摘要:

A semianalytic (finite layer) technique that will readily allow modelling of the interaction between different landfill cells is presented. The cells may be either adjacent or separated and may have different dimensions (length, thickness) and differentsource leachate characteristics. The technique also allows modelling of the finite service life of engineered components of thebarrier system such as the service life of the primary leachate collection system and, if present, geomembrane liner. Theapplication of the technique is illustrated by first considering the longitudinal expansion along the alignment of leachate migrationof a landfill and examining the interaction between the original and subsequent landfill in terms of impact on the underlyingaquifer. Consideration is then given to the vertical expansion of existing landfills and finally to the modelling of the finite servicelife of a primary leachate collection system and geomembrane liner. It is demonstrated that a vertical expansion hasconsiderable potential for increasing long-term impact and that the impact is also controlled by the service life of the engineeredsystem.Key words: landfill, expansion, analysis, service life.

ISSN:0008-3674    

DOI:10.1139/t97-069

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Sabkha soils are coastal and inland saline deposits of arid climates consisting mainly of loosely cemented sandy silt to silty clay particles. Invariably the soils contain an appreciable amount of organic material and are characterized as being highly compressible. Despite increased interest in various aspects of sabkha soil behavior, little is yet known about the nature and magnitude of secondary compression of these distinct sediments. In this paper, the secondary compression behavior of a typical sabkha formation from the southwestern coast of Saudi Arabia was investigated. Series of conventional and long-term, one-dimensional consolidation tests were conducted on natural and preloaded undisturbed samples taken from the compressible sabkha layer. The results of the laboratory investigation, substantiated by existing field data, indicated that a significant portion of sabkha settlements takes place as a secondary compression. The coefficient of secondary compression,C&agr;, was found to be constant, and the ratio ofC&agr;to the compression index,Cc, is within the range reported in the published literature for various geotechnical materials. The applicability of theC&agr;/Ccconcept to sabkha soils was further ascertained by comparing the secondary settlements estimated based on this concept with those measured directly in the field under an instrumented test embankment. Reasonable agreement was found between predictions and field observations.Key words: sabkhas, consolidation, coefficient of secondary compression, preloading, test embankment.

ISSN:0008-3674    

DOI:10.1139/t97-053

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The objective of the present research was to study the effect of rate of probe expansion in pressuremeter testing for cohesive soil. Emphasis in this paper was given to quantifying and modeling the effect of strain rate on the undrained shear strength. The strain path followed by an element of clay adjacent to the expanding probe was simulated using an automated flexible boundary cuboidal shear device (CSD) typically up to a magnitude of strain level of 10%. Two types of soil (kaolin, kaolin-silica mix) were used consistently for all the testing. Repeatable cubical cohesive specimens were obtained from a high water content slurry consolidation technique.K0consolidation was performed by using a constant vertical stress - zero lateral strain boundary condition using a closed-loop pneumatic system. A series of strain-controlled tests with increasing strain rates from 0.01 to 5%/min was performed under undrained conditions. The effects of increase of strain rate on shear stress - strain behavior and undrained shear strength were quantified. A numerical model based on cylindrical cavity expansion theory which accounts for higher strain rate and its variation with radial distance from an expanding probe membrane was calibrated using the single-element CSD test data.Key words: strain rate, pressuremeter, stress-strain, shear strength, strain path, cavity expansion.

ISSN:0008-3674    

DOI:10.1139/t97-076

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A quasi-two-dimensional method is presented for predicting liquefaction flow slides in a slope with saturated loose sand. The initial stresses at the start of the actual flow slide process are predicted assuming completely drained conditions during the gradual change in slope geometry caused by erosion or sedimentation. The condition for a flow slide is considered to be the presence of at least one sand element in a metastable stress state, i.e., a state in which the undrained response to any quick change in load, however small it may be, consists of a sudden large increase in pore pressure. The metastability of any sand element is predicted as a function of its constitutive properties, its location in the slope, and the slope geometry. The constitutive properties are derived from dry triaxial tests and basically describe the liquefiability (brittleness) of the sand. The metastability criterion for a soil element in a slope is different from that under triaxial loading. Flow slides observed in large-scale tests occurred at the conditions predicted with the model.Key words: loose sand, flow slides, liquefaction, collapse, slope instability.

ISSN:0008-3674    

DOI:10.1139/t97-068

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

It is now commonly recognized that many geotechnical problems are related to the unsaturated behavior of soils. Such is the case for phenomena occurring at shallow depths in the so-called vadose zone. Unsaturated flow is also very important for the management of milling wastes, especially for seepage in and around tailings ponds. Suction properties constitute a key element for the functional representation of unsaturated flow conditions. These are usually shown by the water retention curve, which gives the relationship between volumetric water content ( theta ) and matric suction ( psi ). Laboratory measurements have been performed on three different tailings from hard-rock mines in the Abitibi region to study the effect of various factors, including grain size and porosity, on the theta - psi relationship. The main results are presented in this paper. The data are first analyzed using a well-known descriptive model. The experimental results are also used to estimate the air-entry value according to various procedures including a simple method proposed by the authors. Then, it is shown how an existing predictive model can be modified to obtain, from basic material properties, the complete water retention curve.Key words: unsaturated flow, tailings, water retention curve, moisture content, saturation ratio, porosity.

ISSN:0008-3674    

DOI:10.1139/t97-080

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A series of laboratory model tests and numerical analyses has been carried out to study the behaviour of vertically embedded cylindrical anchors in sand. Due to the cylindrical shape of the anchor, both the shaft friction and the end resistance have substantial contribution to the pullout capacity. But shaft friction and end resistance do not reach peak values at the same anchor displacement. As a result, analyzing the anchorage behaviour of cylindrical anchors is complicated. The pullout behaviour of the anchor is significantly influenced by the embedded depth. There exists a critical depth (about seven to eight times the anchor diameterD) which differentiates the behaviour of a deeply embedded cylindrical anchor from that of an anchor with shallow embedment. The complete load-displacement relationships for shallow and deep anchors can be simulated by the numerical analysis proposed herein. A minimum horizontal spacing of 10Dis needed between neighbouring cylindrical anchors to be free of interference.Key words: cylindrical anchor, uplift behaviour, laboratory model test, numerical analysis, sand.

ISSN:0008-3674    

DOI:10.1139/t97-067

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper reviews the process used to design the construction dewatering system at the Influent Pumping Station at Annacis Island Wastewater Treatment Plant. The design process followed the "observational method," as applied to soil mechanics by K. Terzaghi and set out by R.B. Peck in the Ninth Rankine Lecture. The design was based on a working hypothesis of behaviour anticipated under the most probable conditions identified in the data gathering and assessment program. The sensitivity of the design was evaluated by considering potentially unfavourable conditions evident in the available data. The design development included a review of monitoring feedback obtained during the pumping-well installation, a pumping test, and the dewatering system start-up. The monitoring program and review process are presented.Key words: dewatering, observational method, case study, pumping test.

ISSN:0008-3674    

DOI:10.1139/t97-077

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Numerous laboratory swelling tests have been reported for the measurement of swelling pressure and the amount of swell of an expansive soil. These test methods generally involve the use of a conventional one-dimensional oedometer apparatus. Few attempts, however, have been made to formulate a theoretical framework to simulate the testing procedures or to visualize the different stress paths followed when using the various methods. The simulation of the oedometer tests on expansive soils is required to fully understand the prediction of heave. The correct measurement of swelling pressure is required for an accurate prediction of heave. It is further anticipated that some information on unsaturated soils property functions may be approximated from the back-analysis of the data. A theoretical model is proposed to describe the pore-water pressures with time and depth in a specimen as well as the volume changes during various oedometer swell tests. The model is formulated based on equilibrium considerations, constitutive equations for an unsaturated soil, and the continuity requirement for the pore fluid phases. The transient water flow process is coupled with the soil volume change process. The model can be used to describe the volume-change behaviour, pore-water pressure, and vertical total stress development in an unsaturated soil during an oedometer test performed by any one of several test procedures. The model has been put into a finite element formulation using the Galerkin technique. All the parameters required to run the model can be obtained by performing independent, common laboratory tests. The proposed model was used to simulate the results from free-swell, constant-volume, constant water content, and loaded-swell oedometer tests. Computed values of volume change, vertical total stress, and pore-water pressure are in good agreement with measured values.Key words: unsaturated soil, expansive soil, swelling pressure, theoretical simulation, constant-volume oedometer test, free-swell oedometer test, loaded-swell oedometer test.

ISSN:0008-3674    

DOI:10.1139/t97-071

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper presents the procedures and the results of numerical analyses of a multipropped deep excavation at Lion Yard, Cambridge, using the nonlinear Brick model. The computed results are compared with the comprehensive case record. The observed small deflections and bending moments of the wall, low prop forces, and relatively small ground movements during the main excavation have been taken into account. Shear strains which developed around the site during the main excavation were generally less than 0.3%. Significant reduction of lateral stress in the ground during wall installation and the highly nonlinear stress-strain characteristics of the Gault Clay are the chief reasons for the observed unusual behaviour. The Gault Clay exhibits first yield at a threshold shear strain of about 0.001%, beyond which the stiffness deteriorates significantly from an initial very high value. This high stiffness at very small strains may be due to cementation bonding between soil particles, as a result of the presence of calcium carbonate. Simple drainage assumptions for the stiff fissured clay on both sides of the diaphragm wall appear to be inadequate for design analyses.Key words: numerical analysis, multipropped excavation, Gault Clay, nonlinear brick model, small strain stiffness.

ISSN:0008-3674    

DOI:10.1139/t97-074

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Strong soils are not typically problem soils, and hence their behaviour has not been extensively studied. Strong soils are best defined on the basis of their geologic history, but for this paper they can be roughly defined as cohesive soils with anNvalue of about 15 or over and cohesionless soils withNvalues over 30. Settlement of tall buildings on strong soils has always been of interest. The means of estimating settlement of the large foundations or pile foundations associated with these structures varies but is generally understood to be predominantly elastic. Although predictions of settlement based on laboratory tests or in situ tests may vary as much as an order of magnitude, there now exists a reasonable data base which suggests that large buildings will settle similar amounts regardless of the size or bearing pressure of the foundations or, for that matter, the type of foundations. No data base exists for quantifying the maximum bearing pressure that will be tolerated by large foundations without failure. The angle of internal friction is known to be critical and to decrease with increasing pressure. It is difficult to measure the undisturbed strength of strong soils, since undisturbed samples are very difficult to secure. Centrifuge model tests of large foundations of different shapes confirm that the bearing capacity factorNgammadecreases with increased size of footing, but the decrease ofNgammamay not be accounted for entirely by the friction angle change with pressure. Selection of a friction angle to determine the peak capacity of very large foundations must be done very carefully and with a great deal of judgement, since it cannot be accurately measured.Key words: settlement, bearing capacity, foundation behaviour.

ISSN:0008-3674    

DOI:10.1139/t97-070

出版商:NRC Research Press    

年代:1998

数据来源: NRC