bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of strength non-homogeneity on the shape of failure envelopes for combined loading of strip and circular foundations on clay
Authors: Gourvenec S. , Randolph M.
Published: October 2009

The capacity of surface foundations on clay under pure vertical (V), horizontal (H) or moment (M) loading may be expressed in non-dimensional form through the use of appropriate bearing capacity factors, with values that will be affected by the shape of the foundation and also any variation of undrained shear strength with depth. A common assumption has then been that the shape of the complete failure envelope in three-dimensional loading space (V, M, H) will be similar regardless of foundation shape and soil non-homogeneity, once scaled to the appropriate apex points. The appropriateness of this assumption has been explored by means of two- and three-dimensional finite element analyses of strip and circular footings, for a simple Tresca soil model where the shear strength varies linearly with depth. With a view to applications involving partially embedded foundations, such as offshore skirted foundations, full suction and ‘bonding’ with the underlying soil has been assumed. The paper documents the normalised capacities under uniaxial (V, M or H) loading, and compares the shapes of the failure envelopes in the three planes H = 0, M = 0 and V = 0 for a practical range of strength gradients. The broad conclusion is that a single shape does indeed hold in the M = 0 plane, for both strip and circular foundations, but that for the H = 0 and V = 0 planes the overall size of the normalised failure envelope reduces as the degree of strength non-homogeneity increases. Hence the assumption of a failure envelope shape derived for homogeneous strength conditions would be unconservative.
Characteristics of stress waves recorded in small-scale field blast tests on a layered rock–soil site
Authors: Wu C. , Hao H. , Lu Y. , Zhou Y.
Published: October 2009

A series of field blast tests was carried out in Singapore to study the properties of stress waves inside (free field) and on the surface of a granite site. The stress wave properties inside the granite mass and on the rock surface, such as the peak value and principal frequency, as well as their spatial variations, were reported in a previous paper. Before the blast test, a soil layer of 1·5 m thickness was backfilled and compacted on the quarry test site. Accelerometers were also placed on the surface of the backfilled soil layer, inside the soil mass and on the rock–soil interface. This paper presents the recorded data associated with the backfilled soil layer. The attenuation relations of the peak particle acceleration (PPA), peak particle velocity (PPV) and especially the principal frequency (PF) of the stress wave on the soil surface, inside the soil mass and on the rock–soil surface are derived. They are compared with those recorded inside the granite mass and on the rock surface. Based on the results, the effects of different media on the stress wave propagation are discussed.
Soil deformation measurement using particle image velocimetry (PIV) and photogrammetry
Authors: White D. J. , Take W. A. , Bolton M. D.
Published: October 2009

A deformation measurement system based on particle image velocimetry (PIV) and close-range photogrammetry has been developed for use in geotechnical testing. In this paper, the theory underlying this system is described, and the performance is validated. Digital photography is used to capture images of planar soil deformation. Using PIV, the movement of a fine mesh of soil patches is measured to a high precision. Since PIV operates on the image texture, intrusive target markers need not be installed in the observed soil. The resulting displacement vectors are converted from image space to object space using a photogrammetric transformation. A series of validation experiments are reported. These demonstrate that the precision, accuracy and resolution of the system are an order of magnitude higher than previous image-based deformation methods, and are comparable to local instrumentation used in element testing. This performance is achieved concurrent with an order of magnitude increase in the number of measurement points that can be fitted in an image. The performance of the system is illustrated with two example applications.
Effects of long-term pre-loading on the performance of a footing on clay
Authors: Lehane B. M. , Jardine R. J.
Published: October 2009

An instrumented footing test in Bothkennar clay is described, which examines the effects of a long period of drained pre-loading on the footing's undrained bearing capacity. It is seen that pre-loading induced a significant increase in the subsequent foundation stiffness due to consolidation but also due to creep and ageing processes that led to an outward expansion of the clay's large-strain yield surface. Pre-loading also resulted in a downward shift of the bearing capacity mechanism and an ultimate bearing capacity that was substantially greater than that expected due to consolidation effects alone. Evolving anisotropy and creep are identified as being important contributory factors to the enhanced undrained capacity after pre-loading.
Upper-bound solution for seismic bearing capacity of shallow foundations near slopes
Authors: Askari F. , Farzaneh O.
Published: October 2009

An upper-bound technique of limit analysis is used to determine the bearing capacity of a shallow strip foundation near a slope. The approach used is pseudo-static, and the seismic forces consist of a horizontal load applied to the foundation and the inertia of the soil mass. The failure mechanism is composed of an active wedge, a passive wedge, and a shear transition zone between the two wedges. The results are compared with those of other investigators.
Upper bound limit analysis of circular foundations on clay under general loading
Authors: Randolph M. F. , Puzrin A. M.
Published: October 2009

The bearing capacity of shallow foundations is a classical problem with widespread applications, particularly in modern offshore engineering. Design is typically based on limit solutions for plane strain situations and vertical loading, with semi-empirical adjustments to allow for shape, inclination and eccentricity of the applied load, and for situations where the soil strength varies with depth. The ultimate accuracy of this approach is questionable, and indeed has been shown to be non-conservative where moment loading is involved. Although numerical techniques such as the finite element method are capable, in principle, of providing accurate solutions to specific situations, they are cumbersome to use for parametric studies, and also can lead to unacceptable errors for inexperienced users. The present paper presents new upper bound solutions for circular foundations on clay under general loading conditions. Computation of the three-dimensional mechanisms has been simplified through recent theoretical developments, and the derived failure envelopes offer good accuracy in comparison with finite element solutions. The approach not only provides a relatively simple computational basis for foundation design, regardless of the strength profile with depth, but also opens the door to novel upper bound solutions for a variety of geotechnical problems.
Cavity expansion in cemented materials: structure degradation effects
Authors: Schnaid F. , Mántaras F. M.
Published: October 2009

A numerical solution of a cylindrical cavity expansion problem is presented herein, which is formulated within the framework of non-associated plasticity. The work extends the solution proposed by Mántaras & Schnaid in a companion paper in which a drained analysis has been developed based on postulates embedded on Rowe's stress dilatancy theory. This new formulation aims at demonstrating the significance of structure degradation during shear for a bonded cohesive-frictional material. The proposed solution makes it possible to derive the continuous variations of strains, stresses and volume changes produced around an expanding cavity. The significance of the method is demonstrated by a parametric study designed to highlight the influence of strength reduction during shear on cavity expansion analysis.
A state-dependent elasto-plastic model for saturated and unsaturated soils
Authors: Chiu C. F. , Ng C. W. W.
Published: October 2009

A state-dependent elasto-plastic constitutive model for both saturated and unsaturated soils is presented in this paper. The model, which is developed under an extended critical-state framework, uses two independent stress state variables: net normal stress and matric suction. In addition, the influence of a simplified non-linear soil-water characteristic curve on mechanical behaviour is incorporated in the model by using a bi-linear function. Most importantly, a state-dependent dilatancy formulation is introduced to account for the effects of stress level or stress ratio, internal state (density) and soil suction. In this paper, details of the model formulation and the determination of model parameters are described and reported. By using the new model, numerical simulations of triaxial tests have been carried out on both saturated and unsaturated fine-grained (sandy silt) and coarse-grained (gravelly sand) weathered soils. The simulated triaxial tests include undrained shear tests on saturated specimens, constant water content tests and wetting tests under constant deviator stress on unsaturated specimens. The computed results show that the stress–strain and volumetric-shear–strain relationships at both loose and dense and saturated and unsaturated states can be modelled properly with a single set of parameters. Moreover, the model is capable of capturing some key observed features, such as a sudden increase in shear strain and volumetric strain as suction is reduced under a constant deviator stress.
Fluidisation in artesian flow conditions: Hydromechanically stable granular media
Authors: Vardoulakis I.
Published: October 2009

In this paper a two-phase continuum theory for fully fluidised, fluid-flowing, granular media is presented. The analysis is restricted to the fluidisation process involving internally stable granular media in artesian conditions. Based on fluidised column test results it is demonstrated that, at the state of incipient fluidisation, the material undergoes a discontinuous transition that can be seen as a phase change. The stationary fluidised state is characterised by the development of particle repulsion and the effect of weak inertia on the resistance of the granular bed to flow. Based on Richardson's expansion law it is demonstrated that the adjustment of porosity to small increases in the fluid flow rate may be approximately described by small-amplitude kinematic porosity rarefaction waves. Linear stability analysis of perturbations out of the stationary state of uniform fluidisation shows that granular inertia plays a destabilising role that leads to mathematical ill-posedeness, which in turn is removed by considering the effect of the mixture's viscosity.
Laboratory investigation of multiple grout injections into clay
Authors: Soga K. , Au S. K. A. , Jafari M. R. , Bolton M. D.
Published: October 2009

Compensation grouting is a multiple injection process in which large numbers of grout injections are carried out in a designated grouting zone. Each injection alters the in-situ stress state at the site of neighbouring injections, influencing the grout behaviour as well as the deformation of the surrounding soil. In this study, multiple grout injection tests were performed in the laboratory on clay specimens prepared at different overconsolidation ratios ranging from 1 to 10. Two types of grouting mode for compensation grouting were examined: (a) facture grouting by injecting epoxy resin, and (b) compaction grouting by expanding a latex balloon placed inside the soil specimen. The sequence of multiple injections was also varied by injecting either simultaneously or sequentially with different waiting periods. For highly overconsolidated clay the grout efficiency, defined as the ratio of the volume of heave achieved to the injected grout volume, was close to 1 irrespective of grout spacing and injection sequence. For normally consolidated and lightly overconsolidated clays the grout efficiency increased when the separation in space and time between the injections was reduced. A better grout efficiency was obtained in compaction grouting than in fracture grouting. The results from finite element analyses of the laboratory tests show that the magnitude and extent of excess pore pressure reduce when many closely spaced simultaneous injections are performed. A few non-simultaneous injections create large stress concentrations around the injection points, leading to larger soil consolidation.
Equations for effective stress and permeability of soft mud–sand mixtures
Authors: Merckelbach L. M. , Kranenburg C.
Published: October 2009

Equations for the Terzaghi effective stress and permeability of clay–silt–sand mixtures are derived on the basis of a scale-invariant structure of the soil to enhance physical interpretation of the empirical coefficients. The behaviour of soft sediment is assumed to be dominated by the clay fraction, but the sediment may also contain silt and sand. A theoretical model is presented of the structure of the sediment, based on the concept of a scale-invariant structure of the clay–silt matrix. Using this scale-invariant model, equations for effective stress and permeability are derived. The equations take effects due to partial segregation into account. The equations for effective stress and permeability are validated against data (effective stress, permeability and particle size distributions) obtained from a consolidation experiment with a sandy soft mud. It is shown that the equation for effective stress relates the effective stress to the clay and sand volume fraction accurately for the present data set. The correspondence between modelled and measured permeabilities is only fair, which may be caused either by a shortcoming of the model or by the poor quality of the data.
On the behaviour of deep-ocean sediments
Authors: Baudet B. A. , Ho E. W. L.
Published: October 2009

The behaviour of deep-ocean sediments from the North Atlantic abyssal plains is examined within the context of a recognised framework, the Sensitivity Framework, which was developed by Cotecchia & Chandler for structured terrestrial clays. The deep-ocean sediments have very high sensitivities, of the order of those of quick clays, but in volumetric compression their destructuration occurs at more moderate rates, similar to those usually found in terrestrial clays of medium sensitivities. The deep-sea sediments were retrieved using different types of sampler, which influenced greatly the strength and stiffness of the different samples. In particular, in the lower-quality samples the greater disturbance caused by sampling is responsible for changing their behaviour from brittle to ductile during shearing after compression to stresses post-gross yield, giving them an apparent insensitivity to shear strains. Results from numerical analyses using a constitutive model that was developed for structured terrestrial clays are presented. They show that such a model, which accounts for natural structure, can be used to simulate the behaviour of deep-ocean sediments provided an appropriate destructuration law is used in the model.
Determining effective stress and permeability equations for soft mud from simple laboratory experiments
Authors: Merckelbach L. M. , Kranenburg C.
Published: October 2009

Applying models to describe the self-weight consolidation of soft mud soils requires specification of constitutive equations for the vertical effective stress and permeability. A wide range of constitutive equations exist, each involving soil-dependent coefficients. This paper presents a method for determining the constitutive equations for soft mud from low-cost and easy-to-do laboratory settling column experiments. The method assumes the validity of Gibson's consolidation equation and of the power law constitutive equations proposed by Merckelbach & Kranenburg. Analytical expressions, which take into account partial segregation that may have occurred during the suspension phase of the experiment, were derived for the initial settlement of the mud–water interface as a function of time and for the volume fraction of solids as a function of the depth below the mud–water interface when consolidation is (almost) completed. Determining the coefficients in the constitutive equations with these expressions requires only recording the interface height and a single density measurement at the end of the consolidation process. In addition, an expression for the final bed height is given. This expression can be used as an alternative for the expression for the volume fraction of solids as a function of the depth below the mud–water interface if no density measurement is available. The methods were applied to a data set of settling column experiments with a natural mud from the Dollard tidal basin (The Netherlands). The results were compared with conventionally determined constitutive equations for effective stress and permeability. It is concluded that the coefficients that are determined by new methods compare well with the coefficients that are conventionally determined, even if significant segregation occurred during the suspension phase of the experiment.
3D effects in seismic liquefaction of stochastically variable soil deposits
Authors: Popescu R. , Prevost J. H. , Deodatis G.
Published: October 2009

The natural variability of soil properties within geologically distinct and uniform layers has been proven to greatly affect soil behaviour and to induce significant variability in the predicted response. Previous studies concluded that small-scale heterogeneity greatly affects the liquefaction potential of saturated soil deposits, and provided geotechnical design guidelines to account for the effects of various characteristics of spatial variability. Those studies were based on two-dimensional analyses of soil liquefaction (in a vertical plane) assuming plane strain behaviour. Therefore the correlation distance of soil variability in a direction normal to the plane of analysis was implicitly taken as infinite (i.e. no variability in the third direction). In this study, a Monte Carlo simulation approach involving generation of sample functions of non-Gaussian, multivariate, multidimensional random fields and non-linear finite element analyses is used to investigate the effects of soil heterogeneity on the liquefaction potential of a ‘stochastically heterogeneous’ soil deposit subjected to seismic loading. To assess the 3D effects, Monte Carlo simulation results obtained for a 3D soil deposit are compared with corresponding results from 2D plane strain analyses. The calculations are performed for a range of seismic acceleration intensities, and the results are presented in terms of fragility curves expressing the probability of exceeding various thresholds in the response as a function of earthquake intensity.
On horizontal variability in lime-cement columns in deep mixing
Authors: Larsson S. , Stille H. , Olsson L.
Published: October 2009

The variability with respect to results from hand-operated penetrometer tests on lime-cement column cross-sections is investigated by means of spatial correlation structures. Experimental directional semi-variograms are evaluated for a large number of column cross-sections from two field tests. Analyses of variance (ANOVA) are performed in order to investigate the influence of various factors in the installation process on the inherent variability. The paper also briefly discusses the concept of sufficient mixing: the link between the mixing process and the mechanical system. The results have been interpreted within the framework of variance reduction based on an averaging model for axially loaded columns. The results from the two field tests show that the radius is the dominating variable in the variability, and different types of correlation structure can be obtained in spite of the fact that they have been equally installed. The mechanical mixing work does not significantly influence the type of spatial correlation structure. Furthermore, a simple design consideration shows that the variance reduction has a major influence on the determination of the partial factor of safety.
Reliability of traditional retaining wall design
Authors: Fenton G. A. , Grifﬁths D. V. , Williams M. B.
Published: October 2009

Retaining wall design has long been carried out with the aid of either the Rankine or Coulomb theories of earth pressure. To obtain a closed-form solution, these traditional earth pressure theories assume that the soil is uniform. The fact that soils are actually spatially variable leads, however, to two potential problems in design: do sampled soil properties adequately reflect the effective properties of the entire retained soil mass, and does spatial variability of soil properties lead to active earth pressure effects that are significantly different from those predicted using traditional models? This paper combines non-linear finite element analysis with random field simulation to investigate these two questions and assess just how safe current design practice is. The specific case investigated is a two-dimensional frictionless wall retaining a cohesionless drained backfill. The wall is designed against sliding using Rankine's earth pressure theory. The design friction angle and unit weight values are obtained by sampling the simulated random soil field at one location, and these sampled soil properties are then used as the effective soil properties in the Rankine model. Failure is defined as occurring when the Rankine predicted force acting on the retaining wall, modified by an appropriate factor of safety, is less than that computed by the random finite element method employing the actual soil property (random) fields. Using Monte Carlo simulation, the probability of failure of the traditional design approach is assessed as a function of the factor of safety used and the spatial variability of the soil.
A generic approach to soil–structure interaction considering the effects of soil heterogeneity
Authors: Breysse D. , Niandou H. , Elachachi S. , Houy L.
Published: October 2009

The longitudinal variation of soil properties has a major influence for many types of structure, including pavements, buried pipes, raft foundations and railways, as it induces stresses and/or displacements that cannot be predicted when assuming soil homogeneity. A set of simple numerical models has been developed to describe how soil–structure interaction can be influenced by soil variability. These models include: (a) a description of the soil spatial variability, within the frame of geostatistics, where the correlation length of soil properties is the main parameter; and (b) a mechanical description of the soil–structure interaction, which depends on the structure resting on the ground. There are some differences between a (more or less) rigid raft on piles, a set of buried pipes with (more or less) flexible connections and a hyperstatic beam, but the basic principles of mechanics are similar in all these cases. Several very general conclusion are drawn. (a) Soil heterogeneity induces effects (differential settlements, bending moments, stresses and possible cracking) that cannot be predicted if homogeneity is assumed. (b) The magnitude of the induced stresses depends on three factors: the magnitude of the soil variability (i.e. its coefficient of variation); a soil–structure stiffness ratio (in some cases, where the mechanics are more complex, one can consider two stiffness ratios, as in buried pipes for example, when one has to account for the flexibility both of the pipes and of the connections); a soil–structure length ratio, which combines the soil fluctuation scale and a structural characteristic length (distance between supports, buried pipe length, etc). In all cases, a worst value, corresponding to the value leading (from a statistical point of view) to the (statistically) largest effects in the structure, can be found. The principal benefit of such an approach is to provide some new approaches for better considering phenomena such as the geometrical irregularities in the longitudinal profile of pavements or during the control of soil compaction of sewer trench filling. This kind of approach can also give experts new tools for better calibration of safety in soil–structure interaction problems, when the soil variability is an influential parameter. Some practical conclusions are drawn in this direction.
Geostatistical method for analysing soil displacement from underground urban construction
Authors: El Gonnouni M. , Riou Y. , Hicher P. Y.
Published: October 2009

The aim of this study was to assess the influence of uncertainties related to soil variability in the numerical modelling of settlements caused by underground work. Based on a large number of in situ tests, a geostatistical method, kriging, applied to the stratigraphy of the sub-surface was justified and used in order to determine the mean position of the soil layers and their estimation variances. In a first stage, the influence of the uncertainty in the soil stratigraphy on the calculated surface settlements was analysed. In a second stage, a stochastic finite element method was used to introduce the influence of uncertainty in the soil mechanical parameters on the predicted surface settlements.
Laboratory investigation of permeability measurement in clay using outflow from unsupported cavities
Authors: Hird C. C. , Srisakthivel S.
Published: October 2009

Specimens of reconstituted clay were contained under vertical pressure in a 250 mm diameter cylindrical test cell fitted with a peripheral drain. Using a self-boring device, a 35 mm diameter cavity was formed in the centre of each specimen, and outflow permeability tests were performed to simulate possible in situ test procedures. Either the cavity extended over the whole specimen height and radial flow conditions prevailed, or the cavity was shorter and a steel lining was progressively withdrawn to induce both vertical and radial flow. Generally, the cavities were observed to degrade and partially fill with softened material, yet the measured permeabilities were higher than expected on the basis of other information. Pore water pressure measurements suggested that hydraulic fracturing was taking place around the cavities, even though applied pressure heads were very small. Fractured material is then thought to have fallen into the cavities. In specimens containing silt layers, the cavities did not degrade so much, and more satisfactory permeability measurements proved possible. The results suggest that the assumption of a stable cavity, necessarily made when interpreting some in situ tests, may not be justified.
The causes of apparent overconsolidation in the Namak marine deposit, Korea
Authors: Won J. Y. , Chang P. W.
Published: October 2009

An intensive experimental study was carried out to investigate the causes of the overconsolidation phenomena in the Namak New City site, Korea. Geological events in conjunction with sea level changes, groundwater fluctuation, weathering, leaching and cementation were examined as possible causes of overconsolidation. In addition to oedometer and triaxial tests, radiocarbon dating, geochemical components and pore water chemistry were analysed. It was shown that the overconsolidation in the upper marine clay deposit was not caused by stress reductions such as erosion and groundwater fluctuation. Furthermore, weathering or leaching seemed unlikely. The apparent overconsolidation can be explained by cementation, which is indicated by profiles of the sulphate and potassium ion concentrations in the pore water. At the early stage of the Holocene marine deposition, the rate of deposition was 4·4 mm/yr; thereafter it was reduced to 1·4 mm/yr, controlling chemical processes such as sulphate reduction and ion exchanges and, in turn, apparent overconsolidation. Some mechanical and chemical properties of the apparent overconsolidated clay were compared with the geologically overconsolidated Palaeosol layer in the site.
Limit analysis with anisotropic fibre-reinforced soil
Authors: Michalowski R. L.
Published: October 2009

Fibre reinforcement is a technology to improve the strength of soils used as fill in geotechnical structures. The properties of the fibre-reinforced sand are anisotropic because of the distribution of orientation of the fibres, which is characterised by a preferred bedding plane. The development of an anisotropic yield condition for fibre-reinforced sand is presented. Application of the kinematic approach of limit analysis to anisotropic frictional materials is demonstrated. An interesting implication of anisotropy is a lack of uniqueness in the internal friction angle along a shear surface with given orientation. The anisotropic internal friction angle was found to be a function of the major principal strain rate direction, and not just a function of the orientation of the shear surface. While the inclination of principal strain rate directions can be inferred from the kinematics of the mechanism for a given boundary value problem, the internal friction angle cannot be determined a priori as a unique function of orientation in space. Two examples are presented to illustrate the use of the kinematic approach for anisotropic frictional materials: retaining wall loading, and the bearing capacity of a footing.
Load–displacement solutions for piles and shallow foundations based on deformation fields and energy conservation
Authors: Klar A. , Osman A. S.
Published: October 2009

The paper presents an energy approach for the prediction of non-linear foundation behaviour. The formulation entails three main stages: (a) assumption of admissible pattern functions from which displacement fields can be assembled; (b) equating external work to internal work; and (c) minimisation of internal work by variation of the displacement field using the different pattern functions. The approach is demonstrated on two problems: (a) a vertically loaded shallow foundation; and (b) laterally loaded piles. The approach is evaluated by comparison with finite difference analyses using three different constitutive models. It is shown that the approach provides a fair estimation of the overall foundation response. Under large displacements the method degenerates into conventional upper-bound calculations.
Probabilistic soil identification based on cone penetration tests
Authors: Jung B.-C. , Gardoni P. , Biscontin A.
Published: October 2009

In geotechnical engineering, soil classification is an essential component in the design process. Field methods such as the cone penetration test (CPT) can be used as less expensive and faster alternatives to sample retrieval and testing. Unfortunately, current soil classification charts based on CPT data and laboratory measurements are too generic, and may not provide an accurate prediction of the soil type. A probabilistic approach is proposed here to update and modify soil identification charts based on site-specific CPT data. The probability that a soil is correctly classified is also estimated. The updated identification chart can be used for a more accurate prediction of the classification of the soil, and can account for prior information available before conducting the tests, site-specific data, and measurement errors. As an illustration, the proposed approach is implemented using CPT data from the Treporti Test Site (TTS) near Venice (Italy) and the National Geotechnical Experimentation Sites (NGES) at Texas A&M University. The applicability of the site-specific chart for other sites in Venice Lagoon is assessed using data from the Malamocco test site, approximately 20 km from TTS.
Collapse load of deep reinforced concrete beams
Authors: Kumar Prabhat
Published: October 2009

Synopsis

A truss model is analysed to estimate the collapse load of a deep beam with a shear-span|effective-depth ratio of less than 1·0. The expressions for collapse load in the flexural and shear-proper modes of failure, as well as expressions for the value of the reinforcement ratio separating them are derived and verged against the available test results. Good agreement is found. An analysis of the beams containing web reinforcement is also presented and verified against the available test results with good agreement. Finally the design of deep beams in practice is considered and a design example is given.
Creep, shrinkage and elastic strain in concrete bridges in the United Kingdom, 1963–71
Authors: Tyler R. G.
Published: October 2009

Synopsis

Long-term creep and shrinkage measurements carried out on concrete bridges in England in the period 1963–71 are summarized. The concretes used were mainly of the 50 N/mm2 class. Typically, on the full scale, shrinkage was shown to be about 200 × 10−6 and the creep factor, defined as the ratio of creep to elastic strain to time infinity at the centroid of a prestressed concrete member for a decaying prestressing force, to be about 2·0. The most likely cause of cracking soon after casting was shown to be the early-age thermal movement caused by the hydration of the cement. Results show that creep and shrinkage usually increase linearly with the logarithm of time, with cyclic seasonal variations. The effect of the seasons upon the calculation of movements is discussed.
The strain capacity of compression-zone concrete subjected to short-term loading
Authors: Phipps M. E.
Published: October 2009

Synopsis

Values and distribution of concrete compression strain from prism and structural member tests have been reported by many investigators. Much of the information indicates that strain measurements in concrete are irregular and unpredictable. In this paper, tests are described which show that, for eccentrically loaded plain concrete prisms, the surface compression strain over the length of the failure zone can be assessed to within ± 20%. This strain is shown to be dependent upon the depth to the neutral surface and the depth of any tension concrete adjacent to the compression concrete. The length of the compression failure zone is related to the depth to the neutral surface, but does not appear to be affected by adjacent tension concrete. In studying the effects of different depths of compression and tension concrete, a theory of failure for concrete in compression was evolved. This theory suggests that the strain capacity of concrete in compression, and so the deformation capacity of structural concrete in general, is dimension- or size-dependent.
The disintegration of concrete containing sulphate-contaminated aggregates
Authors: Samarai Mufid A.
Published: October 2009

Synopsis

Problems related to concreting in the Middle East and similar localities have renewed interest recently in the disintegrating effect of sulphate-contaminated aggregates. The paper describes a research programme initiated to study the influence of sulphate-contaminated fine aggregates upon the strength and volume changes of cement mortars. Experimental details are given of tests carried out on more than three thousand specimens. Factors such as type of cement, sulphate content and tricalcium aluminates were fully studied. Allowable limits for the SO3 content that can be incorporated into the concrete without adversely affecting its properties were established.
Ultrasonic assessment of concrete strength at early ages
Authors: Elvery R. H. , Ibrahim L. A. M.
Published: October 2009

Synopsis

This paper describes tests carried out to examine the relationship between ultrasonic pulse velocity and cube strength of concrete from ages of about 3 h over a curing temperature range from 1 to 60°C. It is found that this relationship is practically independent of water/cement ratio and temperature but influenced by both aggregate content and type of cement. Strength estimation from pulse velocity was found to be less reliable for velocities less than about 2 km/s than it is for higher velocities. Prediction of 28 day cube strength from early-age pulse velocity is possible with some limitations, particularly with regard to temperature effects.
A study of the applicability to the fatigue of concrete of the Palmgren-Miner partial damage hypothesis
Authors: Tepfers Ralejs , Fridén Claes , Georgsson Leif
Published: October 2009

Synopsis

This investigation provides some information concerning the applicability to the fatigue of concrete of the Palmgren-Miner partial damage hypothesis. The results do not contradict this hypothesis. The tests were performed on small concrete cylinders at high load-alternation frequencies. A Wöhler curve plotted for the concrete cylinders shows that fatigue in these occurs in the same way as in large specimens subjected to lower load-alternation frequencies. Fatigue of concrete due to non-alternating variable load pulses can be calculated from an expression relating to the Wöhler curve for concrete, combined with the Palmgren-Miner partial damage hypothesis.
Tests on concrete beams with mixed types of reinforcement
Authors: Taylor R. , Mills P. E. , Rankin R. I.
Published: October 2009

Synopsis

Tests are reported on twenty-five concrete beams in which the reinforcement at the soffit of each beam consisted of a combination of a structural steel channel and very-high-strength reinforcement. In some cases, this very-high-strength reinforcement took the form of prestressing strand. The tests fall into two parts, one relating to the flexural strength of the beams, the other relating to their shear strength. In all cases, the behaviour of the beams was similar to that of normal reinforced concrete. For the beams failing in flexure, it was found that the strain-compatibility method of calculation in CP 110 predicted the failure load quite accurately, even though stresses in the reinforcement attained values up to three times the maximum at present permitted in the code of practice. The beams failing in shear were somewhat stronger than the requirements for shear in CP 110 would suggest.
Compressive strength and ultimate strain of concrete under impact loading
Authors: Hughes B. P. , Watson A. J.
Published: October 2009

SYNOPSIS

A drop-hammer test has been used to measure the compressive strength, ultimate strain, energy absorption and deformation modulus of concrete cubes under impact loading. By assuming a trapezoidal function for both the hammer impact pulse and the cube impedance function, hypothetical load and strain records have been derived which are similar to the initial experimental records measured on an oscilloscope. Concretes with varying mix proportions and two different coarse aggregates were examined and the results for compressive strength and ultimate strain are reported.
Deformation and fracture of plain concrete
Authors: Lowe P. G.
Published: October 2009

SYNOPSIS

Despite a great volume of investigation of the deformation and fracture of concrete, there appears to be no coherent model available to explain the observations. In this paper there is attempted an explanation of the available experimental data derived from 'triaxial' testing of concretes in terms of a theory of simple elastic deformation and tensile strain fracture. It is argued that there is sufficiently good agreement between theory and a number of the prominent features of the experimental data to warrant further investigation and elaboration of the general theme of strain rather than stress limitation as the primary feature of concrete fracture behaviour.
Expansion of concrete due to alkali—silica reaction: an explanation
Authors: Hobbs D. W.
Published: October 2009

SYNOPSIS

The literature dealing with the alkali—silica reaction is briefly introduced and experimental data are given which illustrate the relationship between expansion, reactive-aggregate content and concrete age. A simple explanation is given to account for the observed data.
A mathematical description of the deformational behaviour of concrete under complex loading
Authors: Kotsovos M. D. , Newman J. B.
Published: October 2009

Synopsis

A mathematical description of the deformational behaviour of concrete under any type of short-term static loading is developed, using a model material with the same strength characteristics. The mechanical properties of the model are defined by analysing experimental data obtained at Imperial College from tests on concrete under various states of multiaxial stress. The testing techniques used have been validated by comparing the results obtained with those produced by other institutions investigating the behaviour of concrete under similar stress conditions but with different apparatus. In the analysis, each stress and strain state is resolved into a hydrostatic and a deviatoric component and it is assumed that any non-linear material behaviour is dictated mainly by fracture processes occurring under increasing stress.
Further development of the two-point test for workability and extension of its range
Authors: Tattersall G. H. , Bloomer S. J.
Published: October 2009

Synopsis

Apparatus has been developed to measure the flow curve of concretes of medium to high workability. An impeller in the form of an interrupted helix is rotated uniaxially in the concrete by means of a hydraulic transmission and the torque is determined from measurement of the oil pressure. The flow curves conform closely to the Bingham model and, by suitable calibration, it is possible to express values of yield stress and plastic viscosity in fundamental units.
The effect of aggregate concentration upon the strength and modulus of elasticity of concrete
Authors: Stock A. F. , Hannantt D. J. , Williams R. I. T.
Published: October 2009

Synopsis

The paper presents details of art investigation into the effect of aggregate concentration upon the strength and modulus of elasticity of concrete in both uniaxial tension and uniaxial compression. The test results relate to cement paste and to mixes containing 20 to 80% by volume of a graded aggregate. Emphasis was placed on accurate determination of the specific gravity and absorption of the constituent aggregate size fractions in an attempt to maintain a constant free water Icement ratio in the various mixes. The specimens were continuously rotated during the setting period in order to minimize settlement of the aggregate particles. The results suggest that the strength of cement paste in tension and in compression is reduced by the addition of 20% by volume of graded aggregate, falling to a minimum value at a volume fraction of 30 to 35% and then increasing with further addition of aggregate. In contrast, the modulus in tension and in compression increases with the addition of aggregate and the measured values are compared with theoretical predictions based upon the laws of mixtures.
Workability of flowing concrete
Authors: Banfill P. F. G.
Published: October 2009

Synopsis

By using the two-point test for workability, the effect of concentration of superplasticizing admixture upon workability has been found to be independent of the types of admixture and cement, Differences in the effects of proprietary admixtures are due to their different solids contents. The yield value of concrete decreases to a minimum, beyond which further additions of admixture promote segregation. Loss of workability is not necessarily more rapid in flowing concrete, and re-dosing enables workability to be maintained for more than 160 minutes without detriment the hardened strength. The melamine formaldehyde admixture caused more rapid workability loss than the naphthalene formaldehyde admixture tested, but a specific interaction between the former and a cement of low C3A/SO4 ratio was found. An acceptance criterion for flowing concrete is proposed.
Rigid–plastic theory v. truss analogy method for calculating the shear strength of reinforced concrete beams
Authors: Campbell T. I. , Chitnuyanondh L. , de V Batchelor B.
Published: October 2009

Synopsis

A comparison is made between the web crushing strengths of reinforced concrete beams predicted by a model based on the theory of plasticity and by a variable-angle truss model. The theory of plasticity model assumes rigid–plastic behaviour of the constituent materials, whereas the variable-angle truss model incorporates their actual stress–strain characteristics. It is shown that neglect of the deformations in the web steel prior to yielding and in the concrete prior to crushing leads to a high prediction for both the amount of web reinforcement required for a balanced section and the ultimate capacity of a section which is over-reinforced for shear. However, both approaches yield the same capacity for a section which is under-reinforced for shear.
The practical use of ultrasonic pulse velocity measurements in the assessment of concrete quality
Authors: Tomsett H. N.
Published: October 2009

Synopsis

The wider use of limit-state methods for the design of structures has increased the desirability of being able to assess the quality of a structure as built rather than isolated test pieces of the material supplied. Ultrasonic pulse velocity measurements are a particularly suitable way to measure the quality of a concrete structure, although the importance of competent engineering judgement in their analysis must be properly stressed. This paper indicates some ways in which the pattern of pulse velocity measurements may be used to assess the quality of concrete construction. The suggested patterns have been derived by applying the fundamental relationships, obtained by research, to site surveys and assessing the deviations permissible before the variations from the normal indicate a defect of engineering significance. The comparative evaluation of structural strength is also discussed.
The point-load strength test for concrete cores
Authors: Robins P. J.
Published: October 2009

Synopsis

The point-load test, commonly used in geotechnical practice, is evaluated for application in concrete testing. The method uses portable equipment to test concrete cores which require no further preparation after removal from the structure. This paper examines the results of a laboratory investigation in which over 450 cores were cut and tested. The influence of specimen and aggregate size, core-length/diameter ratio, and aggregate type upon point-load strengths is examined, and minimum values for the length/diameter and diameter/aggregate-size ratios are proposed. For concrete strengths greater than 20 N/mm2 a linear relationship between core point-load index and cube compressive strength was observed, and the variability of the point-load strengths compared favourably with values reported for compressive testing of cores. The advantages of both the point-load test and the uniaxial compression test for cores are discussed, and it is argued that, provided a satisfactory method can be found for estimating the effect of the coarse aggregate type upon the point-load strength index, this simple test offers a practical alternative to the compressive testing of cores.
Behaviour in shear of beams with flexural cracks
Authors: Hamadi Y. D. , Regan P. E.
Published: October 2009

Synopsis

The paper aims to clarify the way in which a reinforced concrete beam with a plain web resists shear, with particular reference to the transfer of shear forces across jkxural cracks by the action known as ‘aggregate interlock’ or ‘interface shear’. Tests were made on special specimens to study the interlock phenomonen and dowel action in isolation and on ordinary rectangular reinforced concrete beams without web reinforcement. Measurements of movements at cracks in all the tests enabled the distributions of forces at cracked sections to be estimated. From the information obtained in this way, a rational equation is developed for the prediction of diagonal tension strength. The study was made using three different aggregates – a natural gravel, and two types of lightweight aggregate.