## 4 Discussion
### Mechanical Behavior in Unsaturated Soils: Effect of Suction and Sample Type
An exponential function relating the elastic modulus to matric suction provided a good fit (R\({}^{2}\) = 0.964) in this range. Conversely, Figure 19b depicts the behavior of the elastic modulus under high-suction conditions, where a logarithmic function offers a better representation of the data, albeit with a lower coefficient of determination (R\({}^{2}\) = 0.886). Notably, no decrease in the elastic modulus was observed as suction increased. Figure 19: Curve relating elastic modulus and matric suction at: (**a**) Low-suction range; (**b**) High-suction range. Figure 18: Three-dimensional representation of the relationship between shear strength and total normal stress based on the Mohr-Coulomb criterion at: (**a**) Low-suction range; (**b**) High-suction range. This behavior aligns with [PERSON] [37], who reported that, in several silty soil samples, the elastic modulus neither increases linearly nor decreases at any point. Instead, it shows a pronounced increase at high volumetric water contents (corresponding to the low-suction range) and a more moderate increase at low volumetric water contents (corresponding to the high-suction range). [PERSON] [38] reported that an increase in suction contributed to a significant increase in soil stiffness within the capillary regime in the low-suction range, followed by a substantial reduction in the rate of increase in the high-suction range, with an additional increase during the adsorption regime. However, this latter increase was not observed in the present results, possibly because of the limited number of tests conducted at water contents below 8%, restricting the coverage of the water content range where the adsorption regime would occur. Figure 20a shows an exponential increase in the peak compressive stress as the matric suction increased within the low-suction range. In contrast, Figure 20b illustrates a less pronounced increase in peak compressive stress under high-suction conditions. Although this increase was less pronounced, a decreasing trend was not observed. The highest recorded peak compressive strength qu is 462.10 kPa, corresponding to the highest elastic modulus of 42.40 MPa. This result was obtained from a sample with a water content of 8.60%, degree of saturation of 29.50%, and matric suction of 4933.28 kPa. Under these conditions, the sample exhibited a shear strength of 177.01 kPa and a normal stress total of 82.54 kPa. Undisturbed samples do not exhibit a clear trend, nor do they conform to the patterns observed in reconstituted samples for the soil water characteristic curve (SWCC), elastic modulus, unconfined compressive strength, and shear strength. This discrepancy could be attributed to several factors:  
1. It was not possible to determine the soil water characteristic curve (SWCC) for the undisturbed samples because, although a bimodal model was applied for its estimation, an insufficient number of samples were available to measure suction in the high-suction range. The undisturbed samples analyzed from the 8-m depth consisted mainly of silts and clays, with a plasticity index (PI) ranging from 4 to 14, sand contents between 30% and 50%, and a maximum gravel content of 5% at 5 m depth. Figure 20: Curve relating maximum compressive strength and matric suction at: (**a**) Low-suction range; (**b**) High-suction range. In contrast, the reconstituted samples were composed of silt with a PI of 9, liquid limit (LL) of 33, plastic limit (PL) of 25, and 30% sand content, with no gravel. The samples that best fit the SWCC curve shown in Figure 9 correspond to the 8-and 6-m depths, with PI, LL, and PL values of 9, 33, and 22, respectively, sand contents of 32% and 50%, and no gravel. Samples from other strata deviated significantly from this curve; therefore, they could not adequately represent the suction behavior of those layers, particularly at the 5-and 3-m depths, where the presence of gravel led to a dual pore-size distribution and, consequently, a pronounced bimodal behavior, as described by [PERSON] [17]. 2.