摘要:

The isotopes3H (tritium),18O (oxygen-18), and2H (deuterium), which appear to have been concentrated in the leachate at the Confederation Road landfill site, Sarnia, Ontario, Canada, are shown to have migrated into the underlying natural clay barrier by molecular diffusion. The theoretical best-fits to the observed concentration profiles, using the error function solution to the transient diffusion equation (analogous to Fick's second law), give diffusion coefficients of 13 × 10−6, 13 × 10−6, and 8.5 × 10−6 cm2/s for18O,2H, and3H, respectively. Field concentration profiles for Cl−and Na+are also presented for comparison. Diffusion coefficients obtained for Cl−and Na+were 6.4 × 10−6and 3.3 × 10−6 cm2/s, respectively. Tritium and chloride appear to have migrated a similar distance of ~2.0 m from the clay–waste interface, compared with only 1.2 m for Na+, which has probably been retarded by adsorption onto clay exchange sites. Oxygen-18 and deuterium appear to have migrated the furthest at ~2.3 m.The3H profile indicates that post-1953 rainwater entered the landfill site, probably mostly in 1967 when the landfill trench was excavated. High δ18O and δ2H values, especially near the clay–waste interface, suggest mixing of 1967 rainwater with an isotopically enriched water, probably produced in the landfill either directly from enriched organic wastes such as leaves or by biodegradation processes.Key words: diffusion, landfill leachate, oxygen-18, tritium, clay barrier, chloride.

ISSN:0008-3674    

DOI:10.1139/t90-037

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Although the literature provides a reasonable range of information concerning the fracture toughness of relatively hard rocks, there is virtually no data for saturated soft rocks of uniaxial compressive strengths less than about 10 MPa. To gain some insight into the plane strain fracture toughness of such a soft rock for use in the numerical modelling of crack propagation during pressuremeter testing, a large number of laboratory tests were conducted. The material used in these tests was a synthetic soft rock that modelled soft mudstone rocks reasonably accurately. This paper describes the test techniques adopted and the results obtained. The variation of fracture toughness with loading rate and with size and shape of the test specimens is presented and discussed. On the basis of these results, guidelines are suggested for the determination of plane strain fracture toughness of a soft rock.Key words: fracture mechanics, fracture toughness, laboratory testing, soft rock, weak rock.

ISSN:0008-3674    

DOI:10.1139/t90-038

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

During the exceptionally dry summer of 1983, extensive settlement problems developed in lightweight buildings founded in the clay deposits of the Montréal area. In this paper a modified budget method that keeps a running balance of precipitation (P) and potential evapotranspiration (PET) is applied to the region of study to obtain the soil moisture depletion or rainfall deficit (RD) throughout the period 1930–1988. It is shown that extensive foundation problems have developed whenever the rainfall deficit has exceeded 170 mm of water.Key words: settlement problems, clay deposits, evapotranspiration methods, precipitation, rainfall deficit, dry weather.

ISSN:0008-3674    

DOI:10.1139/t90-039

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A laboratory investigation on the quicklime stabilization of sensitive clays has shown that, even at a water content above the liquid limit, significant strength increase can be obtained if enough time and lime are provided. The understanding of strength development is based on the recognition of physical bridging between soil particles, as in a cementation process. The physical and mechanical significance of lime stabilization is described by means of conceptual models. The better the mixing, the better the dispersion and the diffusion of lime and, consequently, the stabilization process. It has been found that the relationship between water content and strength, at a given time, follows a power law that makes possible the establishment of laboratory charts for lime stabilization of such clays.Key words: quicklime stabilization, sensitive clays, cementation, cohesion, shear strength, microstructure, conceptual model, laboratory charts.

ISSN:0008-3674    

DOI:10.1139/t90-040

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Thein situmeasurement of soil permeability has become an important part of geotechnical engineering. New equipment has made the execution ofin situconstant-head tests simple and reliable. However, the theories used for the interpretation of constant-head tests in low-permeability soils still present some shortcomings. A finite element analysis of the constant-head test in clays is carried out to evaluate the various expressions of shape factor published in the literature and to provide a basis for extrapolating transient state observations to steady state conditions from which the permeability may be computed. The resulting method of interpretingin situpermeability tests is applied to series of field results obtained from a Champlain clay deposit.Key words: clay, permeability, constant-head test,in situtest, shape factor, finite element analysis.

ISSN:0008-3674    

DOI:10.1139/t90-041

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

This case record shows that when a surface load is applied to a sensitive, normally consolidated clay, the effective stresses increase rapidly to the measured preconsolidated stresses, and remain at that level while consolidation continues for several decades. Only after more than 30 years was there an indication that thein situeffective stresses were beginning to increase to their final value. These observations have important implications with respect to the design of foundations in such areas.Key words: consolidation, foundations, secondary consolidation, sensitive clay settlements, marine clay.

ISSN:0008-3674    

DOI:10.1139/t90-042

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

An energy method for assessing liquefaction potential of granular soils was developed based on laboratory tests and observational data obtained in past major earthquakes. Cyclic triaxial and cyclic simple shear tests were conducted and the results show that a unique relation exists between the dissipated energy during cyclic load and the excess pore pressure that eventually led to liquefaction failure. This unique relation has been combined with an energy attenuation equation to develop a criterion for defining the liquefaction potential of a site. Parameters for the criterion were evaluated from 136 sites involved in 13 major earthquakes over the world. A comparison was made between the energy method and the commonly used stress method. The energy method was found to be simpler to apply and more reliable.Key words: energy, earthquake, liquefaction potential, standard penetration test, laboratory cyclic test, excess pore pressure, granular soils, case records.

ISSN:0008-3674    

DOI:10.1139/t90-043

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Results are presented for 3 soft clay sites forming part of a larger response study of 11 soil sites subjected to earthquakes of varying intensity and frequency content. The results are presented in the form of spectral ratios (surface to rock), base shear coefficients, and foundation factors. They indicate that large amplifications can be expected at structural periods close to the site period. Comparisons are made with the National Building Code of Canada (NBCC) 1990 provisions for base shear coefficients and foundation factors. These show that the NBCC provisions are adequate when the excitation is low or medium period in nature. For high-period excitation of low intensity, high amplifications that exceed the code provisions are produced.Key words: seismic, design, clay, soft, site, response, spectra, amplification, base, shear.

ISSN:0008-3674    

DOI:10.1139/t90-044

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Results are presented for 4 sand sites forming part of a site response study of 11 soil sites. The results are in the form of spectral accelerations and ratios, base shear coefficients, and foundation factors. They indicate that significant amplifications can be expected at sand sites, especially for low-intensity excitation. Comparisons are made with the provisions of the proposed National Building Code of Canada (NBCC) 1990. They show that, depending on the site and the nature and level of the excitation, the expected base shears can be well in excess of the values specified by the NBCC.Key words: seismic, design, sand, soil, site, response, spectra, amplification, base, shear.

ISSN:0008-3674    

DOI:10.1139/t90-045

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Model tests have been performed in a large centrifuge to investigate the conditions for critical stability of a circular cavity formed by removal of underlying support strata beneath a soft to very soft cohesive overburden. Initial tests used a fixed geometry and were subjected to increasing self-weight by the "gravity turn-on" technique, while later tests utilized a dynamic material extraction process at constant acceleration levels. The mechanics of failure are described and a simple upper-bound analysis is found to predict the critical void size within acceptable limits for a range of the ratio of overburden depth to critical diameter from 0.5 to 1.5.Key words: cohesive overburden, stability, centrifuge, models, voids.

ISSN:0008-3674    

DOI:10.1139/t90-046

出版商:NRC Research Press    

年代:1990

数据来源: NRC