جستجوی مقالات مرتبط با کلیدواژه "colloidal silica" در نشریات گروه "عمران"

Chemical injection is a useful geotechnical procedure for stabilizing soils and also making them impermeable. For characterizing the soil stabilized by colloidal silica, the clean and silty sand samples with silt values of 20 and 40 percent, in both unstabilized and stabilized conditions, were prepared with different concentrations of the stabilizer from 5 to 30 percent, and the effects of colloidal silica on its behavior were evaluated under cyclic loading. 30 cyclic triaxial tests were performed on various samples. A 100 kPa confining pressure was used in these tests. All 15 experimental samples were loaded at cyclic stress ratios of 0.2 and 0.4 with a frequency of 1 Hz and up to 200 sinusoidal cycles. In this research, for the stabilized and unstabilized samples, the double amplitude of axial strain of five percent or the pore water pressure ratio of one, whichever occurs earlier, was considered as the liquefaction criterion. By performing cyclic triaxial tests, it was observed that by stabilizing clean and silty sand with colloidal silica, liquefaction phenomenon is postponed. Thus, adding even low concentration of colloidal silica such as 5 percent can prevent liquefaction of soil at the low level of dynamic loads (such as cyclic stress of 0.2). By adding colloidal silica, the double amplitude of axial strain and the pore water pressure ratio were reduced in cyclic loading. For example, in silty sand with a silt content of 40%, by increasing the stabilizing concentration from 10% to 30%, the pore water pressure ratio reduced from 1 (the state of full liquefaction) in 10 cycles to about 0.1 in 100 cycles, and also the double amplitude of axial strain decreased from 5% in 10 cycles to about 0.7% in 100 loading cycles. Gelatinization of colloidal silica between soil grains causes elastic behavior for the soil sample and prevents permanent deformation between soil grains. Reducing permanent deformation in undrained conditions reduces the development of excess pore water pressure in the soil during cyclic loading. The choice of colloidal silica concentration to prevent the liquefaction of sand and silty sand in a specific area depends on the cyclic stress ratio in that area; thus, at a cyclic stress ratio of 0.2, colloidal silica concentration of five percent is sufficient. However, at a cyclic stress ratio of 0.4 (higher level of dynamic loads), colloidal silica with a concentration of 20% or more should be used.

Crude oil is one of the soil and water pollution sources which changes the geotechnical properties of the soil via both physical and chemical processes. Carbonate sand which found in oil-rich and continental regions is exposed to oil pollution so that studying the effect of oil and petroleum products contamination is unavoidable. On the other hand, injecting colloidal silica solution, stabilization and improvement of oil-contaminated sand has been investigated broadly. In this research, several triaxial undrained-unconsolidated tests were conducted to investigate the shear strength of carbonate sand contaminated with crude oil as well as contaminated sand stabilized by colloidal silica injection. The results showed that oil pollution reduced the maximum shear strength and the friction angle of carbonate sand, as well as a significant decrease in elasticity modulus while oil content increased. In injected specimens, colloidal silica increases the shear strength, cohesion and stiffness significantly relative to the oil-contaminated ones.

Electro kinetic approach is a conventional method to improve soil characteristics. Dewatering, heavy metal remediation as well as injection stabilizers such as sodium silicate, colloidal silica and ionic solutions, especially in clayey and silty soil, which are sensitive to high pressure methods, are applicable via electro kinetic way. As a green product stabilizer, colloidal silica a dispersion of nano silica particles in water medium phase has been widely investigated by researchers. To quantify the effect of various factors such as solution electrochemical properties and electro kinetic injection conditions on stabilized soil and pore fluid, a suitable apparatus is necessary for laboratory tests. The apparatus should facilitate control and management of hydraulic and electro kinetic conditions. So, the main objective of the paper is to study the electro kinetic injection synced with hydraulic one into loose sand via appropriate instrument. An appropriate device has been designed and constructed and validated by feasibility tests. The trend of current intensity was compatible with previous works as well as uniaxial shear strength and shear wave velocity increase of soil. In conclusion, built apparatus could be useful for future studies.

Saturated deposits of sands and silty sands are liquefiable during earthquakes. One of the new methods proposed for non-disruptive mitigation of liquefaction risk at developed sites is passive site stabilization. It involves slow injection of colloidal silica at the edge of a site and delivery of the stabilizer to the target location using natural groundwater flow [1]. Colloidal silica is an aqueous suspension of microscopic silica (SiO2) particles produced from saturated solutions of silicic acid [2]. The particles size can range in size from 2 to 100 nm, although the particle size is fairly constant in a given suspension. During manufacturing, colloidal silica solutions are stabilized against gelation so they can have long induction periods during which the viscosity remains fairly low up to a few months. A few studies have investigated the behavior of sands stabilized with colloidal silica. Persoff et al. measured short term strength of about 430 kPa at concentration of 20 wt% colloidal silica [3]. Gallagher and Mitchell found the baseline unconfined compressive strength ranged from 32 to 222 kPa in period of 7-30 days at sands samples treated with 5-20 wt% colloidal silica. They also did a series of cyclic triaxial tests and found that for passive site remediation, a 5 wt% concentration of colloidal silica is expected to be able to adequately mitigate the liquefaction risk of loose sands [4]. The stabilization of loose silty sand with colloidal silica has not been studied comprehensively so the present study was undertaken to investigate the unconfined compressive strength and microstructure analysis of silty sands stabilized with colloidal silica.