摘要:

The 99-ha Keele Valley Landfill is located in a former sand and gravel pit at Maple, Ontario. The base and sides of the pit are lined with a minimum of 1.2 m of excavated clayey silt till recompacted to achieve a design hydraulic conductivity of 1 × 10−8 cm/s or less. Extensive construction controls and monitoring programs have been implemented to determine the hydraulic conductivity and advective performance of the liner. A total of 267 postcompaction laboratory hydraulic conductivity (k) tests indicated that the first two stages of the liner had a geometric meankof 7.7 × 10−9 cm/s. Calculations ofin situhydraulic conductivity based on lysimeter effluent collection rates show decreases inkto field values close to the laboratory values.In situelectrical conductivity sensors and lysimeter effluent chemistry measurements have monitored the advance of leachate-derived chemicals into the liner. Concurrent field verification by liner exhumation and chemical analysis has confirmed the importance of diffusion as the dominant migration mechanism through this low-kliner. Similar concentration trends for major ions have been observed in the field lysimeter effluents, effluents from laboratory liner–leachate compatibility tests, and pore water extracted from core samples of sections of exhumed liner exposed to leachate. The multicomponent field and laboratory testing and monitoring programs have shown good cross-agreement, and the actual performance of the liner has been close to preconstruction predictions.Key words: landfill, clayey liner, field hydraulic conductivity, field diffusion, municipal solid waste leachate, field lysimeter test, laboratory hydraulic conductivity, liner–leachate compatibility.

ISSN:0008-3674    

DOI:10.1139/t93-011

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

This paper describes field measurements and analysis carried out on the Elkhart Creek soil–arch culvert structure in British Columbia, Canada. The structure has a span of 13.4 m, a rise of 7.3 m, and a soil cover of 9.6 m. The original structure collapsed during backfilling in October 1987. A new structure of the same design was built in the fall of 1989, and because of controversy regarding the design thrust value, it was instrumented to measure thrust and displacements in the arch. Displacements and stresses in the soil were also measured. The measured thrust values were much lower than expected and indicated that significant positive soil arching occurred, similar to that observed at the Vieux Comptoir soil–stucture in Quebec in 1975. A nonlinear finite element analysis of the soil–structure system was carried out simulating the construction procedures used, and the computed response was compared with the measurements. The computed and observed responses were in reasonable agreement in all aspects, namely thrust, displacements, and soil stresses, provided an allowance was made for slip at the bolted connections.Key words: culvert, finite element, arching, stress, displacements.

ISSN:0008-3674    

DOI:10.1139/t93-012

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Shear displacements caused by excavation through a fracture zone can decrease the overall fracture-zone transmissivity. The complex arrangement of flow channels found in fracture zones creates a situation where imposed shear displacements will reduce the aperture of critically oriented fractures. This paper presents a simple flow model based on the en echelon structure found in many fracture zones from which a phenomenological relationship between shear displacement and transmissivity change is established. This model is then used to demonstrate the effect of shear displacement around a circular opening. The effects of shear-induced decreases in transmissivity are most dramatic when a continuous low-transmissivity zone is created around the opening. In this case, the steady-state heads can be relatively high and the resulting hydraulic gradient into the excavation can be extremely large. If the low-transmissivity zone around the opening is discontinuous because, for example, the shear displacements are nonaxisymmetric, then the inflow becomes channelled and the steady-state heads and hydraulic gradients near the excavation substantially decrease. The concept of shear-induced transmissivity reduction in fracture zones provides an alternative mechanism to shear-induced dilation and normal stress induced fracture closure for interpreting and explaining the observed hydraulic response in fracture zones.Key words: transmissivity, shear displacement, fluid flow, en echelon fractures, fracture zone, excavation.

ISSN:0008-3674    

DOI:10.1139/t93-013

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

During an excavation-response experiment performed at the Underground Research Laboratory (Atomic Energy of Canada Limited, Pinawa, Man.) a decrease in fracture-zone transmissivity was measured as a tunnel intersected the room 209 fracture zone. The decrease in transmissivity was greatest as the pilot and the slash faces passed the fracture zone. The transmissivities increased towards their preexcavation values as the faces proceeded past the fracture zone. This response suggested that shear stresses or displacements controlled the hydraulic behaviour of the fractures. The hydraulic response in the fracture zone was analyzed using finite element models. Predictions of shear-displacement distributions in the fracture zone as a function of face position were obtained from a three-dimensional finite element model using joint elements to represent the fracture zone. A phenomenological relationship between shear displacement and transmissivity change was used to modify the transmissivity distributions in the fracture zone based on shear displacements for different excavation stages. Seepage analyses with these transmissivities provided predictions that matched closely the field measurements obtained from the room 209 fracture zone. These results and the inability of conventional, normal stress dependent, fracture closure to predict consistently the hydraulic response support the concept of shear causing a reduction in fracture-zone transmissivity. Excavation-dependent, shear-induced reduction in transmissivity provides an alternate mechanism for interpreting and understanding the hydraulic response of disturbed fracture zones.Key words: transmissivity, shear displacement, fluid flow, fracture zone, excavation.

ISSN:0008-3674    

DOI:10.1139/t93-014

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The objective of this investigation was to evaluate the potential use of the borehole stress relaxation test to determine the creep and strength properties of frozen soilsin situ. The paper presents the results of a series of laboratory pressuremeter relaxation tests performed in frozen sand and compares three possible interpretation methods for deducing from the test results the creep and strength parameters of frozen soils.Key words: borehole relaxation, pressuremeter,in situtesting, creep and strength properties, frozen soil.

ISSN:0008-3674    

DOI:10.1139/t93-015

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The permeability indexCk, similar to the compression index, is the slope of the void ratio – coefficient of permeability relationship. Literature shows that, in general, for sensitive clays it can be related to initial void ratio byCk = 0.5e0. The possibility of obtaining such a relationship for Cochin marine clays in terms of liquid limit void ratio is indicated in this paper. Analysis of permeability behaviour of Cochin marine clays and the test results available in published literature using generalized state parameter approach show that, in principle, these forms of equations for the permeability index are tenable, even though they were obtained based on experimental observation alone.Key words: permeability index, initial void ratio, void ratio at liquid limit, generalized state parameter approach.

ISSN:0008-3674    

DOI:10.1139/t93-016

出版商:NRC Research Press    

年代:1993

数据来源: NRC