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 [version 2; peer review: 1 approved, 2 approved with reservations]

Дата публикации: 16-09-2026 10:50:49

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 (R2) 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 (R2 = 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 (R2 = 0.028, p = 0.376), as did void ratio with φ (R2 = 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.

Основное содержимое страницы с новостью.

Research Article

Revised

[version 2; peer review: 1 approved, 2 approved with reservations]

Arini Syafri

https://orcid.org/0009-0000-0468-6124

¹, Zufialdi Zakaria², Nana Sulaksana², [...] Teuku Yan W.M Iskandarsyah², Dea Tyas Fatmala

https://orcid.org/0009-0009-7484-0989

³, Fatma Kusuma Probodani

https://orcid.org/0009-0009-4087-2560

³, Anastasya Pattiasina

https://orcid.org/0009-0004-5936-3946

³, Yosi Asterina Maharani

https://orcid.org/0009-0005-2286-0620

³, Marhamah Nur Azizah Tubaka

https://orcid.org/0009-0002-7101-9238

⁴, Cannavaro V.R. Pattiasina

https://orcid.org/0009-0006-5580-3232

⁵, Nabila Kalsum Tuanany

https://orcid.org/0009-0007-9359-6681

⁶

Arini Syafri

https://orcid.org/0009-0000-0468-6124

¹, Zufialdi Zakaria², [...] Nana Sulaksana², Teuku Yan W.M Iskandarsyah², Dea Tyas Fatmala

https://orcid.org/0009-0009-7484-0989

³, Fatma Kusuma Probodani

https://orcid.org/0009-0009-4087-2560

³, Anastasya Pattiasina

https://orcid.org/0009-0004-5936-3946

³, Yosi Asterina Maharani

https://orcid.org/0009-0005-2286-0620

³, Marhamah Nur Azizah Tubaka

https://orcid.org/0009-0002-7101-9238

⁴, Cannavaro V.R. Pattiasina

https://orcid.org/0009-0006-5580-3232

⁵, Nabila Kalsum Tuanany

https://orcid.org/0009-0007-9359-6681

⁶

PUBLISHED 16 Sep 2026

Author details Author details

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

OPEN PEER REVIEW

REVIEWER STATUS

Corresponding author: Nabila Kalsum Tuanany Competing interests: No competing interests were disclosed.

Grant information: This publication was supported by the Indonesia Endowment Fund for Education Agency (Lembaga Pengelola Dana Pendidikan/LPDP). The funders had no role in study design, data collection and analysis the decision to publish or preparation of the manuscript.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2026 Syafri A et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. How to cite: Syafri A, Zakaria Z, Sulaksana N et al. 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 [version 2; peer review: 1 approved, 2 approved with reservations]. F1000Research 2026, 15:1195 (https://doi.org/10.12688/f1000research.184697.2) First published: 22 Jul 2026, 15:1195 (https://doi.org/10.12688/f1000research.184697.1) Latest published: 16 Sep 2026, 15:1195 (https://doi.org/10.12688/f1000research.184697.2)

Revised Amendments from Version 1

This revision responds to two peer review reports and involves substantive corrections to the reported data and analysis. Data transposition errors between the original laboratory tables were identified and corrected against the raw laboratory sheets, and the three original results tables have been consolidated into two: physical properties and mechanical properties. The regression analysis for plasticity index versus friction angle and water content versus cohesion was recalculated using all 30 individual raw data points rather than an averaged subset, which changes the reported relationships from strong and highly significant to weak and mostly non-significant (R² = 0.151 for plasticity index versus friction angle, R² = 0.028 for water content versus cohesion). The Discussion and Conclusion have been revised accordingly, along with an expanded discussion of the limitations of total-stress triaxial testing for interpreting rainfall-induced slope failure. Cohesion values are now also reported in kPa alongside the original kg/cm² values. The Abstract has been restructured into Background, Methods, Results, and Conclusions sections and shortened to meet the journal's word limit. New figures and a summary table covering the distribution and normality of all five soil parameters have been added, along with new figures and a summary table for the relationships between parameters, including a new void ratio versus friction angle pair. The underlying dataset was reorganized on Zenodo, which changed its DOI; the Data availability statement and reference list have been updated to reflect this. Language and terminology have been revised throughout the manuscript

See the authors' detailed response to the review by Nugroho Aji Satriyo
See the authors' detailed response to the review by Merley Misriani

1. Introduction

Indonesia is highly vulnerable to geological hazards because it sits at the meeting point of active tectonic plates (Luthfiya, 2025). One of the most frequent and recurring of these hazards is landslides, in which a mass of soil moves down a slope under gravity once triggered by specific controlling factors (Vulcanological Survey of Indonesia, 2024). These controlling factors include slope morphology, the geological character of the material that makes up the slope, and external triggers such as extreme rainfall and human activity (Rahardjo et al., 2008).

This vulnerability is evident in Curug Panjang Village, specifically Kampung Cihuni, Cikulur District, Lebak Regency, Banten Province. The area is regionally underlain by rock of the Pleistocene Bojong Formation (Qpb), whose lithology is dominated by sandy marl, sandy clay, and tuffaceous sandstone (Rusmana et al., 1991). Under the region’s tropical climate and high rainfall, this rock has weathered intensively, forming a thick residual soil layer with a dominant clay fraction. Geomorphologically, following the classification of (Van Zuidam, 1985), the area shows a marked contrast in terrain, with about 23.33% of it falling into the moderately steep to steep unit, at slope angles of 8 to 35°. The combination of steep slopes, a thick, clay-rich weathered soil layer, and low permeability creates a subsurface condition that is critical and highly susceptible to slope failure (Das & Sobhan, 2018). This vulnerability was borne out in early 2022, when a large landslide damaged dozens of homes, places of worship, and educational facilities, and cut the main road network, forcing a local evacuation (Rizkoh, 2022).

Studies of landslide susceptibility have so far relied largely on macro-scale approaches, such as slope-angle analysis, land-use mapping, or geophysical subsurface mapping, leaving out the fundamental engineering aspect that laboratory testing can provide. Physical and mechanical soil characterisation of this kind can give a more representative picture of landslide susceptibility, yet it remains comparatively underused (Rahmawati & Virgawati, 2024).

Building on this background, the present study characterises the physical and mechanical properties of the soil in Kampung Cihuni through laboratory testing. The distribution of each soil parameter is evaluated statistically, and the pattern of relationships among parameters is examined to understand how soil strength tends to change. The results are intended to give a picture of the engineering parameters that act as controlling factors for landslides in the study area, and to serve as a scientific basis for policymakers.

2. Methods

The soil characteristics used in this study comprise physical properties (water content, void ratio, and plasticity index (PI)) and mechanical properties (cohesion (c) and internal friction angle (φ)). The research process is outlined in the following stages:

2.1 Sampling stage

Samples were collected around Cihuni Village, Cikulur Sub-district, Lebak Regency, Banten Province. Physical and mechanical soil testing was carried out on 30 soil samples. The sampling method used was the Grid Sampling, a form of systematic sampling (Harjayanti et al., 2022). The study area was divided into 50 x 50 m grid cells, which served as the reference for determining the observation points.

2.2 Laboratory testing stage

Laboratory testing was carried out to determine the physical and mechanical characteristics of the soil as a basis for evaluating slope stability and analysing landslide susceptibility. Were performed on the soil samples collected in the previous stage and fell into two main groups:

a. Soil Physical Property Testing

Soil physical property testing was carried out to determine natural state and index characteristics of the soil at the study site. Water content was determined following ASTM D2216 (ASTM International, 2019). Specific gravity (Gs) was determined following ASTM D854 (ASTM International, n.d.), while unit weight (natural, saturated, and dry) was determined on undisturbed samples using the ring/core cutter method. Void ratio, porosity, and degree of saturation were not measured directly in the laboratory; instead, they were calculated from the soil phase relationships using the specific gravity, water content, and unit weight values obtained above. Atterberg limit tests (liquid limit and plastic limit) were also carried out following ASTM D4318 (ASTM International, 2017) to obtain the plasticity index (PI) and to classify the soil under the USCS and AASHTO systems.

b. Soil Mechanical Property Testing

Soil mechanical properties were determined through Unconsolidated Undrained (UU) triaxial testing following ASTM D2850 (ASTM International, 2015), to obtain the shear strength parameters cohesion (c) and internal friction angle (φ) based on the Mohr-Coulomb failure criterion. Because the test does not allow the sample to drain or consolidate during loading, the resulting shear strength parameters describe the soil under conditions of (total stress), rather than effective stress.

2.3 Soil characteristics analysis stage

Soil characteristics were analysed for five parameters: water content, void ratio, plasticity index, cohesion, and internal friction angle. The analysis proceeded in two stages. First, the distribution and normality of each parameter were assessed using histograms, Q-Q plots, and the Shapiro-Wilk normality test, to determine whether the data were consistent with a normal distribution. Second, the relationships among parameters were analysed for three parameter pairs, plasticity index against friction angle, water content against cohesion, and void ratio against friction angle, using linear regression (the fitted equation and coefficient of determination, R²) and Spearman correlation (ρ), to evaluate the strength and significance of each relationship.

3. Result

3.1 Sampling

The study area in Cihuni Village was divided into 50 x 50 m blocks using a grid sampling approach. Thirty sampling points were identified and distributed across the study area. Soil samples were taken at a shallow depth of 0–1 m, the zone of active weathering in the Bojong Formation, and also the layer most exposed to saturation from direct rainfall infiltration. The spatial distribution of the sampling points is shown in Figure 1.

Figure 1. Distribution of soil samples in Cihuni Village.

3.2 Laboratory result

The 30 residual soil samples collected during the sampling stage were subsequently tested in the laboratory to determine their physical and mechanical properties. The complete laboratory results are presented in Table 1 and Table 2.

a. Physical Property Test Results

Table 1. Laboratory Test Results for Soil Physical Properties.

SOIL LABORATORY TEST
CIHUNI SOIL GEOTECHNICAL RESEARCH
BORE HOLE No	SPECIFIC GRAVITY	NATURAL STATE							ATTERBERG LIMITS
		Water Content	Wet Density	Saturated Density	Dry Density	Void Ratio	Porosity	Degree Of Saturation	Liquid Limits	Plasticity Limit	Plasticity Index
		(Wn)	(ɣ_m)	(ɣsat)	(ɣ_dry)	(e)	(n)	(Sr)	(%)	(%)	(%)
		(%)	(gr/cm³)	(gr/cm³)	(gr/cm³)		(%)	(%)	(%)	(%)	(%)
ST-01	2.4823	29.96	1.800	1.385	1.827	0.792	44.20	93.88	45.71	31.88	13.83
ST-02	2.4733	30.85	1.869	1.428	1.851	0.732	42.25	104.29	47.38	20.35	27.03
ST-03	2.5345	28.96	1.874	1.453	1.880	0.744	42.67	98.61	43.61	24.51	19.10
ST-04	2.5057	40.30	1.672	1.192	1.716	1.102	52.43	91.64	56.86	31.52	25.34
ST-05	2.4430	31.98	1.648	1.249	1.738	0.956	48.88	81.72	57.59	30.38	27.21
ST-06	2.4704	40.63	1.499	1.066	1.634	1.318	56.86	76.17	Non Plastic
ST-07	2.5494	36.29	1.738	1.275	1.775	1.000	49.99	92.55	Non Plastic
ST-08	2.6308	31.93	1.897	1.438	1.891	0.829	45.34	101.28	36.52	18.54	17.98
ST-09	2.5564	29.29	1.858	1.437	1.875	0.779	43.79	96.10	39.29	8.28	31.00
ST-10	2.5312	29.82	1.888	1.454	1.880	0.740	42.54	101.96	43.63	17.99	25.64
ST-11	2.5411	28.69	1.764	1.371	1.831	0.854	46.06	85.37	47.96	13.55	34.41
ST-12	2.5634	36.57	1.763	1.291	1.787	0.986	49.65	95.06	Non Plastic
ST-13	2.5374	34.23	1.791	1.334	1.808	0.902	47.42	96.30	35.90	18.80	17.10
ST-14	2.4034	49.92	1.621	1.081	1.631	1.223	55.01	98.11	85.62	19.89	65.73
ST-15	2.5249	41.62	1.749	1.235	1.746	1.045	51.09	100.58	79.50	18.37	61.13
ST-16	2.5814	42.78	1.741	1.219	1.747	1.117	52.76	98.86	59.16	18.59	40.57
ST-17	2.5719	51.75	1.595	1.051	1.642	1.448	59.14	91.94	118.54	31.86	86.68
ST-18	2.5406	26.88	1.784	1.406	1.853	0.807	44.66	84.63	51.00	9.27	41.73
ST-19	2.6522	40.23	1.797	1.282	1.798	1.069	51.67	99.78	57.57	39.46	18.11
ST-20	2.6625	40.88	1.768	1.255	1.784	1.121	52.86	97.06	57.01	33.56	23.45
ST-21	2.6198	37.14	1.758	1.282	1.792	1.044	51.08	93.19	58.54	17.26	41.28
ST-22	2.4259	30.68	1.791	1.370	1.805	0.770	43.52	96.60	48.99	13.81	35.17
ST-23	2.5644	37.31	1.749	1.274	1.777	1.013	50.32	94.46	76.05	36.72	39.33
ST-24	2.5409	28.60	1.786	1.389	1.842	0.829	45.34	87.62	42.70	23.22	19.47
ST-25	2.5734	39.01	1.698	1.222	1.747	1.107	52.53	90.73	69.49	29.63	39.85
ST-26	2.5169	50.02	1.629	1.086	1.654	1.318	56.86	95.53	82.45	49.29	33.16
ST-27	2.5346	37.26	1.757	1.280	1.775	0.980	49.49	96.37	57.07	17.16	39.91
ST-28	2.5198	32.68	1.821	1.372	1.828	0.836	45.54	98.46	47.47	6.16	41.31
ST-29	2.5063	35.54	1.736	1.281	1.770	0.957	48.89	93.10	Non Plastic
ST-30	2.5751	28.17	1.848	1.442	1.882	0.786	44.01	92.30	45.35	12.82	32.53

Table 2. Laboratory Test Results For Soil Mechanical Properties.

BORE HOLE No	Cohesion		Angle of Internal Friction
	(C)		(φ)
	(kg/cm²)	kPa	(°)
ST-01	0.326	31.97	8.301
ST-02	0.415	40.70	10.724
ST-03	0.371	36.38	9.808
ST-04	0.255	25.01	7.606
ST-05	0.535	52.47	11.401
ST-06	0.191	18.73	20.508
ST-07	0.307	30.11	17.804
ST-08	0.045	4.41	5.704
ST-09	0.125	12.26	6.192
ST-10	0.172	16.87	7.954
ST-11	0.131	12.85	8.102
ST-12	0.143	14.02	14.681
ST-13	0.087	8.53	6.831
ST-14	0.201	19.71	5.481
ST-15	0.319	31.28	10.733
ST-16	0.172	16.87	7.651
ST-17	0.319	31.28	15.052
ST-18	0.294	28.83	11.713
ST-19	0.241	23.63	9.629
ST-20	0.272	26.67	9.87
ST-21	0.289	28.34	9.517
ST-22	0.316	30.99	10.173
ST-23	0.304	29.81	10.757
ST-24	0.345	33.83	9.35
ST-25	0.451	44.23	9.43
ST-26	0.147	14.42	6.289
ST-27	0.183	17.95	7.763
ST-28	0.317	31.09	8.724
ST-29	0.383	37.56	10.927
ST-30	0.415	40.70	9.757

The physical properties of the 30 residual soil samples, comprising the natural-state parameters (water content, wet unit weight, saturated unit weight, dry unit weight, void ratio, porosity, and degree of saturation) and the Atterberg limits (liquid limit, plastic limit, and plasticity index), are presented in Table 1. It should be noted that four samples (ST-06, ST-07, ST-12, and ST-29) are non-plastic and therefore have no measurable plasticity index.

b. Mechanical Property Test Results

The mechanical properties of the soil, cohesion (c) and internal friction angle (φ), were obtained from Unconsolidated Undrained (UU) triaxial testing carried out on each of the 30 samples. The complete results are presented in Table 2.

3.3 Soil characteristic analysis

Soil characteristics were analysed in two stages: distribution and normality analysis for each soil parameter, and analysis of the relationships among parameters. Both stages covered the five parameters used in this study: water content (Wn), void ratio (e), plasticity index (PI), cohesion (c), and internal friction angle (φ)

a. Distribution and Normality of Soil Parameter Data

The distribution and normality of the five soil parameters were analysed using histograms, Q-Q plots, and the Shapiro-Wilk test at a 5% significance level.

The water content (Wn) data show a right-skewed histogram (skewness = 0.75) (Figure 2), with most samples falling in the 27%–36% range. The Q-Q plot (Figure 3) shows some points departing from the reference diagonal at the extremes. The Shapiro-Wilk test gave p = 0.025 (< 0.05), indicating that the water content data are not statistically consistent with a normal distribution.

Figure 2. Histogram of water content in the Cihuni residual soil (n = 30).

Figure 3. Q-Q plot of water content in the Cihuni residual soil (n = 30).

The void ratio (e) data show a slightly right-skewed histogram (skewness = 0.69) (Figure 4), with the Q-Q plot points (Figure 5) lying close to the diagonal overall. The Shapiro-Wilk test gave p = 0.051, right at the 5% significance threshold, so the void ratio data can be described as close to, but not fully satisfying, the assumption of normality.

Figure 4. Histogram of void ratio in the Cihuni residual soil (n = 30).

Figure 5. Q-Q plot of void ratio in the Cihuni residual soil (n = 30).

The plasticity index (PI, n = 26, excluding the four non-plastic samples) shows a sharply right-skewed histogram (skewness = 1.44) (Figure 6), and the Q-Q plot (Figure 7) shows a marked departure from the diagonal at high values. The Shapiro-Wilk test gave p = 0.003, indicating a significant departure from normality.

Figure 6. Histogram of plasticity index (PI) in the Cihuni residual soil (n = 26).

Figure 7. Q-Q plot of plasticity index (PI) in the Cihuni residual soil (n = 26).

The cohesion (c) data show a fairly symmetric histogram (skewness = 0.11) (Figure 8), with the Q-Q plot points (Figure 9) consistently following the reference diagonal. The Shapiro-Wilk test supports this (p = 0.854), indicating that the cohesion data are consistent with a normal distribution.

Figure 8. Histogram of cohesion in the Cihuni residual soil (n = 30).

Figure 9. Q-Q plot of cohesion in the Cihuni residual soil (n = 30).

The friction angle (φ) data show a sharply right-skewed histogram (skewness = 1.40) (Figure 10), with the Q-Q plot (Figure 11) showing departure from the diagonal mainly at high values. The Shapiro-Wilk test gave p = 0.002, indicating a significant departure from normality.

Figure 10. Histogram of friction angle in the Cihuni residual soil (n = 30).

Figure 11. Q-Q plot of friction angle in the Cihuni residual soil (n = 30).

A summary of the normality test results for all five parameters is given in Table 3. Overall, only cohesion (c) is consistent with a normal distribution; water content, plasticity index, and friction angle all show a significant, right-skewed departure from normality, and void ratio sits right at the threshold.

Table 3. Summary of the distribution and normality tests.

Parameter	n	Mean	SD	Skewness	Shapiro-Wilk (W)	p-value	Conclusion
Water Content (%)	30	36.00	6.79	0.75	0.919	0.025	Not normal
Void Ratio	30	0.97	0.19	0.69	0.931	0.051	Borderline
Plasticity Index (%)	26	34.54	16.51	1.44	0.865	0.003	Not normal
Cohesion (kPa)	30	26.38	11.28	0.11	0.981	0.854	Normal
Friction Angle (°)	30	9.95	3.39	1.40	0.873	0.002	Not normal

b. Relationships Among Soil Parameters

The relationships among soil parameters were analysed to examine how the physical and mechanical properties of the residual soil at the study site relate to one another. Because the Shapiro-Wilk results above show that most parameters are not consistent with a normal distribution, this analysis used two complementary approaches: linear regression (to obtain the fitted equation and R²) and Spearman correlation, a non-parametric method that does not assume normality.

The relationship between plasticity index (PI) and friction angle (φ) is shown in Figure 12. Of the 30 samples tested, 26 had a measurable PI value (the four non-plastic samples were excluded from this analysis). Linear regression gave a positive relationship, φ = 0.0503·PI +7.283 (R² = 0.151, p = 0.050), indicating a weak linear relationship that sits right at the threshold of statistical significance. Spearman correlation gave ρ = 0.244 (p = 0.229), indicating that the monotonic relationship between the two parameters is not statistically significant.

Figure 12. Relationship between plasticity index (PI) and friction angle (φ) in the Cihuni residual soil (n = 26), with the linear regression line and 95% confidence band.

The relationship between water content (Wn) and cohesion (c) is shown in Figure 13. Linear regression over the 30 samples gave c = −0.0028·Wn + 0.371, with R² = 0.028 and p = 0.376. Spearman correlation gave ρ = −0.165 (p = 0.385). Both approaches agree that there is no statistically significant relationship between water content and cohesion in this dataset.

Figure 13. Relationship between water content (Wn) and cohesion (c) in the Cihuni residual soil (n = 30), with the linear regression line and 95% confidence band.

The relationship between void ratio (e) and friction angle (φ) is shown in Figure 14. Linear regression gave φ = 5.322·e + 4.767, with R² = 0.089 and p = 0.110. Spearman correlation gave ρ = 0.070 (p = 0.713). These results show that the relationship between void ratio and friction angle in this dataset is weak and not statistically significant.

Figure 14. Relationship between void ratio (e) and friction angle (φ) in the Cihuni residual soil (n = 30), with the linear regression line and 95% confidence band.

A summary of the relationship analysis for all three parameter pairs is given in Table 4. Overall, all three pairs show weak to very weak relationships (R² ranging from 0.028 to 0.151), and most are not statistically significant at α = 0.05. This high variability is consistent with the natural behaviour of tropical residual soil, whose heterogeneity reflects varying degrees of weathering from one sampling point to another, even within a single geological formation.

Table 4. Summary of the inter-parameter relationship analysis.

Parameter Pair	n	Regression Equation	R²	p (regression)	Spearman ρ	p (Spearman)
PI vs Friction Angle	26	φ = 0.0503·PI +7.283	0.151	0.050	0.244	0.229
Water Content vs Cohesion	30	c = −0.2785·Wn + 36.4102	0.028	0.376	−0.165	0.385
Void Ratio vs Friction Angle	30	φ = 5.322·e + 4.767	0.089	0.110	0.070	0.713

4. Discussion

The physical and mechanical characteristics obtained from the laboratory testing reflect the strong influence of the regional geology and geomorphology of Curug Panjang Village. Lithologically, the study area is characterised by the Bojong Formation (Qpb), dominated by sandy marl, sandy clay, and tuffaceous sandstone (Rusmana et al., 1991). Under the region’s tropical climate, this Pleistocene rock has undergone intensive biochemical weathering, producing a thick, clay-rich residual soil layer (Departemen Permukiman dan Prasarana Wilayah, 2002). This material is inherently much weaker than its parent rock, with lower shear strength and much greater susceptibility to deformation (Das & Sobhan, 2018). The heterogeneity in weathering and local water infiltration is borne out by the spread in natural water content across the site (27% to 52%). Samples ST-06, ST-17, and ST-26 exhibit notably higher void ratios (e = 1.318 to 1.448) than the rest of the dataset. Mineralogical composition, microporosity, and organic matter content were not tested in this study, so the specific cause cannot be confirmed; however, the pattern is consistent with localized zones of more advanced weathering within the residual soil profile, and would benefit from targeted mineralogical or organic-content testing in future work.

The UU triaxial test under ASTM D2850 (ASTM International, 2015) measures shear strength under total-stress, undrained loading, and so does not directly represent the gradual loss of matric suction that occurs in unsaturated residual soil during rainfall infiltration. In the field, an advancing wetting front reduces matric suction and, with it, the effective stress within the soil mass, which in turn lowers the shear strength mobilised along the potential slip surface (Rahardjo et al., 2008). The cohesion and friction angle values reported here therefore represent total-stress strength parameters obtained under controlled laboratory conditions, and are best interpreted as an index of the soil’s intrinsic mechanical weakening rather than a direct simulation of field pore-water pressure or effective-stress conditions during an actual rainfall-triggered failure.

The relationship analysis in this study shows that the association between plasticity index (PI) and friction angle (φ), and between water content (Wn) and cohesion (c), is weak and mostly not statistically significant (R² ranging from 0.028 to 0.151; see Table 4). The direction observed for water content and cohesion, higher water content tending to be followed by lower cohesion, is consistent with the mechanism reported in the geotechnical literature, where water lubricates the surfaces of clay particles and lowers shear strength (Purnomo, 2011; Haris et al., 2018). The plasticity index-friction angle relationship, however, was weakly positive rather than negative, which runs against the more commonly reported pattern of decreasing friction angle with increasing plasticity. Given how weak this relationship is (regression p = 0.050; Spearman p = 0.229), it most likely reflects the high natural variability of tropical residual soil, whose weathering intensity differs markedly from one sampling point to another even within a single geological formation, rather than a genuine departure from the expected mechanism.

Under the Mohr-Coulomb failure criterion, a decline in cohesion and friction angle contributes to a reduction in the soil’s overall shear strength (Sukandi & Malikah Hr, 2021). This mechanical weakening in the residual soil, combined with the steep slope geomorphology (8°–35°) and high potential for rainfall infiltration, may have contributed to the landslide susceptibility at the study site. However, this study did not directly measure pore-water pressure, effective stress, or the actual slip surface of the 2022 landslide, so any conclusion about the triggering mechanism remains interpretive and would need further validation through direct field monitoring.

5. Conclusion

Based on the laboratory testing and statistical analysis carried out, this study characterised the physical and mechanical properties of the residual soil in Kampung Cihuni, Curug Panjang Village, Lebak Regency. Distribution analysis using histograms, Q-Q plots, and the Shapiro-Wilk test showed that, of the five parameters analysed, only cohesion (c) is consistent with a normal distribution. Water content, plasticity index, and friction angle all show a significant, right-skewed departure from normality, while void ratio sits right at the threshold, reflecting the natural heterogeneity of the residual soil at the study site.

The relationship analysis shows that the association between plasticity index and friction angle, and between water content and cohesion, is weak to very weak (R² ranging from 0.028 to 0.151) and mostly not statistically significant. The water content-cohesion relationship follows the direction commonly reported in the geotechnical literature, where soil with a higher water content tends to have lower cohesion. The plasticity index-friction angle relationship, however, was weakly positive rather than negative, which departs from the pattern more commonly reported in the literature; given how weak and inconsistent this relationship is, it should not be read as a reliable mechanistic trend.

The weak statistical relationships among parameters in this dataset indicate that the mechanical characteristics of the residual soil at the study site vary considerably from one sampling point to another, most likely reflecting differences in local weathering intensity even within a single geological formation (the Bojong Formation). The combination of mechanical weakening at some sampling points, the steep slope geomorphology (8°–35°), and high potential for rainfall infiltration may have contributed to the landslide susceptibility at the study site. However, this study did not directly measure pore-water pressure, effective stress, matric suction, or the actual slip surface of the 2022 landslide, so any conclusion about the triggering mechanism remains interpretive.

Future research should include direct field measurement of matric suction and pore-water pressure monitoring, to more comprehensively validate the infiltration-triggered landslide mechanism proposed in this study.

Ethical considerations

Ethics approval was not required as this study is based solely on laboratory test data from soil samples.

Use of artificial intelligence (AI) tools declaration

During the preparation of this work, the authors utilized Google Gemini (Large Language Model) to assist with language editing, structuring, and formatting the manuscript to adhere to journal guidelines. After using this tool/service, the authors reviewed and edited the content as needed and take full responsibility for the accuracy and originality of the publication.

Acknowledgments

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.

References

Abdillah LA; HS, SMuniarty P: Metode Penelitian Dan Analisis Data Comprehensive [Research Methods and Data Analysis]. Yayasan Kita Menulis; 2021; vol. 1. .
Arsyad, Muh A, Karim MA, et al.: Pengaruh Derajat Kejenuhan Terhadap Tingkat Kepadatan Tanah [Research Methods and Data Analysis Comprehensive]. JILMATEKS: Jurnal Ilmiah Mahasiswa Teknik Sipil. 2025; 7(4). Reference Source
ASTM International: Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils (ASTM D2850-15). ASTM International; 2015.
ASTM International: Standard test methods for liquid limit, plastic limit, and plasticity index of soils (ASTM D4318–17).2017.
ASTM International: Standard test method for laboratory determination of water content of soil and rock by mass (ASTM D2216-19). ASTM International; 2019.
Badan Standardisasi Nasional: Cara uji penentuan batas plastis dan indeks plastisitas tanah [Method for determining the plastic limit and plasticity index of soil] (SNI 1966:2008). Badan Standardisasi Nasional; 2008.
Darmawan ZR, Hutama DA: Studi Muka Air Tanah dan Kemiringan Lereng terhadap Faktor Keamanan [A Study of the Groundwater Table and Slope Gradient in Relation to Safety Factors]. Jurnal Konstruksia. 2025; 16(2): 73–82. Publisher Full Text
Das BM, Sobhan K: Principles of Geotechnical Engineering. Cengage Learning; 9th ed. 2018.
Departemen Permukiman dan Prasarana Wilayah: Panduan Geoteknik 1: Proses Pembentukan dan Sifat-sifat Dasar Tanah Lunak [Geotechnical Guide 1: Formation Processes and Basic Properties of Soft Soil] (Pedoman Kimpraswil Pt T-8-2002-B; Timbunan Jalan Pada Tanah Lunak, p. 82). Pusat Litbang Prasarana Transportasi. 2002. Reference Source
Haris VT, Lubis F, Winayati W: Nilai Kohesi dan Sudut Geser Tanah Pada Akses Gerbang Selatan Universitas Lancang Kuning [Cohesion Values and Angle of Inclination of Soil at the South Gate Access Road of Lancang Kuning University]. SIKLUS: Jurnal Teknik Sipil. 2018; 4(2): 123–130. Publisher Full Text
Harjayanti H, Indrasari W, Budi E: Pemetaan Sebaran Kualitas Tanah Dengan Menggunakan Parameter Suhu, Kelembaban, pH, Salinitas, dan Medan Magnet [Mapping Soil Quality Distributiom Using the Parameters of Temperature, Moisture, pH, Salinity, and Magnetic Field].2022; 10. Publisher Full Text
Idrus M, Suparman P: Studi Daya Dukung Pondasi Bored Pile pada Tanah Pasir Jenuh Akibat Liquefaksi di Palu Sulawesi Tengah [A Study of the Bearing Capacity of Bored Piles in Saturated Sandy Soil Affected by Liquefaction in Palu, Central Sulawesi]. Institut Sains dan Teknologi Nasional; 2015. Reference Source
Listyawan AB, Oktaviani NC, Fitriani D, et al.: Kuat Geser Tanah Lempung Desa Beluk Kecamatan Bayat Yang Distabilisasi Dengan Serbuk Limbah Marmer [The strength of the clay soil in Beluk Village, Bayat Sub-district, stabilised with marble waste powder]. Prosiding Seminar Nasional Teknik Sipil 2025. Surakarta: Universitas Muhammadiyah; 2025.
Luthfiya A: Studi Perbandingan Tingkat Kesiapsiagaan Mahasiswa dalam Menghadapi Potensi Bencana Gempa Bumi di Universitas Pendidikan Indonesia Kampus Bumi Siliwangi [A Comparative Study of Students’ Preparedness Levels in Facing the Potential Risk of Earthquakes at the University of Education Indonesia, Bumi Siliwangi Campus]. Skripsi, Universitas Pendidikan Indonesia; 2025. Reference Source
Miranda Hutabarat G, Widjaja B: Correlation of Undrained Shear Strength and Liquidity Index of Fine-Grained Soils in West Java, Indonesia. IOP Conf. Ser.: Mater. Sci. Eng. 2020; 852(1): 012011. Publisher Full Text
Muhammad Abdul Ghony, Mhd. Dian Afriza2: Pengaruh Kandungan Air Terhadap Plastisitas Tanah Pada Titik Bor XX [The Effect of Water Content on Soil Plasticity at Borehole XX]. Jurnal Ilmiah Teknik Dan Sains. 2024; 2(2): 111–116. Publisher Full Text
Mulyaningsih S: Pengantar Geologi Lingkungan [Introduction to Environmental Geology]. AKPRIND PRESS; 2018. Reference Source
Nurdian S, Setyanto: Korelasi Parameter Kekuatan Geser Tanah Dengan Menggunakan Uji Triaksial Dan Uji Geser Langsung Pada Tanah Lempung Substitusi Pasir [Correlation of Soil Shear Strength Parameters Using Triaxial Tests and Direct Shear Tests on Sand-Substituted Clay]. JRSDD. 2025; 3(1): 13–26. Publisher Full Text
Panitia Teknis Bahan Konstruksi Bangunan dan Rekayasa Sipil: Pedoman Konstruksi dan Bangunan: Rekayasa Penanganan Keruntuhan Lereng pada Tanah Residual dan Batuan [Construction and Building Guidelines: Engineering Measures for Slope Failure on Residual Soil and Rock] (Pd T-09-2005-B). Departemen Pekerjaan Umum; 2005. Reference Source
Purnomo M: Korelasi Antara CBR, PI dan Kuat Geser Tanah Lempung [The Correlation Between CBR, PI and the Shear Strength of Clay Soil]. Jurnal Teknik Sipil & Perencanaan. 2011; 13(1): 81–90.
Rahardjo H, Leong EC, Rezaur RB: Effect of antecedent rainfall on pore-water pressure distribution characteristics in residual soil slopes under tropical rainfall. Hydrol. Process. 2008; 22(4): 506–523. Publisher Full Text
Rahmawati E, Virgawati S: Sifat Fisik Tanah Sebagai Dasar Mitigasi Gerakan Tanah di Kelurahan Sidorejo Kapanewon Godean Kabupaten Sleman Yogyakarta [Soil Physical Properties as a Basis for Landslide Mitigation in Sidorejo Village, Godean Sub-district, Sleman Regency, Yogyakarta].2024; 1: 66–67. 1. Reference Source
Rizkoh F: Ibu dan Anak Terdampak Pergerakan Tanah di Lebak Ngungsi di Lapangan [Mothers and children affected by landslides in Lebak have taken refuge in a field]. detikNews. 2022, February 24. Reference Source
Rusmana E, Suwitodirdjo K, Suharsono.: Peta Geologi Lembar Serang, Jawa [Geological Map of the Serang Sheet, Java]. [Map]. Pusat Penelitian dan Pengembangan Geologi; 1991.
Silvianengsih, Liliwarti, Satwarnirat: Pengaruh Kadar Air Terhadap Kestabilan Lereng (kampus Politeknik Negeri Padang) [the Effect of Moisture Content on Slope Stability (padang State Polytechnic Campus)]. Rekayasa Sipil. 2015; 12(2).
Sukandi, Malikah Hr B: Evaluasi Tegangan-Regangan Lereng Jalan Ampenan—Pemenang KM. 12+800 (Studi Kasus Longsoran Lereng Tanjakan Alberto Senggigi) [Stress-Strain Analysis of the Ampenan–Pemenang Road Slope at KM 12+800 (Case Study of the Landslide on the Alberto Senggigi Ascent)]. Jurnal Konstruksia. 2021;12(2): 153–164. Publisher Full Text
Suradi.: Beberapa Teknik Statistik Dalam Analisa Data Penelitian [some Statistical Techniques in Research Data Analysis]. Ekonomi Bisnis & Kewirausahaan. 2014;3(2): 73.
Syafri A, Tuanany NK: Cihuni Geotechnical Laboratory Test Results [Dataset]. Zenodo. 2026. Publisher Full Text
Teixeira EK d C, de Azevedo RF , Ribeiro AGC, et al.: Influence of Rainfall Infiltration on the Stability of a Residual Soil Slope. Electronic Journal of Geotechnical Engineering (EJGE). 2011; 15(J): 1–16.
Ullah R: Assessment of Residual Soil Properties for Slope Stability Analysis. International Journal of GEOMATE. 2021; 21(86). Publisher Full Text
Utami GS, Caroline J: Analisis Pengaruh Perubahan Kadar Air Terhadap Parameter Kuat Geser Tanah [Analysis of the Effect of Changes in Moisture Content on Soil Shear Strength Parameters]. Seminar Nasional Sains dan Teknologi Terapan VI. 2018; 2018.
Van Zuidam RA: Aerial Photo-Interpretation in Terrain Analysis and Geomorphology Mapping. Smits Publishers; 1985.
Vulcanological Survey of Indonesia: Pengenalan Gerakan Tanah [Introduction to Landslides]. Departemen Energi dan Sumber Daya Mineral; 2024.
Wiqoyah Q, Sasongko HFH, Listyawan AB, et al.: Nilai Parameter Kuat Geser Tanah Lempung Dengan Campuran Serbuk Batu Kumbung [shear Strength Parameters of Clay Soil Mixed with Kumbung Gravel]. Simposium Nasional RAPI XXIII – 2024 FT UMS. 2024.
Zhang J, Hu F, Zhang Q, et al.: Evaluation of the Effects of Rainfall Infiltration Boundaries on the Stability of Unsaturated Soil Slopes Using the Particle Flow Code. Water. 2024;16(24): 3704. Publisher Full Text

Grant information

This publication was supported by the Indonesia Endowment Fund for Education Agency (Lembaga Pengelola Dana Pendidikan/LPDP). The funders had no role in study design, data collection and analysis the decision to publish or preparation of the manuscript.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

© 2026 Syafri A et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Download

Export To

metrics

	Views	Downloads
F1000Research	-	-
PubMed Central Data from PMC are received and updated monthly.	-	-

Citations

CITE

how to cite this article

Syafri A, Zakaria Z, Sulaksana N et al. 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 [version 2; peer review: 1 approved, 2 approved with reservations]. F1000Research 2026, 15:1195 (https://doi.org/10.12688/f1000research.184697.2)

NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.

track

receive updates on this article

Track an article to receive email alerts on any updates to this article.

Open Peer Review

Current Reviewer Status: ?

Key to Reviewer Statuses VIEW HIDE

ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions

Version 2

VERSION 2

PUBLISHED 16 Sep 2026

Revised

Reviewer Report 12 Oct 2026

Mohammed Fattah, College of Civil Engineering, University of Technology – Iraq, Baghdad, Iraq

Approved with Reservations

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

References

1. Hassan H, Ammar Mohammed H, Wasife jassim N, Yousif Fattah M, et al.: Finite Element Analysis of Skirted Strip Footing Resting on Cohesive Slopes. Journal of Engineering and Sustainable Development. 2025; 29 (1): 47-56 Publisher Full Text
2. Ayasrah M, Fattah M: 3D numerical response of different pipe pile under combined loadings condition embedded in loose sand. International Journal of Geotechnical Engineering. 2024; 18 (7-10): 702-718 Publisher Full Text
3. Fattah M, Mohsin I, Ayasrah M, Salim N: Analysis of pile shaft resistance embedded in unsaturated clayey soils. Geomechanics and Geoengineering. 2025; 20 (4): 805-825 Publisher Full Text
4. Fattah M, Al-Khafaji M, Mohsen M, Hafez M: Comparative Analysis of Soft Clay Improvement Using Ordinary and Grouted Sand Columns with Geosynthetic Reinforcement. Infrastructures. 2025; 10 (3). Publisher Full Text

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: See the reviewers' comments

Reviewer Report 01 Oct 2026

Merley Misriani, University of Riau, Pekanbaru, Indonesia

Approved

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Geotechnical Engineering (Soil mechanics, slope stability and Landslide Hazard Mitigation)

Version 1

VERSION 1

PUBLISHED 22 Jul 2026

Reviewer Report 28 Aug 2026

Nugroho Aji Satriyo, National Research and Innovation Agency (BRIN), Bandung, Indonesia

Approved with Reservations

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Geology, engineering geology, remote sensing, disaster mitigation, disaster management, etc.

Reviewer Report 25 Aug 2026

Merley Misriani, University of Riau, Pekanbaru, Indonesia

Approved with Reservations

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Geotechnical Engineering (Soil mechanics, slope stability and Landslide Hazard Mitigation)

Comments on this article Comments (0)

Version 2

VERSION 2 PUBLISHED 22 Jul 2026

Comment

Схожие новости

#	Наименование новости	Информативность	Дата публикации
1	Decreased Land Use Intensity Improves Surface Soil Quality on Marginal Lands	8.24	12-08-2026
2	6.5 million Americans face landslide risks — a new database shows where they live	9.54	29-07-2026
3	Seismic response and postseismic stability of an investigation-constrained loess–mudstone slope	20.51	19-08-2026
4	Structural aspects of diapiric mélange emplacement: the Duck Creek diapir	6.34	27-08-2026
5	Dominant Controls on Preferential Flow and Their Implications for Future Soil Water Fluxes	6.79	20-08-2026
6	Geological, Geophysical and Hydrological Controls on Sinkhole Formation in Saudi Arabia: Linking Karst Processes to Anthropogenic Impacts	8.61	12-04-2026
7	Understanding Sub‐Lithospheric Small‐Scale Convection by Linking Models of Grain Size Evolution, Mantle Convection, and Seismic Tomography	5.04	27-08-2026
8	Application of Geopolymer Technology and Pile Raft Foundation in a Soil, Review Study	7.88	12-04-2026
9	Continuum Description of Granular Materials	5.53	30-05-2035

Классификация: . Схожих патентов: 0. Схожих новостей: 9. Тональность: 0. Информативность: 8.98. Источник: f1000research.com.

Вход на сайт

Просмотр новости

Найдите то, что Вас интересует

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 [version 2; peer review: 1 approved, 2 approved with reservations]

Дата публикации: 16-09-2026 10:50:49

Основное содержимое страницы с новостью.

Схожие новости