Canadian Geotechnical Journal
Permanent URI for this communityhttps://hdl.handle.net/1807/67555
Published since 1963, this monthly journal features new developments in geotechnical and geoenvironmental engineering, and applied sciences.
Below is a collection of manuscripts accepted for publication in CGJ. These manuscripts have not undergone copy editing or page composition.
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Below is a collection of manuscripts accepted for publication in CGJ. These manuscripts have not undergone copy editing or page composition.
By using TSpace for its journal article repository, CSP grants University of Toronto Libraries a universal non-exclusive license to distribute and preserve all content that CSP deposits in the repository. Copyright of all articles in CSP journals remains with the authors, or the authors' organization, unless specified otherwise, TSpace users must follow the usage rights set out on CSP's web site. Refer to CSP's License to Publish Forms for information on current licensing.
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Item Open Access Field Performance of In-service Cast Iron Water Reticulation Pipe Buried in Reactive Clay(Canadian Science Publishing, 2015-04-30) Chan, Derek Chun Chuen; Gallage, Chaminda; Rajeev, Pathmanathan; Kodikara, JayanthaField monitoring is an important means for understanding soil behaviour and its interaction with buried structures such as pipeline. This paper details the successful instrumentation of a section of an in-service cast iron water main buried in an area of reactive clay where frequent water pipe breakage has been observed. The instrumentation included measurement of pipe strain; pipe water pressure and temperature; soil pressure, temperature, moisture content and matric suction, as well as the meteorological conditions on site. The data generally indicated that changes in soil temperature, suction and moisture content were directly related to the local climatic variations. The suction and moisture content data indicated that the soil profile at the site down to around 700 mm, and probably down to 1000 mm, is affected by changes in surface weather, while soil conditions below this depth appear to be more stable. Analysis of pipe strain indicated that the pipe behaves like a cantilever beam, with the top experiencing predominantly tensile strains during summer. Subsequently, these trends reduce to compressive strains as soil swelling occurs due to increase of moisture content with the onset of winter.Item Open Access Improvements to the Calculation of Actual Evaporation from Bare Soil Surfaces(Canadian Science Publishing, 2015-05-04) Tran, Dat T. Q.; Fredlund, Delwyn G.; Chan, Dave H.Evaporation of water from a saturated soil surface with ample free water is known as potential evaporation, PE, and the associated physical processes are quite well understood. However, evaporation of water from an unsaturated soil surface is known as actual evaporation, AE, and the associated physical processes are more complex and less understood. The calculation of actual evaporation is important for many geotechnical engineering applications. Soil suction and the corresponding water content at which the AE rate begins to depart from the PE rate during a drying process are re-assessed using a series of laboratory tests (i.e., thin soil section drying tests and soil column drying tests). Laboratory results show that the suction at which the actual rate of evaporation begins to depart from PE rate for soil columns (or thick soil layers) may be different than for thin soil layers. The suction at the “evaporation-rate reduction point”, (ERRP) appears to be approximately 3,000 kPa for thin soil layers, but is between the air-entry value and residual soil suction for thick soil layers or soil columns. The analyses presented in this paper have resulted in the development of a methodology for the estimation of the suction corresponding to the ERRP in soil columns. Equations are also proposed to calculate the coefficient of surface moisture availability, the vapour pressure and “surface resistance” at ground surface. The paper also presents an equation (i.e., new soil-atmosphere moisture flux equation) for predicting the evaporation rate from a soil surface using “surface resistance” to vapour water diffusion from the soil to the atmosphere. The proposed soil-atmosphere model is verified using evaporation rate data collected from various drying tests on thin soil layers and soil columns. Reasonably good agreement was found between the computed and measured rates of evaporation. The findings and recommendations in this paper contribute to an improved understanding of the prediction of AE from unsaturated soil surfaces.Item Open Access Examination of the estimation of relative permeability for unsaturated soils(Canadian Science Publishing, 2015-05-31) Zhang, Feixia; Fredlund, Delwyn G.The unsaturated permeability function is an important soil property function used in the numerical modeling of saturated-unsaturated soil systems. The permeability function is generally predicted by integrating along the soil-water characteristic curve (SWCC) starting at saturated soil conditions. The integration is based on a particular integral formula. The Fredlund-Xing-Huang permeability function is a flexible integration techniques used for calculating the unsaturated permeability function. The original permeability theory published by Fredlund et al., (1994) specified that the air-entry value, ψaev (AEV), be used as the lower limit of the integration when calculating the permeability function. However, since there was no analytical procedure available for the calculation of the air-entry value on the SWCC, it became common practice to start the integration procedure from a value near zero. The assumption was made that the error associated with starting the integration from an arbitrary low value was minimal. While this might be the case in some situations, the error can be quite substantial in other situations. This paper undertakes a study of the effect of the lower limit of integration on the calculation of the permeability function. Comparisons are made between starting the integration from various values below the AEV and starting the integration from the calculated air-entry value, ψaev. A mathematical algorithm is also proposed for the calculation of the AEV for integration purposes. The results show that the relative coefficient of permeability can be significantly under-estimated when the lower limit of integration is smaller than the AEV. The recommendation is that the AEV always be used as the lower limit of integration in the Fredlund-Xing-Huang permeability equation.Item Open Access Reactive Transport of Chemicals in Unsaturated Soils: Numerical Model Development and Verification(Canadian Science Publishing, 2015-06-23) Sedighi, Majid; Thomas, Hywel Rhys; Vardon, Philip JThis paper presents the development of a numerical model for reactive transport of multicomponent chemicals in unsaturated soils. The model has been developed based on a coupled thermal, hydraulic, chemical and mechanical formulation and extended by inclusion of geochemical processes under mixed equilibrium and kinetically controlled reactions in/between the solid, aqueous and gas phases in soil. This has been achieved by coupling the transport model (COMPASS) with geochemical model PHREEQC. Key coupling between the geochemical modelling and flow of chemicals has been established via the inclusion of porosity modification from mineral precipitation/dissolution reactions and the consequential effects on flow processes. Verification of the developed model is addressed via a series of benchmark simulations with a focus on testing the coupling between the transport model and geochemical model. Good results have been achieved for the verification of the theoretical and numerical implementation of the new developments in the model. A simulation is presented to demonstrate the effects of mineral reactions on porosity evolution and chemical diffusion in a low porosity soil. The model developed is an advanced tool for studying the hydro-geochemical processes in unsaturated soils under variable thermal, hydraulic, chemical and mechanical (THCM) conditions.Item Open Access Laboratory development of a vertically oriented penetrometer for shallow seabed characterization(Canadian Science Publishing, 2015-06-26) Sahdi, Fauzan; White, David; Gaudin, Christophe; Randolph, Mark F.; Boylan, NoelCurrent site investigation practice for offshore pipeline design relies on soil parameters gathered from boreholes or in-situ test soundings to depths of 1-2 m below the mudline. At these depths, the fine-grained seabed is very soft and possesses low undrained strength, which can be difficult to measure. This paper describes a centrifuge test programme undertaken to evaluate the feasibility and performance of a novel penetrometer designed to assess the shallow strength of soft seabed over continuous horizontal profiles. This device is termed the vertically oriented penetrometer (VOP). Tests were performed on a normally consolidated kaolin sample, with the VOP translated horizontally at velocities ranging from 1 – 30 mm/s, after embedding the VOP at 30 mm and 45 mm depths. All tests involved many cycles of VOP forward and backward movement to assess its potential to derive the ratio of intact to fully remoulded strength. Strength determination is achieved by dragging the VOP at a specified embedment depth along the soil surface, and deriving the soil strength from the measured resistance as if the VOP were a laterally loaded pile. The VOP is shown to yield comparable strength measurements to that of a T-bar penetrometer. The VOP is a potentially valuable addition to the range of tools used to characterize soil strength, both in small scale centrifuge models and, following practical development, potentially also in the field.Item Open Access Swelling phenomena and effective stress in compacted expansive clays(Canadian Science Publishing, 2015-07-01) Mašín, David; Khalili, NasserThe central aim of the paper is to discuss the applicability of the effective stress principle as defined by Terzaghi (total stress minus pore water pressure) to predict the behaviour of expansive clay aggregates. Phenomena occurring between individual clay minerals are reviewed first at the molecular level obtained in the colloid science research. In particular, it is noted that, for inter-particle distances higher than approx. 1.5 nm, the pore water pressure in bulk equilibrium solution forms an additive component of the inter-particle disjoining pressure. It is concluded that for these distances the Terzaghi's effective stress principle should be adequate to describe the clay behaviour. To support the developments, an extensive experimental database of nine different sodium and calcium bentonites available in publishhed literature was analysed. With the aid of double structure constitutive modelling, procedures were developed to extract the information on the behaviour of clay aggregates from the experimental measurements. It was then shown that unconfined water retention curves, swelling pressure tests, swelling under constant load tests and mechanical unloading tests are all uniquely related in terms of the dependency of dry density (or void ratio) of clay aggregate vs. mean effective stress. By considering reversibility of aggregate behaviour and full saturation of aggregates, this implies that the effective stress principle is valid in predicting expansive clay aggregate volumetric deformation.Item Open Access Reliability-Based Geotechnical Design in the 2014 Canadian Highway Bridge Design Code(Canadian Science Publishing, 2015-07-09) Fenton, Gordon A.; Naghibi, Farzaneh; Dundas, David; Bathurst, Richard J.; Griffiths, D. VaughanCanada has two national civil codes of practice that include geotechnical design provisions: the National Building Code of Canada and the Canadian Highway Bridge Design Code. For structural designs, both of these codes have been employing a Load and Resistance Factor format embedded within a Limit States Design framework since the mid-1970's. Unfortunately, Limit States Design in geotechnical engineering has been lagging well behind that in structural engineering for the simple fact that the ground is by far the most variable (and hence uncertain) of engineering materials. Although the first implementation of a geotechnical limit states design code appeared in Denmark in 1956, it was not until 1979 that the concept began to appear in Canadian design codes, i.e., in the Ontario Highway Bridge Design Code which later became the Canadian Highway Bridge Design Code (CHBDC). The geotechnical design provisions in the CHBDC have evolved significantly since their inception in 1979. This paper describes the latest advances appearing in the CHBDC along with the steps taken to calibrate its recent geotechnical resistance and consequence factors.Item Open Access On the quantitative determination of coal seam thickness by means of In-Seam Seismic Surveys(Canadian Science Publishing, 2015-07-09) Schott, Wolfgang; Waclawik, P.By means of ISS surveys carried out at Karvina coal mine of OKD, Czech Republic in two neighbouring panels it is shown how the distribution of the coal seam thickness can be investigated if the coal seam consists of almost pure coal. The coal seam under investigation was considerably affected by erosion which resulted in thickness changes amounting from about 30 cm up to around 4.40 m. By applying ISS tomographic inversion to the group travel-times for a constant frequency value first the distribution of the related group velocity was determined which already showed the extension of the erosions within the survey areas. By correlating the group velocity distribution with known values of the coal seam thickness along a gate a relation in terms of a polynomial approximation between these quantities could be derived. This relation is specific for a chosen frequency value and resolves in general only some thickness range. For the application presented in this paper a value of 200 Hz was chosen for the constant frequency value by which a range of the coal seam thickness from about 100 cm to about 300 cm was resolved. This was also the main objective of the surveys. For the investigation of a greater variation of the coal seam thickness (or even the complete thickness distribution) the described procedure has to be repeated for different constant frequency values. The final thickness map has then to be combined from the individual results for the different constant frequency values. The thickness range which had to be investigated by the surveys was in good agreement with the thickness encountered by mining the panel.Item Open Access Experimental study on dynamic interference effect of two closely spaced machine foundations(Canadian Science Publishing, 2015-07-09) Swain, Abhijeet; Ghosh, PriyankaThis paper presents an experimental study on the dynamic interaction effect of closely spaced square foundations under machine vibration. Under dynamic condition, a number of large-scale model tests were conducted in the field, which include a wide range of study on the isolated as well as the interacting footing response resting on the local soil available at Kanpur, India. The dynamic interaction of different combinations (size) of two-footing assembly was investigated by inducing vertical harmonic load on one of the footings (active footing), where the other footing (passive footing) was loaded with the static weight only. The active footing was excited with different magnitudes of dynamic loading and the response was recorded for both the footings, placed at different clear spacing (S). The results are compiled and shown as the variation of displacement amplitude with frequency. The transmission ratio, which predicts the effect of dynamic excitation of the active footing on the passive one, is determined for the interacting footings and plotted with respect to the frequency ratio.Item Open Access Effect of Hysteresis of Soil-Water Characteristic Curves on Infiltration under Different Climatic Conditions(Canadian Science Publishing, 2015-07-24) Bashir, Rashid; Sharma, Jitendra; Stefaniak, Natasja HalinaThis paper presents the results of a numerical modelling exercise to investigate the role of the hysteresis of soil-water characteristic curve (SWCC) on the infiltration characteristics of soils subjected to four different climatic conditions from very dry to wet within the Canadian province of Alberta. Multi-year climate datasets from four different natural regions and sub-regions of Alberta are compiled and classified and applied as the soil-atmosphere boundary condition in one-dimensional finite element unsaturated flow models using the Hydrus-1D software. Multiyear simulations are carried out with and without the consideration of SWCC hysteresis. Simulation results are analyzed in terms of water balance at the ground surface and temporal distribution and storage of water within the soil domain. It is demonstrated that the hysteresis of SWCC can significantly affect the prediction of flow, redistribution and storage of water in the unsaturated zone. It is found that for soils that exhibit hysteretic SWCC, consideration of hysteresis in unsaturated flow modelling results in prediction of lower infiltration and less movement of water through the soil. It is also found that the use of wetting parameters results in prediction of increased infiltration and movement of water compared with the predictions using the drying or hysteretic parameters. It is concluded that, for soils that exhibit greater degree of SWCC hysteresis, it is important to measure both the drying and the wetting branches of the SWCC accurately and that accurate simulation of hysteretic behaviour requires climate datasets at appropriate resolution. The results presented in this paper highlight the importance of considering SWCC hysteresis for a wide range of geotechnical problems, such as soil cover design, prediction of groundwater recharge, contaminant transport through unsaturated soils, soil erosion, slope stability, and swelling/shrinkage of expansive soils.Item Open Access Influence of initial fines content on fabric of soils subjected to internal erosion(Canadian Science Publishing, 2015-07-24) Ouyang, Mao; Takahashi, AkihiroSeepage-induced internal erosion often happens in earth structures. This paper presents experimental investigations on the influence of initial fines content on fabric of soils subjected to internal erosion. The tested materials were the binary mixtures of Silica No. 3 and Silica No. 8, which correspond to the coarse and fine fractions, respectively. One group of specimens was prepared with initial fines contents of 0, 15, 25 and 35% by weight, respectively. The undrained monotonic compression tests were performed on this group to examine the influence of fines content on the undrained behavior. The other group was prepared with initial fines contents of 15, 25 and 35% by weight, respectively, on which the seepage tests and subsequent undrained compression tests were carried out to demonstrate the mechanical influence of the internal erosion. The undrained behavior of the first group of specimens reveals that the presence of fines would decrease the peak and residual strengths. A comparison between the undrained behavior of soils with erosion and that of soils without erosion shows that the soils become less contractive after the internal erosion. When the axial strain is less than 0.4%, the undrained secant stiffness of soils with erosion is larger than that without erosion at the same axial strain. Meanwhile, the undrained peak strength and residual strength are larger for soils with erosion than that for soils without erosion. The less amount of excess pore water pressure is generated during the undrained compression for the eroded soils comparing to those of the uneroded soils. Furthermore, the eroded soils show a wider instability zone than that of the uneroded soils, which suggests that the instability zone be enlarged by the internal erosion. Besides, one-dimensional upward seepage tests were performed to investigate the change of fabric of the mixed sand with 15, 25 and 35% fines contents due to internal erosion. The recorded microscopic images of soils before and after erosion reveal that the fabric is altered by the internal erosion.Item Open Access Observations of hydraulic fracturing in soils through field testing and numerical simulations(Canadian Science Publishing, 2015-07-28) Chang, Muhsiung; Huang, Ren-ChungHydraulic fracturing is a potential cause for the leakage of earth dams or the loss of fluid in drilling and field permeability testing. Hydraulic fracturing is also a major concern on the effectiveness of soil grouting. Although hydraulic fracturing has been adopted in petroleum industry for decades for oil recovery in rock formations, studies on the fracturing in soils are relatively few and inconclusive. The aim of this study is to provide more insights on the mechanism of hydrofracturing in soils through a field grouting trial and numerical simulation. We observe hydraulic fracturing in soils dur-ing this field trial as predicted by generally accepted groutability requirements. The hydraulic frac-tures are found vertically developed up to the ground surface. Numerical simulations show the hy-draulic fracturing is easier to be initiated in anisotropic stress conditions, where the minor principal stress is the key factor. Numerical simulations also demonstrate significant compressions and shears during injection, suggesting the mechanism of fracturing in soils would be a shearing type. Based on this study, we propose a punching and splitting mode for the hydrofracturing in soils. The associated relationship for fracturing pressure estimation is verified and found in good agreement with the cases examined.Item Open Access Measuring Unsaturated Soil Deformations during Triaxial Testing Using A Photogrammetry-Based Method(Canadian Science Publishing, 2015-08-10) Li, Lin; Zhang, Xiong; Chen, Gang; Lytton, RobertWhen characterizing an unsaturated soil using the triaxial test apparatus, it is required to measure the soil deformation during loading. Recently, a photogrammetry-based method has been developed for total and localized volume change measurements on unsaturated soils during triaxial testing. In this study, more in-depth discussions on the photogrammetry-based method are addressed such as system setup, measurement procedure, accuracy self-check, data post-processing, and differences from the conventional image-based methods. Also, an application of the photogrammetry-based method on unsaturated soil deformation measurements is presented through a series of undrained triaxial tests with different loading paths. After testing, three-dimensional (3D) models of the tested soils at different loading steps were constructed based on the 3D coordinates of measurement targets on the soil surface. Clear barreling processes for soils during deviatoric loading were observed through the constructed 3D models at different axial strain levels. Soil volume changes and volumetric strain non-uniformities during isotropic and deviatoric loadings were extracted based upon detailed analyses on different soil layers. Through a full-field strain distribution analysis, a shear band evolution process was captured for the soil during deviatoric loading at a low confining stress. The photogrammetry-based method proved to be very powerful for in-depth soil deformation characteristics investigation.Item Open Access Finite Element Modeling of Lateral Pipeline-Soil Interactions in Dense Sand(Canadian Science Publishing, 2015-08-10) Roy, Kshama Sundar; Hawlader, Bipul C.; Kenny, Shawn; Moore, Ian D.Finite element (FE) analyses of pipeline-soil interaction for pipelines buried in dense sand subjected to lateral ground displacements are presented in this paper. Analysis is performed using the Arbitrary Lagrangian-Eulerian (ALE) method available in Abaqus/Explicit FE software. The pipeline-soil interaction analysis is performed in the plane strain condition using the Mohr-Coulomb (MC) and a modified Mohr-Coulomb (MMC) models. The MMC model considers a number of important features of stress-strain and volume change behaviour of dense sand including the nonlinear pre- and post-peak behaviour with a smooth transition and the variation of the angle of internal friction and dilation angle with plastic shear strain, loading conditions (triaxial or plane strain), density and mean effective stress. Comparing FE and experimental results, it is shown that the MMC model can better simulate the force-displacement response for a wide range of lateral displacements of the pipe for different burial depths, although the peak force on the pipe could be matched using the MC model. Examining the progressive development of zones of large inelastic shear deformation (shear bands), it is shown that the mobilized angle of internal friction and dilation angle vary along the length of the shear band, however constant values are used in the MC model. A comprehensive parametric study is also performed to investigate the effects of pipeline diameter, burial depth and soil properties. Many important aspects in the force-displacement curves and failure mechanisms are explained using the present FE analyses.Item Open Access Multi-scale Laboratory Evaluation of the Physical, Mechanical and Microstructural Properties of Soft Highway Subgrade Soil Stabilized with Calcium Carbide Residue(Canadian Science Publishing, 2015-08-16) Jiang, Ning-Jun; Du, Yan-Jun; Liu, Song-yu; Wei, Ming-Li; Horpibulsuk, Suksun; Arulrajah, ArulCalcium carbide residue (CCR) is an industrial by-product, stockpiles of which are rapidly accumulating worldwide. Highway embankment construction has been identified as an avenue to consume huge quantities of CCR as an economical, less energy intensive and environmental-friendly chemical additive for soil stabilization. Previous studies have investigated the mechanical behavior of soils stabilized by CCR or blends of CCR with other additives; however, interpretation of the macro-scale geomechanical behavior of CCR stabilized soft soils from a systematically microstructural observation and analysis is relatively unknown. This paper presents a multi-scale laboratory investigation on the physical, mechanical and microstructural properties of CCR stabilized clayey soils with comparison to quicklime stabilized soils. Several series of tests were conducted to examine the Atterberg limits, particle size distribution, compaction characteristics, unconfined compressive strength, California-Bearing-Ratio and resilient modulus of the CCR stabilized clayey soils. The influences of binder content, curing time, and initial compaction state on the physical and mechanical properties of treated soils are interpreted with the aids of physicochemical and microstructural observations including soil pH, soil mineralogy obtained from X-ray diffraction and thermogravimetric analysis, and pore size distribution obtained from mercury intrusion porosimetry. Soil particle flocculation and agglomeration at the early stage and pozzolanic reactions during the entire curing time, which originate from the finer particle size, greater specific surface area and higher pH value of calcium carbide residue, are the controlling mechanisms for the superior mechanical performance of CCR stabilized soils. The outcomes of this research will contribute to the usage of CCR as a sustainable and alternative stabilizer to quicklime in highway embankment applications.Item Open Access Analysis of the removability and stability of rock blocks by considering the rock bridge effect(Canadian Science Publishing, 2015-08-19) Zheng, Yinhe; Xia, Lu; Yu, QingchunIn traditional block theory, the removability and stability of rock blocks are analyzed independently; that is, the stability of a removable block is analyzed in detail, and non-removable blocks are regarded as stable. However, in practical situations, non-removable blocks may pose more danger than removable blocks. This paper presents a unified method for analyzing the removability and stability of rock blocks. In this method, the cracking of rock bridges is considered and non-removable blocks are not assumed to be stable. First, possible cracking rock bridges are identified by extending finite-sized fractures and comparing the boundary surfaces of the resulting blocks with those of the original blocks. Then, the sliding direction associated with each possible moving block is determined by solving an optimization problem. The normal force acting on each sliding surface is determined, and the resisting force on each rock bridge is calculated and integrated into the total resisting force when calculating the safety factor of a possible moving block. Procedures to determine all possible moving blocks are introduced, and the possible moving block with the minimum safety factor is regarded as the actual moving block. The corresponding minimum safety factor is defined as the actual safety factor of the block. The proposed method is verified by considering a few examples. The results show that non-removable blocks may be unstable if the cracking of rock bridges is considered.Item Open Access Long-term-effect of potassium chloride treatment on improving the soil behavior of highly sensitive clay – Ulvensplitten, Norway(Canadian Science Publishing, 2015-08-28) Helle, Tonje Eide; Nordal, S.; Aagaard, Per; Lied, Ole KristianRe-establishing high salt concentration in leached low-saline, highly sensitive clays significantly improves their mechanical properties. Long-term effects on quick clay exposed to diffusion of potassium chloride (KCl) from salt wells installed in 1972 at Ulvensplitten, Oslo, Norway, are investigated. The increased undrained and remolded shear strengthS, as well as increased Atterberg limits, remain thirty to forty years later. The undisturbed shear strength increased from less than 10 kPa to25-30 kPa, and the remolded shear strength increased from less than 0.5 kPa to more than 6 kPa. The liquid limit increased beyond the natural water content. Adding KCl to quick clay improved the properties to such an extent that it no longer appears as quick. Recent ground investigations in the area suggest a permanent effect on an engineering time-scale. Consequently the method may be suitable to prevent large flow slides in quick clay areas.Item Open Access Investigations on corrosion and mechanical properties of a 20-year-old ground anchor exhumed at a power station site(Canadian Science Publishing, 2015-09-03) Wang, Yujie; Ren, Aiwu; Wang, Yanshu; He, Jiquan; Chen, ZuyuThis paper presents the observed findings and laboratory test results of an anchor exhumed from Manwan hydropower station, China which was installed 20 years ago. The prestressed cables are 25.6 m long with a working load of 1000 kN. It consists of eight strands, and each strand consists of seven wires. The anchor was installed using the ‘single protection’ technique (i.e., the steel strands without greased sheath and was backfilled directly with cement mortar). The anchor was unearthed by excavating a 1.5 m 1.7 m tunnel. Visual inspection shows that the steel strands in the free and fixed lengths are basically stainless except for a few places where the grout failed to cover the anchor completely, thereby allowing direct contact of the strands with air. The magnitude of rebound of the tendon during the advancement of the tunnel face was simultaneously measured indicating a gradual release of bonding force, which was up to 62 % of the prestressed load. This shows that the existence of the bonding force is provided by the bonding between the strand and the grout, while this bonding does not exist in the ‘double protection’ system. The results of the mechanical test confirm that the tensile strengths in all the 33 steel wires exceed the requirement as specified by current Chinese Standard (NBS 1985). The concentrations of various chemicals also satisfy the requirements as specified by CSBTS (1999). The results of the X-ray Diffraction test show that the stains taken from the surface of the strand are composed of FeO and FeOOH, both being oxide products of iron. This shows that exposure of the material to air is an important condition to initiate corrosion. By following ASTM test procedure (ASTM International 1999), the average corrosion rate is found to be between 3-6 10-4 mm/year. This investigation generally supports the use of unprotected steel strands in rock anchor.Item Open Access Shear and normal stresses measured on the SLF Snow Chute(Canadian Science Publishing, 2015-09-03) Schaefer, MariusShear stresses on the running surface are believed to crucially determine the flow of snow avalanches. We present measurements of shear and normal stresses on the running surface as well as measurements of flow depth of snow flows down the SLF Snow Chute before and after a reduction of the chute's inclination. In the measurements before the inclination change, maxima of measured normal stresses agreed with the maxima of the normal component of the column weight calculated using pre-release snow density. After the reduction of inclination stresses increased considerably and the magnitude of the increase depended on the density of the flow. Using the measurements of normal stress and flow depth before the inclination change, a depth-averaged flow density was computed. The flow density was lower in the front and the tail of the avalanches and approached the pre-release density in the avalanche body. The ratio of measured shear to normal stresses, the coefficient of friction, was higher in wet snow flows than in dry snow flows. Analysing the dependence of the coefficient of friction on parameters varying between the experiments, we found higher coefficients of friction for higher densities, snow and air temperatures and average avalanche velocities. The total avalanche volume correlated negatively with the coefficient of friction. Measured coefficients of friction were generally lower as expected for flows of constant velocity which might indicate the importance of other frictional processes such as friction at the snow-air interface, which is supported by the evolution of small dilute snow clouds in top of the flows that consisted of dry snow.Item Open Access Application of an Advanced Bounding Surface Plasticity Model in Static and Seismic Analyses of Zipingpu Dam(Canadian Science Publishing, 2015-09-11) Esfahani Kan, Mojtaba; Taiebat, HosseinThe strong ground motion of Wenchuan earthquake which hit Zipingpu dam in China in 2008 has provided an excellent benchmark to study the behaviour of large modern rockfill dams subjected to seismic loading. The performance of the dam during construction and prior and after the earthquake loading has been recorded with good accuracy and provides a reliable database to examine the reliability of available constitutive models and numerical methods in predicting the static and dynamic behaviour of embankment dams. In this paper, an advanced bounding surface plasticity model has been used in a series of numerical analyses to study the static and dynamic behaviour of Zipingpu dam. The model can take in to account particle breakage that may occur in monotonic and cyclic loading of rockfill materials. The material parameters required for the model are calibrated based on the results of available monotonic and cyclic triaxial tests. In the numerical procedure the staged construction of the dam and the subsequent impounding of the reservoir are simulated followed by dynamic loading. At each stage, the results of the numerical analysis are compared with in situ monitoring records of the dam. The results of the numerical simulation and the displacements measured after the earthquake are also compared with those estimated by two simplified engineering procedures which are routinely used in practice. The effectiveness and applicability of the simplified procedures to such a large dam subjected to an earthquake with a long duration is also discussed.