Physical Modeling of Sand Beds Using a New Approacha of Rainer System

Document Type : Original Research

Authors
E. saeedi 1
A. Razmkhah 1
M. Kamalian 2
F. Askari 2
1 Department of Civil Engineering, Faculty of Engineering, South Tehran Branch, Islamic Azad University, Ahang Bld., Abouzar Bld., Basij Highway, Tehran, Iran.
2 Geotechnical Engineering Research Centre, International Institute of Earthquake Engineering and Seismology (IIEES), No. 21, Arghavan Street, North Dibajee, Farmanieh, Tehran, Iran.
10.22034/24.6.55
Abstract
 It is common to apply physical modeling for a more precise investigation of phenomena in geotechnical engineering. The reconstitution of specimens is an appropriate way to study soil behavioral parameters in laboratories due to the restrictions of acceptable undisturbed sample preparation. Reconstitution of the sand sample is one of the most well-known challenges of physical modeling. One of the most significant aspects of physical modeling geotechnical engineering is the repeatability of bed preparation. The reconstitution of sample and bed preparation in physical modeling are divided into two general approaches, depending on the type of porosity control employed. Methods where the porosity is adjusted after deposition, is only appropriate for dense beds with diverse layers. This category includes the methods of tamping and vibration. Another methods where the porosity is controlled during deposition, which aim at obtaining any porosity within the maximum-minimum porosity limits of the material that is pluviation technique. Because of the favorable conditions and prompt modeling it enables, the preparation of layers by the pluviation technique is one of the most reliable bed preparation methods. The pluviation technique can be divided into three categories, air pluviation, vacuum pluviation, and water pluviation. In addition, each category is divided into three minor subgroups that monitor sand-rain outflow intensity as follows, controlling the deposition intensity of sand output from single or multiple nozzles of various shapes, controlling the deposition intensity of the sand output from single or multiple sieves, controlling the deposition intensity of the sand output from longitudinal aperture (curtain pluviation). The effective parameters on pluviation system are deposition intensity and fall height. Deposition intensity, itself, is affected by aperture width, traveling pluviator speed, and the number of opening. The sand reconstitution technique must properly provide real sample conditions in a wide range of soil density (loose to dense), the uniform void ratio in the entire reconstructed specimen, fully saturated conditions for undrained status, the samples should be well mixed without particle size segregation, regardless of particle size gradation and simulation of the studied depositional fabric characteristic.

In this research, a novel approach focusing on a traveling sand pluviator with two apertures was developed for the reconstitution of large-scale samples. Experiments on Iran’s Firuzkuh sand (#161) _Silica sand with fine-grained content of about 1% that is known as the standard sand in Iran and has been the most widely used sand for laboratory studies_ evaluated the effects of opening width, traveling pluviator speed, fall height, and number of openings on deposition intensity and relative density. The results showed that a decrease in deposition intensity is correlated with a decrease in aperture width and an increase in traveling pluviator speed, which significantly enhances relative density. With changes in the effective parameters, a broad range of relative densities could be obtained—from 12 to 93 percent. Comparisons between the findings of the experiments revealed that double-aperture pluviation plate, given the increases in sand outlet and deposition intensity, had a density equivalent to that of single-aperture pluviation plate whit; moreover, each aperture behaved as separate, resulting in prompt sand bed preparation. The findings also revealed that increase in fall height leads to increase in relative density.

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Modares Civil Engineering journal
Volume 24, Issue 6
November and December 2024
Pages 55-68