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Daliri F.,Thurber Engineering Ltd. | Kim H.,DY Engineering | Simms P.,Carleton University | Sivathayalan S.,Carleton University
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

Various forms of thickened or high-density tailings, characterized by exhibition of a yield stress that facilitates deposition in gently sloped stacks, are increasingly used for a variety of mining operations. Although this technology reduces reliance on containment by dams and the associated risk of catastrophic failure, regulators are concerned with remobilization of such unbounded deposits by earthquakes or extreme rainfalls. Therefore, the monotonic and cyclic shear strength of thickened tailings layers are of significant interest. Thickened tailings experience a particular stress history during deposition, which may include desiccation, rewetting, and subsequent consolidation by burial under new tailings. The effect of this stress history on their shear response is investigated using a Norwegian Geotechnical Institute (NGI)-type simple shear device. Samples are alternately mechanically overconsolidated or subjected to desiccation and subsequent rewetting because of burial by fresh tailings before consolidation. The two sets of data, one overconsolidated by load, the other by matric suction, were compared using the suction stress concept to quantify an equivalent overconsolidation ratio (OCR) caused by desiccation. However, the effects of mechanical overconsolidation and desiccation were found to be qualitatively different for both the monotonic and cyclic responses; therefore, it is not possible to quantify the effects of desiccation using mechanical overconsolidation and one stress-state variable. Desiccated samples exhibited much weaker strength at phase transformation but more strain hardening compared with mechanically overconsolidated samples at the same OCR. For the desiccated samples, both monotonic strength at phase transformation and cyclic resistance continuously increased with increasing desiccation to air entry value (AEV). Past the AEV, a much smaller increase in strength was observed. Even a small amount of desiccation changed the monotonic response of the tailings from contractive to dilative behavior. ©2014 American Society of Civil Engineers.

Daliri F.,Thurber Engineering Ltd | Simms P.,Carleton University | Sivathayalan S.,Carleton University
Canadian Geotechnical Journal | Year: 2016

Tailings may undergo desiccation stress history under varied climatic and depositional parameters. While tailings substantially dewatered prior to deposition may experience desiccation under the greatest range of climatic variation, even conventionally deposited tailings may desiccate in arid climates at lower rates of rise. Bench-scale research has shown that the stress history imparted by desiccation substantially improves strength in gold tailings. The present study further investigates this phenomenon by simulating multi-layer deposition of high-density tailings using a modular drying box, 0.7mby 1 m inplan. The box is instrumented for directly measuring evaporation, drainage, water content, vertical volume change, and matric suction. Additional measurements included total suction at the surface as well as observations of crack development. The dewatering behaviour conforms to that predicted by previously published generic modelling, specifically that the presence of partially desiccated tailings initially accelerates, but then decelerates dewatering of fresh tailings. The shear behaviour of samples obtained using buried tubes and by driving thin-wall tubes into the multi-layer simulation are compared with shear behaviour of samples from bench-scale experiments. Shear strength of samples from the multi-layer simulation is independent of the sampling method, and shows higher strength than the bench-scale samples. The higher strength may be due to the greater number of wet-dry cycles or other age-related processes. © the author(s) or their institution(s).

Groves P.,University of Waterloo | Cascante G.,University of Waterloo | Dundas D.,Ontario Ministry of Transportation | Chatterji P.K.,Thurber Engineering Ltd
Canadian Geotechnical Journal | Year: 2011

A geophysical investigation was performed to evaluate the effectiveness of three geophysical methods (electrical resistivity imaging (ERI), seismic refraction (SR), and multiple-channel analysis of surface waves (MASW)) for geotechnical site characterization in swamps and environmentally sensitive wetland areas. The geophysical test results were verified against the results from borehole and cone penetrometer test logs. The ERI results were best for determining the depth to the glacial till. However, the resolution of the ERI survey was not sufficient to accurately predict the upper lithologies. The electrode spacing (4 m) was instead selected to reliably predict the depth to the till, which in this case varied between 4.6 and 10.7 m. The SR results overestimated the depth to the till because of the presence of a stiffness reversal. The MASW results predicted the depth to the refusal till layer less accurately than the ERI method. However, this method was able to detect the three distinct layers above the till, even though the layer thicknesses were consistently underestimated. The complementary use of geophysical techniques was a successful approach in determining the main soil units and the depth to the competent layer (till) at the site. These methods can be used as a basis for further development to optimize a procedure to reduce the number of boreholes required for conventional site investigations in areas that are environmentally sensitive or where access is restricted.

Elshimi T.M.,Thurber Engineering Ltd | Brachman R.W.I.,Queen's University | Moore I.D.,Queen's University
Canadian Geotechnical Journal | Year: 2014

Long-span metal culverts have been used for almost 50 years as an economical alternative to short-span bridges. Current design methods are based on two-dimensional finite element analysis using beam theory to represent the structure, or three-dimensional analysis employing orthotropic shell theory. However, neither analysis has been used to investigate the most critical position for trucks at the surface of long-span metal culverts. This paper shows results of three-dimensional finite element analysis, employing orthotropic shell theory and explicitly modeling the geometry of corrugated plates for a specific box culvert tested using a fully loaded dump truck. The analysis was then extended to study the effect of truck position on the response of long-span box and arch culverts. The finite element models, employing orthotropic shell theory and explicitly modeling the geometry of corrugated plates, successfully produced the behaviour of the culvert under truck loading for different truck positions. Culvert deformations were calculated within 7%-13% of the measured values at different locations. The bending moment at the crown was within 4%-17% of the values calculated using the measured strains. If three-dimensional finite element analysis is used to design these culverts, two design trucks should be considered (current design considers a single design truck). The highest moment or thrust is obtained when the truck tandem axles are located above the crown of the culvert.

Suzanne Powell J.,Thurber Engineering Ltd | Andy Take W.,Queen's University | Siemens G.,Royal Military College of Canada | Remenda V.H.,Queen's University
Canadian Geotechnical Journal | Year: 2012

Time-dependent behaviour can have a significant influence on the compressibility characteristics of soils. However, most of the research on this topic has investigated the behaviour of soft soils. In this paper, the time-dependent behaviour of a hard clay shale (Bearpaw Shale) is investigated using both one-dimensional multi-staged loading (MSL) oedometer and constant rate of strain (CRS) oedometer consolidation tests conducted on 25.0 and 16.9 mm diameter specimens. The results show that soft clays and hard clay shales that share the same C αe/C c * ratio (where C αe is the secondary compression index and C c * is the incremental compression index) will show the same approximately 7% change in pre-consolidation pressure for an increase of one log cycle of strain rate despite the many orders of magnitude difference in pre-consolidation pressure. In the case of the Bearpaw Shale, this 7% change in pre-consolidation pressure corresponds to approximately 700 kPa. The time-dependent behaviour of the Bearpaw Shale during unloading (C αe/C s *, where C s * is the incremental swelling index) was observed to follow a similar ratio to that observed in compression (C αe/C c *). While the exact nature of the compression and swelling events that have occurred over the life of the Bearpaw Formation is not clear, the influence of secondary compression cannot be ignored for interpretation of the geological history of this deposit.

Elshimi T.M.,Thurber Engineering Ltd. | Moore I.D.,Queen's University
Journal of Pipeline Systems Engineering and Practice | Year: 2013

Compaction of the soil placed beside culverts (the side-fill) can have a significant effect on the behavior of flexible and rigid structures. This is particularly true for shallow buried structures when the stresses resulting from compaction represent a greater proportion of the total stresses present. Different techniques have been reported in the literature to model soil compaction during finite-element analyses. A new semiempirical technique is proposed, which takes into consideration the increase in lateral stress and soil kneading during compaction. A simple procedure is discussed toincorporate the compaction of granular material in finite-element analysis. The new technique is used to model five different pipe products composed of different materials and dimensions, and the results are compared to measured values reported in the literature. A new factor is proposed to account for soil kneading during compaction to provide an upper limit for the pipe deformations and stresses that result during installation. The technique can be used to estimate peaking in flexible culverts and the additional crown moments and thrust that result in rigid culverts. © 2013 American Society of Civil Engineers.

Wang X.,Thurber Engineering Ltd | Morgenstern N.R.,University of Alberta | Chan D.H.,University of Alberta
Canadian Geotechnical Journal | Year: 2010

Flow slides and debris flows incorporate a broad range of sediment-fluid mixtures that are intermediate between dry rock avalanches and hyperconcentrated flows. Following a comprehensive review of some existing analytical approaches to debris flow runout analysis, a new analytical model based on energy conservation has been formulated. The new analytical model was developed to deepen the understanding of fundamental aspects in modeling of granular flows and to improve the geotechnical mobility analysis of flow slides and debris flows. The Lagrangian finite difference method was used to solve the governing equations. The model and numerical scheme have been tested against analytical solutions and experiments of granular flows with simplified geometries for sliding mass and basal topography. Results of granular flow simulations indicate that the model based on energy conservation performs well and is robust. The model can be used for geotechnical analysis of a wide range of dense granular flows, such as flow slides and debris flows.

Tara D.J.,Thurber Engineering Ltd.
Geotechnical Special Publication | Year: 2012

To validate the foundation design for the main piers for Pitt River Bridge Design-Build (DB) project, a conventional, head-down, static pile loading test was carried out using production piles for both the test and reaction piles to minimize costs. The piles comprised of an 1824 mm diameter, open-toe, steel pipe driven into very dense Pleistocene deposits (glacial till or drift and inter-glacial sediments) at approximately 100 m depth. The loading test was completed successfully in December 2007 to a load of 45 MN by the design-build contractor, Peter Kiewit Sons. Design of the piles was based on information provided by the owner to the DB proponents and included results of test holes and static pile loading tests conducted in the 1970s on 36 and 55 m long, open toe steel pipe piles, CPT and SCPT profiling conducted in the 1990s and mid-2000s, and dynamic load tests (DLTs) conducted on an 100 m long, 1067 mm diameter, open toe indicator pile installed in 2005. Test pile installation records and Pile Driving Analysis (PDA) records and signal matching analyses for the 2005 test pile were used to calibrate the design and confirm pile installation requirements. Supplementary test holes, and CPTs and SCPTs were conducted to over 100 m depth to calibrate pile resistance, particularly pile toe resistance. DLTs were also conducted on several of the production piles to validate the design. This paper presents key aspects of each of the points mentioned above. © 2012 American Society of Civil Engineers.

Wan R.,University of Calgary | Pinheiro M.,Thurber Engineering Ltd
International Journal for Numerical and Analytical Methods in Geomechanics | Year: 2014

SUMMARY: This paper is concerned with a fundamental assumption in the theory of plasticity: the direction of plastic strain increments is independent of the loading (stress) increment direction. This assumption, also known as plastic flow rule postulate, works quite well for metal-like materials. However, geomaterials such as sand present deformational mechanisms that are distinctive from those of metals when they are loaded. As such, we hereby examine the validity of this postulate for granular media accounting for their discrete nature. This is accomplished by analysing the mechanical behaviour of a cubic assembly of polydispersed spherical articles using a particle flow code. An extension to Gudehus' response envelope to three-dimensional conditions is used to study the incremental character and influence of loading direction on the behaviour of these materials. It is found that plastic flow in granular media is governed by both current state variables and incremental loading direction and magnitude, especially under non-axisymmetric stress conditions. The flow rule postulate of plasticity remains valid only in axisymmetric and biaxial conditions. We also verified that the plastic response might be significantly influenced by the stress path (or history) taken prior to loading. These findings raise the question of whether or not classic elastoplastic models based on the above postulate will have serious shortcomings, especially in true-triaxial conditions. © 2013 John Wiley & Sons, Ltd.

Sobkowicz J.C.,Thurber Engineering Ltd.
Tailings and Mine Waste'10 - Proceedings of the 14th International Conference on Tailings and Mine Waste | Year: 2011

Oil sand mine operators have encountered many challenges in storing and treating fine tailings since commercial mining started in 1967. A remarkably broad research and development effort has addressed these challenges, finding solutions such as enhanced capture of fines in beaches, non-segregating tailings and thickened tailings - all intended to improve fines capture and reduce fluid fine tailings inventories. Recently developed treatment methods, such as in-line thickening of tailings combined with thin-lift dewatering or with centrifuging, or freeze-thaw consolidation of tailings, are in advanced stages of pilot testing. Industry efforts to find effective and economically responsible solutions to the fine tailings challenge have been focused by the release of the ERCB Tailings Directive 074 in 2009. This paper reviews the history of oil sands tailings research, presents recent developments, discusses the value and weaknesses of Directive 074, and comments on where treatment of fine tailings is likely headed. © 2011 Taylor & Francis Group, London.

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