bluuebunny/crossref_metadata_2025 huggingface dataset:
Full-height piled bridge abutments constructed on soft clay
Authors: Ellis E. A. , Springman S. M.
Published: October 2009

Full-height piled bridge abutments constructed on soft clay are prone to lateral soil–structure interaction effects resulting from placement of the retained fill, and associated deformation of the underlying soil. The interaction increases lateral structural loading and displacement, and hence may result in unserviceable behaviour of the abutment or bridge deck. A series of geotechnical centrifuge tests and finite element method analyses are reported, examining the effect of clay layer depth and the rate of embankment construction. Agreement of data from the two methods is good, and the results confirm the existence of established lateral soil–pile interaction in the clay layer. However, additional interaction effects associated with the retained embankment material were also identified, causing a significant additional component of lateral loading on the structure. Such interaction increases bending moments in the piles, which are therefore of concern. Many existing empirical methods attempt to estimate these moments directly. However, it is argued that the moment loading is most logically viewed as a consequence of the lateral loading components acting on the pile, and that a simple calculation based on this information is likely to be considerably more reliable.
Stability of plate anchors in undrained clay
Authors: Merifield R. S. , Sloan S. W. , Yu H. S.
Published: October 2009

Soil anchors are commonly used as foundation systems for structures requiring uplift resistance, such as transmission towers, or for structures requiring lateral resistance, such as sheet pile walls. To date, the design of these anchors has been largely based on empiricism. This paper applies numerical limit analysis to rigorously evaluate the stability of vertical and horizontal strip anchors in undrained clay. Rigorous bounds on the ultimate pull–out capacity are obtained by using two numerical procedures that are based on finite element formulations of the upper and lower bound theorems of limit analysis. These formulations follow standard procedure by assuming a rigid perfectly plastic clay model with a Tresca yield criterion, and generate large linear programming problems. By obtaining both upper and lower bound estimates of the pull–out capacity, the true pull–out resistance can be bracketed from above and below. Results are presented in the familiar form of break–out factors based on various soil strength profiles and geometries, and are compared with existing numerical and empirical solutions.
Piled raft foundations: design and applications
Authors: Poulos H. G.
Published: October 2009

In situations where a raft foundation alone does not satisfy the design requirements, it may be possible to enhance the performance of the raft by the addition of piles. The use of a limited number of piles, strategically located, may improve both the ultimate load capacity and the settlement and differential settlement performance of the raft. This paper discusses the philosophy of using piles as settlement reducers and the conditions under which such an approach may be successful. Some of the characteristics of piled raft behaviour are described. The design process for a piled raft can be considered as a three-stage process. The first is a preliminary stage in which the effects of the number of piles on load capacity and settlement are assessed via an approximate analysis. The second is a more detailed examination to assess where piles are required and to obtain some indication of the piling requirements. The third is a detailed design phase in which a more refined analysis is employed to confirm the optimum number and location of the piles, and to obtain essential information for the structural design of the foundation system. The selection of design geotechnical parameters is an essential component of both design stages, and some of the procedures for estimating the necessary parameters are described. Some typical applications of piled rafts are described, including comparisons between computed and measured foundation behaviour.
Pre-failure strain softening and pre-failure instability of sand: a comparative study
Authors: Chu J. , Leong W. K.
Published: October 2009

Strain softening in the form of decreasing shear resistance and instability, the inability to sustain given loads, can occur before the failure state is attained. This so-called pre-failure strain softening or pre-failure instability has been observed to occur for very loose sand in undrained tests and for dense sand in strain path controlled tests. Experimental data are presented in this paper to compare the pre-failure strain softening and pre-failure instability behaviour. It is established that the factors that control the occurrence of pre-failure strain softening and pre-failure instability are essentially the same, although the two types of behaviour are different. The similarities and differences between strain softening and instability are discussed for both loose and dense sand.
Case study of lateral spreading forces on a piled foundation
Authors: Berrill J. B. , Christensen S. A. , Keenan R. P. , Okada W. , Pettinga J. R.
Published: October 2009

A case study is presented of the effect of lateral spreading on the piled foundations of the Landing Road Bridge, Whakatane, New Zealand, during the ML 6·3, 1987 Edgecumbe earthquake. Trenching at two piers on the floodplain of the left bank revealed slip surfaces in the 1·5 m thick non-liquefied crustal layer, consistent with passive failure as the buried piers and raked piles resisted its displacement towards the river channel. The passive force on the buried portion of the slab piers is estimated at 850–1000 kN per pier, compared with roughly 50 kN in drag forces between the underlying liquefied sand and the set of eight, 400 mm square raked piles per pier. The collapse load of the foundation system is estimated to be about 1200 kN. Thus the force imposed by the non-liquefied crust was close to the ultimate capacity of the foundation. Our main conclusion is that the chief threat to piled foundations from lateral spreading comes from loads imposed by the non-liquefied crust, not from the drag forces of the liquefied soil. In this case, clear evidence was found of passive failure as the crust drove against the buried pier, piled through to firm ground.
Characteristic values of ground parameters and probability of failure in design according to Eurocode 7
Authors: Cardoso A. S. , Fernandes M. M.
Published: October 2009

Limit state design applied to geotechnical structures requires the selection of characteristic values of ground parameters and the use of partial safety factors. These factors, and the way that characteristic values are selected, will govern the calculated probability of failure of the structure. The paper presents a methodology for estimating the probability of failure provided by the application of Eurocode 7 to the design of spread foundations and embankments. A parametric study is presented enabling the identification of the reduction factors by which the mean value of soil resistance parameters should be multiplied to obtain the characteristic value that will ensure a target probability of failure.
Particle shape characterisation using Fourier descriptor analysis
Authors: Bowman E. T. , Soga K. , Drummond W.
Published: October 2009

A novel technique for the objective assessment of particle shape is presented. The technique uses Fourier shape descriptors and image analysis of scanning electron microscope photographs of sand grains to provide an accurate quantification of particle morphology and texture. Three lower order Fourier descriptors, denoted ‘signature descriptors’, provide measures of elongation, triangularity and squareness, while an additional descriptor, denoted ‘asymmetry’, provides a measure of particle irregularity. Together, these four descriptors quantify the overall shape of soil particles (defined as ‘morphology’). A summary of higher-order descriptors provides textural information that is related to local roughness features (defined as ‘texture’). The results of studies on three silica sands (two standard, laboratory-use and one natural, unprocessed) and one carbonate sand are presented. Breakage of particles by crushing is shown to affect the morphological signature differently depending on the type of sand, though it does not significantly alter texture. The study highlights the value of microscopy, combined with image analysis, in revealing sand grain shape and texture, and shows that simple statistical tools may be used to translate the information provided by relatively few grains to that of a larger body of soil.
Factors affecting rainfall-induced flowslides in laboratory flume tests
Authors: Wang G. , Sassa K.
Published: October 2009

Using a small flume, a series of tests has been conducted to cause rainfall-induced flowslides. Based on monitoring of sliding distance and pore pressures, the process of pore-pressure generation in relation to sliding distance is examined. A set of test results on the temporal and longitudinal variation of sliding velocity is presented. By changing the initial dry density and sample thickness in tests on a silica sand, the effects of these two factors on the pore pressure build-up after failure and flowslide motion have been analysed. The test results showed that there was an optimal density for pore pressure build-up, at which both the moving velocity and run-out distance were greatest, and this optimal density was dependent on sample thickness. Additionally, a series of tests on mixtures of silica sand with different loess contents has been carried out to investigate the effects of fine-particle content on the flowslide motion, in which different modes of flowslide motion were observed; these probably were affected by the different rates of pore-pressure dissipation in the shear zone.
Consolidation of naturally gassy soft soil
Authors: Sills G. C. , Gonzalez R.
Published: October 2009

Biogenic gas is produced and contained in fine-grained soils in environments such as river estuaries and landfill sites. Planning dredging operations or predicting the volume capacity of a landfill requires information about the amount of gas that can be held in the soil, and about the effect that the gas has on the soil behaviour. The purpose of this paper is to present some experimental results and interpretation relevant to these and related topics. A series of experiments has been carried out at Oxford University with soil of estuarine origin from the Slufter disposal site in the Netherlands. The soils were introduced in settling columns, and the different stages of consolidation were documented by measuring height, densities, excess pore pressures and amount of gas. At the end of primary consolidation the gassy soil was consolidated to higher stress levels by applying a hydraulic gradient. The growth rates of bacteria producing gas within the soil were accelerated or reduced by controlling the temperature in the range 10–30°C. The experimental results show a sequence of events during consolidation. In the first phase, gas was produced and accumulated within the soil. The overall density of the gassy soil decreased and pore pressures fluctuated unpredictably. At the end of this phase the amount of gas within the soil reached a critical threshold value and thereafter began to escape through cracks and fissures. This marked the start of a second phase of events. Although the gas production continued to be high, the total amount of gas within the soil slowly decreased. The soil began a new phase of consolidation, with the settlement accelerating, as the cracks and fissures provided a quick route for pore water dissipation. The self-weight stresses in these experiments do not exceed 1 kPa, so that higher stress levels were achieved by the application of a hydraulic gradient. During this stage, the gas within the soil became less influential as the soil gained in strength.
An investigation of the effect of soil state on the capacity of driven piles in sands
Authors: Klotz E. U. , Coop M. R.
Published: October 2009

A series of model pile tests was carried out in the centrifuge, pushing the pile into two sands of very different geological origins and particle strengths. This was accompanied by series of triaxial tests allowing the critical state line of each sand to be established so that the initial in situ state of each sample, prior to pile installation, could be quantified. The work demonstrated that the initial state, defined as the combination of density and stress level relative to the critical state line, is a controlling factor in determining pile capacity, and hence that design approaches based solely on relative density could not be expected to be widely applicable. It was also found that state had to be defined as a ratio of stresses rather than the more usual state parameter in terms of volume. Attempts to verify the method using existing field pile test data were hampered by a dearth of laboratory data accompanying the in situ tests.
Radiographic and microscopic observation of shear bands in granular materials
Authors: Nemat-Nasser S. , Okada N.
Published: October 2009

Shear localisation in granular materials has been studied radiographically and microscopically. Thin columns and rows (lines) of lead silicate granules of distinct colour were embedded in a large hollow cylindrical specimen of granular materials, and a series of X-ray photographs were taken to capture the local micromechanical response during shear deformation, in both drained and undrained experiments. In drained tests, shear localisation, produced by monotonic deformation of the specimen, was directly observed. In undrained tests, the local deformation of the granular mass during liquefaction, induced by cyclic shearing, was examined. It was directly observed that shear localisation does occur in liquefied specimens. After shear bands were formed in drained tests, the specimen was frozen in situ. Later, samples were cut from the frozen large specimen, and their ice was replaced by a polymer resin, using a novel technique. The portion of the sample containing a shear band and a sheared section of a column of lead silicate granules was cut by a diamond saw along the column of lead granules, and the cut surface was polished in order to directly observe the arrangement of the particles within the shear band and measure the corresponding deformation. The lead silicate granules trace the localised zone, and provide details of the deformation pattern within and close to the localised zone. The shear strain at the middle of the shear band zone exceeds 500% although the overall nominal shear strain is only 10%. The localisation is accompanied by extensive necking. Based on these experiments, the deformation of the shear band zone is quantified.
Dilatancy in general Cambridge-type models
Authors: Jefferies M. G. , Shuttle D. A.
Published: October 2009

Cambridge-type models for soil (Cam-clay, Modified Cam-clay and NorSand) are idealised soil models based on a few simple postulates. This gives the models predictive power, and they offer interesting insight into soil behaviour. But the symmetry of the triaxial conditions for which the models were derived leaves an additional degree of freedom when generalising to arbitrary 3-D stress and strain states. The additional freedom creates unresolved inconsistencies in the plastic strain rates—usually dilatancy from the plastic potential not matching that implied by the work dissipation postulate (flow rule) under general 3-D stress states. It is shown that Cambridge-type models may be consistently generalised for arbitrary strain paths by adopting work conjugate invariants and by requiring primacy of the work dissipation postulate. The unresolved freedom for the strain rates is handled by interpolation between the limit conditions (triaxial compression and extension) that are fully defined because of symmetry. The approach is illustrated in the context of NorSand, using calibration under triaxial compression for published tests on Brasted sand to predict behaviour in the practically important case of plane strain. Excellent predictions are obtained over a range of sand densities from loose to dense.
Science and empiricism in pile foundation design
Authors: Randolph M. F.
Published: October 2009

Scientific approaches to pile design have advanced enormously in recent decades and yet, still, the most fundamental aspect of pile design—that of estimating the axial capacity—relies heavily upon empirical correlations. Improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile, but quantification of the changes in stress and fabric is not straightforward. This paper addresses the degree of confidence we can now place (a) on the conceptual and analytical frameworks for estimating pile capacity, and (b) on the quantitative parameters required to achieve a design. The discussion is restricted to driven piles in clays and siliceous sands, with particular attention given to extrapolating from design approaches derived for closed-ended piles of relatively small diameter to the large-diameter open-ended piles that are used routinely in the offshore industry. From a practical viewpoint, we need design approaches that minimise sensitivity to the estimated pile capacity. This may be achieved partly through a greater reliance on pile load testing, where significant advances have been made in the last decade, but also by adopting design approaches that are focused more on guarding against unacceptable deformation of the complete foundation. Example applications in the paper are drawn both from offshore applications, where current challenges include estimating the axial capacity of ultra-thin-walled, large-diameter caissons, and from onshore applications such as bridge piers and piled raft foundations, where inelastic displacement of the piles is not only acceptable, but often essential for efficient design.
Performance of miniature piezocones in thinly layered soils
Authors: Hird C. C. , Johnson P. , Sills G. C.
Published: October 2009

Two piezocones, with cross-sectional areas of 1 cm2 and 5 cm2 and a variety of pore pressure filters, were driven at the standard rate of 20 mm/s into models of thinly layered soil, and pore pressure dissipation tests were also performed. The models consisted of alternating layers of pre-consolidated kaolin clay and more permeable layers of silt or fine sand, enclosed in a 400 mm diameter cell with either a rigid or a flexible lateral boundary. Control tests were performed on a clay model without any sand or silt layers. The experiments demonstrate the feasibility of using miniature piezocones to detect individual permeable layers as thin as 2 mm in normally and lightly overconsolidated clay deposits, provided their vertical spacing is at least two cone diameters and a sufficiently fast data recording rate is used. However, the lateral extent of a permeable layer cannot be gauged from a single piezocone probe. Pore pressure dissipation tests in clay layers are not significantly affected by neighbouring permeable layers provided they are more than two cone diameters above or below the filter element. On the basis of the experimental results, it is suggested that miniature piezocones could be used to improve the investigation of thinly layered ground, as might be found in alluvial and estuarine areas.
Performance of an unsaturated expansive soil slope subjected to artificial rainfall infiltration
Authors: Ng C. W. W. , Zhan L. T. , Bao C. G. , Fredlund D. G. , Gong B. W.
Published: October 2009

A major infrastructure project, the South-to-North Water Transfer Project, has been proposed to carry potable water from the Yangtze River region in the south to many arid and semi-arid areas in the northern regions of China, including Beijing. The proposed 1200 km ‘middle route’ of the project is likely to be an open channel with a trapezoidal cross-section. At least 180 km of the proposed excavated canal will pass through areas of unsaturated expansive soils. An 11 m high cut slope in a typical expansive clay with medium plasticity in Zaoyang, close to the ‘middle route’ in Hubei, was selected for a comprehensive and well-instrumented field study of the effects of rainfall infiltration. Two artificial rainfall events were created during a month of field investigation and monitoring. Prior to the rainfall events, high soil suction was measured within the top 1 m of soil. This high initial soil suction created an upward flux of water and moisture. The abundant cracks and fissures near the ground surface played a key role in the soil suction–water interaction. After the rainfall, there was a delayed response of about 2 days before any significant changes of pore water pressure, earth pressure and ground movement were measured. A perched water table was deduced at a depth of about 1·5 m below the slope surface. Two distinct modes of down-slope deformations were observed: a cantilever deformation within the top 1·5 m at the midslope, and a deep-seated down-slope displacement at the toe of the slope. The observed continual soil swelling after the start of the rainfall appears to be governed by the low coefficient of permeability to water and the expansive nature of the soil. After heavy and prolonged rainfalls, earth pressure measurements suggest that passive failures may take place within the softened clay at shallow depths.
Micromechanical considerations of unsaturated pyramidal packing
Authors: Molenkamp F. , Nazemi A. H.
Published: October 2009

To develop an interaction model of moisture suction, saturation and intergranular stress for granular materials, the properties of unsaturated regular packing of isodiametrical rough spheres are investigated theoretically. These micromechanical considerations demonstrate the existence of the effective pore suction tensor, which depends on the saturation, the liquid–solid contact angle, the surface roughness, the grain size, and the fabric tensor of the granular skeleton. This tensor is shown to involve a deviatoric part.
Isotropic yielding in an artificially cemented soil cured under stress
Authors: Rotta G. V. , Consoli N. C. , Prietto P. D. M. , Coop M. R. , Graham J.
Published: October 2009

The work simulates, in the laboratory, the formation of a cemented sedimentary deposit in which cement bonding occurs after burial and under geostatic stresses. Isotropic compression tests were carried out on artificially cemented specimens made with variable cement contents. After consolidating the samples to the uncemented normal compression line, the specimens were allowed to cure for 48 h before testing. The curing confining stresses ranged from 50 to 2000 kPa, and were intended to represent soil elements at different depths in the fictitious sedimentary deposit when the cementing occurred. The contribution of the cement bonds to soil compression and the changes in the isotropic yield stress as a function of void ratio and cement content were analysed. The results showed the importance of the void ratio during the formation of cement bonds and also of the degree of cementation for the compressive behaviour of the cemented soil, and demonstrated that the variation in yield stress with void ratio and cement content is dependent on the curing stress and independent of the stress history.
Delineation of a collapse feature in a noisy environment using a multichannel surface wave technique
Authors: Xia J. , Chen C. , Li P. H. , Lewis M. J.
Published: October 2009

A collapse developed at Calvert Cliffs Nuclear Power Plant, Maryland, in early 2001. The location of the collapse was over a groundwater drainage system pipe buried at an elevation of +0·9 m (reference is to Chesapeake Bay level). The cause of the collapse was a subsurface drain pipe that collapsed because of saltwater corrosion of the corrugated metal pipe. The inflow/outflow of sea water and groundwater flow caused soil to be removed from the area where the pipe collapsed. To prevent damage to nearby structures, the collapse was quickly filled with uncompacted sand and gravel (∼36 000 kg). However, the plant had an immediate need to determine whether more underground voids existed. A high-frequency multichannel surface-wave survey technique was conducted to define the zone affected by the collapse. Although the surface-wave survey at Calvert Cliffs Nuclear Power Plant was conducted at a noise level 50–100 times higher than the normal environment for a shallow seismic survey, the shear (S)-wave velocity field calculated from surface-wave data delineated a possible zone affected by the collapse. The S-wave velocity field showed chimney-shaped low-velocity anomalies that were directly related to the collapse. Based on S-wave velocity field maps, a potential zone affected by the collapse was tentatively defined.
Three-dimensional swelling of clay lumps
Authors: Robinson R. G. , Dasari G. R. , Tan T. S.
Published: October 2009

The disposal of large volumes of clay lumps obtained from underground construction activities and seabed dredging is a problem in a highly built-up environment such as Singapore. The use of such clay lumps for reclamation of land is an environment-friendly proposition. The clay lumps, when placed under water, will undergo three-dimensional swelling. Calculation of the degree of swelling is important for making decisions on when to place surcharge, and in what quantity, on top of the fill for closing the inter-lump voids. This paper reports the results of experimental and numerical studies that were carried out to understand the swelling behaviour of clay lumps when placed under water. Experimental results were compared with finite element method results using linear and non-linear elastic models. The study shows that the suction present in the lumps increases initially, before dissipation, suggesting the presence of the Cryer-Mandel effect during three-dimensional swelling. The importance of simulating continuous changes in soil modulus and permeability for realistic simulation of three-dimensional swelling of clay lump is reported. The influence of lateral restraint on the swelling behaviour is also analysed.
A constitutive framework for anisotropic sand including non-proportional loading
Authors: Li X. S. , Dafalias Y. F.
Published: October 2009

An existing platform model for inherently anisotropic sands is extended to account for deformations induced by non-proportional loadings. The platform model is within the framework of critical-state soil mechanics, and the inherent anisotropy is accounted for by rendering the critical-state line in the e–p plane and the deviatoric plastic modulus functions of a scalar-valued anisotropic parameter, Ā. The latter is defined in terms of joint isotropic invariants of a symmetric fabric tensor and a properly defined loading direction tensor. Proportional and some non-proportional loading responses, including stress reversals, can be successfully simulated by the platform model, but the response under loading involving significant principal stress rotations requires the introduction of an additional loading mechanism. This new mechanism is associated with components of the stress ratio rate and plastic strain rate, which are orthogonal to a loading direction coaxial with the stress ratio. The novelty in this respect is associated with the dependence of the dilatancy and plastic modulus of this new mechanism on a second anisotropic parameter, A, to account for the fabric anisotropy effect along the lines of the plat-form model. The resulting comprehensive model success-fully simulates experimental data reflecting the complex combined effects of fabric anisotropy and non-proportional loading histories.
Fluidisation in artesian flow conditions: Hydromechanically unstable granular media
Authors: Vardoulakis I.
Published: October 2009

The present analysis focuses on fluidisation and erosion processes involving hydromechanically unstable granular materials in artesian flow conditions, as these phenomena were documented in column tests with gap-graded soils by Skempton & Brogan. It is shown that the observed abnormal decrease in hydraulic resistivity can be attributed to fluidisation of the fines fraction of the soil, which eventually leads to unplugging of the pore space and segregation piping erosion in the form of a runaway instability. For the description of the erosion process a continuum theory for three-phase media consisting of stationary grains, transported grains and pore fluid is presented. The governing mass balance and momentum balance equations, and the constitutive law for particle erosion are formulated and discussed in the light of the experimental evidence.
A new technique for rapid measurement of continuous soil moisture characteristic curves
Authors: Toker N. K. , Germaine J. T. , Sjoblom K. J. , Culligan P. J.
Published: October 2009

The soil moisture characteristic (SMC) curve of a soil describes the relationship between the soil suction (tension in the soil pore water) and its water content. The majority of traditional methods used to obtain SMC curves involve gathering individual point measurements of soil water content over a range of applied soil suctions, and then fitting a curve through these points. Each point measurement requires at least a day of testing to gather, leading to a total testing time of weeks to assemble the whole SMC curve. This paper presents a technique to obtain a complete, continuous SMC curve in a total preparation and testing time of 3–5 days. During evaporative drying of the soil specimen under examination, a digital laboratory balance and a high-capacity tensiometer, both connected to a data acquisition system, monitor continuous pore water loss and suction data respectively. The tensiometer is composed of a pressure transducer for suction measurement and an extremely fine porous ceramic that interfaces between the specimen and the transducer. To date, the technique has been successfully applied to resedimented, non-clay soils. Experimental results from the new method are in agreement with results from capillary fall tests. The paper also provides some insight into tensiometer behaviour and features of SMC curves.
Analyse tridimensionnelle en différences finies de l'interaction entre une structure en béton et le creusement d'un tunnel à faible profondeur: 3D-finite difference analysis of the interaction between concrete building and shallow tunnelling
Authors: Jenck Orianne , Dias Daniel
Published: October 2009

This paper presents a numerical analysis of the interaction between shallow tunnelling and structure on surface. The analysis is done using the software Flac3D, based on three-dimensional finite differences. The TBM tunnel excavation is simplified and is taken into account by volume loss. First, a reference calculation without structure on surface is presented. A numerical model coupling ground mass and structure on surface is then used to study the soil–structure interaction. The structure is composed by columns and floors, founded on a raft. The material has elastic properties of a reinforced concrete. Results are analysed in term of ground displacement on surface. The last part presents the influence of the structure stiffness on soil displacements on surface.
Admissible stress fields and arching in piles of sand
Authors: Michalowski R. L. , Park N.
Published: October 2009

Stress distributions under conical and prismatic heaps of sand can exhibit a local minimum at the centre of the base. Occurrence of the ‘dip’ in the stress distribution is affected by the sand deposition history and the deflection of the base. The dip is due to arching of sand over the centre core of the heap. Radial stress fields in prismatic piles of sand are constructed, and distributions with a dip indicative of arching are found. Arching is promoted in stress fields where the sections adjacent to the sloping surfaces are in the yielding state whereas the inner core of the heap is in the elastic state. The static approach of limit analysis is used to find that the tendency to arching increases with an increase in the horizontal component of the reaction under half of the mound.
The influence of soil anisotropy and K0 on ground surface movements resulting from tunnel excavation
Authors: Franzius J. N. , Potts D. M. , Burland J. B.
Published: October 2009

Finite element (FE) analysis is now often used in engineering practice to model tunnel-induced ground surface settlement. For initial stress regimes with a high coefficient of lateral earth pressure at rest, K0, it has been shown by several studies that the transverse settlement trough predicted by two-dimensional (2D) FE analysis is too wide when compared with field data. It has been suggested that 3D effects and/or soil anisotropy could account for this discrepancy. This paper presents a suite of both 2D and 3D FE analyses of tunnel construction in London Clay. Both isotropic and anisotropic non-linear elastic pre-yield models are employed, and it is shown that, even for a high degree of soil anisotropy, the transverse settlement trough remains too shallow. By comparing longitudinal settlement profiles obtained from 3D analyses with field data it is demonstrated that the longitudinal trough extends too far in the longitudinal direction, and that consequently it is difficult to establish steady-state settlement conditions behind the tunnel face. Steady-state conditions were achieved only when applying an unrealistically high degree of anisotropy combined with a low-K0 regime, leading to an unrealistically high volume loss.
One-dimensional consolidation of lumpy clay with non-linear properties
Authors: Yang L.-A. , Tan T.-S.
Published: October 2009

When dredged clay lumps are used as reclamation fill, large voids exist between the lumps. Thus consolidation of the lumps themselves, and closing up of inter-lump voids, contribute to the overall settlement, making the fill a complicated non-linear medium. Yang et al. (2002 , Géotechnique 52, No. 10, 713–725) have used the double porosity model to describe the consolidation of this type of fill using linear properties to arrive at analytical solutions. In reality, the behaviour is highly non-linear, and the finite element (FE) method is used to solve the non-linear equations. Results from the FE analysis of the consolidation of the lumpy clay fill were shown to be able to match the analytical solutions. Two one-dimensional consolidation tests were conducted for this study. In the first case, water was used to fill the inter-lump voids, whereas in the second case, slurry was used. The procedure for determining the permeability and the e–logσ′ relationships for the inter-lump and intra-lump systems is explained in this paper. All the parameters could be estimated from various tests, except for the fluid transfer parameter, and this was back-analysed, using data from other works as a guide. The results presented show that the model can predict well the measured settlement and pore pressures in inter-lump and intra-lump systems in both experiments, essentially because this is a back-analysis. But the fact that the model can provide consistent prediction of numerous parameters indicates that the model is able to capture the essence of the mechanics of a lumpy clay system.
Mechanism of rupture of shaft linings in coal mine areas buried by thick over-soils in East China
Authors: Li W. P. , Li X. Q.
Published: October 2009

Non-mining ruptures of shaft linings in coal mines, which have repeatedly occurred in coal mine areas of East China in recent years, are a new kind of geological disaster. In this paper the characteristics of non-mining ruptures of the shaft linings are presented. The engineering geology conditions of the ruptures are analysed. A method for testing the interaction between soil and shaft wall by high-pressure direct shear apparatus and triaxial servo test system has been presented. The shear stress– displacement curves, coefficient of unit stiffness and strength parameters of the interaction between soil and shaft wall are obtained. Combining with the test results, the deformation characteristics of the interaction between soils and shaft wall during deep soil compression due to water loss are analysed: they are elastic in the shallow and bottom parts and plastic in the deep part. An elastic perfectly plastic analysis model of the interaction between soil and shaft wall has been set up. Some analytic formulae are obtained to calculate the additional vertical displacement, strain and stress of the shaft lining. Their variation laws with depth, compression value of deep soils and so on are discussed. Finally, one example is presented to show the practicability of the theoretical researches.
Field trials of suction caissons in clay for offshore wind turbine foundations
Authors: Houlsby G. T. , Kelly R. B. , Huxtable J. , Byrne B. W.
Published: October 2009

A programme of testing of caisson foundations in clay at the Bothkennar test site is described. The tests are relevant to the design of foundations for offshore wind turbines, in the form of either monopod or tetrapod foundations. Records are presented for installation of the caissons, cyclic moment loading under both dynamic and quasi-static conditions, cyclic inclined vertical loading, and pullout of the caisson. Variation of stiffness of the foundation is observed, with high initial stiffness followed by hysteretic behaviour at moderate loads and degradation of response at high loads. Some implications for the design of wind turbine foundations are briefly discussed.
Numerical modelling of plane strain tests on sands using a particulate approach
Authors: Powrie W. , Ni Q. , Harkness R. M. , Zhang X.
Published: October 2009

This paper describes the results of a series of numerical plane strain test simulations on a particulate material, carried out using the three-dimensional particle flow code PFC-3D. Samples comprised about 10 000 non-spherical particles, each formed by strongly bonding two spheres together. The simulations demonstrate the ability of such a model to capture the essential macro-features of soil behaviour as observed in laboratory tests, including the dependence of peak strengths on the initial void ratio relative to the critical. The development of strain localisations or shear bands associated with the use of rough loading platens, and the sensitivity of the model to the initial sample porosity, particle shape factor and interparticle friction angle, were also investigated.
Dynamic centrifuge model tests on asphalt-concrete core dams
Authors: BAZIAR M.H. , SALEMI SH. , MERRIFIELD C.M.
Published: October 2009

In this research, the dynamic behaviour of a rockfill dam with an asphalt-concrete core has been studied utilising centrifuge modelling. Instruments including accelerometers and LVDTs were installed within and on the models and response accelerations and induced deformations were recorded. The recorded data and observations of the centrifuge models showed that the induced deformations in the asphalt core under an impact load with a large acceleration of 0·7g were very small. On the other hand, comparing the results of centrifuge tests with the results of three-dimensional numerical dynamic analyses of a prototype dam indicated that the numerical results corresponded well with the data recorded during centrifuge tests and the asphalt core showed similar behaviour in both numerical and centrifuge models. The results of non-linear three-dimensional dynamic response analyses of the case study selected for this research showed that under a severe earthquake, the induced shear strains in most parts of the asphalt core zone were still small and the dam behaved in a safe manner.
On the behaviour of Thanet Sand: an example of an uncemented natural sand
Authors: VENTOURAS K. , COOP M.R.
Published: October 2009

An extensive laboratory investigation was made of the mechanics of Thanet Sand, testing the soils from a number of locations and depths in the triaxial apparatus over a wide range of stress levels. Comparisons between tests on intact and reconstituted samples and between vertically and horizontally trimmed intact samples highlighted the effects of structure on the behaviour of this uncemented sand, in particular a significant effect of anisotropy. Two distinct substrata have previously been identified with different fines contents, and the key difference in their behaviour has been found here to be the location of their Critical State Line in the v:lnp′ plane, which has a significant effect on the engineering behaviour of the two substrata and can explain recent unusual observations of decreasing pile capacity with depth. Tests in which the glauconite content was removed from the sand showed that it did not affect its behaviour.
A mathematical model relating the flow curve of a cement paste to its water/cement ratio
Authors: Jones T. E. R. , Taylor S.
Published: October 2009

Synopsis

This paper describes an experimental and empirical study of the rheological properties of cement pastes under the action of a steady shear. Experimental results were obtained by using a Weissenberg rheogoniometer for a range of water/cement ratios of ‘fresh’ pastes. Particular reference is made to a mixing method which produces reversible flow curves. Various models are considered as empirical relationships between shear stress and shear rate. It is shown that the Robertson Stiff model provides a very accurate description of the rheology of the cement paste for a range of concentrations. An indication is given of the possibility of predicting flow curves by the use of a proposed empirical equation. Qualitative agreement is obtained between theory and experiment.
Sulphate resistance and long-term strength properties of regulated-set cements
Authors: Osborne G. J. , Smith M. A.
Published: October 2009

Synopsis

The results of compressive strength tests and durability tests on mortars and concretes made with two commercially produced regulated-set cements manufactured outside the UK for ages up to 6 months have been reported previously. The present paper gives the results of longer-term strength tests and sulphate-resistance tests up to 2 years. At ages greater than 24 h the regulated-set cements show little advantage over ultra-rapid-hardening Portland cement in terms of compressive strength, whilst at ages beyond 28 days performance is similar to that of ordinary Portland cement. Sulphate resistance is poor, but is much improved by the addition of pulverized-fuel ash. Some information is given on the performance of ultra-rapid-hardening Portland cement for comparison.
Activation energy of creep of concrete under short-term static and cyclic stresses
Authors: Hirst G. A. , Neville A. M.
Published: October 2009

Synopsis

A theoretically derived relation which has previously been shown by other authors to agree well with static creep is extended and transformed so that cyclic creep can be related to static creep as a function of the range of stress and time. Experimental results for periods under load up to 160 h show excellent agreement with the theory. The time dependence of the relation between cyclic creep and static creep is unclear from the short-term data used, but long-term data should clarify the function. With the relation fully defined, it would be a useful extension to the methods of predicting creep given in a number of codes of practice.
Fluid-pressure testing of concrete cylinders
Authors: Clayton N.
Published: October 2009

Synopsis

The paper describes experiments on the behaviour of standard concrete cylinders subjected to fluid pressure applied to their curved surface without the use of an intervening membrane. The results of two sets of tests are given: one set carried out by using water pressure, the other by using nitrogen gas pressure. The fracture pressures of the cylinders are given at each of four different rates of applied pressure, and the significance of the results is stated.
Torsion–shear–flexure interaction in reinforced concrete members
Authors: Ewida A. A. , McMullen A. E.
Published: October 2009

Synopsis

An analysis for predicting stresses, strains and rotations at all levels of load and for predicting the strength of members under combined torsion–shear–flexure loads is presented. Equilibrium and compatibility are considered and the analysis predicts the phenomenon of ‘shear relief’, whereby the torsional strength of an over-reinforced beam is enhanced by a small shear load. A torsion–shear–flexure interaction surface is proposed which is actually a combination of two surfaces. An equation defining the space curve formed by the intersection of these two surfaces is derived. Use of this equation indicates the portion of the interaction surface that is appropriate for a particular combination of loads. The proposed interaction surface is compared with test results available in the literature and good correlation is noted.
Influence of loading history upon the tensile properties of concrete
Authors: Cook D. J. , Chindaprasirt P.
Published: October 2009

Synopsis

In this paper, the influence of sustained and cyclic load regimes upon the tensile properties of concrete and paste is reported. The results indicate that prior loading of any form reduces the strength of concrete on reloading. For paste, however, the effect is not so marked and a slight increase in strength is observed after cyclic preloading. Strain to peak stress on reloading follows the same trends as strength, whilst the elastic modulus of both paste and concrete is reduced on reloading, irrespective of the mode of previous loading. It is considered that, for concrete, the damage resulting from the initial loading produces limited microcracking at the aggregate-matrix interface, which propagates due to a time- (and load-) dependent mechanism previously proposed. For cement paste, the initial damage and hence microcracking is much less and hence the consequent effect of the prior loading regimes upon the properties of the paste is also less than for concrete.
Modelling the stress-strain relationship of structural concrete
Authors: Noor F. A. , Wijayasri S.
Published: October 2009

Synopsis

Recent research has led to an improvement in the properties of model reinforcement, but similitude of deformations, over the complete range of loading, andshear strength has not been achieved. It is well known that a number of size effects are due mainly to the properties of microconcrete because, in comparison with structural concrete, this material is stronger in tension and more ductile in compression. As a result of a detailed investigation into the compressive to tensile strength ratio and the stress-strain relationship of various model concrete mixes, a new type of microconcrete has been produced. The new mix is gap-graded, some of the coarsesand particles being replaced by glass beads, It has been tried in a number of model beams with an over-all depth of 30 mm and has given useful results.
Bimoment design of some rectangular slabs
Authors: Gurley Colin R.
Published: October 2009

Synopsis

This paper continues the development of practicable design-office methods for the plastic (‘yield-line’) design of slabs considered as torsion-free (Hillerborg) grillages. In particular it recognizes a more general class of problem in which the yield lines will be curved on plan andsuggests some expedient approximate methods for such problems. It also treats some cases of slabs which are irregular in that they incorporate cut-outs and/or line loads as well as area-distributed loads.
A graphical solution for predicting the increase in strength of concrete slabs due to membrane action
Authors: Eyre J. R. , Kemp K. O.
Published: October 2009

Synopsis

A simple graphical procedure for determining the effect of membrane action upon the load capacity of a rigid-perfectly-plastic reinforced concrete slab is presented. The load-enhancement-deflection curve is derived by asimple reflection of the yield criterion curve for the concrete section under axial force and moment. The method provides an immediate understandingof the effect of section design upon the load enhancement to be expected from membrane action.