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Antlion larvae localize long distant preys by a mechanism based on time diference
Vanessa Martinez, David Sillam-Dussès, Dušan Devetak, Vincent Lorent, Jan Podlesnik, 2024, original scientific article

Abstract: Pit building antlions Euroleon nostras have been submitted to artifcial cues in order to delineate their faculty to localize a prey. Series of propagating pulses in sand have been created from an extended source made of 10 piezoelectric transducers equally spaced on a line and located at a large distance from the pit. The envelope of each pulse encompasses six oscillations at a carrier frequency of 1250 Hz and up to eight oscillations at 1666 Hz. In one set of experiments, the frst wave front is followed by similar wave fronts and the antlions respond to the cue by throwing sand in the opposite direction of the wave front propagation direction. In another set of experiments, the frst wave front is randomly spatially structured while the propagation of the wave fronts inside the envelope of the pulse are not. In that case, the antlions respond less to the cue by throwing sand, and when they do, their sand throwing is more randomly distributed in direction. The fnding shows that the localization of vibration signal by antlions are based on the equivalent for hearing animals of interaural time diference in which the onset has more signifcance than the interaural phase diference.
Keywords: Euroleon nostras, localization, phase time diference, onset time diference, sand-borne vibrations
Published in DKUM: 18.04.2024; Views: 97; Downloads: 4
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Shear modulus of clay-sand mixtures using bender element test
Ali Firat Cabalar, M. M. Khalaf, Zuheir Karabash, 2018, original scientific article

Abstract: Bender-element (BE) tests were conducted on clay-sand mixtures to investigate the variation of small strain-shear modulus (Gmax) with the sand content and the physical characteristics (size, shape) of the sand grains in the mixtures. Three different gradations (0.6–0.3 mm, 1.0–0.6 mm and 2.0–1.0 mm) of sands having distinct shapes (rounded, angular) were added to a low-plasticity clay with mixture ratios of 0% (clean clay), 10%, 20%, 30%, 40%, and 50%. For the purposes of performing a correlation analysis, unconfined compression (UC) tests were also carried out on the same specimens. The tests indicated that both the Gmax and unconfined compressive strength (q u) values of the specimens with angular sand grains were measured to be lower than those with rounded sand grains, for all sizes and percentages. As the percentage of sand in the mixture increases, the Gmax values increase, while the qu values decrease. The results further suggested that the Gmaxvalues decrease as the q u values decreases as the size of the sand grains reduces.
Keywords: sand, clay, bender element, unconfined compressive strength
Published in DKUM: 11.10.2018; Views: 1499; Downloads: 371
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Effects of particle characteristics on the shear strength of calcareous sand
Pham Huu Ha Giang, P. O. Van Impe, W. F. Van Impe, Patrick Menge, Veerle Cnudde, Wim Haegeman, 2017, original scientific article

Abstract: The paper presents a 3D analysis (3DA) to evaluate the particle shape and size of silica and calcareous sands. The particles of calcareous sand are found to be less spherical than those of silica and crushed calcareous sands. Furthermore, the results indicate that the average sphericity (SPH) holds an inverse relationship to the particle size. However, in each sample the larger particles have higher SPHs than the smaller particles. In addition, the 3DA yields smaller particles than the sieve analysis (SA). Owing to a variety of particle shapes, causing particle interlocking, especially for calcareous sand, the particles cannot pass through the sieves by their shortest dimension. This paper discusses the effects of particle characteristics on the shear strength properties. Although the calcareous sand shows higher peak and residual shear strength properties, it tends to reach a lower shear strength at a small shear strain and a lower dilation than the silica sand. Moreover, the findings prove that the residual shear strength increases with the mean particle size. The sample with smaller particles shows less dilation under low vertical stress, while high vertical stress yields less compression. The relationship between the particle shape and shear strength properties is discussed based on the 3DA results.
Keywords: shear strength, sphericity, particle shape, calcareous sand
Published in DKUM: 18.06.2018; Views: 1160; Downloads: 63
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Stress-dilatancy behavior of sand incorporating particle breakage
Fangwei Yu, 2017, original scientific article

Abstract: This paper presents the stress-dilatancy behavior of sand incorporating particle breakage. A series of the drained triaxial tests were conducted on the Silica sand No.5 and the pre-crushed sands that were produced by several drained triaxial tests on Silica sand No.5 under 3MPa confining pressure in simulating the high-pressure shear process to result in particle breakage, to investigate the stress-dilatancy behavior of sand incorporating particle breakage. For a given initial void ratio, particle breakage was found to result in deterioration of the stress-dilatancy behavior in the impairment of the dilatancy of sand to become more contractive with a reduction in the maximum dilatancy angle and the excess friction angle (the difference between the peak-state friction angle and the critical-state friction angle). By introducing the concept of the skeleton void ratio in considering particle breakage, a linear stress-dilatancy relationship between the maximum dilatancy angle-over-the excess friction angle and peak-state skeleton void ratio was proposed in semi-logarithmic plane and popularized to the mobilized stress-stain state as a stress-dilatancy equation pertaining to particle breakage, which would be useful in assessing the evolution of the stress-dilatancy behavior of sand during particle breakage.
Keywords: dilatancy angle, friction angle, particle breakage, sand, triaxial tests
Published in DKUM: 18.06.2018; Views: 1618; Downloads: 103
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Determining the grain size distribution of granular soils using image analysis
Nihat Dipova, 2017, original scientific article

Abstract: Image-processing technology includes storing the images of objects in a computer and processing them with the computer for a specified purpose. Image analysis is the numerical expression of the images of objects by means of mimicking the functioning of the human visual system and the generation of numerical data for calculations that will be made later. Digital image analysis provides the capability for rapid measurement, which can be made in near-real time, for numerous engineering parameters of materials. Recently, image analysis has been used in geotechnical engineering practices. Grain size distribution and grain shape are the most fundamental properties used to interpret the origin and behaviour of soils. Mechanical sieving has some limitations, e.g., it does not measure the axial dimension of a particle, particle shape is not taken into consideration, and especially for elongated and flat particles a sieve analysis will not yield a reliable measure. In this study the grain size distribution of sands has been determined following image-analysis techniques, using simple apparatus, non-professional cameras and open-code software. The sample is put on a transparent plate that is illuminated with a white backlight. The digital images were acquired with a CCD DSLR camera. The segmentation of the particles is achieved by image thresholding, binary coding and particle labeling. The geometrical measurements of each particle are obtained using an automated pixel-counting technique. Local contacts or limited overlaps were overcome using a watershed split. The same sample was tested by traditional sieve analysis. An image-analysis-based grain size distribution has been compared with a sieve-analysis distribution. The results show that the grain size distribution of the image-based analysis and the sieve analysis are in good agreement.
Keywords: image analysis, image processing, grain size, sand
Published in DKUM: 18.06.2018; Views: 1434; Downloads: 154
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Effects of the particle shape and size of sands on the hydraulic conductivity
Ali Firat Cabalar, Nurullah Akbulut, 2016, original scientific article

Abstract: This study aims to investigate the effects of some physical properties of sands (e.g., size and shape) on the hydraulic conductivity (k). The paper presents the results of an extensive series of experimental investigations performed using sands with different sizes and particle shapes. Three different particle size ranges (0.60- 1.18 mm, 1.18- 2.00 mm, and 0.075- 2.00 mm) of sands (i. Crushed Stone Sand, CSS; ii. Trakya Sand, TS; iii. Narli Sand, NS; iv. Fly Ash Pellets, FAP; v. Leighton Buzzard Sand, LBS) having distinct shapes, including roundness, R, and sphericity, S (Ri=0.15, Si=0.55; Rii=0.43, Sii=0.67; Riii=0.72, Siii=0.79; Riv=0.65, Siv=0.89; Rv=0.78 Sv=0.65) were tested in a constant-head permeability testing apparatus at a relative density (Dr) of about 35% and constant room temperature (20°C). The experimental results showed that the sands having different shapes (R, S) with the same size and gradation characteristics (cc , cu , D10 , D30 , D50 , D60) result in different k values. The scanning electron microscope (SEM) images indicate the physical differences/similarities among the sands used during this investigation. A comparative study of the tests results and the estimated hydraulic conductivity values using empirical equations previously developed for the hydraulic conductivity prediction of soils by certain researchers are presented.
Keywords: sand, shape, size, hydraulic conductivity
Published in DKUM: 18.06.2018; Views: 1046; Downloads: 71
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Experimental and numerical studies of T-shaped footings
Nihat Kaya, Murat Ornek, 2013, original scientific article

Abstract: In addition to vertical axial loads, the footings of structures are often subjected to eccentric loads caused by the forces of earth pressures, earthquakes, water, wind, etc. Due to eccentric loading, the two edges settle by different amounts, causing the footing to tilt and then the pressure below the footing does not remain uniform. The T-shape is proposed as a footing shape for improving the bearing capacity of shallow footings against the action of eccentric loads. The vertical insertion of the rigid T-shaped footing, into the bearing soil, provides considerable resistance, against both of sliding and overturning, enough to regain the reduction in bearing capacity and increase in settlement. In this study, a series of experimental and numerical results from the ultimate loads and settlement of T-shaped footings are reported. A total of 48 model tests were conducted for investigating the effects of different parameters, such as the problem geometry and soil density. The problem geometry was represented by two parameters, the load eccentricity (e) and the insertion depth (H) of the T-shape into the loose and dense sand soil. After the experimental stage, the numerical analyses were carried out using a plane strain, two-dimensional, finite-element-based computer program. The behaviour of the T-shape footing on sand beds is represented by the hardening soil model. The results of the experimental and numerical studies proved that the ultimate bearing capacity of a footing under eccentric loads could be improved by inserting a vertical central cut-off rigidly connected to the footing bottom. The load settlement curves indicate that the higher load eccentricity results in a decrease in the bearing capacity of the strip footing. It was also proved that the ultimate bearing capacity values can, depending on the soil density, be improved by up to four times that of the loose sand case. This investigation is considered to have provided a useful basis for further research, leading to an increased understanding of the T-shaped footing design.
Keywords: model test, finite-element method, T-shaped footing, eccentric loading, sand
Published in DKUM: 14.06.2018; Views: 1223; Downloads: 54
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Post-liquefaction volume change in micaceous sandy of Old Gediz River Delta
Ender Basari, Gurkan Ozden, 2013, original scientific article

Abstract: Post-liquefaction settlement characteristics of micaceous sands are not well investigated topic. Currently available charts relating post-liquefaction volumetric strain to relative density were developed for clean sand. Estimation of post-liquefaction settlement of micaceous sands, therefore, may stay on the unsafe side, since there is evidence indicating that mica grains could increase volume change tendency. Influence of mica content on post-liquefaction volumetric strain of sand-mica mixtures is studied in this article. Soil samples were prepared at various relative densities. Influence of fine content that could be present in the field was also investigated on tamped natural field samples recovered from boreholes drilled in a highly populated alluvial site known as the Old Gediz River Delta of Izmir. It was found that increasing mica content at a certain relative density resulted in higher volumetric strains as compared with the data on clean sands. It is deduced that influence of mica grains on sand behavior depends on initial void ratio of sand. Effects of mica grains decrease with increasing of relative density. Simple empirical relationships were derived relating mica content and relative density to volumetric strain. It was also noticed that fine content accelerated and increased post-liquefaction volumetric strains.
Keywords: sand, mica, non-plastic fines, post-liquefaction volume change
Published in DKUM: 14.06.2018; Views: 867; Downloads: 88
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Yielding in the isotropic compression of Porto silty sand
Miguel Ferreira Amaral, Sara Rios, António Viana da Fonseca, 2012, original scientific article

Abstract: The yielding locus of a well-graded silty sand was analysed by means of isotropic compression tests and scanning electron microscopy (SEM). The tests were performed with precise instrumentation, for internal and external strain measurements, and shear-wave velocity measurements by means of bender elements. Finally, aiming at an accurate evaluation of the yield stress, four different methods were applied – two quite well know and the other two being innovative – leading to interesting conclusions.
Keywords: silty sand, yield point, isotropic compression, high pressure, seismic waves
Published in DKUM: 13.06.2018; Views: 1138; Downloads: 90
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Lateral resistance of a short rigid pile in a two-layer cohesionless soil
Erdal Uncuoğlu, Mustafa Laman, 2011, original scientific article

Abstract: The behavior of a laterally loaded short rigid pile founded in a two-layer sand soil profile has been investigated. For this purpose, a series of model tests were carried out on model piles. The effects of the elasticity modulus, dilatancy and interface behavior of the sand have been explored numerically by performing a series of three-dimensional non-linear finite-element analyses. The lateral load capacities in the layered sand conditions have been calculated using the methods proposed by Brinch Hansen (1961) and Meyerhof et al. (1981). The results obtained from experimental studies, numerical analyses and a conventional method were compared with each other. The results proved that the parameters investigated had a considerable effect on the behavior of short rigid piles subjected to lateral loads. It was also shown that the value of the ultimate lateral load capacity could vary significantly, depending on the methods used.
Keywords: lateral load, short pile, two-layered sand, model test, finite element, lateral effective stress
Published in DKUM: 13.06.2018; Views: 1146; Downloads: 95
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