摘要:

This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Bothcv(SPLT)/cv(tri) andcv(SPLT)/cv(oed) ratios compared favorably with thecv(field)/cv(laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values.Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.

ISSN:0008-3674    

DOI:10.1139/t90-069

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The influence of embedment, base diameter, and backfill density on the uplift behaviour of piles with enlarged bases embedded in sand was investigated in a centrifuge. Comparitive tests on straight-shafted piles are also reported. For piles in dense sand, sensible agreement was found with earlier research on anchor plates and published field data. However, uplift capacities in loose sand were considerably lower than previously observed for anchor plates. A number of theories for anchors considerably overpredict the observed capacity for belled piers in both dense and loose sand, although in the case of dense sand, reasonable values are obtained using an empirical equation derived from centrifuge tests on anchor plates and a finite element based design approach. The normally conservative vertical slip-surface model is alone in providing reasonable agreement with the surprisingly low observations for piles in loose sand.Key words: piles, uplift capacity, centrifuge tests, sand.

ISSN:0008-3674    

DOI:10.1139/t90-070

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The evaluation of groundwater quality has become increasingly important as more industrial waste and solid domestic refuse come into contact with groundwater. One method of detecting contaminated groundwater is by noting the electrical resistivity of the contaminated soil. This method has been applied at the University of British Columbia by the development and use of a new resistivity cone. The resistivity cone consists of four circumferential surface electrodes contained in a separate module behind a 15 cm2piezocone. The cone has a capability of providing a continuous record of resistivity with depth.Initially, a laboratory testing program was carried out using a simplified probe design to ensure the feasibility of the project. On the basis of favourable laboratory results the module was constructed, calibrated in the laboratory, and then field tested. The paper describes the design and operation of the resistivity cone, theory and laboratory calibration, and test results from three sites in the lower mainland of British Columbia. The results of the testing program provided evidence of the reliability of the instrument and illustrated its application in determining changes in groundwater quality. Factors affecting results and applications of the resistivity cone in contaminant site investigations are discussed.Key words: electrical, resistivity, cone, groundwater, contamination, plumes, mapping,in-situtesting, soil.

ISSN:0008-3674    

DOI:10.1139/t90-071

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Seven series of tests have been performed on specimens from five natural soft clay sites to determine the variation of the vertical and horizontal permeabilities when the soil is unidimensionally compressed. The results show that the permeability anisotropy does not increase significantly with compression up to strains of 25% for marine clays. In varved clays, mostly because the clay laminae are more compressible than the silty laminae, the anisotropy increases with vertical compression.Key words: permeability, clay, anisotropy, laboratory, compression.

ISSN:0008-3674    

DOI:10.1139/t90-072

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Ongoing geological and geotechnical investigations are under way for two sites in Ferland, Quebec, where sand boil deposits, ground fissures, and liquefaction-related damage to homes were documented immediately following theM = 5.9 Saguenay earthquake of November 25, 1988. Both sites are about 26 km from the epicentre. To date, the geological investigation of the sites suggests that (i) liquefaction and ground failure have occurred in this area in the past, (ii) lateral spreading was the principal mode of ground failure in 1988 and in the past, (iii) 1988 and earlier displacements due to lateral spreading were on the order of centimetres, and (iv) topography played an important role in the localization and characterization of ground failure. The geotechnical investigation suggests that (i) liquefaction at these sites is predictable using Seed's method, and (ii) the material that liquefied during the Saguenay earthquake is a gray, siltysand or sandy silt that is about 0.3 m thick and occurs at a depth ranging from 2.5 to 4.5 m below the surface. These preliminary results suggest that the potential for liquefaction and related damage may be higher than previously recognized in the Ferland–Boilleau valley in particular and in the Saguenay area in general.Key words: liquefaction, ground failure, earthquake, geological investigation, geotechnique, silty sand, damage.

ISSN:0008-3674    

DOI:10.1139/t90-073

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The ability of the classical quasi three-dimensional formulation to describe steady-state groundwater flow problems in complex multiaquifer environments is examined. In the present formulation, discontinuities in the aquifer and aquitard units can be accommodated along with partial or complete aquifer dewatering and confined or unconfined flow conditions. Some of the main assumptions underlying classical quasi three-dimensional schemes are scrutinized, including the requirement of a two orders of magnitude permeability contrast between aquifers and aquitards. Performance of the numerical scheme is studied through a series of test problems by comparing with results obtained from a conventional finite element model. A high degree of accuracy and flexibility is achieved with the extended quasi three-dimensional technique, yet the numerical efficiency inherent in the classical formulation is maintained. By dividing an aquifer into a series of horizontal sublayers, vertical resolution of the flow field can be achieved without resorting to a numerically intensive fully three-dimensional scheme. Because it is possible to compute a three-dimensional representation of the hydraulic head distribution in individual aquifers with the quasi three-dimensional formulation, even in the absence of layers of contrasting hydraulic conductivity, the technique provides a viable alternative to the much more complex fully three-dimensional schemes for a wide variety of groundwater flow problems.Key words: groundwater flow, multiaquifer, complex stratigraphy, numerical analysis, quasi three-dimensional, steady state.

ISSN:0008-3674    

DOI:10.1139/t90-074

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A new hollow cylinder torsional shear apparatus is described. The apparatus is suitable for investigating soil behaviour under generalized stress paths, including principal stress rotations, characteristic of earthquake and offshore-wave loadings. A new, more rational assessment of stress nonuniformity across the wall of the hollow cylinder specimen is made, and the "no go" regions of the stress space are delineated that limit stress nonuniformity to acceptable levels. Operation of the apparatus and experimental procedures for tests on reconstituted specimens of sand are described. Typical results of drained tests on loose and dense sand are presented to illustrate the capabilities of the apparatus as a general stress-path loading device and to highlight the stress-path dependence of soil behaviour, in particular, the deformation response to principal stress rotations.Key words: hollow cylinder apparatus, generalized stress paths, principal stress rotation, sand, deformations.

ISSN:0008-3674    

DOI:10.1139/t90-075

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The purpose of this study is to show that geostatistics can help in finding the structure of the spatial variability of the undrained shear strength within a clay deposit. The site under study, B-6, owes its name to the earth dam that will be constructed on it; the site is located on the shore of the Broadback River in the James Bay area of Quebec. The geostatistical analysis is carried out on the unaltered zone of the B-6 clay; it shows an anisotropic structure for the spatial variability. The knowledge of the structure (variogram) of the undrained shear strength is used in the kriging theory to compute estimations at points of the deposit where experimental measurements are not available. Kriging is also used to identify weak zones within the B-6 clay. The geostatistical analysis of the B-6 clay gives the opportunity to test the capability of the method. Even if the errors of measurements were small, the variogram has permitted detection and correction of a bias that affected a certain number of vane profiles.Key words: clay, geostatistics, undrained shear strength, variogram, measurements errors, kriging.

ISSN:0008-3674    

DOI:10.1139/t90-076

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The Underground Research Laboratory access shaft was excavated from the surface to about the 185 m depth in jointed pink granite. Below this depth to the 443 m depth the shaft was excavated in massive grey granite. The grey granite is essentially unjointed, except for a major low-dipping thrust fault and associated minor splays. Overcoring, hydraulic fracturing, convergence measurements, microseismic monitoring, and observations of shaft-wall failure and core discing indicate that unusually highin situstresses can be associated with large volumes of massive, unjointed granite at fairly shallow depth. The database ofin situstress measurements collected at the Underground Research Laboratory indicates that major geological features, such as thrust faults, can act as boundaries forin situstress domains and that both the magnitude and direction of thein situstress state can change when these geological features are traversed.Key words:in situstress, anisotropy, stress domains, thrust faults, overcoring, hydraulic fracturing, convergence measurements, excavation damage zones.

ISSN:0008-3674    

DOI:10.1139/t90-077

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Field permeability tests in cased boreholes have been modelled in a sand tank with controlled and measured hydraulic conditions. The testing program included "end of the casing" and "Lefranc" tests, as described in Canadian standards 2501-135 and 2501-130, for field permeability tests in a casing driven in a granular soil (valid for 10−5 < K < 10−2 cm/s approximately). The theoretical solutions for these tests require a list of assumptions that may be difficult to satisfy under field conditions. The method for detecting the common error in the assumed piezometric level gave in all cases a local piezometric level equal to that determined independently by a set of 22 piezometers. In accordance with the theoretical solutions, theKvalues given by the tests do not depend on the controlled upward or downward seepage in the sand tank. The averageKvalue given by such field tests is strongly influenced by the preparation of the injection zone, which includes a natural soil in a more or less disturbed condition adjacent to an injection aperture or lantern of poorly known geometry and condition, so losses in hydraulic heads there may be different from those assumed in theory. From a practical point of view, all drilling operations have a major impact on the results and must be strictly controlled to have a reasonable estimate of theKvalue.Key words: permeability, field, borehole, model tests, piezometric level.

ISSN:0008-3674    

DOI:10.1139/t90-078

出版商:NRC Research Press    

年代:1990

数据来源: NRC