Physical and Mechanical Characteristics of Soil as a Controlling Factor in Landslides in Curug Panjang Village, Cihuni Hamlet, Lebak, Banten: Analysis of Distribution, Normality, and Inter-Parameter Relationships

Background Landslide occurrence is strongly influenced by the physical and mechanical properties of subsurface soil; this study evaluates these properties in residual soil from Kampung Cihuni, Lebak Regency, as a controlling factor in landslides. Methods Thirty residual soil samples were collected at a depth of 0–1 m using a grid sampling method. Laboratory testing covered natural water content (w); specific gravity and unit weight, used to derive void ratio (e); the plasticity index (PI) from the Atterberg limits; and Unconsolidated Undrained (UU) triaxial testing for cohesion (c) and internal friction angle (φ). The distribution of each parameter was evaluated using histograms, Q-Q plots, and the Shapiro-Wilk normality test, while inter-parameter relationships were analysed using linear regression (R 2 ) and Spearman correlation (ρ). Results The Shapiro-Wilk test showed that cohesion (c) and void ratio (e) are normally distributed, whereas water content (w), PI, and friction angle (φ) are not. PI values for the plastic samples (n = 26) ranged from 13.8% to 86.7%, and φ ranged from 5.48° to 20.5°; the relationship between the two was weakly positive (R 2 = 0.151, p = 0.050; Spearman ρ = 0.244, p = 0.229). Cohesion ranged from 4.41–52.47 kPa but showed a very weak, non-significant relationship with water content (R 2 = 0.028, p = 0.376), as did void ratio with φ (R 2 = 0.089, p = 0.110). Conclusions Relationships among the physical and mechanical parameters were weak and mostly non-significant, so the reduction in soil shear strength cannot be explained by any single parameter alone. Because the UU triaxial test represents total-stress conditions, it cannot directly explain rainfall infiltration and pore-water pressure change as a landslide trigger, though it offers an initial picture of the residual soil’s engineering characteristics as a controlling factor in the area’s landslide susceptibility.