Document Type : Original Article

Authors

• Nader Abbassi ¹
• Maral Sarkari ²
• Afshin Khorsand ³
• Reza Bahramlou ⁴

¹ Professor, Agricultural Engineering Research Institute (AERI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran

² Master's degree graduate, Islamic Azad University, Science and Research Branch, Tehran, Iran

³ Researcher, Agricultural Engineering Research Institute (AERI), Agricultural Research, Education and Extension, Karaj, Iran.

⁴ Associate professor, Agricultural Engineering Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Hamadan, Iran.

Abstract

Extended Abstract
Introduction
         Swelling and shrinking soils are problematic soils that destroy structures built on them if their behavior is not recognized and the necessary measures are not taken. The potential of swelling or shrinkage soils depends on various factors, such as the type of clay minerals and the chemical properties of the water. When developing the theoretical concept of swelling soil, factors such as mineralogy, soil structure, and pore water affecting physical factors (such as density, moisture value, and plastic properties) should be considered. Determining the swelling percentage and swelling pressure of clay soils is an important tool to explain and predict the behavior of clay soils. One of the most important properties of clay soils is their sensitivity to volume changes due to swelling and contraction, which lead to soil movement. According to the studies conducted on various aspects of swelling, shrinkage and also the effect of the amount and type of salinity on soil properties such as structure, grain stability and shear strength, it seems that much research on the effect of the amount and type of salinity on the swelling and shrinkage behavior of soil has not yet been conducted; therefore, this research attempts to investigate as much as possible the effects of different amounts of sodium carbonate on the swelling and shrinkage behavior of clay soils. Several objectives were pursued in compiling and conducting this research, including investigating the effects of different amounts of sodium carbonate on swelling percentage, swelling pressure, volumetric and linear shrinkage, and determining the effects of chemical characteristics such as EC on the indices of shrinkage and swelling.
Methodology
In order to investigate the effects of the amount of sodium carbonate on the swelling and shrinkage properties of soils, synthetic samples with different amounts of sodium carbonate were used in this study. For this purpose, a sample of clay soil from Kamalabad region of Karaj was first prepared. In order to identify and determine the physical and mechanical properties of the soil used, identification and classification tests were carried out including granularity, Atterberg limits, compaction properties, specific gravity, swelling and shrinkage indices and also chemical properties were studied on the samples based on ASTM standards.
The shrinkage limit was used to determine the shrinkage capacity and specifications of the samples. There are two methods, volumetric and linear, to determine the shrinkage limit. The laboratory method for determining the shrinkage limit is provided as a standard by the ASTM Institute under the number D-427. To determine the percentage of swelling and the swelling pressure of soils with different proportions of sodium carbonate, the swelling test was carried out according to the standard (ASTM D4546). First, the soil sample prepared by the dynamic method was tamped into special rings, and then each of the rings containing the sample was placed in a normal consolidation device.
Results and Discussion
The results show that the sodium carbonate salt had no significant effect on the optimum moisture values and the maximum dry density of the soil samples tested. With the increase in the amount of EC, caused by the change in the amount of sodium carbonate in the original soil, the linear shrinkage and volume shrinkage limit also increased with an almost regular trend, and for the sample with EC=12.58 ds/m, the linear shrinkage and volume shrinkage limit decreased.
The results show that when the sodium carbonate content is increased from zero to 1%, the swelling percentage increases with a sharp slope, and when the sodium carbonate salt content is increased to 2%, the swelling percentage decreases from 32.75 to 9.87. If you increase the percentage of sodium carbonate salt from 2 to 5%, the percentage of swelling increases from 9.87 to 11.53 with a slight slope. As you increase the EC from 1.47 to 2.8 (dS/m) the inflation percentage increases from 11.13 to 32.75 and as you increase the EC from 2.8 to 12.58 (dS/m) the inflation percentage decreases from 32.75 to 9.87 and as you increase the EC from 12.58 to 51.8 (dS/m) the inflation percentage increases from 9.87 to 11.53.
The graphs of changes in swelling pressure with changes in EC and percentage of sodium carbonate also showed that with an increase in EC from 1.47 to 2.8 (dS/m), the level of swelling pressure increased from 10.12 to 79 kilopascals, with an increase in EC from 8 2.58 to 12.58 (dS/m), the swelling pressure decreased from 79 to 17.30 with a steep increase, and with the increase in EC from 12.58 to 51.8 (dS/m), the swelling pressure decreased from 17.30 to 23 with a very slight increase. By increasing the percentage of sodium carbonate from zero to 1 %, the source pressure increased, and by increasing the percentage of salt from 1 to 2 %, the source pressure decreased, and by increasing the percentage of sodium carbonate from 2 to 5 %, the source pressure decreased with a slight gradient.
Conclusions
Based on the surveys and experiments carried out as part of this study, the following conclusions can be drawn and established:

From the results of the density test of synthetic samples, it was concluded that the effect of sodium carbonate depends on the amount of salt; thus, up to about 1% with the increase of salt content, there is no particular relationship between salt content and optimum moisture and maximum dry density, but at values between 1 and 5%, optimum moisture decreases and maximum dry density increases.
From the results of the swelling test of synthetic samples, it was concluded that the effect of sodium carbonate depends on the amount of salt; thus, up to about 1%, the swelling pressure increases with increasing salt content, but at values between 1 and 5%, the swelling pressure decreases.
From the results of the volume contraction test of synthetic samples, it was concluded that the effect of sodium carbonate salt depends on the amount of salt; thus, up to about 1%, the amount of volumetric shrinkage decreases with the increase of the salt percentage, but at values between 1 and 10%, the amount of the volumetric shrinkage limit increases.
From the results of the linear shrinkage test of synthetic samples, it was concluded that the effect of sodium carbonate salt depends on the amount of salt; so that up to about 1%, the linear shrinkage limit increases with the increase of salt content, but at values between 1 and 5%, the number of linear shrinkage decreases.

Keywords

• Linear shrinkage
• Problematic soils
• Soil salinity
• Swelling characteristics
• Volume shrinkage

Main Subjects

• Geotechnic