2017

Permanent URI for this collectionhttps://hdl.handle.net/1807/75480

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Analysis of Surface Erosion of Cohesionless Soils using a 3D Coupled CFD-DEM Model
(Canadian Science Publishing, 2017-09-22) Guo, Yuan; Yu, Xiong
A fluid-solid interaction model has been implemented by coupling two numerical methods, Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM), which captures the meso-scale behaviors of the fluid-solid system. The model is first validated by comparing the results of simulations with two types of experiments: free settling of a single sphere in water and formation of angle of repose of particles under water, which show its capability in modeling the behaviors of both particle phase and fluid phase. The verified model is then used to study factors affecting the soil erodibility, where case studies are designed for soil particles deposited inside a pipe and subsequently subjected to water flow induced surface erosion. Influencing factors for soil erodibility, including particle diameter and inter-particle bond, are analyzed. For cohesionless soils without bond strength, the critical shear stress is found to be linearly related to particle size; while for soils with bond strength, the simulation results show that inter-particle bond largely decelerates the erosion process and causes a much lower erosion rate. To further the understanding of soil surface erosion under turbulent flow, the k-Îľ turbulence model has been successfully implemented for the fluid phase. Comparison between the laminar model and the turbulence model shows turbulence significantly accelerates the erosion process.
Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk
(Canadian Science Publishing, 2017-12-05) Buckley, Roisin; Jardine, Richard J.; Kontoe, Stavroula; Lehane, B.
This paper reports experiments with 102mm diameter closed-ended instrumented Imperial College Piles (ICPs) jacked into low to medium density chalk at a well characterised UK test site. The â ICPâ instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalisation periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local CPT cone resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, pilesâ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and/or installation method.
Correlation of acoustic emissions with patterns of movement in an extremely slow moving landslide at Peace River, Alberta, Canada
(Canadian Science Publishing, 2017-06-07) Berg, Nancy; Smith, Alister; Russell, Shawn; Dixon, Neil; Proudfoot, Don; Take, W. Andy
The Peace River region, Alberta, Canada, has experienced extensive landslide activity since deglaciation. Shear zones within weak lacustrine silt and clay layers typically experience continuous creep, damaging highway and utilities infrastructure. However, occasionally, movement accelerates and potentially catastrophic failures occur. Conventional deformation monitoring approaches provide incremental measurements with low temporal resolution and do not necessarily allow rapid changes in stability to be detected and communicated sufficiently in advance to provide early warning. The study objectives were to (i) acquire a long-term dataset of continuous deformation measurements with high temporal resolution of a case study slope in Peace River, (ii) enhance understanding of a typical creeping Peace River slope’s behavior in response to climatic drivers, and (iii) investigate the potential of an acoustic emission (AE) monitoring system to provide early warning of accelerating deformation behavior. ShapeAccelArray (SAA) and AE instruments were installed, in addition to conventional inclinometers and piezometers. Measurements show that the landslide is “extremely slow”, moving on average 5 mm annually, and reveal seasonal activity with periods of acceleration and deceleration driven by pore-water pressures. Measured AE correlated strongly with the rate and magnitude of SAA-measured displacement, demonstrating the potential of the AE technique to warn of accelerating deformation behavior.
Test fill to failure on soft plastic marine clay at Onsøy, Norway
(Canadian Science Publishing, 2017-08-31) Berre, Toralv
The test fill at OnsĂ¸y, close to the town of Fredrikstad in Norway, was built on a very soft marine clay with in situ vane strength as low as 11 kPa and a plasticity index varying from 34 to 50. The dimensions at the bottom of the long test fill were 20 m*60 m and the height 2.3 m. The fill, as placed in the first stage, had a computed factor of safety against foundation failure of 1.35 based on in situ vane strength. The fill was allowed to sit for about 3 years (from 1972 to 1975) before it, in a second stage, was brought to failure in about 4.3 days by raising the height. This second stage is the subject of this paper. Back calculation of the failure by undrained stability analysis based on in situ vane tests performed shortly before the start of the second stage, and based on undrained triaxial and constant volume direct simple shear tests on specimens from tube samples taken shortly before the start of the second stage and reconsolidated to the in situ effective stresses, gave factors of safety varying from 0.88 to 1.45. Settlement values computed at the centreline of the fill for the second stage based on the results from undrained compression triaxial tests, agreed reasonably well with the field measurements.
Colloquium 2016: Assessment of the subsurface thermal conductivity for geothermal applications
(Canadian Science Publishing, 2017-11-20) Raymond, Jasmin
The construction of green buildings using geothermal energy requires knowledge of the ground thermal conductivity, assessed when designing the heating and cooling system of commercial buildings with ground-coupled heat pumps. The most commonly used method for active field assessment is the thermal response test (TRT), which consists of circulating heated water in a pilot ground heat exchanger (GHE) where temperature and flow rate are monitored. The transient thermal perturbation is analyzed to evaluate the subsurface thermal conductivity. Heat injection can also be performed with a heating cable in the GHE to conduct a TRT without water circulation, which can be affected by surface temperature variations. Passive methods, such as the interpretation of geophysical well logs and the analysis of temperature profiles measured in exploration wells, are emerging as alternatives to TRTs. Steady-state and transient laboratory measurements performed on samples collected in surface outcrops or drill cores can also be achieved. Methods to characterize the subsurface in the context of geothermal system design have greatly evolved since the original TRT concept proposed during the 1980s with different techniques inspired from the Earth science sector.
Influence of Polyacrylamide Conformation on the Fabric of a “Tunable” Kaolin-Polymer Composite
(Canadian Science Publishing, 2017-12-18) Halder, Bijoy; Palomino, Angelica; Hicks, Jordan
â Tunableâ clay-polymer composites have the potential to improve the engineering properties of clay materials. The importance of these materials derives from the ability of the responsive polymer to adopt various conformations (coiled, partially extended, or extended), which in turn impacts the meso-scale properties of the material. However, the influence of polymer molecule conformation on particle arrangement and overall composite behavior is not well understood. The purpose of this study is to understand the fabric development due to the conformational behavior of the polymer, and thus the clay-polymer composite, over a wide range of solids content and stress levels. The polymer molecule conformation was controlled using selected fluid pH and ionic concentrations. Results show that the polymer conformation significantly influences clay fabric formation. When the polymer molecules are likely to have extended conformation, the dominant fabric mode is face-to-face and particle mobilization increases. Both face-to-face and edge-to-edge fabric formation dominate the behavior of the composite when coiled conformation is likely, resulting in a decrease in interparticle movement. Thus, the polymer conformation can be used to manipulate both the interparticle spacing between particles and/or aggregates and arrangement of particles.
Design and construction of a compacted clay liner in the cover system of a MSW landfill using not standard procedures
(Canadian Science Publishing, 2017-11-07) Moraci, Nicola; Busana, Stefano; Cortellazzo, Giampaolo; Favaretti, Marco; Mandaglio, Maria Clorinda; Schepis, Micol
Design and construction of mineral barrier layer involve many experimental and technological aspects. After having chosen a specific soil water content and laboratory compaction energy, required to obtain permeability values according to the national regulation in force must be determined. It is also necessary to control water content, compaction energy, and permeability of liner actually compacted in situ. The paper shows how a compacted mineral barrier mainly composed of silty clay soil (the excavated soil is a natural but potentially re-usable waste product) was put in place to cover a large MSW landfill and compacted using a heavy dumper, capable to achieve an adequate compaction degree. In situ hydraulic properties of liner were compared to those obtained by laboratory tests and to the limits imposed by the Italian regulation. The actual compaction degree was checked by in situ tests. Hydraulic conductivity tests were carried out in situ, using Boutwell and Guelph permeameters, and in laboratory using rigid wall and flexible wall permeameter. In situ testing provides permeability values more realistic than laboratory ones and demonstrated that the actual construction procedure used was effective in order to obtain the design targets.
Lateral compression response of overlapping jet-grout columns with geometric imperfections in radius and position
(Canadian Science Publishing, 2017-12-18) Liu, Yong; Pan, Yutao; Sun, Miaomiao; Hu, Jun; Yao, Kai
Spatial variability in the radius of a jet-grout column is commonly encountered in practice. Although various prediction models for the column radius are available, they were generally used to predict a nominal radius. The radius variation within a column has been seldom considered. In this study, the intra-column radius variation was simulated as a lognormal stochastic process. This was done based on the existing prediction models where the column radius can be correlated with the undrained shear strength of in-situ soils. A slab consisting of overlapping jet-grout columns was considered. The slab serves as an earth retaining stabilizing structure in a deep excavation. The effects of radius variation on the mass performance of the slab were examined with the finite-element method. In addition, the positioning errors in jet-grout columns were also investigated. Owing to the random nature of the radius variation, the Monte-Carlo simulations were performed to estimate the statistic characteristics of the mass performance of the slab. A strength reduction factor was introduced and tabulated to account for the effects of geometric imperfections in the column radius and the column position. With the strength reduction factor, practitioners could quantitatively evaluate the effects of these geometric imperfections in design considerations. Practical recommendations on the column length and column spacing were also proposed.
Laboratory investigation of pore pressure dissipation in clay around permeable piles
(Canadian Science Publishing, 2017-12-19) Ni, Pengpeng; Mangalathu, Sujith; Mei, Guoxiong; Zhao , Yanlin
Excess pore water pressures induced by pile driving could have detrimental effect in the project, especially on the construction sequence and ground settlement. Measures that can effectively accelerate dissipation of pore pressures are therefore valuable. One way to reduce the pore pressure is the use of permeable piles. This paper presents a series of model-scale laboratory tests conducted on piles with drainage holes around the pile circumference. It is found that permeable piles could accelerate soil consolidation significantly, and the beneficial effect are more apparent for group pile tests. An approximate influencing zone of permeable piles was derived in this study based on the experimental observations.
A modified method for estimating the permeability of clayey soils based on piezocone sounding results
(Canadian Science Publishing, 2017-12-19) Chai, Jinchun; Chanmee, Nachanok
A modified method for estimating the permeability of clayey deposits in the horizontal direction (kh) based on piezocone sounding (uCPT) results was proposed. Most of the currently available methods relate the value of kh with the Δu/σꞌv0 ratio (∆u is the measured excess pore pressure from uCPT at the shoulder of the cone, and σ’v0 is the initial vertical effective stress at the measurement location). However, it has been understood that the effect of the overconsolidation ratio (OCR) on the Δu/σꞌv0 ratio is more significant than that on the value of kh. As a result, for an overconsolidated deposit, there is no suitable method for estimating the value of kh based on uCPT results. Based on the results of laboratory model uCPT, an empirical equation for considering the effect of the OCR on Δu/σꞌv0 and then kh corresponding to the yield vertical effective stress (σvmax) and initial vertical effective stress (σv0) for OCR > 1.0 is established. The modified method for kh corresponding to σvmax requires two parameters: OCR and a model parameter (α). In addition, for kh corresponding to σv0, two more soil parameters are needed: the swelling index (Cs) and the initial void ratio (e0). The methods for estimating these parameters are also proposed. Finally, the modified method was applied to three field case histories to show its usefulness.
Using molecular dynamics to unravel the phase composition behavior of nano-size pores in frozen soils-Does Young-Laplace equation apply in the low temperature range?
(Canadian Science Publishing, 2017-08-03) Zhang, Chao; Liu, Zhen; Deng, Peng
The phase composition curve of frozen soils is a fundamental relationship in understanding permafrost and seasonally frozen soils. However, due to the complex interplay between adsorption and capillarity, a clear physically-based understanding of the phase composition curve in the low temperature range, i.e., less than 265 K, is still absent. Especially, it is unclear whether the Young-Laplace equation corresponding to capillarity still holds in nano-size pores where adsorption could dominate. In this paper, a framework based on molecular dynamics simulations was developed to investigate the phase transition behavior of water confined in nano-size pores. A series of simulations was conducted to unravel the effects of the pore size and wettability on the freezing and melting of pore water. It is the first time that the phase composition behavior of frozen soils is analyzed using molecular dynamics. It is found that the Young-Laplace equation may not apply in the low temperature range.
Effect of various treatments on consolidation of oil sands fluid fine tailings
(Canadian Science Publishing, 2017-09-18) Wilson, G. Ward; Kabwe, Louis K.; Beier, Nicholas A.; Scott, J. Don
Regulatory policy and regulations in Alberta require oil sands companies to reduce their production and storage of fluid fine tailings by creating deposits that can be reclaimed in a timely manner. To meet the regulatory requirements, some companies are adding flocculants to the fluid fine tailings and then using thickeners, inline flocculation or centrifuges to increase the solids content. Freeze/thaw and drying processes are then used to further dewater the tailings. The effects of flocculating, thickening and freeze/thaw treatments were investigated by performing large strain consolidation and shear strength tests on these treated fluid fine tailings. The consolidation and shear strength results were then compared to those of untreated fluid fine tailings. All of the treatments increased the hydraulic conductivity of the fluid fine tailings to some degree, but had little to no effect on the compressibility and shear strength. The effects of the treatment processes are discussed and evaluated.
Back-analysis of geophysical flows using 3-dimensional runout model
(Canadian Science Publishing, 2017-10-13) Koo, R.C.H.; Kwan, J.S.H.; Lam, Carlos; Goodwin, Saoirse Robin; Choi, Clarence; Ng, C.W.W.; Yiu, Jack; Ho, K.K.S; Pun, W.K.
Predicting the mobility and delineating the extent of geophysical flows remains a challenge for engineers. The accuracy of predictions hinges on the reliability of input parameters of runout models. Currently, limited field data for landslide case histories are available for benchmarking the performance of runout models. Key rheological parameters, such as the equivalent internal friction angle, cannot be measured directly using laboratory experiments, and must instead be determined through back-analyses. A series of dynamic back-analyses was carried out for notable landslide case histories in Hong Kong, accounting for the effects of pore water pressure on the equivalent internal friction angle, using a three-dimensional finite-element mobility model. The recorded and simulated run-out distances, as well as lateral spreading, were compared. Results reveal that the back-analysed equivalent internal friction angles resulting from open-hillslope failures and from channelised geophysical flows are from 25째 to 30째, and 15째 to 20째, respectively. This is attributed to incised geophysical flow channels having an elevated water head and higher degree of saturation compared to open-hillside slope surfaces, wherein the induced elevated pore water pressure profoundly lowers the equivalent internal friction angle. The back-calculated values may be useful for finite-element-based design of mitigation measures.
Modelling Deformation and Strains induced by Waste Settlement in a Centrifuge Test
(Canadian Science Publishing, 2017-12-13) Yu, Yan; Rowe, Kerry
A numerical model to estimate the tensile strains (loads) of the geomembrane liner in the waste containment facility due to waste settlement is presented. A centrifuge test of the geomembrane-lined landfill is used to validate the numerical model. The calculated surface settlement at the centre of the landfill and the geomembrane tensile strains on intermediate benches are generally in good agreement with the measured data. Parametric analyses associated with foundation shear strength, interface shear strength and stiffness, and geomembrane stiffness are performed. The influence of geometric nonlinearity on the geomembrane tensile strains is also examined. The numerical analyses indicate that the maximum geomembrane tensile strain occurs at the crest of the side slope near the intermediate bench for the cases and conditions examined. The lessons learned are likely to be useful to landfill design engineers using numerical models to aid in the design of the geosynthetic liner system for the waste containment facilities.
Thermal effects on yielding and wetting-induced collapse of recompacted and intact loess
(Canadian Science Publishing, 2017-11-30) Ng, C.W.W.; Cheng, Qing; Zhou, Chao
Yielding and wetting-induced collapse are two important interrelated aspects of unsaturated loess behaviour. Previous studies on loess are generally under a single temperature condition. The principal objective of this study is to investigate thermal effects on yielding and wetting-induced collapse of recompacted and intact loess. Isotropic compression tests were carried out to determine yield stress at different suctions (0 and 100 kPa) and temperatures (5, 23 and 50째C). Moreover, wetting tests were conducted at various temperatures and stresses. The results of wetting tests were interpreted using the measured yield stress at various suctions and temperatures. It is found that yield stress decreases with decreasing suction (wetting-induced softening). The wetting-induced softening of recompacted loess is more significant at a higher temperature. The observed thermal effects on wetting-induced softening are likely because with decreasing suction, the stabilizing inter-particle normal force decreases more at a higher temperature. On the other hand, when the applied stress reaches the yield stress during wetting, yielding and plastic volumetric contraction can be observed. More importantly, wetting-induced contraction of recompacted loess at 50째C is about three times of that at 5째C. The larger contraction at 50째C is mainly because the wetting-induced softening is larger at a higher temperature
Effective Friction Angle of Clays and Silts from Piezocone Penetration Tests
(Canadian Science Publishing, 2017-12-12) Ouyang, Zhongkun; Mayne, Paul W.
An existing effective stress limit plasticity solution for piezocone penetration tests (CPTu) is calibrated to evaluate the effective stress friction angle (Φ’) for undrained conditions for a variety of soils ranging from natural lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic and glacio-fluvial origins. Data from 105 clay sites are compiled to examine the CPTu-interpreted Φ’ values in comparison with laboratory benchmark values obtained from CAUC/CIUC triaxial tests made on undisturbed samples. An approximate inversion of the theoretical solution is developed to allow profiles of Φ’to be evaluated with depth. Five well-documented case studies in Illinois, Louisiana, South Carolina, Ireland, and Massachusetts are presented to illustrate the application of the solution. Lastly, results from 1-g chamber tests involving kaolin and kaolinitic-silica mixtures tested by miniature piezocone probes are shown for additional verification.
Assessment of Rock Strength from Measuring While Drilling Shafts in Florida Limestone
(Canadian Science Publishing, 2017-11-13) Rodgers, Michael B; McVay, Michael; Horhota, David; Hernando, Jose
The focus of this research is the real time assessment of rock strength (unconfined compressive strength, qu) during drilled shaft installations in Florida Limestone; where measures of rock strength are provided through five monitored drilling parameters: torque, crowd, rotational speed, penetration rate, and bit diameter. In order to complete the study, both a laboratory and field investigation were required. This paper covers drill rig instrumentation, measuring rock strength during field drilling, and the comparative analysis of rock strength with conventional methods. Real time measurements were recorded for each drilling parameter and graphically displayed on an in-cab monitor and wirelessly transmitted to an external computer. Measures of rock strength were estimated using a laboratory developed equation with the monitored drilling parameters for real time field assessment. Measuring while drilling (MWD) in the field took place at three separate locations where drilled shaft load testing occurred. Comparative analyses between the monitored shaft installations and core samples subjected to unconfined compression indicated the results aligned well when recoveries were good. As recoveries diminished, the mean strengths were comparable, but more variable.
Accuracy assessment of default and modified FHWA simplified models for estimation of facing tensile forces of soil nail walls
(Canadian Science Publishing, 2017-12-03) Liu, Huifen; Tang, Liansheng; Lin, Peiyuan; Mei, Guoxiong
The accuracy of the default Federal Highway Administration (FHWA) simplified model for estimation of facing tensile forces for soil nail walls under in-service conditions was evaluated using a large number of measured long-term and short-term facing tensile force data collected from the literature. The estimation accuracy was quantified by the mean and coefficient of variation (COV) of the bias where bias is defined as the ratio of measured to calculated facing tensile force. Based on the available data, the default FHWA simplified model equation was found to overestimate long- and short-term facing tensile forces by about 15% and 23% on average, respectively. The corresponding spreads in estimation accuracy expressed as the bias COV were about 43% and 67%. Undesirable correlations between bias values and calculated facing tensile forces using the default FHWA simplified model equation were detected. A modified FHWA simplified model was proposed to improve the on average accuracy, reduce the spread in estimation accuracy, and remove the hidden correlations noted above. In addition, the modified equation has fewer empirical coefficients than the current formulation (i.e., four versus five). The facing tensile force equations developed in this study is a contribution to the design of facing of soil nail walls within the current FHWA soil nail wall design framework.
Thirty-ninth Canadian Geotechnical Colloquium: Unsaturated Soil Mechanics: Bridging the Gap Between Research and Practice
(Canadian Science Publishing, 2017-10-22) Siemens, Gregory A
The majority of geoengineering applications occur in the unsaturated zone, which is in the near-surface region forming the connection between meteorological phenomena above and saturated ground below. The key characteristic of the unsaturated zone is that water is in tension or, put another way, pore water pressure is negative. Moisture content, as well as most material properties, vary spatially and temporally in the unsaturated zone and coupled processes are common. In geoengineering applications in the vadose zone, unsaturated soils may be present during part or all of its design life. The question is how or when to consider the unsaturated soils principles in an analysis or design. Although most geoengineering applications have an unsaturated component, use of unsaturated soil mechanics in practice lingers behind the prolific number of publications due uncertain benefit of accounting for unsaturated effects, complexity, and conservativeness among other reasons. The focus of this colloquium is to continue bridging the gap by illustrating unsaturated soils principles using application-driven examples in the areas of capillarity as well as flow, strength, and deformation phenomena. As principles of unsaturated soils become more understood and demand increases for incorporating climate change effects in design, use of unsaturated soils principles in practice will continue to increase.
Global semi-empirical relationships for correlating soil unit weight with shear wave velocity by void-ratio function
(Canadian Science Publishing, 2017-11-28) Moon, Sung-Woo; Ng, Yannick C. H.; Ku, Taeseo
Numerous studies have attempted to relate shear wave velocity (V_s) to the geotechnical properties of soils. However, most correlations were empirically developed only for a particular site or soil type. In this study, we propose a novel approach to incorporate a generalized void ratio function with analytical phase relations for estimating the total unit weight of soils. Based on an extensively compiled soil database, the validation of semi-empirical model was carried out and its performance was also compared against existing V_s â total unit weight correlations. Moreover, a sensitivity analysis of the model input parameters was conducted to assess their significance on total unit weight estimates. It was demonstrated that the proposed semi-empirical model is successful in providing a first-order estimate of the total unit weight of soils based on the V_s, without the consideration of the overburden stresses.

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