# An Experimental Study for Swelling Effect on Repairing of Cracks in Fine-Grained Clayey Soils
## 3 Results and Discussion
### Geo-Engineering Characteristics  
The geo-engineering characteristics of the soils are represented by the physiomechanical properties description of materials that can cover several features such as gradation, clay content, porosity, density, plasticity, water content, etc. [21; 22; 23]. ASTM provides extensive instruction for conducting geotechnical experiments that are used to estimate such parameters. Experiments such as particle-size distribution [24] and hydrometer [25] can be mentioned. Figure 1 illustrates the particle-size distribution results for the studied clayey soil samples. As is shown in the figure, adding Kaolin and Bentonite causes an increase in the fine-grained portion of the clayey soil and moves the base soil granulation curve towards the fine-grained part. This is more noticeable in the case of adding Bentonite due to its finer grains. Obviously, by adding Bentonite to the mixture, its fine-grained nature causes the fine particles to stay within the clay particles. In addition, when water flows into the mixture, Bentonite particles become hydrated and reduce porosity, increase cohesion, and decrease the permeability in clayey soils [26; 27]. Several relations have been presented in technical sources to predict the permeability coefficient, the most important of which is the Hazen relation. There is a direct relationship between the permeability coefficient and the effective grain diameter (\(K=CD_{10}^{2}\)). According to Figure 1, adding 10% Bentonite to the clay in the sample changes the effective grain size from 0.002 mm to 0.0023 mm, which does not appear to have a significant effect on the permeability. This variation prevents the clayey soil from draining, resulting in hydraulic failure. Therefore, the addition of 10% Kaolin and Bentonite cannot have a negative impact on the drainage of the studied soils. The physiomechanical properties of clayey soil used in this research are presented in Table 1. These index properties are estimated according to the ASTM [24; 25; 26; 28]. This table shows the physical and mechanical characteristics obtained from the soil samples. Table 2 provides the relevant information about the plasticity and Afterberg limits of the studied soil. Afterberg limits tests were performed under ASTM D4318 [29] regulations. The table demonstrates the plasticity indexes, clay mineral majority, clay activity number, and swelling index, which establish the proper understanding of the geo-engineering characteristics of soils. Compared to the results of the Atterberg limits, it is demonstrated that the increase in Bentonite and Kaolin results in an increase in water content, liquid limit (LL), and, therefore, the increase in plasticity index (PI). Based on the obtained results, the PI of pure Kaolin is 19 and the PI of pure Bentonite is 355. Figure 1: Results of the particle-size distribution for the studied soils from the hydrometer test. Given that the PI of a clayy soil is 15, it is evident that mixing Kaolin with clay will not have much influence on raising the PI of the clay sample, which is observed in the test results presented in Table 2, which shows that the combination of 10% Kaolin with the clayy soil has changed the plastic index by two units. However, the combination of clay with Bentonite due to the high PI of Bentonite has caused a noticeable change and a significant increase in the PI. Increases in the PI result in absorbing further moisture and soil swelling, which can considerably help seal the created cracks. On the other hand, higher rates of water absorption and the increase in soil volume during shrinkage time due to the dryness in hot and arid seasons of the year cause cracking of the soil. Therefore, the rate of PI has been limited. Based on the recommendations found in technical texts, the rate of the clay plasticity index (PI) applied in soil dam cores has been limited to 25. PI for the clay with 12.5% Bentonite mixture is evaluated as 27%.