-3674    

DOI:10.1139/t87-072

出版商:NRC Research Press    

年代:1987

数据来源: NRC