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  • 1
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    Fractal characteristics of synthetic soil for cut slope revegetation in the Purple soil area of China (2012)
    Canadian Science Publishing
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    Publication Date: 2012-02-01
    Description: Ai, Y., Chen, Z., Guo, P., Zeng, L., Liu, H., Da, Z. and Li, W. 2012. Fractal characteristics of synthetic soil for cut slope revegetation in the Purple soil area of China. Can. J. Soil Sci. 92: 277–284. Revegetation of the cut slopes formed during railroad construction can reduce potential hazards, improve the quality of the environment, and beautify the landscape along the railways. Artificial backfill soil is required to anchor the plant roots and satisfy the plant's moisture and nutritional demands on the bare rock face. The soil particle size distribution (PSD), fertility and stability of the reconstructed topsoils are affected by the soil type used as a backfill. In this study, a fractal method was used to characterize the PSD. The relationships between the fractal dimension of the PSD and selected soil properties, including soil moisture, bulk density, and organic carbon are discussed. Various soil samples were obtained from four different land-use environments in the purple soil area in southwest, China: a cut slope reconstructed from rock fragments (RF), a cut slope reconstructed with agricultural soil (AS), a naturally developed slope (NS), and a cropland used for growing Vicia faba (CL). Analysis of the soil samples revealed that: (1) from CL to RF, the sand content increased from 59.6 to 83.9%; (2) the fractal dimension of PSD ranged from 2.605 for RF to 2.725 for CL, being the greater the sand content and the lower the fractal dimension; (3) there existed marked linear relationships between the fractal dimensions and selected physicochemical properties of the soils. Therefore, the fractal dimension of PSD can be a useful parameter with which to monitor the structural deterioration and nutrient loss of the synthetic soils used for the revegetation of a cut slope.
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 2
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    Limit equilibrium slope stability analysis using rigid finite elements (2008)
    Canadian Science Publishing
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    Publication Date: 2008-05-01
    Description: This paper revisits the interslice force assumptions associated with the method-of-slices approach to slope stability analysis. A brief review is presented on analysis procedures for this class of problem and a comparison is made between the factor of safety equations derived by Fellenius and a modified form of Bishop’s equation. A simplified rigid finite element method that takes into account progressive yielding through a sliding law is proposed, eliminating the need to provide constraint equations for the variation of interslice forces required by more advanced procedures, such as that developed by Morgenstern and Price. An example is given to demonstrate the proposed procedure and to investigate the sensitivity of the global and local factors of safety to the interslice and basal shear forces. It is demonstrated that the global factor of safety tends not to be sensitive to interslice shear forces when dealing with circular slip. For the slip circles that were analyzed, the Morgenstern and Price procedure yielded slice forces that were similar to those predicted by the proposed method, which takes into account the deformation and failure characteristics of the material comprising the slope.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 3
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    Shear strength, interparticle locking, and dilatancy of granular materials (2007)
    Canadian Science Publishing
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    Publication Date: 2007-05-01
    Description: The effect of particle angularity on the strength and dilation of granular materials is investigated through a series of laboratory tests on two materials, Ottawa standard sand (Sand O) and crushed limestone (Sand L), that are made up of rounded and angular particles, respectively. Triaxial tests on both materials at different confining pressures and initial void ratios show that particle angularity has a substantial effect on both the peak friction angle ϕp and the mobilized friction angle at the onset of dilation, ϕf. It is found that ϕf is smaller than the critical friction angle ϕcv for Ottawa sand; nevertheless ϕf is larger than ϕcv for Sand L owing to interparticle locking induced by particle angularity. The experimental results clearly show the contributions to shear resistance from both dilation and interlocking, with interlocking still largely existing at the peak stress ratio but not at the critical state. Suggestions are made to modify the stress–dilatancy formulations for sand to take into account the effect of interparticle locking associated with particle angularity.Key words: granular material, dilatancy, interlocking, and particle shape.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 4
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    Frost heave and thaw consolidation modelling. Part 1: A water flux function for frost heaving (2020)
    Canadian Science Publishing
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    Publication Date: 2020-10-01
    Description: Although much effort has been made to develop various frost heave models in the past decades, a simple yet versatile model is still needed for engineering applications. This paper presents a method to estimate frost heave in frozen soil using a macroscopic water flux function that extends the segregation potential to make it applicable for both steady state and transient freezing and thawing states. The formation of an individual ice lens is modelled by combining previously developed stress and strain criteria. The water flux function, which includes various factors in accordance with the porosity rate function, can describe the growth of both new and old ice lenses. More importantly, every component of the water flux function is physically explained by the theory of pre-melting dynamics, where all the influencing factors are traced back to their impacts on the ice volume distribution. The performance of the model is demonstrated via simulations of one-dimensional freezing and thawing processes after the model is validated by a specific case from previous literature. Although adequate data are not available for a stricter experimental verification of the model, it is observed that the simulations predict the general course of events together with significant specific features that were identified in previous experimental studies.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 5
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    Observed long-term differential settlement of metro structures built on soft deposits in the Yangtze River Delta region of China (2020)
    Canadian Science Publishing
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    Publication Date: 2020-06-01
    Description: In this study, the measured differential settlements of five metro lines built on soft deposits were analyzed. The different structural combinations at various characteristic locations in the metro lines were examined, including at 67 joints of stations and tunnels, 55 connecting passage locations, 4 wind well locations, and at 3 joints of U-shaped grooves and adjacent structures. Moreover, the differential settlement between the track slabs and the bridge piers of a 16.57 km long elevated structure was analyzed. The results showed that the settlements of ∼85% of the stations were less than those of adjacent shield tunnels, and the settlements at the connecting passages of ∼73% of the tunnels were greater than those on either sides of the tunnel. The wind well exhibited lower settlement than its adjacent tunnels. The settlement of the U-shaped groove was greater than that of its adjacent elevated structure, but was less than those of the cut-and-cover and shield tunnels. Approximately 86% of the track slabs exhibited arch deformation, and the settlements of the bridge piers were greater than those of the track slabs. The stiffness transition between the different structures should be considered in the design of metro structures on soft deposits.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 6
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    Experimental study of the evolution of soil arching effect under cyclic loading based on trapdoor test and particle image velocimetry (2020)
    Canadian Science Publishing
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    Publication Date: 2020-06-01
    Description: Arching effect, which is a common phenomenon in any system involving soil–structure interaction, has been found to be inevitably affected by various factors, including loading conditions. This study investigated the evolution of arching effect induced by cyclic loading by conducting a series of tests using a trapdoor apparatus. The test box was instrumented to control the displacement of the moving gate and to record the variation of vertical stress distribution by using a set of dynamic load cells. Digital images were captured during tests and processed using particle image velocimetry (PIV) to determine the displacement field and hence to examine the variation of geometric features of arch and particle movements. The evolution process of arching effect, from the initial formation to the finial collapse, was identified. Depending on the analysis for the geometry appearance, displacement region, and variation of cyclic stresses, both stable and collapsed arches were observed. By increasing the amplitude of cyclic loading step by step, critical loading amplitude corresponding to the threshold of collapse of the arching effect was determined. Based on the results, the effects of trapdoor displacement, cyclic loading frequency, and filling height on arching effect are discussed.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 7
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    A practical approach to falling-weight deflectometer (FWD) data reduction (2005)
    Canadian Science Publishing
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    Publication Date: 2005-04-01
    Description: The authors present a simplified methodology for preprocessing falling-weight deflectometer (FWD) data, which identify a pseudo-static pavement response to surface loading. This allows one to employ static analysis to back-calculate the mechanical properties of the pavementsubgrade system. It is shown that the subgrade modulus can be identified, independent of the details of the pavement structure itself, at least for a two-layer system. The quality of the effective shear modulus is sensitive to the value of Poisson's ratio selected.Key words: pavementsubgrade system, subgrade modulus, back-calculation, FWD.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
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  • 8
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    Frost heave and thaw consolidation modelling. Part 2: One-dimensional thermohydromechanical (THM) framework (2020)
    Canadian Science Publishing
    Details
    Publication Date: 2020-10-01
    Description: This paper presents a thermohydromechanical framework to model frost heave and (thaw) consolidation simultaneously, in which effective and total stresses are taken as the stress variables for unfrozen and frozen soils, respectively. “Effective (total) stresses – void ratio – permeability” relations are proposed to interpret the frost heave behavior of soil in different cooling modes, (thaw) consolidation processes, and changes in key parameters induced by freeze–thaw cycles. The water flux function proposed by Yu et al. in a companion paper is used to calculate frost heave in the frozen zone and to determine the moving boundary of the unfrozen zone during thaw consolidation. Compared with conventional methods, two other modifications are made to characterize the effect of residual stress and the influence of freeze–thaw cycling on permeability in the thaw consolidation analysis. After the governing equations developed in Lagrangian coordinates are implemented in a finite-element system, the framework is firstly verified by a comparison with both small- and large-strain thaw consolidation theories, in terms of simulating a semi-infinite thaw consolidation case, and is then examined with a focus on the three modifications one-by-one. Following that, the framework is assessed by two numerical examples that reasonably reproduce the freeze–thaw cycling processes in both seasonal frost and permafrost regions.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 9
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    A physically meaningful homogenization approach to determine equivalent elastic properties of layered soil (2018)
    Canadian Science Publishing
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    Publication Date: 2018-03-01
    Description: A simple, yet physically meaningful, homogenization approach to determine the “equivalent” elastic properties for a layered medium is proposed. The proposed approach makes use of the Reuss and Voigt approximations without employing auxiliary stresses and strains related to the different elastic properties of the material layers. When assuming that the constituent materials are isotropic, some special features of the equivalent homogeneous medium are discussed for special cases in which all layers have either the same Poisson’s ratio, elastic modulus or shear modulus. A methodology to determine the equivalent anisotropic elastic properties of multi-layered soils is proposed, in which all required quantities are physically meaningful and can be determined directly. The applicability of the proposed methodology is demonstrated through tests on two types of soils, one of which has a varved structure while the other is isotropic.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
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  • 10
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    A look at the use of an equivalent homogeneous medium (2007)
    Canadian Science Publishing
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    Publication Date: 2007-05-01
    Description: The technique of homogenization is important in modeling. It allows the scope of the numerical problem to be reduced, thus making the analysis computationally more efficient and allowing the engineer to focus on important larger scale features that influence overall behaviour rather than getting caught up in details that can also lead to numerical difficulties. This paper begins by demonstrating using photoelasticity the importance of taking into account layering details. The inability to capture stress variations due to homogenization is also demonstrated by comparing finite element solutions that take into account details with those which do not. The paper then investigates the consequences of homogenizing a layered system to express its stress–strain response in terms of an equivalent homogeneous anisotropic medium. This is accomplished by analyzing via the finite element method an idealized layered system and comparing the averaged constitutive relation from the numerical solution with that corresponding to an equivalent homogeneous transverse isotropic medium. Thereafter, stress and failure patterns corresponding to a structured medium are examined, as are the consequences of free surfaces and interfaces between layers on the nonhomogeneity of failure.Key words: homogenization, layered soils, photoelasticity, finite element analysis.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
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