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Page 337 of 977 Results 3361 - 3370 of 9762

Mirko Marracci, Alessandro Sbrana, Michele Sbrana, Bernardo Tellini
Measurement of subsoil parameters in geothermal heat pump plants

This paper explores the measurements of subsoil parameters in geothermal heat pump systems located in historical centers. A closed loop geothermal system serves the heating and cooling requirements of a wing of the Grand Duke historic Palace in the old town district of Pisa. The subsoil temperatures are measured at different depths and positions around the closed loop probes to investigate the thermal diffusion in the subsoil. Water flows, electrical power, flow and return temperatures and other plant data are analyzed to study the geothermal plant energy behavior during the operation.

Augusto Penna, Gianmario Sorrentino, Alessandro Flora, Armando Lucio Simonelli
An original dynamic interpretation of acceleration time-histories recorded during undrained Triaxial Cyclic Tests

The paper presents the results of laboratory tests carried out on undisturbed specimens of a gravelly soil sampled by in situ freezing. Because of the heterogeneity of the natural deposit, the grain size distribution of the specimens ranged from uniform sand with a very low percentage of gravel to wellgraded sandy gravel, and three different soil groups could be defined according to grain size (respectively named A, B and C). The testing programme comprised drained and undrained monotonic triaxial tests and undrained cyclic triaxial tests, carried out on both isotropically and anisotropically (K0) consolidated specimens. Because of the coarse gradations of the soils, a special large triaxial cell was used. This cell was set up with a wave generator, to apply both shear and compression wave at the base of the specimen, and a devoted acquisition system was set up as well. With these devices, measurements of the soil shear waves velocity (Vs) were achieved, even during the undrained cyclic tests. Thanks to this system it was possible to carry out an original dynamic interpretation of the acceleration timehistories recorded during undrained Triaxial Cyclic Tests.

Augusto Penna, Gianmario Sorrentino, Anna d’Onofrio, Francesco Silvestri, Armando Lucio Simonelli
Dynamic behaviour of the Leighton Buzzard Sand-B under very low confining stresses

The dynamic response of cantilever retaining walls under seismic actions was studied by means of 1-g shaking table at the Earthquake and Large Structures Laboratory (EQUALS) which is part of the Bristol Laboratories of Advanced Dynamics Engineering (BLADE), of the University of Bristol. The soil material used to build the geotechnical model consists of dry, yellow Leighton Buzzard (LB) Fraction B. This soil has been used extensively in experimental researches on shaking table. However, no information on the dynamic behaviour at low confining stress is available for this soil. To fill this gap, dynamic laboratory tests were performed at the Soil Dynamic Laboratory (DynaLab) of the University of Naples Federico II. The main purpose of this experimental activity was to evaluate the dynamic soil behaviour of LBS-fraction B, by means of Resonant Column tests (RC) and Torsional Shear tests (TS) at several confining stresses and different strain levels.

Daniela Dominica Porcino, Valentina Diano
Shear-Wave Velocity-Based Assessment of Liquefaction Resistance of Carbonate Sands

Owing to some peculiar properties of “unusual” calcareous sands, most of which is linked to grain crushability, an accurate evaluation of liquefaction resistance (CRR) of such sediments requires the development of new soil-type specific relationships. An experimental laboratory study based on undrained cyclic simple shear (SS) tests and bender element (BE) tests in triaxial apparatus was performed on a biogenic uncemented carbonate sand, Quiou sand, dug out from a site close to Plouasne (Brittany region, France), in order to seek a relationship between CRR and normalized shear wave velocity (Vs1). Sand specimens were reconstituted for a range of relative densities varying between 30% and 85% by water sedimentation method. The influence of factors affecting Vs and CRR measurements, such as initial void ratio, effective confining stress and reconstitution method were investigated and discussed. The results obtained in the present research together with those of previous studies evidence that the liquefaction resistance of carbonate sands is lower than that predicted by the field-based curves drawn for corresponding silica sands.

Sha Luo, Andrea Diambra, Erdin Ibraim
Particle crushing: passive detection

When the confining pressure is sufficiently large, soil grain breakage can occur and this can have a significant influence on the performance of a wide range of geotechnical systems such as shallow foundations, embankments and dams, railway substructures. However, the mechanics of particle crushing still remains one of the most difficult problems in geomechanics, while the link between the breakage of particles and the mechanical response of the soil through adequate continuum constitutive models has not been solved satisfactorily. This study investigates the possibility of using Acoustic Emission (AE) technique to predict the extent of soil particle breakage and its evolution under loading. Insight into the use of AE to characterize the breakage signature of particles is gained through testing of individual glass spherical particles of different sizes. It is shown that the frequency content of the AE breakage signals does not appear to be affected by the particle size and that suggests that the AE can be directly linked to a typical particle breakage mechanism. At the breakage point all the glass particles disintegrate instantly into small pieces.

Giovanni Biondi, Paola Capilleri, Ernesto Motta
Seismic displacements of retaining walls: shaking table test results vs numerical predictions

The seismic performance of retaining walls is usually evaluated through simplified displacementbased approaches which neglect the change in the soilwall system geometry as displacements develop. In this vein, the paper describes the results of several shaking table tests carried out on a reduced-scale model of a retaining wall placed inside a flexible soil container and subjected to harmonic input motions. In the paper the permanent displacements of the wall and of the retained soil were presented and compared with numerical predictions obtained using a modified Newmark-type model, which encompasses the kinematic compatibility between the wall and the soil.

Alessandro Mandolini, Andrea Diambra, Erdin Ibraim
Evolution of small strain stiffness of granular soils with a large number of small loading cycles in the 3-D multiaxial stress space

The effect of the application of a large number of small loading cycles on the small strain stiffness of granular soils has been explored in the generalized multiaxial stress space using the Hollow Cylinder Torsional Apparatus (HCTA). The experimental investigation has been carried out on an angular to sub-angular silica sand. The sequence of cyclic loading has been performed for a range of stress levels and orientation of the principal stress axes. Accurate measurements of the quasi-elastic properties of the material were obtained using six non-contact dis placement transducer (based on eddy current effect) with a resolution of 0.1 µm. Vertical, circumferential and radial strains of the sample could be accurately measured to obtain accurate estimation of Young and Shear moduli at very small strain levels. Changes in both moduli under a sequence of both axial and torque loading cycles will be presented for different initial multiaxial stress conditions.

Alessandro Pagliaroli, Alessandra Avalle, Paolo Tommasi, Francesca Budillon, Giuseppe Lanzo
Cyclic behavior of soft offshore clays at small to large strains

Two soft offshore clays, recovered from the Adriatic shelf and the Tyrrhenian shelf margin (Italy), were subjected to cyclic simple shear tests. The influence of the cyclic shear strain amplitude as well as of vertical stress, void ratio and stress history on stiffness and damping properties of the soils, in a wide strain range (i.e. from 10-4 % to more than 1%), is examined and discussed. The role of soil structure on the cyclic behavior is also explored.

Grzegorz Andrzej Bialowas, Andrea Diambra, David Nash
Small strain stiffness evolution of reconstituted medium density chalk

The mechanical behaviour of reconstituted chalk deposited has been investigated in a comprehensive experimental campaign using measurement and dynamic testing in the form of bender elements. Characterisation of the small strain shear stiffness (G0) of this material has been performed over a range of the isotropic stress levels and over-consolidation ratios. A variation of (G0) with current stress and overconsolidation ratio is, for the first time, proposed for this material. Following the widespread idea that the process of remoulding chalk may release calcium carbonate, which provides a cementing agent for grain contact overgrowth, the G0 evolution at the constant stress state, over time, has been investigated for curing periods up to 23 days. Regardless of the previous stress path history prior to curing, an increase of the small strain shear stiffness with time was observed under a constant effective stress condition. This appeared to be partly associated with creep (or secondary) deformation but further increase was also observed when measurable creep deformations ceased.

Salvatore Erminio, Andò Edward, Viggiani Gioacchino, Modoni Giuseppe
Compression and extension triaxial tests on sand, studied with X-ray microtomography and digital image correlation

In the usual execution of triaxial tests, the longitudinal and volumetric strains are computed cumulatively from displacements measured outside the sample, and thus interpretation is based on the implicit assumption that samples deform homogeneously. This evident misconception often leads to inconsistent sometimes surprising results, mostly near failure where intensive strain localization usually takes place. Aiming to observe the distribution of strains, a series of triaxial compression and extension tests have been carried out at the Laboratoire 3SR of Grenoble. The tests have been performed on small samples of a uniform sand, tracking the particles movement with x-ray tomography and digital image correlation. This paper illustrates this experimental technique and the methodology adopted for image processing with reference to selected experimental results. The results show that strains tend to concentrate in smaller portions of the sample, starting from early loading steps and evolve in largely different ways for compression and extension tests depending on the applied confining stress.

Page 337 of 977 Results 3361 - 3370 of 9762