bluuebunny/crossref_metadata_2025 huggingface dataset:
Ground Deformations Resulting from Shield Tunnelling in London Clay
Authors: Attewell P. B. , Farmer I. W.
Published: April 2011

The paper describes the results of a field measurement program aimed at determining the ground movements created by the hand excavation of a 4.146 m diameter shield-driven tunnel at a depth of 29.3 m in stiff, fissured, heavily overconsolidated London clay. Approximately half of the recorded maximum surface settlement of 6.1 mm is both measured and calculated to have taken place during passage of the shield, the remainder being attributed to post-shield deformations. Calculations are based on a field and laboratory-determined average radial yield rate for the clay at the tunnel of 0.0055 mm/min. It is concluded that a normal probability surface settlement profile is developed over the shield and tail.Post-shield inward decompressions (K0 ≈ 1.65) and possible recompression as a clay–grout interaction effect could then be responsible for a slight reconsolidation of the clay at soffit and for distortion of the final settlement profile out of concordance with an error curve.
Repeated load testing of a model plane strain footing
Authors: Raymond Gerald P. , Komos Fadel El
Published: April 2011

A study is reported of experiments on model plane strain footings subject to repeated loading. The load was returned to zero at the end of each cycle. This is characteristic of a train wheel load passing over a railroad tie.Four series of tests were conducted. Series A consisted of static tests, which provided a comparison with series B. Series B consists of applying a cyclic load on the footing between zero load and a constant upper value. The upper value was varied from test to test and ranged from 13.5 to 90% of the static failure load. Series C was acyclic test that was a continuation of series B after a considerable deformation had occurred. The berms caused by the cyclic load test of series B were removed and a second cyclic test was conducted on the same foundation soil as the original test. Series D was a static test that was done as a continuation of series B. After removing the berms, as in series C, a static test was conducted in a manner similar to that for series A.The results have been quantified by the use of a hyperbolic fit and show that wider footings should perform better than narrower ones. This has been substantiated by examination of experimental railroad tests conducted by the Association of American Railroads.
Review of engineering behaviour of marine clays in Eastern Canada
Authors: Penner E. , Burn K. N.
Published: April 2011

Leda clay deposits are thought to belong to a single marine episode that sedimented in the Champlain Sea between 12000 and 9000 years BP. Differential uplift ended the marine episode and subsequent sediments were deposited in estuarine followed by near-freshwater to lacustrine conditions. Rock-forming minerals consisting of feldspars, quartz and amphiboles make up a large part of the clay size fraction. The dominating phyllosilicates are micas and illites, or hydrous micas. The fabric of the deposit consists of an assemblage of silt and clay size rock fragments in which clay minerals are generally randomly oriented.Major engineering problems are reviewed against the background of depositional history, nature of the soil fabric formed during sedimentation, subsequent structural alterations, mineral composition and pore water chemistry, all among the more important factors responsible for the engineering behaviour of these soils.
Frost-heaving rate predicted from pore-size distribution
Authors: Reed M. A. , Lovell C. W. , Altschaeffl A. G. , Wood L. E.
Published: April 2011

The purpose of this study was to examine the relation of frost heave to pore-size distribution of compacted silty soils, and to propose that frost-susceptibility criteria based upon the distribution of porosity are more logical and versatile than those based upon texture and grain size.Rapid freezing laboratory tests were conducted to evaluate the heaving rate. The soils were compacted at different energy levels and water contents, and consisted of three different combinations of silt and kaolin.Mercury intrusion tests were performed to obtain the pore-size distributions of the compacted soils. Since this procedure requires the soil to be free of moisture, the soil samples were freeze-dried. This type of drying minimized the volume change and consequent structural modification expected from air or oven drying.The relation of frost heave to pore size was obtained using the method of linear regression. For a given soil, it is the quantity of interaggregate pores that controls the frost heave. These pores are, in turn, controlled by the compaction variables of water content and effort.
Observations on moisture migration in frozen soils
Authors: Mageau D. W. , Morgenstern N. R.
Published: April 2011

Artificially prepared, previously frozen specimens of a clayey silt have been subjected to thermal gradients under both closed and open systems. Direct observation of moisture content changes reveals that substantial amounts of water are imbibed by frozen soil under an open system. If an ice lens exists within the system, the increase in water content on the cold side of the lens is small compared with that on the warm side. Heave rate is governed primarily by the frozen fringe of soil between the warmest ice lens and the frozen–unfrozen interface.
The hydraulic failure of a cofferdam
Authors: Bauer G. E. , Scott J. D. , Shields D. H. , Wilson N. E.
Published: April 2011

The method of control of water in open excavations by pumping from sumps, from deep wells, or from well points is such an accepted practice that sometimes little attention is given to its complex and difficult hydraulic nature.This paper describes the causes leading to a hydraulic failure of a 15 m deep temporary sheeted cofferdam required to found a concrete slab for a pump house. The construction of the new pump house was for the extension of facilities of a sewage treatment plant. The piping failure caused a considerable construction delay and it also served as a field case to reassess the construction procedure of the excavation and the inadequacy of the well point installation.
Soft zones in the glacial till in downtown Edmonton
Authors: Thomson S. , Martin R. L. , Eisenstein Z.
Published: April 2011

High-rise buildings in downtown Edmonton have generally been founded on spread footings in glacial till. Early geotechnical work proposed a geological model comprising uniform, very dense basal (lodgement) till. However, recent work shows that the till is more complex, being variable in both material type and consistency. A case history is described that exemplifies this variability. It is concluded that early experience with the dense tills has led to an overconfident approach to soil investigation in this area and that a thorough site investigation is required.
On the stability of supported excavations
Authors: Britto A. M. , Kusakabe O.
Published: April 2011

Unsupported plane strain trenches and axisymmetric shafts cannot be excavated to great depths in a purely cohesive soil. Therefore, it is standard practice to provide some form of support. Timber supports with struts are conventional and quite common. Bentonite slurry support has become more popular in recent years especially in the construction of diaphragm walls. In this paper the effect of rigid lateral support and slurry support on the stability (mode of failure) for both plane strain and axisymmetric excavations are investigated under undrained conditions. When immediate failure is of interest in saturated clays the changes in the water content can be neglected and the soil can be treated as a [Formula: see text] material. For the purposes of the analyses presented here the lateral support is assumed to be rigid and the soil is idealized as an elastic perfectly plastic material with cohesion Cu. The results from upper bound calculations, finite element collapse analyses, and centrifuge tests are presented. The analogy between deep footing failure and base failure of excavation allows the solutions for the footing problem to be interpreted for trench excavations. It is found that slurry support is more effective than rigid lateral support for axisymmetric excavations. The slurry support reduces the amount of surface settlement and also stabilises the trench against base failure. For excavations with rigid lateral support the possibility of base failure is greatly increased. The results are presented in the form of stability charts. Keywords: limit analysis, slurry support, stability number, supported excavation, upper bound solution.
The behaviour of clay shales in water
Authors: Seedsman Ross
Published: April 2011

A set of clay shales associated with coal measure strata has been examined to determine the mechanisms that lead to slaking on immersion in water. The two main mechanisms for the slaking of small unconfined samples are (a) compression of entrapped air and (b) osmotic swelling of expansive clay minerals if the dominant exchangeable cation is sodium. In the absence of osmotic swelling, pore-air compression can induce slaking in clay shales of bulk densities less than 2.27 Mg/m3. Osmotic swelling of clay shales occurs in samples with bulk densities less than about 2.45 Mg/m3, but slaking by this mechanism occurs only for samples with densities less than 2.34 Mg/m3. Dispersion of clay from clay shales develops only after slaking commences, and the extent of dispersion depends on the nature of the interparticle bonds. Key words: clay shales, clays, coal measure rocks, slaking, dispersion, porosity, density.
Identifying hydraulically conductive fractures with a slow-velocity borehole flowmeter
Authors: Hess Alfred E.
Published: April 2011

The U.S. Geological Survey used a recently developed heat-pulse flowmeter to measure very slow borehole axial water velocities in granitic rock at a site near Lac du Bonnet, Manitoba, Canada. The flowmeter was used with other geophysical measurements to locate and identify hydraulically conducting fractures contributing to the very slow vertical water flow in the two boreholes selected for study. The heat-pulse flowmeter has no moving parts and operates on the tag–trace principle. It is an improved version of the flowmeter developed by the Water Research Centre in England in 1975. The U.S. Geological Survey's heat-pulse flowmeter has a flow-measuring range in water of 0.06–6 m/min, and can resolve velocity differences as slow as 0.01 m/min. This is an order of magnitude slower than the stall speed of spinner flowmeters. The flowmeter is 1.16 m long and 44 mm in diameter. It was calibrated in columns of 76 and 152 mm diameter, to correspond to the boreholes studied. The heat-pulse flowmeter system is evaluated, and problems peculiar to the measurement of very slow axial water velocities in boreholes are discussed. Key words: flowmeter, borehole flow, low flow, borehole geophysics.
Geotechnical aspects of recovery processes in oil sands
Authors: Settari A. , Ito Y. , Fukushima N. , Vaziri H.
Published: April 2011

The geomechanical aspects of oil sand behaviour are important for the understanding of the thermal processes for bitumen recovery from oil sands. The paper describes the study of the geomechanical response of oil sand to fluid injection, which causes formation parting in oil sands. The behaviour of constitutive models in the low effective stress range is examined, and it is shown by modelling that the frictional properties at low effective stress control the development of the failure zone around injection wells and fractures. Based on the matching of laboratory data for the PetroCanada–CanOXY–Esso–JACOS (PCEJ) project, a generalized hyperbolic model is proposed. Modelling of a field design involving horizontal fracture shows that the stress paths and the amount of dilation experienced by the formation can be very different from those measured in standard laboratory tests. Laboratory measurements should be done at the very small stresses and along the stress paths expected in the field. These can be predicted by modelling. Key words : oil sands, constitutive models, fluid injection, hyperbolic model, sand dilation, horizontal fracture, oil sands modelling, bitumen recovery, sand failure.
A reexamination of the permeability index of clays
Authors: Babu G. L. Sivakumar , Pandian N. S. , Nagaraj T. S.
Published: April 2011

The permeability index Ck, similar to the compression index, is the slope of the void ratio – coefficient of permeability relationship. Literature shows that, in general, for sensitive clays it can be related to initial void ratio by Ck = 0.5e0. The possibility of obtaining such a relationship for Cochin marine clays in terms of liquid limit void ratio is indicated in this paper. Analysis of permeability behaviour of Cochin marine clays and the test results available in published literature using generalized state parameter approach show that, in principle, these forms of equations for the permeability index are tenable, even though they were obtained based on experimental observation alone. Key words : permeability index, initial void ratio, void ratio at liquid limit, generalized state parameter approach.
Effect of rainfall on matric suctions in a residual soil slope
Authors: Lim T T , Rahardjo H , Chang M F , Fredlund D G
Published: April 2011

A slope stability study involving shallow slip surfaces should include the effect of negative pore-water pressures in a slope. A field instrumentation program was carried out to monitor negative pore-water pressure (i.e., in situ matric suction) in a residual soil slope in Singapore. Variations in matric suction and the matric suction profiles under (1) a canvas-convered grassed surface, (2) a grassed surface, and (3) a bare ground surface, in response to rainfalls were investigated. Changes in matric suction due to changes in climatic conditions decrease rapidly with depth. The change was found to be most significant in the bare slope and least significant under the canvas-covered slope. The amount of decrease in matric suction after a rainstorm was observed to be a function of the initial matric suction just prior to the rainstorm. Positive pore-water pressures were observed above the groundwater table, suggesting the development of a perched water table within the slope. These observations are also typical of other regions experiencing high seasonal rainfalls. The field monitoring program presented can be adopted for investigating rainfall-induced landslides in other parts of the world.

Key words: matric suction, negative pore-water pressure, field instrumentation, rainfall, residual soil, slope stability.
Swelling and softening behaviour of La Biche shale
Authors: Wong RCK
Published: April 2011

Free swell, semiconfined swell, and one-dimensional oedometer swell tests were performed on La Biche shale specimens in solutions of different salinities. The swelling behaviour of La Biche shale was found to be highly anisotropic and dependent on electrolyte concentration, stress, and swelling history. Drained triaxial compression tests were conducted on La Biche shale specimens subjected to different degrees of swelling. The test results indicate that the Young's modulus decreases with increasing swelling. The strength loss due to swelling can be explained by the Hvorslev failure theory. A descending power law is proposed to describe the cohesion reduction with the swelling.Key words: shale, salinity, swelling, strength weakening, modulus softening.
Static liquefaction of sands under multiaxial loading
Authors: Uthayakumar M , Vaid Y P
Published: April 2011

A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.
Detecting a hydraulic short circuit along a monitoring well with the recovery curve of a pumping test in a confined aquifer: method and example
Authors: Chapuis Robert P , Chenaf Djaouida
Published: April 2011

It is important to verify if a monitoring well was correctly sealed into the ground to avoid preferential flow between aquifer layers (hydraulic short circuit). Previous papers have shown how to check this by variable-head permeability tests interpreted with the velocity-graph method. This paper presents a new method to make this check with the recovery curve of an aquifer test. The theory of this new method is presented. When there is a hydraulic short circuit, the drawdowns and recoveries due to a pumping test in a confined aquifer do not yield unique values of transmissivity and storativity as they should theoretically. An example is provided, that of monitoring well E1 of the Pelican River aquifer test. The pumping phase was interpreted using the methods of Theis and Cooper-Jacob. The recovery phase was interpreted by two methods: (i) the usual graph of sprime versus log (t/tprime) gave transmissivity T and either the Jacob method or the U.S. Department of the Interior Ground Water Manual gave storativity S; and (ii) the method of (sp - sprime) versus log tprime gave both T and S. As a result, four values of T and S were obtained. They differed by 9% for T and by 186% for S. According to the proposed method there was a hydraulic short circuit close to the monitoring well: it gave an initial water level that differed from the real piezometric level by 40 cm. Drawdown and recovery values were corrected for reinterpretation. The new log-log and semilog graphs yielded identical T and S values, thus validating the diagnosis of a hydraulic short circuit and illustrating the detection method.Key words: monitoring well, pumping, recovery, quality control, transmissivity, storativity.
Hoek-Brown parameters for predicting the depth of brittle failure around tunnels
Authors: Martin C D , Kaiser P K , McCreath D R
Published: April 2011

A review of underground openings, excavated in varying rock masstypes and conditions, indicates that the initiation of brittlefailure occurs when the damage index, Di, expressed as theratio of the maximum tangential boundary stress to the laboratoryunconfined compressive strength exceeds approx0.4. When thedamage index exceeds this value, the depth of brittle failure around a tunnel can be estimated by using a strengthenvelope based solely on cohesion, which in terms of theHoek-Brown parameters implies that m = 0. It is proposed that inthe brittle failure process peak cohesion and friction are notmobilized together, and that around underground openings thebrittle failure process is dominated by a loss of the intrinsiccohesion of the rock mass such that the frictional strengthcomponent can be ignored for estimating the depth of brittlefailure, an essential component in designing support for theopening. Case histories were analyzed using the Hoek-Brownfailure criterion, with traditional frictional parameters, and withthe proposed brittle rock mass parameters: m = 0 and s = 0.11. Theanalyses show that use of a rock mass failure criteria withfrictional parameters (m > 0) significantly underpredicts thedepth of brittle failure while use of the brittle parametersprovides good agreement with field observations. Analyses usingthe brittle parameters also show that in intermediate stressenvironments, where stress-induced brittle failure is localized, atunnel with a flat roof is more stable than a tunnel with anarched roof. This is consistent with field observations. Hence,the Hoek-Brown brittle parameters can be used to estimate thedepth of brittle failure around tunnels, the support demand-loadscaused by stress-induced failure, and the optimum geometry of theopening.Key words: spalling, depth of failure, rock mass strength, brittle failure criterion, cohesion loss, Hoek-Brown brittle parameters
An examination of simplified earthquake-induced displacement procedures for earth structures
Authors: Rathje Ellen M , Bray Jonathan D
Published: April 2011

A critical examination of the procedures commonly used to estimate earthquake-induced sliding displacements of earth structures is essential due to their widespread use and application to new types of systems such as solid-waste landfills. Rigid sliding block analyses are performed, along with decoupled and fully coupled deformable sliding block analyses using a distributed mass model with a mode shape appropriate for an earth structure. Results from using several earthquake ground motions and a sinusoidal input indicate that a decoupled analysis does not always provide a conservative estimate of sliding displacement. Conservative decoupled displacements are calculated for lower values of yield acceleration (i.e., ky/kmax < 0.6) when the fundamental period of the sliding mass is less than twice the mean period of the input ground motion. For systems with larger values of ky/kmax or large fundamental periods, a decoupled analysis may predict smaller displacements than a fully coupled analysis. However, in these cases, the displacements calculated from both analyses are generally small (i.e., less than a few centimetres). A decoupled analysis generally provides an estimate of the coupled sliding displacement within a factor of three, which is conservative, except for particular cases where caution is warranted. A rigid sliding block analysis can be significantly unconservative, and it should not be used.Key words: computation, decoupled, displacements, embankments, seismic performance, seismic response, soil dynamics, solid-waste landfills.
Seismic site response in the greater Vancouver, British Columbia, area: spectral ratios from moderate earthquakes
Authors: Cassidy John F , Rogers Garry C
Published: April 2011

Three-component, digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater Vancouver area, particularly on the Fraser River delta. The 1996 M = 5.1 Duvall, Washington, earthquake (180 km southeast of Vancouver) triggered strong-motion seismographs at seven sites and the 1997 M = 4.3 Georgia Strait earthquake (37 km west of Vancouver) triggered instruments at 13 sites in the greater Vancouver area. The latter data set is especially important because it contains the first three-component recordings made on bedrock in greater Vancouver. Both data sets represent weak ground motion, with peak horizontal accelerations of 0.5-1.5% gravity (g) for the Duvall earthquake, and 0.2-2.4% g for the Georgia Strait earthquake. Using the method of spectral ratios, we estimate the site response for each of the strong-motion instrument soil sites. On the Fraser River delta amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period), with peak amplification of 4-10 (relative to competent bedrock) for the thick soil delta centre sites, and about 7-11 for the delta edge sites. Relative to firm soil, the peak amplification ranges from 2 to 5 for the thick soil delta centre sites, and 2 to 6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation, is observed.Key words: seismic site response, Fraser delta, earthquakes.
A relationship describing the shear strength of unsaturated soils
Authors: Rassam Daud W , Williams David J
Published: April 2011

A relationship describing the shear-strength profile of a desiccating soil deposit is essential for the purpose of analysis, especially when a numerical method is adopted where each zone in a discretised grid is assigned an elevation-dependent shear-strength value. The matric-suction profile of a desiccating soil deposit is nonlinear. Up to the air-entry value, an increase in matric suction is associated with a linear increase in shear strength. Beyond air entry, as the soil starts to desaturate, a nonlinear increase in shear strength occurs. The soil-water characteristic curve is stress dependent, as is the shear-strength gain as matric suction increases. In this paper, a three-dimensional, nonlinear regression analysis showed that a power-additive function is suitable to describe the variation of the shear strength of unsaturated soils with matric suction. The proposed function incorporates the effect of normal stress on the contribution of matric suction to the shear strength.Key words: air-entry value, matric suction, nonlinear regression, soil-water characteristic curve, tailings, unsaturated shear strength.
Tension tests on smooth and rough model piles in dry sand
Authors: Alawneh Ahmed Shlash , Malkawi Abdallah I. Husein , Al-Deeky Husein
Published: April 2011

In order to delineate the significant variables affecting the ultimate uplift shaft resistance of a pile in dry sand, a testing program comprising 64 pullout tests was conducted on open- and closed-ended rough and smooth model piles of two sizes (41 and 61 mm outside diameter). The model piles were installed in medium dense and dense sand to an embedded depth of 0.8 m using two methods of pile placement, static jacking and driving. A rigid steel box measuring 1.1 × 1.1 × 1.3 m was used as a sand container. The results obtained from this study indicated that pile placement method, initial sand condition, pile surface roughness, and pile end type are all significant variables (given in descending order) affecting the ultimate uplift shaft resistance of a single pile in dry sand. Overall, the closed-ended piles showed a 24% increase in shaft resistance compared with the open-ended piles and the average unit shaft resistance of the driven model pile was 1.33 times that of the jacked model pile in the dense sand condition and 1.52 times that of the jacked model pile in the medium dense sand condition. Depending on the test variables, the rough model piles tested in this study experienced a 12-54% increase in capacity compared with the smooth model piles. Also, the lateral earth pressure coefficient values for the rough model piles were greater than those for the smooth model piles. This suggests that part of the increase in capacity due to pile surface roughness is attributed to an increase in the radial effective stress during tensile loading.Key words: piles, shaft resistance, pile placement method, smooth pile, rough pile.
Pore pressure on a submarine pipeline in a cross-anisotropic nonhomogeneous seabed under water-wave loading
Authors: Jeng D S , Lin Y S
Published: April 2011

Conventional investigations for the waveseabedpipe interaction problem have dealt with a uniform and isotropic seabed, despite the influences of anisotropic soil behaviour and variable soil characteristics. This paper proposes a finite-element model to investigate the effects of cross-anisotropic soil behaviour and variable soil characteristics (permeability and shear modulus) on the wave-induced oscillatory pore pressures on a submarine buried pipeline. The present model is verified with previous experimental data for the case of a uniform and isotropic seabed. The numerical results indicate that the effects of cross-anisotropic soil behaviour and variable soil characteristics on the pore pressure around the pipe surface cannot always be ignored. The maximum relative difference of pore pressure may reach 10% of the amplitude of the wave pressure at the seabed surface.Key words:pore pressure, pipeline, cross-anisotropic, nonhomogeneous
Frost susceptibility related to soil index properties
Authors: Konrad Jean-Marie
Published: April 2011

The analysis of frost-heave data on several soils confirmed that segregation potential, hence frost susceptibility, of saturated soils was best related to the average size of the fines fraction, the specific surface area of the fines fraction, and the ratio of the material's water content to its liquid limit. The influence of overburden pressure can also be accounted for by an empirical relationship between the segregation potential, the average size of the fines fraction, and the compressibility index of the soil. The segregation potential was also proportional to the relative fines content in soils where the fines do not completely fill the voids of the coarser fraction. This study led to the development of a new frost-susceptibility assessment methodology based on simple geotechnical routine soil index testing that was validated on a highway site on frost-susceptible subgrade till.Key words: frost heave, index properties, criteria, soil, segregation potential.
Settlement patterns of soft soil foundations under embankments
Authors: Zhang Limin
Published: April 2011

The settlement pattern of an embankment may not always be the typical one in which the maximum settlement occurs at the center. Other patterns may develop with changes of embankment width or surcharge arrangements, which will require special settlement calculation methods and engineering measures. This paper compares the characteristics of shear stress distributions and effective stress paths in foundations induced by several embankment loads. Based on the analyses, the patterns of foundation settlement are classified into four categories, i.e., one-dimensional, sagged, transitional, and typical basin types. A simplified procedure is presented to identify settlement patterns based on shear stress analyses, and a case study is reported to illustrate the procedure. Embankment width, embankment height, and foundation soil conditions are found to be most critical to settlement patterns. However, this paper does not purport to provide methods of estimating the magnitude of settlement.Key words: embankment, soft soil, settlement, lateral deformation, consolidation.
Elastic viscoplastic modelling of the time-dependent stress-strain behaviour of soils
Authors: Yin Jian-Hua , Graham James
Published: April 2011

This paper presents a new framework for elastic viscoplastic (EVP) constitutive modelling. In developing the model, a general one-dimensional elastic viscoplastic (1D EVP) relationship is first derived for isotropic stressing conditions using an "equivalent-time" concept. This 1D EVP model is then generalized into a three-dimensional EVP model based on Modified Cam-Clay and viscoplasticity. Fitting functions are proposed for fitting data when model parameters are being determined. Using these functions, a specific EVP model is developed which describes the time-dependent stress-strain behaviour of soils under triaxial stress states. This model has been calibrated using data from a densely compacted sand-bentonite mixture. The calibrated model is used to compute time-dependent (or strain rate dependent) stress-strain curves from a multistage shear creep test and a step-changed, constant strain rate undrained triaxial compression test. Predictions from the EVP model are in general agreement with measured values. It is demonstrated that the model can simulate accelerating creep when deviator stresses are close to the shear strength envelope in a q creep test. It can also model the behaviour in unloading-reloading and relaxation. Limitations and possible improvements are also indicated.Key words: equivalent time, stress-strain, time dependent, elastic, viscoplastic, triaxial.
Formulation and application of a short-term strength criterion for isotropic rocks
Authors: Aubertin Michel , Li Li , Simon Richard , Khalfi Salah
Published: April 2011

This paper deals with failure of low-porosity rocks and with a multiaxial representation of the corresponding surface in stress space. The proposed failure criterion is based on a mathematical modification of the MSDP function recently developed by the same group. This three-dimensional criterion has been reformulated so that it can be expressed in a unified manner, without having to resort to a transition condition between the curved portion (referred to as the Mises-Schleicher portion) and the linear portion (referred to as the Drucker-Prager portion). The new failure surface has the following characteristics: a forced passage through the uniaxial strength in tension (σt) and in compression (σc), a continuous influence of the minor principal stress for the entire range of behavior considered, a strength under high confining stress that is controlled by the basic friction angle ϕband a loading-geometry effect expressed in the π plane. This new expression of the criterion is presented in the paper. Its main characteristics are also shown, together with its application to various low-porosity rocks using a number of testing results taken from the literature. In the discussion that follows, other attributes of the criterion are highlighted using a qualitative comparison with the Hoek-Brown criterion. Key words: rock mechanics, failure surface, failure criterion, laboratory testing.
Experimental investigation of fracture toughness KIIC of frozen soil
Authors: Li Hongsheng , Yang Haitian , Liu Zengli
Published: April 2011

This paper describes an experimental study on the fracture toughness KIIC of pure frozen soil and the behaviour of the interface between frozen soil and concrete. A four-point bending device is used in the test. Experimental results indicate that water content and temperature are the main factors affecting fracture toughness. Within the range of the experiment, loading rate has a very slight effect on fracture toughness. Some formulae are suggested to evaluate the fracture behaviour of frozen soil.Key words: frozen soil, fracture mechanics, fracture toughness, interface.
A method for stability analysis of vegetated hillslopes: an energy approach
Authors: Ekanayake Jagath C , Phillips Christopher J
Published: April 2011

Stability analyses of vegetated hillslopes are usually carried out by the limit equilibrium (LE) method where shear displacement is not taken into account. Experiments show that soil with roots produces a shear stress - displacement curve with higher peak shear stress at larger shear displacements than fallow soil. If the safety factor is obtained by the LE method, the ability of soil with roots to resist large shear strains due to soil-root interaction may be underestimated. A new approach is proposed that incorporates, within the stability analysis, the ability of soil with roots to withstand strain. It is based on a consideration of the energy consumed during the shearing process of the soil-root system. This is developed using characteristics of the shear stress - displacement curve of a soil-root system obtained from in situ direct shear tests under simulated overburden pressure and pore-water pressure conditions. The method is limited to vegetated hillslopes where the stability analysis can be approximated by a simplified infinite slope model. Shear stress - displacement data for two tree species were obtained from hillslopes where shallow landslides commonly occur in rainstorms under near-saturated conditions. Using these results the energy approach (EA) and LE methods are compared. A procedure is also outlined to predict the safety factor for hillslopes with different plant densities. Extension of the EA method for general two-dimensional slope stability analysis involving nonlinear shear planes is also explained.
On slope instability induced by seepage erosion
Authors: Crosta G , Prisco C di
Published: April 2011

This paper is focused on seepage erosion causing liquefaction processes and rapid slope failures. One case history, which occurred along an old fluvial terrace in the Po Plain (northern Italy), is presented. The failure was the final consequence of a concentrated flow induced by the incisions due to tractor edged-blade-wheels cutting through the soil layer sealing the bottom of a flooded rice field. To clarify the evolution of the seepage and the erosion phenomena which preceded and characterized the collapse, numerical analyses and some experimental tests on small-scale models have been performed. The problems associated with the hydraulic and mechanical description of localized water flows in unsaturated soils, the three-dimensional conditions of the failure mechanism, and the liquefaction phenomenon are discussed.
The encounter probability for mountain slope hazards
Authors: McClung D M
Published: April 2011

In typical risk calculations for the mountain slope hazards one wishes to calculate the encounter probability: the probability of facilities or vehicles being hit at least once when exposed for a finite time period L with events having a return period T at a location. In this note, it is assumed that the events are rare, independent, and discrete, with arrival according to a binomial (or Bernoulli) distribution or a Poisson process. The constraints on the formulations for the processes are provided and it is shown that for typical applications either assumption (binomial or Poisson process) may be used in practice almost interchangeably.
Active earth pressure in cohesive soils with an inclined ground surface
Authors: Gnanapragasam Nirmala
Published: April 2011

An analytical solution is developed to determine the active lateral earth pressure distribution on a retaining structure when it consists of a cohesive backfill (internal friction angle ϕ > 0, cohesion c > 0) with an inclined ground surface. The solution derived encompasses both Bell's equation (for cohesive or cohesionless backfill with a horizontal ground surface) and Rankine's solution (for cohesionless backfill with an inclined ground surface). The orientation of the failure surface is also determined. Results indicate that, unlike the soil-wall scenarios of Bell and Rankine where the failure planes are parallel with a fixed orientation independent of the overburden pressure, for sloping cohesive backfill (ϕ > 0, c > 0) the slope of the failure surface is a function of the overburden pressure and becomes shallower with depth, thus forming a curvilinear failure surface. The solution developed can also be used to check the sustainability of a slope. The analytical solution can be programmed conveniently in a computer.Key words: retaining structure, active earth pressure, cohesive backfill.
The design of a laboratory facility for evaluating the structural response of small-diameter buried pipes
Authors: Brachman R WI , Moore I D , Rowe R K
Published: April 2011

The design of a new laboratory facility for evaluating the structural response of small-diameter buried pipes (e.g., leachate collection pipes in landfills) is presented. The pipe is tested within a 2.0 m wide, 2.0 m long, and 1.6 m high prism of soil, subject to large vertical pressures (1000 kPa), with only minimal roughness and deflection of the lateral boundaries. Results from finite element analyses are presented to examine the effect of proximity, roughness, and stiffness of the lateral boundary on the soil and pipe response and how reasonable the laboratory idealizations are relative to the deep burial conditions expected to prevail in the field. Shear stresses arising from the roughness of the lateral boundaries alter the stresses acting around the pipe and reduce the proportion of the applied surcharge reaching the pipe. Outward deflection of the lateral boundaries also alters the stress state around the pipe, predominantly resulting from decreases in horizontal stresses within the soil. Reducing boundary friction to less than 5° and limiting the boundary deformation to less than 1 mm at a vertical surcharge of 1000 kPa provide a good idealization of field conditions for a deeply buried pipe.Key words: buried pipes, soil-structure interaction, laboratory testing, boundary friction.
A thermomechanical model for saturated clays
Authors: Cui Yu Jun , Sultan Nabil , Delage Pierre
Published: April 2011

A thermomechanical model for saturated clays is proposed within the framework of recent extensions of the Cam-Clay model. The results of some tests found in the literature are analyzed, and the main features of the thermomechanical behaviour of clays are identified. The effect of the overconsolidation ratio (OCR) on the volume change of a soil (expansion-contraction) submitted to heating is well established using experimental data obtained for selected soils by various authors. However, existing models need to be modified to correctly model this feature. For this reason, a new volumetric thermal plastic mechanism is developed that allows for the prediction of plastic strains at higher OCR values. The overconsolidation effect observed when heating a normally consolidated soil is also modelled. Particular attention is paid to the coupling and hardening phenomena related to the combined effects of stress and temperature. A qualitative validation is made by examining the response of the model under a given thermomechanical path. Comparison with existing thermomechanical experimental results shows that the model can provide satisfactory predictions.Key words: clays, constitutive modelling, temperature effects, deformation, elastoplasticity, radioactive waste disposal.
Design and construction of the barrier system for the Halton Landfill
Authors: Rowe R Kerry , Caers Chris J , Reynolds Glenn , Chan Cliff
Published: April 2011

Considerations related to the design of the Halton Landfill as a "hydraulic trap" are summarized together with the research that was conducted to support the design concept. The interrelationship between hydrogeology and the engineered design is examined. Laboratory experiments demonstrated that there can be diffusion away from a source, even with significant inward velocity. Existing theory was found to provide a good prediction of the observed concentration profile in these experiments. It is also shown that a pressurized air pocket below the clay effectively acts as a zero-flux boundary and hence, with respect to migration of chloride, could be conservatively neglected in the impact assessment. The results of the impact calculations predict only a small increase in chloride concentration in the receptor aquifer while there is negligible predicted impact due to organic contaminants. The landfill was designed and constructed with a granular "sub-liner contingency layer" (SLCL) beneath the compacted liner. The operation of this layer is discussed. Finally, the construction of the compacted clayey liner with a hydraulic conductivity of 1 × 10-8 cm/s is documented.Key words: landfill, hydraulic containment, liner, field case, construction.
Efficient method for the preparation of pinacols derived from aromatic and aliphatic ketones by using low-valent titanium reagents in dichloromethane-pivalonitrile
Authors: Kagayama Akifumi , Igarashi Koji , Mukaiyama Teruaki
Published: April 2011

The reductive coupling reaction of aldehydes and ketones, including unsymmetrical aliphatic ketones, proceeded smoothly to give the corresponding pinacols in good to high yields under mild conditions by using combination of titanium(II) chloride and zinc or titanium(IV) chloride and zinc in dichloromethane-pivalonitrile. Meso-selective formation of the coupling products was observed in the cases of some aliphatic ketones. The diastereoselectivities of coupling products depend on both difference of bulkiness of 2-, and 2'-substituents of carbonyl group of the reactant, and overall steric effect around the carbonyl groups.Key words: diastereoselective pinacol reaction, dichloromethane-pivalonitrile, titanium(II) chloride, titanium(IV) chloride, zinc.
Synthesis and reactivity of the stable silylene N,N'-di-tert-butyl-1,3-diaza-2-sila-2-ylidene
Authors: Haaf Michael , Schmedake Thomas A , Paradise Bryan J , West Robert
Published: April 2011

The synthesis and several reactions of the stable silylene 1 (N,N'-di-tert-butyl-1,3-diaza-2-sila-2-ylidene) are reported. Overreduction of 1 with alkali metals results in the formation of a dimeric dianion, which can be trapped with a proton source to give the dihydride derivative 9. In the solid state or in concentrated solutions, 1 undergoes a reversible conversion into the novel tetrameric disilene, 10. 1 reacts with ethanol, phenol, and water via insertion into the OH bond, and with iodomethane by insertion into the CI bond. A reaction of 1 with the diene 2,3-dimethyl-1,3-butadiene affords the silacyclopentene, 15. This reaction is markedly different from the one found for the unsaturated analog of the silylene, 2, which catalyzes the conversion of this diene into a highly cross-linked polymer.Key words: silylene, carbene analog, disilene, divalent compounds, N-heterocycles.
Solubility of diphenyl sulfone in organic nonelectrolyte solvents. Comparison of observed vs. predicted values based upon Mobile Order theory
Authors: De Fina Karina M , Van Tiffany T , Fletcher Kristin A , Acree, Jr. William E
Published: April 2011

Experimental solubilities are reported at 25.0°C for diphenyl sulfone dissolved in 25 different organic nonelectrolyte solvents containing ether-, chloro-, hydroxy-, ester, methyl-, and tert-butyl-functional groups. Results of these measurements, combined with previously reported diphenyl sulfone solubilities taken from the chemical literature, are used to test the applications and limitations of expressions derived from Mobile Order theory. For the 34 solvents for which predictions could be made, computations show that mobile order theory does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 49.3%. In comparison, the average absolute deviation is 5 500% when ideal solution behavior is assumed.Key words: diphenyl sulfone solubilities, organic nonelectrolyte solvents, solubility predictions.
Enantiomerically pure decalinic structures from carbohydrates using intramolecular Diels-Alder and Ferrier carbocyclization
Authors: Taillefumier Claude , Chapleur Yves
Published: April 2011

The synthesis of enantiomerically pure decalinic structures, advanced intermediates for the synthesis of the hexahydronaphtalen part of mevinic acids, is described. The key steps are the intramolecular Diels-Alder cycloaddition of a suitably substituted sugar enone obtained via the Ferrier rearrangement of tri-O-acetyl-D-glucal with the appropriate alcohol representing the diene part of the system. Chemical manipulation of the resulting, diastereomerically pure, cycloadduct led to a 5,6-unsaturated carbohydrate which was submitted to the Ferrier carbocylization. This reaction proved difficult likely because of the embedding of the aglycon in a cycle, the hydration product of the double bond being the main product. This compound was in turn transformed into the decalinic structures by treatment in basic medium. The inverse strategy, Ferrier carbocyclization followed by IMDA of an enone and a diene linked via an ester bond was unsuccessful.Key words: Intramolecular Diels-Alder reaction, enantiomerically pure decalin, Ferrier carbocyclization, carbohydrates.