¹ Doctoral Program Faculty of Geological Engineering, Universitas Padjadjaran, Bandung, West Java, 45363, Indonesia
² Faculty of Geological Engineering, Universitas Padjadjaran, Bandung, West Java, 45363, Indonesia
³ Master Program in Natural Disaster Management Engineering, Department of Civil and Environmental Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Special Region of Yogyakarta, 55281, Indonesia
⁴ Master Program in Civil Engineering, Graduate School, Universitas Muhammadiyah Surakarta, Surakarta, Central Java, 57169, Indonesia
⁵ Master Program in Urban and Regional Planning, School of Architecture, Planning, and Policy Development, Institut Teknologi Bandung, Bandung, West Java, 40132, Indonesia
⁶ Master Program Faculty of Geological Engineering, Universitas Padjadjaran, Bandung, West Java, 45363, Indonesia

Arini Syafri
Roles: Data Curation, Formal Analysis, Investigation, Writing – Original Draft Preparation, Writing – Review & Editing

Zufialdi Zakaria
Roles: Conceptualization, Methodology, Supervision, Validation, Writing – Review & Editing

Nana Sulaksana
Roles: Conceptualization, Methodology, Supervision, Validation, Writing – Review & Editing

Teuku Yan W.M Iskandarsyah
Roles: Conceptualization, Methodology, Supervision, Validation, Writing – Review & Editing

Dea Tyas Fatmala
Roles: Data Curation, Investigation, Writing – Review & Editing

Fatma Kusuma Probodani
Roles: Data Curation, Investigation, Writing – Review & Editing

Anastasya Pattiasina
Roles: Data Curation, Investigation, Writing – Review & Editing

Yosi Asterina Maharani
Roles: Data Curation, Investigation, Writing – Review & Editing

Marhamah Nur Azizah Tubaka
Roles: Data Curation, Investigation, Writing – Review & Editing

Cannavaro V.R. Pattiasina
Roles: Data Curation, Investigation, Software, Writing – Review & Editing

Nabila Kalsum Tuanany
Roles: Formal Analysis, Software, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

Sampling was carried out around Cihuni Village, Cikulur Sub-district, Lebak Regency, Banten Province. Tests on the physical and mechanical properties of the soil were conducted on 30 soil samples. The sampling method used was the Grid Sampling (Systematic Sampling) method (Harjayanti et al., 2022). The study area was divided into grid plots measuring 50 x 50 m, which served as a reference for determining observation points.

Laboratory testing is carried out to determine the physical and mechanical characteristics of the soil, which form the basis for evaluating slope stability and analysing the susceptibility to landslides. The tests are carried out on soil samples that have been collected previously. Laboratory testing comprises two main groups, namely:

Soil physical property testing is carried out to determine the basic conditions of the soil relating to its ability to absorb and retain water. The parameters analysed include moisture content (ASTM D2216) (ASTM International, 2019) and Atterberg consistency limits (ASTM D4318) (ASTM International, 2017). Water content is used to determine the degree of soil saturation, which influences changes in soil strength (Arsyad et al., 2025). A high water content indicates the potential for an increase in pore water pressure, which can reduce slope stability (Silvianengsih et al., 2015). The Atterberg consistency limits, comprising the liquid limit and the plastic limit, are used to determine the Plasticity Index (PI). The PI value describes the degree of soil plasticity, where a high value generally indicates a predominance of clay soil, which is more susceptible to changes in properties due to increased moisture content (Badan Standardisasi Nasional, 2008; Muhammad Abdul Ghony & Mhd. Dian Afriza2, 2024).

Soil mechanical properties testing in this study was carried out using the unconsolidated undrained (UU) triaxial test in accordance with the standard (ASTM D2850) (ASTM International, 2015) to determine the soil shear strength parameters, namely cohesion (c) and internal friction angle (φ).

The cohesion parameter (c) reflects the electrochemical attractive forces between soil particles under undrained conditions (Wiqoyah et al., 2024). Nilai kohesi menjadi indicator ketahanan internal tanah terhadap keruntuhan deformasi. he cohesion value serves as an indicator of the soil’s internal resistance to deformation failure. Meanwhile, the angle of internal friction (φ) describes the internal friction capacity and the interlocking ability between soil particles in resisting slope thrust forces (Haris et al., 2018). Under undrained conditions in clay soils, the internal friction angle tends to be small as it is reduced by the pore water pressure trapped within the pore spaces (void ratio) (Listyawan et al., 2025; Nurdian & Setyanto, 2025).

The laboratory test data were subsequently processed using statistical analysis methods. Tests for data distribution and normality were conducted using descriptive statistical methods, specifically histogram visualisations and quantile-quantile plots (Q-Q plots). This analysis was carried out on all soil parameters to validate whether the field data distribution was representative and met the assumptions of a normal distribution (Suradi, 2014). Then, correlation analysis was carried out using scatter plots to evaluate the interrelationship between specific parameters. The focus of the correlation was on the influence of physical properties on soil mechanics. The strength of the linear relationship was measured using the coefficient of determination (R²) (Abdillah et al., 2021).

Using the grid sampling approach, the study area in Cihuni Village was divided into blocks measuring 50 x 50 m. A total of 30 sampling points were identified, distributed throughout the study area. Soil samples were taken at a shallow depth of 0–1 m, which corresponds to the active weathering zone of the Bojong Formation rocks and is also the top layer most susceptible to saturation due to direct rainwater infiltration. The spatial distribution of the samples is shown in Figure 1.

The samples collected were subsequently tested in the laboratory to determine their physical and mechanical properties. The results of the laboratory tests on these 30 residual soil samples are presented in full in Table 1.

Table 2 summarises data on soil physical properties, including the natural moisture content (w) and plasticity index (PI) obtained from the Atterberg consistency limits. These data reflect the soil’s initial hydraulic conditions and the material’s sensitivity to water.

Table 3 presents the soil shear strength parameters obtained from unconsolidated undrained (UU) triaxial tests, namely the cohesion (c) and internal friction angle. These mechanical parameters represent the soil’s internal resistance to shear stress under undrained conditions.

The histogram in Figure 2 shows that the soil moisture content data exhibits a right-skewed distribution (positive skewness), with the majority of samples falling within the 27% – 30% range. Nevertheless, the results of the Q-Q plot in Figure 3 indicate that the majority of data points still follow and align with the diagonal reference line. Minor deviations are only found at the extremes of the distribution (very low and very high moisture content). Overall, this distribution of soil moisture content data is considered sufficiently representative and close to the assumption of a normal distribution.

The histogram in Figure 4 shows that the distribution of soil cohesion tends to be symmetrical (bell-shaped), with the highest frequency values occurring in the range of 0.28 kg/cm²–0.34 kg/cm². This characteristic is reinforced by the Q-Q plot in Figure 5, where all data points in the linear distribution consistently lie on the diagonal reference line without showing any significant deviation at either end of the extreme values. This visually confirms that the soil cohesion parameter data ideally satisfy the assumptions of a normal distribution.

The histogram in Figure 6 shows fairly even values across the entire sample range, with the highest frequency peak occurring at values between 12° and 14°. The interpretation of the Q-Q plot in Figure 7 confirms the accuracy, as all observed data points align linearly and precisely along the theoretical line. The consistency of the data point distribution in the Q-Q plot confirms that the internal friction angle parameter exhibits data characteristics that satisfy the assumptions of a normal distribution.

An analysis of the relationships between soil parameters was carried out to understand the interrelationships between the physical and mechanical properties of soil, particularly in relation to slope stability. To determine the effect of plasticity on soil shear strength, an analysis of the relationship between the plasticity index (PI) and the internal friction angle (φ) was carried out. In addition, an analysis of the relationship between moisture content and soil cohesion (c) was also conducted. The results of the data plots and trends of these relationships are described as follows:

The authors would like to express their highest gratitude to the Indonesia Endowment Fund for Education (Lembaga Pengelola Dana Pendidikan/LPDP) for the financial support provided during this academic journey. The authors also sincerely thank the Engineering Geology Laboratory, Universitas Padjadjaran for providing the laboratory facilities and technical support during the soil testing phase.

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