The pH Effect of Pore Fluid on the Collapsible Index of Layered Carbonated Sandy and Clayey Soils

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: The pH Effect of Pore Fluid on the Collapsible Index of Layered Carbonated Sandy and Clayey Soils

ارائه دهنده: Provider: Fatemeh Faridi

اساتید راهنما: Supervisors: Dr. Vahid Reza Ouhadi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Mohammad Maleki- Dr. Abbas Qadimi

زمان و تاریخ ارائه: Time and date of presentation: 2024

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: Abstract: In geotechnical engineering, there is a group of soils with special behaviors, and constructing structures on them may lead to major problems during the useful life of the structure. These soils are known as "problematic soils." Collapsible soils are one type of problematic soil. These soils have significant apparent strength in unsaturated conditions, meaning they initially seem very stable. However, if water seeps into them or they become saturated, their volume suddenly decreases, leading to significant settlement. This settlement can cause considerable damage to structures and facilities. In recent years, the phenomenon of soil collapsibility has been observed in various parts of the world, with reports of significant damage to structures. Due to these damages, the importance of studying this issue is increasing day by day. Given that Iran is located in a hot and dry region and a large part of it is covered by aeolian (wind-blown) soils, identifying and studying collapsible soils is very important. The objective of this research is to investigate the effect of pore fluid pH on the collapsibility index of carbonated sand and clay layered soils. The collapsibility index in the samples was evaluated according to ASTM D5333-03 standard using an oedometer apparatus. In this study, laboratory silica sand with specific grading, a uniformity coefficient of 3, and a curvature coefficient of 0.75, kaolinite clay commercially known as Super Zenous Tabriz, and calcium carbonate with the chemical formula CaCO3 were used to prepare samples in three systems: single layer, two layers, and triple layer in consolidation rings with a height of three centimeters and a diameter of five centimeters in the oedometer test. In this regard, in the laboratory research, considering different arrangements of clay and carbonate sand layers, in each stage of sample preparation, the soil was compacted layer by layer with a dry density of 1.5 grams per cubic centimeter in the oedometer ring. Then, to evaluate the maximum collapsibility index, the samples were removed from the oven after 24 hours and loaded in the oedometer apparatus. Subsequently, at a stress of 200 kPa, the samples were saturated with three different pore fluids: distilled water, 0.1 molar hydrochloric acid, and 0.1 molar hydrochloric acid solutions. Through numerous tests conducted in oedometer rings, it was found that silica sand alone does not have a significant collapsibility index. However, the presence of a clay layer, the addition of carbonate salt to the sand, and changes in pore fluid pH increase the collapsibility index. Specifically, the collapsibility index of single-layer sand saturated with distilled water and 0.1 molar hydrochloric acid under normal conditions increased from 1.15% and 1.93% to 2.2% and 3.97%, respectively, in the presence of a clay interlayer. In the sample saturated with a 0.1 molar hydrochloric acid solution, it increased from 3.03% to 5.87%. The results of this study also indicate that for a specific percentage of carbonate additive in sand layers, an increase in the collapsibility index is observable. Key Words: Pore Fluid; Collapsible Index; Layered Soils; Carbonated Sand; Clay.