摘要:

An apparatus has been developed to carry out two- and three-dimensional tests on interfaces between soils and structural materials. The soil container facilitates both the sliding displacement at the interface and the shear deformation in the soil mass. The apparatus has the capability of maintaining the normal stiffness constant during shearing. In constant normal stiffness tests, the normal stress is adjusted continuously by a computer-controlled system to keep the normal stiffness at a desired value. In addition to constant normal stiffness tests, conventional types of tests can be performed during which the average normal stress acting on the interface is kept constant. In all types of three-dimensional tests, the interface can be subjected to tangential loading in two orhtogonal directions simultaneously. Experiments were conducted to study the two- and three-dimensional behaviour of an interface between a dense sand and a rough steel surface under both constant normal stress and constant normal stiffness conditions. The influence of various stress paths on the stress–displacement relations and shear strength characteristics of the interface are investigated. The experimental results indicate that the coefficients of friction corresponding to the resultant peak and residual shear strengths are independent of stress paths. The shear stress – tangential displacement and volume change behaviour of the interface, however, are significantly influenced by stress paths.Key words:interface testing, simple shear, peak and residual shear strength, three-dimensional, constant normal stiffness, stress pat

ISSN:0008-3674    

DOI:10.1139/t96-116-336

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The technique of preloading the deep, compressible soils in the Fraser River delta has been used for more than 40 years to prevent excessive settlement of major structures. This paper documents 22 years of settlement under preloading and after construction of the facilities for a major waste water treatment plant in the delta. These results are similar to observations for as long as 28 years at five additional sites in the delta. It was found that as much as one half of the measured surface settlement occured during or within a few weeks of the full apllication of the preload and that subsequent settlements have the characteristics of secondary consolidation. This could not have been predicted from laboratory tests, and it raises questions concerning the true nature of consolidation in situ. For practical purposes the observations provide guidance for the prediction of long-term settlements in the region.Key words:case history, consolidation, field observations, preloading, settlement.

ISSN:0008-3674    

DOI:10.1139/t96-117

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Dynamic compaction of solid waste is important in landfill operations because increasing the density of the material increases the storage capacity of the landfill. Differential settlements are also reduced, which is important for the integrity of the cover system. In this paper, a case study concerning a waste disposal site situated at Maldegem, Belgium, is presented. It is shown that young landfills behave differently from old landfills. This phenomenon results from the biodegradation of the wastes. Moreover, it is shown that the depth of influence, the crater depth, the enforced settlement, and the peak particle velocity are affected by this ageing process.Key words:dynamic compaction, landfills, SASW method, waste.

ISSN:0008-3674    

DOI:10.1139/t96-118

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

It has been reported in the literature that the settlement of pile foundations in sand under sustained service loads is time dependent. As this phenomenon is not well understood, an experimental study is conducted to investigate the mechanism of pile creep in sand. In the first part of the study involving centrifuge modelling of piles, the test results show that the pile settlement increases with the logarithm of time and the rate of settlement increase is dependent upon the magnitude of applied load and sand density. The changes in the soil and pile stresses observed from instruments installed in the soil and along the pile shaft reveal that under sustained loads, stress relaxation takes place at and around the pile tip area with consequent stress transfer to the shaft. Associated ground surface settlement shows that creep is related to volumetric compression rather than dilation of sand. The centrifuge test findings are then related to the creep behaviour of sand subjected to one-dimensional compression. Examination of sand particles before and after sustained compression loads reveals that sand grains have been broken with their angular protrusions gradually ground off with time. The phenomena of sand particle breakage and stress relaxation around the pile tip provide evidence for the hypothesis that the observed creep is due to the progressive breakdown of sand particules.Key words:centrifuge models, creep, mechanism, one-dimensional compression, pile, sand.

ISSN:0008-3674    

DOI:10.1139/t96-119

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The behaviour of soil–geotextile systems in filtration tests is reported for nonwoven geotextiles under unidirectional flow. A new apparatus was developed to preform filtration tests under an applied vertical stress, and tests were then conducted with different soils and nonwoven geotextiles in order to evaluate the clogging potential and retention capacity of these materials under rather severe combinations of geotextile and soil characteristics. Results show that the geotextiles perfomed well and that observed permeability losses were acceptable even for gradient ratios close to 3. No progressive piping was observed, and it is believed that the retention capacity of the geotextiles may be influenced by their manufacturing process. In general, theoretical predictions for the maximum particle size passing through the geotextile compared well with measurements.Key words:geotextiles, filtration, gradient ratio, permeability, soil retention, clogging

ISSN:0008-3674    

DOI:10.1139/t96-120

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Centrifuge physical modelling of light nonaquaeous phase liquid (LNAPL) transport in an unsaturated sand is discussed with regard to the similitude of the resulting three-fluid flow. Three model series are reported: the first to establish a reproducible unsaturated moisture–suction profile; the second to examine the modelling of models methodology for evaluating similitude of an LNAPL release into an unsaturated fine sand; and the third to prototype-scale data sets for 1000 L surface LNAPL releases at two different rates. Results show that a slower release rate produces deeper LNAPL penetration, and the reasons for this behaviour are discussed. An inexpensive and readily available numerical code called SWANFLOW was used to independently simulate the prototype release rates, and the results are compared with the centrifuge data. The numerical simulations produced compatible predictions of short-term oil transport but did not predict the observed longer term fate of the LNAPL in this highly nonlinear imbibition–drainage problem. A numerical code that incorporates hysteresis between the imbibition and drainage curves would be expected to produce more complete long-term predictions.Key words:centrifuge modelling, numerical simulation, LNAPL fate, unsaturated san

ISSN:0008-3674    

DOI:10.1139/t96-121

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

For a new Police Headquarters Complex in Ottawa, an excavation was required to a depth of 10 m in medium to stiff sensitive silty clays and clayey silts. The risk of a bottom-heave failure due to uplift caused by significant groundwater pressures in the silty soil a few metres below the bottom of the excavation was recognized, and contract requirements included a wellpoint installation assisted by electro-osmosis. The successful bidder was able to develop an alternative method based on the observational approach and completed the foundation at a lesser cost. A small test excavation was instrumented, and digging proceeded cautiously to full depth. The observed bottom heave and pore pressure changes were encouraging, so the test area was enlarged in steps until a workable size of excavation was safely made, then the structural raft was able to be placed. A backup system of pore pressure relief wells using wick drains in the bottom of the excavation was also developed. A large pore pressure reduction, due to the release of overburden pressure, was expected by the contractor's consultant, and a slow regain of the groundwater pressure was also expected due to the low horizontal permeabilities involved. The test excavation instrumentation and observations confirmed these expectations.Key words:bottom heave, excavation, clay, pore pressure.

ISSN:0008-3674    

DOI:10.1139/t96-122

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This paper describes the application of conventional displacement methods to estimate seismic-induced permanent displacements of geosynthetic-reinforced segmental retaining walls constructed on firm foundations. Permanent displacements associated with three sliding mechanisms are investigated: (1) external sliding along the base of the total wall structure; (2) internal sliding along a reinforcement layer and through the facing column; and (3) block interface shear between facing column units. A pseudostatic method based on the Mononobe-Okabe earth pressure theory is used to determine the value of critical acceleration associated with each potential failure mechanism. Newmark's sliding block displacement method and a number of emperical methods are briefly summarized and can be used to estimate the permanent displacements of segmental retaining walls. An example is given to illustrate the application of the methods presented.Key words:segmental retaining walls, geosynthetics, seismic, Newmark, sliding block, displacement methods.

ISSN:0008-3674    

DOI:10.1139/t96-123

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This paper examines the foundation design process in terms of level of safety associated with current state-of-practice, sources of uncertainty and how they are handled, importance of engineering judgement and experience, and the role of codes of practice. Working stress, limit states, reliability-based design approcahes are described and discussed in terms of their historical development, fundamental bases and differences, advantages, and limitations. Limit states are conditions under which a structure no longer performs its intended function. Limit states design considers seperately the two classes of ultimate and serviceability limit states using partial factors of safety. The European factored strength approach and the North American factored overall resistance approach are compared and discussed. The factored resistance approach is a logical extension of working stress design and has the significant advantage that it reflects not only uncertainty in strength, but also in theoretical models, site conditions, construction tolerances, and failure mechanisms. The partial load and resistance factors are interrelated and are a function of characteristic values. A consistent, rational basis for the selection of the geotechnical characteristic value is required. The use of a conservatively assessed mean value is recommended, and an approach for its interpretation is presented.Key words:limit states design, working stress design, characteristic value, partial factors, factored resistance, load and resistance factor design.

ISSN:0008-3674    

DOI:10.1139/t96-124

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The geotechnical engineering profession in Canada is in the process of evaluating limit states design (LSD) for its incorporation into codes of practice for foundation engineering to provide a consistent design approach between geotechnical and structural engineers. This paper describes the work carried out for the initial development of LSD for foundations in the National Building Code of Canada. A load and resistance factor design approach, based on a factored overall geotechnical resistance, is used. The resistance factors for the ultimate limit states of bearing capacity and sliding of shallow and deep foundations are derived from a direct calibration with working stress design (WSD) and from a reliability analysis. The resistance factors derived from both approaches are consistent with each other and provide a reasonably constant reliability index of about 3.0 to 3.5. A relationship is presented that relates the reliability index to a global factor of safety and resistance factor. Design examples are provided that show that the proposed LSD produces designs that are comparable with those produced by traditional WSD. The importance of serviceability limits states is discussed, and the items that require further study and research work to refine code calibration are identified.Key words:limit states design, reliability index, code calibration, resistance factors, foundations, ultimate limit states.

ISSN:0008-3674    

DOI:10.1139/t96-125

出版商:NRC Research Press    

年代:1997

数据来源: NRC