## 3 Results and Discussion
### Matric Suction Determined Using the Filter Paper Method
#### 3.1.2. Matric Suction of Different Compacted Specim Types with a Constant Initial Void Ratio  
The initial void ratio was proven to be a significant factor that affects the suction in previous studies for other kinds of soils. Moreover, it was observed that the initial void ratio affects the matric suction of the compacted clay in the study at the lower suction range. In the previous analysis, it was also discussed that pore structure significantly affects the matric suction considering the varying number of cycles, which was supported by the study of [PERSON] et al. (2018). Thus, to analyze the effect of including polyurethane in the soil mixture with clay in terms of the matric suction, the initial void ratio was held constant. The matric suctions of CPCL and CL were compared and plotted in Figure 17. Both specimens have the same compaction moisture content, which is wet, of the optimum moisture content; however, other properties, such as specific gravity, liquid limit, and grain size distributions, are different. Figure 16. Predicted vs. actual matric suction of CCL and CL. Figure 15. A 3D model of CCL and CL WRC for the (**a**) 1 st, (**b**) 2 nd, and (**c**) 3 rd wet–dry cycles. It can be observed in Figure 17 that the matric suction increases as the moisture content decreases regardless of the number of wet-dry cycles and if polyurethane is included in the soil mixture. Moreover, it can be observed that the matric suction of CPCL has a lower value at the lower suction range below 20,000 kPa or 4.3 log kPa. According to [PERSON] et al. [44], the particle size affects the matric suction, wherein the matric suction is less for specimens with larger particles. Thus, the reduction in the matric suction at the lower range due to the inclusion of polyurethane in the soil mixture may be attributed to the difference in particle size of the soil with and without polyurethane. From the analysis of the soil properties, it was observed that the particle size of the clay is smaller compared to the particle size of the polyurethane-clay. On the other hand, the inclusion of polyurethane in the soil mixture did not affect the matric suction at the higher suction range of around 20,000 kPa to 200,000 kPa or 4.3 log kPa to 5.3 log kPa, since the increased grain size of the loose specimen induced by the inclusion of polyurethane had no effect at the higher suction range. This behavior at the higher suction range was also evident in the specimen comparison of CCL and CL in the previous discussion, wherein the suction at the higher range was not influenced by the soil structure because the water films were influenced by the osmotic and adsorptive fields at that suction range. The deterioration of the soil structure caused by the wet-dry cycle, as shown in Figure 18, also affected the obtained matric suction at the lower suction range. It can be observed in Figure 17 that the matric suction decreases as the number of cycles increases at the lower suction range. This indicates that cyclic wetting and drying induced an increase in intergranular pores. The SEM image, with a magnification of \(\times\)1000, of polyurethane-clay, CPCL before the wet-dry cycles, and CPCL that underwent three wet-dry cycles is shown in Figure 19. It can be observed that compaction reduced the intergranular voids compared to the SEM image of the loose specimen. It can also be observed that the microstructure of CPCL deteriorated after three wet-dry cycles, in which the number of aggregates increased and the aggregate sizes decreased. Furthermore, the change in contact form from the face-to-face to point contact form indicates that the cementing particles were dissolved by the water, which was also the case for CCL and CL in the previous analysis. Thus, the increase in intergranular voids from the deterioration of CPCL caused the matric suction to decrease as the number of cycles increased and further deterioration was experienced. Figure 17: Matric suction of CL and CPCL with the same initial void ratio.