بررسی رفتار ماسه ی لای دار تثبیت شده با سیلیس کلوئیدی در مقابل روانگرایی

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 ۲۰ and ۴۰ percent, in both unstabilized and stabilized conditions, were prepared with different concentrations of the stabilizer from ۵ to ۳۰ percent, and the effects of colloidal silica on its behavior were evaluated under cyclic loading. ۳۰ cyclic triaxial tests were performed on various samples. A ۱۰۰ kPa confining pressure was used in these tests. All ۱۵ experimental samples were loaded at cyclic stress ratios of ۰.۲ and ۰.۴ with a frequency of ۱ Hz and up to ۲۰۰ 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 ۵ percent can prevent liquefaction of soil at the low level of dynamic loads (such as cyclic stress of ۰.۲). 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 ۴۰%, by increasing the stabilizing concentration from ۱۰% to ۳۰%, the pore water pressure ratio reduced from ۱ (the state of full liquefaction) in ۱۰ cycles to about ۰.۱ in ۱۰۰ cycles, and also the double amplitude of axial strain decreased from ۵% in ۱۰ cycles to about ۰.۷% in ۱۰۰ 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 ۰.۲, colloidal silica concentration of five percent is sufficient. However, at a cyclic stress ratio of ۰.۴ (higher level of dynamic loads), colloidal silica with a concentration of ۲۰% or more should be used.

کلیدواژه ها:

ماسه ، ماسه ی لای دار ، بارگذاری دینامیکی ، سیلیس کلوئیدی ، تثبیت خاک ، تزریق