bluuebunny/crossref_metadata_2025 huggingface dataset:
Cement fraction effect on EIS response of chloride migration tests
Authors: Hamami Ameur El Amine , Loche Jean-Michel , Aït-Mokhtar Abdelkarim
Published: November 2015

This paper highlights the electrochemical phenomena that occur during chloride migration tests on construction materials. For this purpose, investigations by electrochemical impedance spectroscopy (EIS) were carried out on cementitious and non-cementitious materials. Materials deals with cement paste, mortar and concrete on one hand, and two types of terracotta, pink and brown, on the other hand. The results obtained for these two types of construction materials show that the electrical charge distribution within the material during the chloride transfer depends on the volumic cement proportion in the material. This was highlighted by the establishment of a plateau region at low frequencies of the EIS in the Nyquist plot. Moreover, the extension of the plateau region is closely linked to the volumic cement proportion. These electrical charges could reduce the transfer electrical current, which distorts the estimation of the diffusion coefficients obtained with accelerated tests.
Effect of sodium gluconate on polynaphthalene sulfonate adsorption
Authors: Wu YongHua , He TingShu , Song XueFeng , Liang GuoZheng
Published: November 2015

The influence of sodium gluconate (SG) on the adsorption of polynaphthalene sulfonate (PNS) superplasticiser on the surface of particles was investigated using cement and fly ash pastes. Below the saturated PNS dosage, SG reduces the fluidity loss of the two pastes and the amount of PNS adsorbed on the particle surface. The similarity of this behaviour for the two pastes indicates that inhibition of cement hydration is not the sole reason for SG reduction of fluidity loss of cement paste with PNS. X-ray photoelectron spectroscopy data show competing adsorption forces between SG and polar groups of PNS on the active points of the cement particle surface. This reduces the transformation rate from a caudal style to either a ring or horizontal PNS adsorptive style, as confirmed by dynamic adsorptive models. These are important mechanisms of SG reduction in the fluidity loss of cement pastes with PNS.
Embedding sustainability into geotechnics. Part A: methodology
Authors: Holt D. G. A. , Jefferson I. , Braithwaite P. A. , Chapman D. N.
Published: November 2015

Geotechnical engineering has a crucial role to play in enhancing sustainability due to its key position in the early stages of the construction process, where potentially adverse impacts are highest. Currently, there is a lack of methods with which to assess the sustainability of geotechnical projects that truly encompass the three core pillars (economic, environmental and social). What is required is a system that can offer a holistic approach that is flexible and easily understood while not having a bias towards rewards and not being prohibitively costly. In addition, ‘tool fatigue’, generating a system never to be used, must be avoided. After a detailed review of the systems available, the SPeAR methodology was selected as fulfilling these key criteria. After detailed discussion, the methodology was adapted to ensure it is rationalised into a system that geotechnical engineers can understand and use relatively easily. The adapted version allows greater communication between masterplanning and geotechnical engineering via their common base, thus avoiding a potential barrier to greater adoption of more sustainable practices through the construction cycle.
Assessing embodied energy of building structural elements
Authors: Vukotic L. , Fenner R. A. , Symons K.
Published: November 2015

Although operational energy is currently the focal point of sustainability in building regulations, embodied energy and carbon dioxide emissions will become more significant as operational energy consumption is reduced. In the near future, embodied energy could account for a significant proportion of a building's carbon footprint over its lifetime, bearing in mind that the construction of energy-efficient buildings is carbon and energy intensive. Unlike operational energy, embodied energy savings have an immediate significant effect on carbon footprint and are independent of human behaviour. However, there is a lack of consensus within the construction industry on how to assess embodied energy and carbon dioxide and where to draw system boundaries, which has impeded advancement on the issue. This paper analyses the life-cycle embodied energy and carbon dioxide emissions of a building's structural elements, and examines which stages within a building's life are the most significant and offer the most opportunities for a reduction of embodied energy and carbon dioxide. The embodied energy and associated carbon dioxide at the product and construction, maintenance and end-of-life stages of a structure are examined, as well as the potential for energy recovery and carbon dioxide offsetting. A simple single-storey structure is used as a case study to perform comparative analyses between two structural design alternatives: glue-laminated timber panels and steel frame with infill concrete blockwork.
Monitoring of swelling pressure in bentonite
Authors: Bendito Enrique , Pintado Xavier
Published: November 2015

This paper presents a methodology for determining the radial swelling pressure that develops in a cylindrical plastic cell when the bentonite sample it contains is hydrated. Strains in the cylindrical cell wall are measured using strain gauges fixed to its external surface. The plastic cell material is assumed to behave in an elastic manner at the level of strain developed, and a best-fit solution for the pressure that results in the measured strains is calculated using an algorithm of optimisation. Even though the solution obtained is unique, it is also checked to verify that the calculated radial pressure results in the quantity of elastic energy developed in the cylindrical cell wall being a minimum. While the measurements obtained using the strain gauges allow the evolution of swelling pressure to be monitored from a qualitative viewpoint, the precise quantification of swelling pressure is difficult because not all the required pressure measurements were available. This paper demonstrates that the proposed methodology allows the qualitative monitoring of swelling pressures in bentonite cores during hydration. It also provides the basis for a quantitative procedure to be developed in the future.
Modelling the geotextile tube dewatering process
Authors: Yee T.W. , Lawson C.R.
Published: November 2015

ABSTRACT: The geotextile tube dewatering process consists of multiple cycles of slurry filling and drawdown in order to achieve a desired final volume reduction and solids concentration increase. Relatively simple relationships have been developed in the past to calculate these final volumes and solids concentration values, but the rate of volume reduction and solids concentration increase (i.e. the time periods over which these occur) requires a more sophisticated analysis and modelling approach. The paper develops an analytical model that accounts for dewatering behaviour over multiple dewatering cycles. The model is based on the maintenance of a mass–volume balance at all points in time. Fundamental to the analytical model are two empirically derived dewatering parameters that characterise behaviour during the filling and drawdown phases. Two full-scale field test cases that involve the dewatering of gypsum slurry and contaminated sediments are presented to demonstrate the validity and accuracy of the analytical model. Very good agreements are obtained for the profiles of geotextile tube heights with time, incoming and exiting volumes and final solids concentrations when comparing the modelled results with the actual results.
Model tests of square footing resting on fibre-reinforced sand bed
Authors: Kumar A. , Kaur A.
Published: November 2015

ABSTRACT: This paper discusses the pressure–settlement response from a steel plate load test on poorly graded sandy soil reinforced with randomly distributed fibres. The sand was reinforced with 0.5%, 0.75%, 1% and 1.25% randomly distributed fibres, and the top reinforced layer was separated from the bottom unreinforced layer with the help of a plastic fabric sheet. Pressure–settlement curves were plotted for a footing resting on sand reinforced up to depths of 0.25B, 0.5B, 0.75B, 1.0B, 1.25B and 1.5B below the base of the footing of width B. The results show that there is a significant increase in the ultimate bearing capacity of footing resting on a fibre-reinforced sand bed, and that the inclusion of fibres is more effective if the reinforced sand layer is compacted at a relative density of 55% as compared with that compacted at 25% relative density.
Key parameter for tensile and compressive strength of fibre-reinforced soil–lime mixtures
Authors: Consoli N.C. , Bellaver Corte M. , Festugato L.
Published: November 2015

ABSTRACT: The enhancement of local soils with fibres and cementitious materials for the construction of stabilised pavement bases, canal lining and support layer for shallow foundations shows great economic and environmental advantages, avoiding the use of borrow materials from elsewhere, as well as the need for a spoil area. A dosage methodology for fibre-reinforced, Portland cement treated soils has been previously established, based on rational criteria where the porosity/cement ratio plays a fundamental role in the assessment of the target unconfined compressive strength (qu). The present research has extended such work by quantifying the influence of the amount of lime, the porosity and the porosity/lime ratio in assessing the tensile (qt) and compressive (qu) strength of polypropylene-fibre-reinforced silt–lime mixtures, as well as in the evaluation of the qt/qu relationship. A programme of splitting tensile and unconfined compression tests was carried out in the present study, considering three distinct dry densities and four lime contents, varying from 3% to 9%. The results show that a linear function fits the qt and qu values well with increasing lime content, and a power function fits them well with reducing porosity of the compacted mixture. The porosity/lime ratio is shown to be an appropriate parameter to assess both qt and qu of the fibre-reinforced silt–lime mixtures studied. Finally, the qt/qu relationship is unique for the fibre-reinforced silt–lime mixtures studied, being independent of the porosity/lime ratio.
Experimental and analytical studies of geosynthetic tubes filled with expanded clay lightweight aggregate
Authors: Górniak J. , Villard P. , Barral C. , Delmas Ph. , Watn A.
Published: November 2015

ABSTRACT: A new type of mechanically stabilised earth structure composed of geosynthetic tubes filled with expanded clay lightweight aggregate and backfill with geosynthetic reinforcement is introduced. The results of the study demonstrate that alternative solutions such as expanded clay lightweight aggregates can be used in interaction with geosynthetics in comparison to classical soil. The new type of geosynthetic tubes filled dynamically with expanded clay lightweight aggregate was tested in situ under compressive loading. The geosynthetic tube was instrumented with load cell transducers and the characteristic cross-section was obtained from three-dimensional scanner measurements after loading. Next, a simplified engineering formulation for geosynthetic tubes under compressive loading and unloading was evaluated including the influence of volume variation of the tube. It is based on the classical approach from soil mechanics and it produces the required design tensile force of the tube dependent on geosynthetic stiffness. The experimental results of compressive loading tests were compared with analytical equations. The results are discussed and show the influence of the geosynthetic stiffness on the behaviour of the tube in terms of loading capacity, volume variation and cross-section of the tube. The agreement between theoretical analyses and experimental results was reasonably good and can be formally accepted for a given volume variation of the geosynthetic tube.
Geomembrane damage due to static and cyclic shearing over compacted gravelly sand
Authors: Fox P.J. , Ross J.D. , Sura J.M. , Thiel R.S.
Published: November 2015

ABSTRACT: Several large-scale laboratory tests were conducted on multi-interface geomembrane liner specimens to assess damage effects from static pressure, cyclic loading, and large-displacement static shear. The specimens consisted of compacted subgrade soil, an LLDPE or HDPE smooth geomembrane, and overlying potash salt. The subgrade soil was gravelly sand with 25% gravel content. Failure occurred at the geomembrane/soil interface for each shear test. Cyclic loading data indicated that the LLDPE geomembrane had slightly lower values of interface shear stiffness and damping ratio than the HDPE geomembrane. Shear stiffness was essentially constant and damping ratio decreased with continued cycling for both geomembranes. Geomembrane damage for the static pressure and cyclic loading tests consisted of minor to moderate dimpling, with no holes created. Damage was considerably more severe for the large-displacement shear tests, and consisted of deep scratching and gouging of the geomembranes. Two holes were created in the LLDPE specimen and no holes were created in the HDPE specimen as a result of shear displacement. The findings indicate that severe geomembrane damage can result from shear displacement against a compacted subgrade soil with gravel. Considering that shear displacements commonly occur within landfill liner systems due to such mechanisms as waste settlement, the findings suggest that additional research is needed on expected levels of shear-induced damage for geomembranes placed adjacent to soil layers with coarse particles, including compacted clay liners containing gravel.
Quantification of the adsorption of phenolic compounds on the geotextile and bentonite components of four geosynthetic clay liners
Authors: Ahari M. , Touze-Foltz N. , Mazéas L. , Guenne A.
Published: November 2015

ABSTRACT: The aim of this paper is to present the experimental results obtained regarding the adsorption on various constitutive geotextiles and bentonites of geosynthetic clay liners of phenol, o-cresol, p-cresol, 2-chlorophenol, 4-chlorophenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,3,5,6-tetrachlorophenol, pentachlorophenol, and bisphenol A. These contaminants, including certain derivatives of halogenated phenols, are known to be toxic even at very low concentrations. Geotextiles and bentonites were sampled from four geosynthetic clay liners (GCLs) representative of the GCLs commonly used in bottom liner systems in France. Adsorption was studied through batch adsorption tests. The effect of the nature of the bentonite (sodium versus calcium activated) was studied. Results obtained in this study show that, contrary to what has been observed for volatile organic compounds (VOCs), the adsorption isotherms are non-linear. For VOCs, linear adsorption isotherms are obtained both for geotextiles and for bentonites. The contrast between the adsorption on geotextiles and bentonites is smaller than for VOCs. Up to two orders of magnitude difference can be obtained between the low adsorption coefficient for bentonite as compared with the large adsorption coefficient for geotextiles when adsorption of VOCs is considered. For phenolic compounds, the adsorption coefficients are of the same order of magnitude for bentonite and geotextiles. Two different trends were observed for woven and nonwoven needle-punched geotextiles as regards the adsorption parameters measured. For chlorophenols, polarity appears to affect adsorption: the adsorption coefficients increased with increasing number of chlorine atoms.
The bearing capacity of footings on granular soils. II: Experimental evidence
Authors: LAU C.K. , BOLTON M.D.
Published: November 2015

Scale effects, especially stress-level effects, cause considerable confusion in the calculation of bearing capacity on granular soils. A companion paper describes a new method of calculation that explicitly allows for the variation of sec φ with mean effective stress p. This approach is validated here for the case of model circular footings on dense beds of silica sand and silica silt. The models were tested at 1g with surcharge to explore the Nq behaviour, and in a centrifuge to determine self-weight effects for Nγ. It is shown that triaxial φ values expressed as a function of the logarithm of p can be used to predict model bearing capacities within a deviation in φ of 2°.
Delayed failure of quarry slopes in stiff clays: the case of the Lucera landslide
Authors: LOLLINO P. , SANTALOIA F. , AMOROSI A. , COTECCHIA F.
Published: November 2015

This paper concerns the landslide process occurring on a cut slope in stiff clays located at the north of the town of Lucera in southern Italy. This unstable slope lies between a hospital at the top and an abandoned quarry at the toe: the quarry was active until the end of the 1970s. A first landslide occurred around 1980, and was characterised by a subsequent retrogressive evolution. This paper presents an interpretation of the slope failure mechanism based on the results of geomorphological studies, field monitoring, laboratory testing, and both limit equilibrium and coupled numerical analyses, these latter carried out with FLAC2D. In particular, the numerical analyses have been performed in order to interpret the evolution of the slope movements with time, and to assess the influence of the quarrying-induced excess pore pressures on the development of the failure process. The numerical results show that during the excavation stages the negative excess pore water pressures due to undrained unloading allowed for a temporary stability of the slope. The analyses also indicate that the process of pore pressure equalisation triggered the 1980 failure, and initiated the retrogressive evolution of the landslide.
The ETH Zurich geotechnical drum centrifuge
Authors: Springman Sarah , Laue Jan , Boyle Richard , White Josh , Zweidler Adi
Published: November 2015

A new 2.2 m diameter drum centrifuge with a maximum acceleration level of 440 g has been installed at the Institute of Geotechnical Engineering of the Swiss Federal Institute of Technology in Zurich (Eidgenossiche Technische Hochschule: ETHZ). Twin concentric shafts allow separate control of a central tool table and a drum channel. Together with multipurpose actuator units, which can be fitted to the tool table, radial, circumferential and vertical control of construction processes or test activities may be achieved. Control and data acquisition systems are provided in modular form, allowing a flexible choice of sampling and recording modes. The development of the facility, the additional accessories required and the first geotechnical centrifuge test are described.
Behavior of double sheet pile wall cofferdam on sand observed in centrifuge tests
Authors: Khan Mohammod Ruhul Amin , Takemura Jiro , Fukushima Hiroki , Kusakabe Osamu
Published: November 2015

Behavior of double sheet pile wall cofferdam on sandy soil subjected to high water was studied through a series of centrifuge model tests. Model ground and fill of the cofferdam were made by fine silica sand in a rectangular model container. The model double sheet pile wall cofferdam consisted of two aluminum sheet pile walls, tie rods at the top and also at ground level. Various factors affecting stability of the cofferdam were examined. Under 70g, water was fed into the upstream of the cofferdam to simulate high floodwater until the water level reached nearly to the top of the cofferdam or large deflection of the cofferdam was observed. Test results imply that: (i) the shear deformation of the fill dominates the failure mechanism of the cofferdam, (ii) as the width of the cofferdam increases, the water height at failure increases, (iii) to a certain depth the embedment does not appreciably increase the resistance against high water, (iv) the relative density of the fill and the friction between the walls and the fill contribute to the resistance of the cofferdam against the shear deformation of the fill, (v) the sheet pile wall at the downstream is subjected to higher stresses than the sheet pile wall at the upstream and (vi) double layers of tie significantly increase the lateral resistance of the cofferdam against high water.
Measuring soil thermal resistivity in a geotechnical centrifuge
Authors: Manthena K. Chakravarthy , Singh Devendra Narain
Published: November 2015

Migration of heat through geomaterials is of great importance to various civil and electrical engineering projects. One of the most important properties of the soil, which is necessary for estimating migration of heat through it, is its thermal resistivity. Recent studies have demonstrated usefulness of a laboratory thermal probe in evaluating thermal resistivity of glycerol and various soils compacted to different compaction states. Further, to study the influence of accelerated environment on thermal resistivity of these media, tests were conducted in a geotechnical centrifuge by modifying the laboratory setup, suitably. This technical note presents details of such a study along with details of instrumentation. It has been demonstrated that thermal resistivity of these media remains unaltered in the accelerated environment.
Characterization of failure in sand under triaxial compression using an industrial X-ray CT scanner
Authors: Otani Jun , Mukunoki Toshifumi , Obara Yuzo
Published: November 2015

A new triaxial compression test apparatus was developed for use with an industrial X-ray computed tomography (X-ray CT) scanner and used to characterize progressive failure with strain localization in sand. Performance of the new triaxial compression apparatus was verified separately prior to use within an X-ray CT scanner system. High quality visualizations obtained from a series of nondestructive tests conducted under triaxial compression with the new test apparatus made it possible to visually characterize progressive failure with propagating strain localization in a soil specimen using three-dimensional CT images. Specifications for the new apparatus and procedures for its use were established and potential applications and avenues of further research were discussed.
Mariotte bottle in a centrifuge: a device for constant water table level
Authors: Thorel Luc , Favraud Claude , Garnier Jacques
Published: November 2015

In centrifuge geotechnical modelling, it is often needed to keep constant water table inside the soil sample. When the fluid is expected to move during the experiment (e.g. capillary rise, drainage,…), a special technique should be used. In lieu of the usual overflow pipe with a permanent flow supply, the Mariotte Bottle, a simple closed system, has been developed. The principles and limitations of this new device are described, and an example is given in the field of geo-environmental centrifuge modelling.
Effects of remedial measures for mitigating embankment settlement due to foundation liquefaction
Authors: Okamura Mitsu , Matsuo Osamu
Published: November 2015

In Japan, after the Hyogoken-nambu earthquake remedial measures have often been constructed for river dikes supported on liquefiable sand beds. In this study a series of dynamic centrifuge tests was conducted to assess seismic performances of embankments with and without countermeasures and to provide a basis for establishing conventional methods to evaluate crest settlement. Three types of countermeasures used in the current practice in Japan (the solidification by the deep mixing method, the densification by the sand compaction piles and the sheet pile enclosure) were tested.

It was observed that the excess pore pressure under the embankment toes tends to be higher for models with countermeasures than benchmark models without countermeasures. The horizontal displacement constraint imposed by the remedial zone is considered to be responsible for this. It was also found that the countermeasure techniques could reduce lateral deformation of the liquefied foundation sand and shear deformation of the embankment significantly, however, some embankment crest settlement was inevitable. The higher excess pore pressure under the embankment due to the existence of the remedial countermeasures resulting in an increase in contractive volume change of sand under embankment was responsible for the inevitable crest settlement. It is concluded that displacement predictions of the remediation zone as well as a volumetric strain of the liquefied sand beneath the embankment are key aspects to assess crest settlements.
Cyclic response of axially loaded tapered piles
Authors: El Naggar M. Hesham , Sakr Mohammed
Published: November 2015

Instrumented model piles were used to investigate the fundamental behaviour of tapered and cylindrical piles in loose sand due to cyclic loading, using a centrifuge facility. The objectives of this study were to understand and evaluate the cyclic performance of tapered and cylindrical piles and to investigate the degradation in the pile capacity due to cyclic loading. The results of controlled-displacement cyclic loading tests on twelve one tenth-scale model piles with different taper angles in a centrifuge setup were presented and discussed. Six piles were instrumented and six were not. The load-movement curves of tapered and cylindrical piles were measured and compared. The load settlement curves due to axial compressive loading tests before and after cyclic loading tests were compared as well. The comparison showed that cyclic loading led to a change in the load transfer patterns so that a greater portion of the load was carried by toe resistance and a smaller portion by the shaft resistance. The degradation in the axial capacity for both tapered and cylindrical piles was more pronounced for longer piles (1/d = 26, where 1 is the embedded pile length and d is the average pile diameter). The results of this study suggest that the tapered pile response due to cyclic loading is comparable to that of straight-sided piles.
Pre - and post-cracking behaviour of fibre reinforced concrete beams on grade
Authors: Lin S. , Bischoff P. H. , Valsangkar A. J.
Published: November 2015

Structural design of strip, combined footings, and raft foundations is commonly based on an elastic subgrade assumption. The subgrade is either assumed to be a continuum or to consist of a series of discrete springs and the foundation is assumed to behave elastically. Experimental verification of the simple case of elastic beam on subgrade reaction is reported in the literature, but the data are not extensive. Furthermore, the data pertaining to concrete beams on elastic subgrade before and after cracking is almost non-existent. Therefore, an experimental program was undertaken to study pre- and post-cracking behaviour of steel fibre reinforced concrete beams on elastic subgrade. Two types of subgrade and different end boundary conditions were studied. The beams were subjected to a concentrated point load at the centre. The results of the experimental program are compared with predictions assuming soil to be represented by a series of discrete elastic springs. The results of this study will also help in developing a better understanding of the soil-structure interaction of fibre reinforced concrete slabs on grade, which are being increasingly used in industrial warehouses.
Evaluation of probes and techniques for water content monitoring in geotechnical centrifuge models
Authors: Günzel Friederike K. , Craig William H. , Crancon Pierre , Cottineau Louis-Marie , Kechavarzi Cedric , Lynch Rod J. , Merrifield Caesar M. , Oung Oubbol , Schenkeveld F. M. , Soga Kenichi , Thorel Luc , Weststrate Frans A.
Published: November 2015

Presented in this paper are measurements from five different laboratories with four different probes to determine the moisture content of sand samples in flight on a geotechnical centrifuge. The sensors are resistivity probes, capacitance probes, TDR sensors and Geiger Müller tubes. Experiments were carried out with a sand-water-air system, resistivity probes and TDR sensors were additionally tested in the sand-water-NAPL system. All probes were fast responding and gave reliable and reproducible results during centrifuge tests at up to 40 g. The work presented in this paper was carried out as part of the NECER programme funded by the European Commission.
Cyclic loading of loose backfill placed adjacent to integral bridge abutments
Authors: Cosgrove Edward F. , Lehane Barry M.
Published: November 2015

Abutments for integral (or jointless) bridge decks experience cyclic rotations/translations due to temperature induced expansion and contraction of the decks. These movements generate cyclic displacements within the backfill placed adjacent to the abutment. To assist understanding of the consequences of such displacements, an experiment is described here in which the movements within a laboratory scale model of an abutment and loose backfill are measured. The distributions of displacements and strains within the backfill are recorded using an optical measurement technique. It is found that the cyclic rotations of an abutment in loose sand results in significant volumetric contraction of the sand mass in the area where an active wedge is created. The degree of contraction is related to the abutment rotation and the number of such rotations. Many of the observed features, including the trend for large increases in lateral stresses on the abutments, may be attributed to the tendency of loose backfill to experience strain hardening due to repeated cyclic straining.
Lateral cyclic loading of single piles in sand
Authors: Verdure L. , Garnier J. , Levacher D.
Published: November 2015

A number of tests have been carried out in the last few years at the LCPC centrifuge facility to study the behaviour of laterally loaded piles. This paper presents a centrifuge test programme of lateral cyclic loading of a single pile in sand. In these tests, the pile head fixity is free and the pile is eccentrically loaded since the point of load application is above soil surface (2.2 times the pile diameter). The experimental set up, the data acquisition and the processing techniques are described. Analyses are focused on the influence of cycles on the soil-pile interaction, on the pile head displacements, on the bending moments and on the P-y reaction curves.
The behavior of driven piles in sand - hydraulic gradient and numerical models
Authors: Cohen S. , Klar A. , Frydman S.
Published: November 2015

Hydraulic gradient models were used to study the behavior of driven piles in sand, both in loading and in pullout. In this method, body forces in the model are increased by applying downward seepage through the soil, with the result that the stress and strain fields simulate those in a full scale problem. The tests were conducted in a modified triaxial apparatus. The hydraulic gradient was monitored by 3 piezometers, located at different levels in the sand layer. The 10 mm diameter pile was constructed of 40 mm long, smooth, hollow, stainless steel segments. Three segments, placed at various locations along the pile, acted as load cells, and together with an external load cell, enabled the axial load distribution along the pile to be monitored during a test. It was observed that extremely high friction forces developed towards the tip of the pile during pullout. Numerical analysis has verified that such high frictions may, in fact, be expected to develop.
Shear wave velocity measurement in centrifuge using bender elements
Authors: Fu Lei , Zeng Xiangwu , Figueroa J. Ludwig
Published: November 2015

Measuring soil properties during a centrifuge flight is important for the interpretation and analysis of experimental data. In recent years, progress has been made in developing devices for in-flight measurement. This paper describes the application of the bender element technique in the measurement of shear wave velocities during the flight, spin-up and spin-down of a centrifuge. Three model tests were conducted on a dry sand deposit. The experimental setup, test procedures, and test results are described in detail. The shear wave velocities in horizontal and inclined planes are measured, which are used to calculate the shear moduli in the corresponding shear planes. Test results have good repeatability and agree well with both the results of resonant column tests and calculations conducted with a commonly used empirical equation. This study shows that the bender element technique has a great potential as a reliable and inexpensive method to measure an important soil property during the flight of a centrifuge.
Shaking table tests on model piled rafts in sand considering influence of superstructures
Authors: Matsumoto Tatsunori , Fukumura Kazuyuki , Horikoshi Kenichi , Oki Asuka
Published: November 2015

A series of shaking table tests were carried out on model piled rafts in dry Toyoura sand using a shaking table at 1-g field. Two experimental variables were considered, i.e. frequency of input acceleration and height of the centre of gravity of superstructure, while keeping the mass of superstructure constant. This paper provides experimental results of piled rafts having a rigid connection condition between the raft and the pile heads, and compares them with the results obtained from the static horizontal load tests of the same models, which have been carried out by Matsumoto et al. (2004). Principal findings from the present study are 1) Resonant frequency of superstructure decreases as height of its centre of gravity increases, as expected; 2) At input frequency lower than the resonant frequency, the behaviours of the piled rafts subjected to shaking are close to those obtained from static horizontal loading tests; 3) Even if the horizontal acceleration responses at the centres of gravity are the same, inclination of the raft, shear forces and bending moments of the piles increase as height of the centre of gravity of the superstructure increases.
Centrifuge modelling of heat migration in soils
Authors: Krishnaiah S. , Singh D.N.
Published: November 2015

Modelling heat migration in soils is of great interest in various civil and electrical engineering projects. Researchers have developed several analytical and numerical models to model heat migration in soils and their validity has been demonstrated by conducting conventional laboratory or field experiments. Though laboratory tests are inexpensive, quick and easy to perform, they lack simulation of the prototype conditions in terms of in-situ stresses. To overcome this, field tests, which are relatively costly, time consuming and difficult to perform, are found to be of immense help. In order to overcome these limitations, a geotechnical centrifuge can be used for studying heat migration in the soil mass. To demonstrate the utility of a geotechnical centrifuge for such studies, standard grade sand compacted to different states has been chosen. Using a line heat source, a thermal probe, thermal gradient has been imposed and migration of heat in the soil mass has been studied by recording its temperature as a function of time and radial distance. The study highlights utility of a geotechnical centrifuge in modelling heat transfer in the soil mass.
Sand characterization by combined centrifuge and laboratory tests
Authors: Gaudin C. , Schnaid F. , Garnier J.
Published: November 2015

The purpose of this paper is to evaluate new methods of interpretation of in situ tests in sand from correlations established from centrifuge and laboratory data. Emphasis is given to methods that are based on the combination of measurements from independent tests, such as the ratio of the elastic stiffness to ultimate strength (G0/qc) and the ratio of cone resistance and limit pressure (qc/ΨL). For that purpose, a series of centrifuge tests using a cone penetrometer and a cone pressuremeter was carried out at the Laboratoire Central des Ponts et Chaussées, France. The experimental work prompted the evaluation and development of correlations to derive relative density, friction angle, state parameter, horizontal stress and coefficient of lateral earth pressure at rest. Assessment of the strain field generated by the penetration of a cone is made by carefully monitoring the magnitude of the horizontal stress during penetration using earth pressure cells embedded into sand samples. A proper account of the increasing of horizontal stresses at the location of the borders of the strongbox ensures that usual correlations between parameters can be used in the centrifuge.
Velocity effects on Piezocone measurements in normally and over consolidated clays
Authors: Schneider James A. , Lehane Barry M. , Schnaid Fernando
Published: November 2015

Cone penetration tests (CPTs) performed under controlled conditions in a centrifuge can improve understanding and interpretation of CPT data obtained in the field. However, the cone diameter and cone penetration velocity employed in the centrifuge differ significantly from their respective full scale values and the effect of these scale differences need to be understood to allow extrapolation to the field. This paper examines the influence of cone velocity on tip resistance and penetration pore pressures, and also investigates trends during pore pressure dissipation when cone penetration is halted. Piezocone penetration tests were performed at different rates in normally consolidated and overconsolidated specimens of clay and silty clay in a beam centrifuge. The penetration rate was varied by over four orders of magnitude to provide information on partially drained and undrained penetration resistance and on the associated pore pressure response. The overconsolidation ratio and silt content are shown to have significant effect on the rate dependency of cone tip resistance and pore pressures.
Physical modelling of helical pile anchors
Authors: Tsuha C.H.C. , Aoki N. , Rault G. , Thorel L. , Garnier J.
Published: November 2015

Helical piles design is based usually on empirical correlations between the uplift capacity and the torque resistance of the pile during installation. A simplified theoretical relationship to predict the uplift capacity of deep helical piles in sand from the installation torque was reported. The purpose of the present study was to verify a component of this relationship, related to the contribution of helical plates to the uplift capacity, using centrifuge modelling. A servo-controlled equipment was adapted to carry out the pile installation and pull-out tests in-flight. Twelve different model piles were tested in two sand samples with different relative densities. The results demonstrate strong influence of sand relative density on installation torque and uplift capacity of helical piles. Also, in almost all tests performed the increase in pile sizes and number of helices causes increases in the uplift capacities and installation torques. Generally, in the pull-out tests, the ratio of the measured displacement at failure to the helix diameter was larger in dense sand models, and was not affected by the number of helices. The magnitude of the relationship between uplift capacity and installation torque found in this investigation was in agreement to that observed in true scale helical piles. Direct shear interface tests were conducted to complement this research. The theoretical results compare favorably with the experimental data. This shows that the presented expression is applicable to different pile dimensions, number of helices, and sand relative density.
Centrifuge study on uniformity of wet deep mixing
Authors: Lee F.H. , Lee C.H. , Dasari G.R. , Zheng J.
Published: November 2015

The strength of the stabilised soil after wet deep mixing (DM) operation has often been found to be highly variable. Potential savings may be achieved by improving the uniformity of the DM process. However, the various factors that affect the non-uniformity of wet DM are not clearly understood. Conventionally, DM study is conducted in the field or using reduced-scaled models in 1g environment, which is either very limited (field results) or do not consider the effects of scale distortion (1g models). Using centrifuge modelling with appropriate scaling, this paper presents the details of three in-flight DM-installers, the use of these DM-installers in a number of centrifuge experiments to systematically study the effect of several factors that affect the uniformity of wet DM. Centrifuge results show that uniformity of mixing is affected by density differences between soil and the binder, the withdrawal rate and re-penetration of mixing blade, number of mixing blades and the blade angle. The effect of withdrawal rate, number of mixing blades and re-penetration can be approximately accounted for by the blade rotation number. Density difference between binder and soil was found to have a very significant influence on the uniformity of mixing and cannot be readily compensated for by increasing the blade rotation number. The blade angle also has an influence on the uniformity of mixing, mainly in the radial distribution of the binder within the improved soil.
Container boundary effects in shaking table tests on reinforced soil wall models
Authors: Krishna A. Murali , Latha G. Madhavi
Published: November 2015

This paper studies the seismic response of reinforced soil retaining walls through shaking table tests. The effect of the container boundary on the behaviour of model retaining walls subjected to dynamic base excitation is examined. Two types of containers, a rigid container made of a perspex sheet and a flexible laminar container were used in the tests. Model tests on wrap-faced and rigid-faced reinforced soil walls and unreinforced rigid-faced walls are discussed in detail, including their construction, instrumentation and results of dynamic tests on a shaking table. Horizontal face displacements and accelerations are analyzed to examine the influence of the container boundary on the performance of the walls. From the results, it is observed that the flexible boundary laminar container allows more displacement and larger accelerations compared to the rigid perspex container. Since the soil in a rigid wall container cannot deform as it would in the field and a strain dissimilarity results between the model and the prototype, the response of model walls tested in the flexible container is believed to be more reliable than that of walls tested in the rigid container.
The effect of pile installation method on dynamic pile response
Authors: Stringer Mark , Madabhushi Gopal
Published: November 2015

The widespread use of piled foundations in areas prone to liquefaction has led to significant research being carried out to understand their behaviour during earthquakes. A key challenge in modelling this problem in a centrifuge is the installation procedure, and in most dynamic centrifuge experiments piles are installed before the test commences, either pushing the piles at 1g, or fixing the piles in the model and the sand poured around them. In this paper, a series of dynamic centrifuge experiments are described in which a 2 × 2 pile group is pushed into the model before the test begins and also once the centrifuge has reached the test acceleration. The paper focuses on the key differences which were observed in the pile group’s response to the earthquake motion, and in particular, the very different settlement responses of the pile groups.
A quantitative method for analysing the dispersion of carbon nanotubes in cement composite materials
Authors: Liu Qiaoling , Sun Wei , Ma Zhengxian , Jia Liqun , Pang Lufeng , Zhang Xiuzhi
Published: November 2015

The dispersion of carbon nanotubes (CNTs) within cement-based composite materials plays a key role in determining many essential properties. In this study, a method to quantify the dispersion of CNTs within cement-based composite materials has been developed. The dispersion quantity, D, is measured by the particle size rather than the free-path spacing between particles. The particle sizes are given in terms of the true length/nm rather than pixels. A Gaussian function is used as the probability density function (PDF) fits a Gaussian distribution better than a lognormal distribution depending on the statistical data and the true diameter of CNTs. Higher D values indicate a better dispersion of CNTs in the matrix. The method works well to quantify the dispersion of particles, especially for filaments such as CNTs, and is simple and useful.
Use of wood waste (Aleppo pine) as a superplasticiser in self-compacting mortars
Authors: Daoui Abdelhakim , Safi Brahim , Rezak Malika , Zerizer Abdellatif
Published: November 2015

This study investigated the effect of waste of Aleppo pine wood on the rheological and mechanical properties of self-compacting concrete. Aleppo pine wood is a compound of cellulose, hemicelluloses and more than 25% lignin. The latter belongs to the admixture family used as plasticiser in concrete. An experimental study was conducted to evaluate the rheological and mechanical properties of mortar containing the coupons of Aleppo pine wood (in liquid form) at different dosages. According to the results, the main rheological parameters of cementitious pastes (shear stress and plastic viscosity) decreased with increasing dosage of waste Aleppo pine. The cementitious pastes containing 5% waste, became more fluid, compared to the reference cement paste (containing 1·0% superplasticiser). Also, compared to the reference mortar prepared with superplasticiser, a decrease in compressive strength of mortars with increasing dosage of Aleppo pine wood was found. However, the resistance values obtained by the mortars (5% of Aleppo pine) were very close and gave a mortar with 30 MPa strength, which is an acceptable value for construction.
Influence of pH on the formation of gypsum in cement materials during sulfate attack
Authors: Liu Kaiwei , Deng Min , Mo Liwu
Published: November 2015

Gypsum is usually considered to be one of the main corrosion products during sulfate attack and its negative role has been widely investigated. However, conditions necessary for the formation condition of gypsum are limited and many structures are located at neutral pH. This paper investigates the influence of pH on the formation of gypsum. The system of CaO-SO3-Na2O-H2O was designed to analyse the precipitation of calcium ions with sulfate ions as gypsum in solutions at different pH conditions. Meanwhile, cement mortars were immersed in sulfate solutions at high pH and neutral pH. The products formed in the system of CaO-SO3-Na2O-H2O were examined by using X-ray diffraction (XRD) and a laser scanning confocal microscope. Besides appearance and compressive strength, products formed in mortars during sulfate attack were also investigated with XRD and scanning electron microscopy. The results showed that low pH is beneficial for gypsum formation and promotes the growth of gypsum crystals. Leached portlandite or decalcification of calcium-silicate-hydrate at neutral pH produced more free calcium ions and caused the formation of much more gypsum in interfacial transition zones or matrix, which resulted in the serious mortar damage.