Erdin Ibraim

Behaviour of Sand Reinforced with Fibres

This study focuses on the effects of randomly oriented discrete crimped polypropylene fibres on the mechanical response of very fine sand. Compaction and direct shear tests were performed on sand specimens of different densities unreinforced and reinforced with fibres in different proportions. The presence of reinforcement provides an extra resistance to the compaction, causing a less dense packing as the quantity of fibres is increased. The results of the direct shear tests indicate that inclusion of fibres increases the peak shear strength and the strain required to reach the peak. The post-peak strength at large strains was also higher when fibres were included. The presence of fibres leads to more dilative behaviour. In this study, for the range of the effective normal stresses employed, a linear failure envelope has been recorded for all densities and fibre concentrations. The increase of the peak shear strength was almost linear for all densities at low effective normal stress and approached a limiting value for higher normal stresses. For the loosest specimens reinforced with the highest percentage of fibres that could be employed in the laboratory using a moist tamping fabrication method, the relative increase of the peak shear strength was more than 50%.

New Local System of Measurement of Axial Strains for Triaxial Apparatus Using LVDT

This paper presents a new local system of measurement of axial strains for triaxial apparatus using LVDT. The bodies of four nonsubmersible transducers are supported by an independent circular ring, while the rods are simply put on local targets (pins pushed through the membrane into the sample). A flexible metal plate is used to attach the body of the LVDT to the circular ring and a nonrigid connection is considered between the rod and the pin. These original developments allow the system to investigate the soil behavior in large strains, up to 15 × 10−2 m/m, and to accommodate the radial deformation, tilting, and usually inevitable barreling of the sand specimen. The soil stiffness in the small strain domain, less than some 10−5 m/m, can be evaluated with good accuracy, as well as its evolution during triaxial compression or extension tests. The assessment of errors is discussed and the performance of the device is shown with results of tests on Hostun RF sand.

Theoretical Derivation of Artificially Cemented Granular Soil Strength

AbstractThis paper provides a theoretical derivation for the unconfined compression strength of artificially cemented granular soils. The proposed developments are based on the concept of superposi...

Dynamic Behaviour of Reinforced Soils – Theoretical Modelling and Shaking Table Experiments

The dynamic response of soil-pile-group systems are modelled both analytically, using homogenisation theory, and physically, using a shaking table to excite a soft elastic material periodically reinforced by vertical slender inclusions. A large soil/pile stiffness contrast is shown to lead to full coupling in the transverse direction of the bending behaviour from the piles and the shear behaviour from the soil. Analytically derived performance predictions capture important characteristics of the experimentally observed response that are missed when using alternative analytical modelling approaches. The homogenisation theory approach to modelling of generalised media is valid.

Multi-Building Interactions and Site-City Effect: An Idealized Experimental Model

This chapter aims at identifying, describing and quantifying multi-building interactions and site-city effects through experimental, theoretical and numerical crossed-analysis. Multiple Structure-Soil-Structure interactions are investigated through an idealized experimental model of a city on a soft layer the properties of which are simple enough to be reproduced in numerical and theoretical models. The experimental set-up is designed to provide a good matching between the fundamental frequencies of the city and of the layer. Experimental results show (i) drastic changes in the layer’s response with two low amplitude resonance peaks favorable to longer coda and beatings and (ii) unconventional depolarization effects. The resulting data is compared with the theoretical city-impedance model derived by homogenization methods (Boutin and Roussillon, Bull Seismol Soc Am 94(1):251–268, 2004) and with a 2D hybrid BEM-FEM numerical model (Padron et al., Calculo de estructuras de barras incluyendo efectos dinamicos de interaccion suelo-estructura. Master thesis, Universidad de Las Palmas de G.C., Spain. http://hdl.handle.net/10553/10472, 2004). The specific features of multiple interactions are successfully reproduced by both models providing a qualitative and quantitative agreement with experimental results and with one another.

A sole empirical correlation expressing strength of fine-grained soils – lime mixtures

This paper advances understanding of the key parameters controlling unconfined compressive strength (qu) of lime stabilized fine-grained soils by considering distinct specimen porosities ( ), different lime types and contents and several curing temperatures and time periods. A sole empirical relationship is proposed establishing the normalized unconfined compression strength for lime stabilized fine-grained materials considering all porosities, lime contents, curing temperatures and curing periods studied. From a practical point of view, this means that a very limited number of unconfined compression tests on specific lime stabilized fine-grained material specimens molded with a given lime type and amount, porosity, moisture content and cured for a given time period at a particular temperature, should be sufficient to estimate the strength for an entire range of porosities and lime contents at any given condition. Examples of the practicality of the proposed relationship are presented.

3D fibre architecture of fibre-reinforced sand

The mechanical behaviour of fibre-reinforced sands is primarily governed by the three-dimensional fibre architecture within the sand matrix. In laboratory, the normal procedures for sample preparation of fibre-sand mixtures generally produce a distribution of fibre orientations with a preferential bedding orientation, generating strength anisotropy of the composite’s response under loading. While demonstrating the potential application of X-ray tomography to the analysis of fibre-reinforced soils, this paper provides for the first time a direct experimental description of the three-dimensional architecture of the fibres induced by the laboratory sample fabrication method. Miniature fibre reinforced sand samples were produced using two widely used laboratory sample fabrication techniques: the moist tamping and the moist vibration. It is shown that both laboratory fabrication methods create anisotropic fibre orientation with preferential sub-horizontal directions. The fibre orientation distribution does not seem to be affected by the concentration of fibres, at least for the fibre concentrations considered in this study and, for both fabrication methods, the fibre orientation distribution appears to be axisymmetric with respect to the vertical axis of the sample. The X-ray analysis also demonstrates the presence of an increased porosity in the fibre vicinity, which confirms the assumption of the “stolen void ratio” effect adopted in previous constitutive modelling. A fibre orientation distribution function is tested and a combined experimental and analytical method for fibre orientation determination is further validated.

Compacted Chalk Putty-Cement Blends: Mechanical Properties and Performance

AbstractCompaction and portland cement addition are among the promising ground improvement procedures to enhance the mechanical properties of chalk putty. The present investigation intends to compu...

Experimental investigation of wave propagation in three dimensions in unbounded particulate assemblies

Understanding wave propagation through soils is essential for site response analysis in earthquake engineering, interpretation of geophysical surveys and SASW (Spectral Analysis of Surface Waves), interpretation of laboratory bender element tests, etc. Analysis of wave propagation has largely been based on continuum descriptions and two dimensional analyses. This study presents recent developments in multiaxial testing that permit the combination of laboratory seismic testing with exploration of three-dimensional principal stress space. A Cubical Cell Apparatus with bender-extender piezoceramic elements fitted in all six faces are used so that wave propagation velocities of an analogue granular material can be determined. The results of a first series of wave propagation tests for a sample under isotropic confinement are presented.

In situ experiments and beam modelling of existing buildings

ABSTRACT This article is devoted to in situ measurements on existing buildings and their practical interest. The response to ambient vibrations, harmonic excitation and shock loading is recorded on an intact building so that the modal characteristics can be evaluated. Measurements gathered after modifications of the building bring quantitative answers on the actual influence of light work elements (like secondary dividing walls). The experimental results show that a Timoshenko beam, simply deduced from the internal structure of the building, describes the dynamic behavior with a good accuracy. The discussion of the results emphasizes the advantages of using the small vibrations measurements for the assessment of existing buildings.