# Laboratory Testing and Analysis of Clay Soil Stabilization Using Waste Marble Powder
## 3 Results and Discussion
### The Physical Behavior of Stabilized and Unstabilized Soils
#### 3.1.2. Afterberg Limits  
Changes in the Atterberg limits (liquid and plastic limits) reflect the plastic behavior of the natural soil and soil modified with different concentrations of marble powder, as shown in Figure 6.  
Liquid limit: Stabilizing the clay with marble dust waste significantly improved the engineering properties of the soil, as evidenced by a decrease in the liquid limit from 62.2% to 31.8%. This research is supported by the previous literature [40; 41]. The reduction in the liquid limit is due to the infilling action of the marble powder, which reduces the void  
Figure 5: The amended and unamended soil sample’s specific gravity characteristics.  
Figure 6: The amended and unamended soil sample’s Atterberg limits characteristics.  
ratio and increases the density of the soil [39]. The infilling action of the marble powder refers to the process by which the powder particles fill the voids between the soil particles. This infilling reduces the void ratio--the ratio of voids to soil volume. Lower void ratios indicate less void space between soil particles. Because the particles are packed closer together, the soil density increases. Density reduces the soil's liquid limit [42]. The liquid limit is the moisture content at which soil becomes plastic. Denser soil resists deformation and requires more moisture to become plastic. Because of the marble powder infill, the liquid limit decreases as soil density increases [43].  
The marble powder also contributes to the formation of a cementitious material that binds the soil particles together, thereby increasing the stiffness and shearing strength of the soil [40]. In furtherance, the pozzolanic reaction between the marble particles and the soil produces stable compounds that increase the durability and resistance of the soil to weathering [44].  
Plastic limit: The plastic limit of clay declined from 29.6 to 15.5 as the marble powder content increased up to 60% (X5) but did not change as the marble powder content increased at 60% and 75%. This result is consistent with that of the [45] investigation, which found that the plastic limit of clay soil decreases up to 60% marble powder content and stays constant. As such, this is intriguing and can be explained by the fact that the marble powder particles occupy the spaces between the clay particles, reducing their plasticity. Importantly, this specific mechanism by which marble powder reduces plasticity may vary depending on the clay and marble powder's composition and properties. Marble powder could affect the lower plastic limit, which is the moisture content at which clay becomes too dry and loses its plasticity. Without additional information or context, it is difficult to determine the exact cause of the decreased plasticity in this particular case.  
More so, this would lead to a decrease in the plastic limit of the clay soil [40]. The clay particles may become coated with marble powder particles at higher marble powder concentrations, resulting in a more stable and less malleable soil mass [46].  
Plasticity index: The plasticity index, which is the mathematical difference that exists between the plastic limit and the liquid limit, reduces as the marble powder content of the soil rises (Figure 7). When WMP is added to clay, the plasticity index drops drastically from 32.6% in clay soil to 22.6%. These results are in agreement with those of Ref. [40]. The inclusion of WMP, which acts as a pozzolanic material, may explain why the plasticity index dropped. The geo-engineering properties of soil can be enhanced by adding pozzolanic minerals, which are known to react with calcium hydroxide in the presence of water to form cementitious compounds. As a result of the WMP reducing the soil's ability to hold water, the plasticity index may have lowered [45].