Indonesian Geotechnical Journal

Stability Assessment of Homogeneous Embankment Dam Under Variable Drawdown Rates Using Unsaturated Soil Parameters

Muhammad Adi Ibrahim — 2026-04-30

Embankment dams are critical for sustainable water resource management, providing irrigation, hydropower, flood control, and water supply. One of the critical threats to an embankment dam stability is rapid drawdown, when reservoir levels fall faster than pore pressure dissipation in the upstream slope. This condition reduces shear strength and can trigger failure. One of the commonly used methods for rapid drawdown assessment is the three-stage approach developed in the early 1990s, which provides a practical framework by combining drained and undrained soil strength. However, these methods do not explicitly consider the influence of drawdown rate, which can strongly affect stability. This study evaluates the effect of drawdown rate on the stability of an embankment dam using unsaturated soil mechanics framework and compares the results with those from the three-stage method. Numerical analyses were carried out using coupled seepage and slope stability modelling. The soil-water characteristic curve of the clay core was estimated from index properties. Three drawdown rate variations were examined: half a meter per day, one meter per day, and two meters per day. The result showed that the three-stage method produced higher factors of safety than the unsaturated framework. Unsaturated framework also showed lower factor of safety for faster drawdown rates. This study highlights that the three-stage method may overestimate the stability of dam embankment during rapid drawdown. Incorporating unsaturated soil mechanics provides a more realistic assessment and offers insights for improving dam safety, particularly under conditions where faster drawdown may occur.

Adhesion Factor (α) of Drilled Piles in Clay Shale with Static and Dynamic Load

Eddy Triyanto Sudjatmiko — 2026-04-30

Adhesion factor (α) is one of the significant parameters in calculating the bearing capacity of pile foundations, both for driven piles and bored piles in clay soils. In practice, the α value is usually estimated based on the available empirical correlations. The applicability of this correlation for bored pile installed in expansive soil and clay shale is questionable. Clay shale is known as one of the problematic soils, due to its physical properties that rapidly soften once exposed to water/moisture and loss of pressure. This physical sensitivity becomes crucial in bored pile constructions. Especially in the drilling and casting process as the soil is exposed to water and loss of horizontal pressure causing reduction in soil shear strength. This study investigates the load transfer behavior of a bored pile installed in clay shale formation. The pile, instrumented with vibrating wire strain gauges, was axially loaded through dynamic and static load test up to 700 tons. The strain gauges provide accurate strain measurement of each pile segment, proportional to the stress induced. Through the pile load-settlement, t-z and q-z curves, the load transfer mechanism and interaction between bored pile and the clay shale soil can be analyzed. By performing back analysis, the actual skin friction (fs), and adhesion factor (α), of bored piles in clay shale can be determined. The results show that in clay shale that have experienced slaking (30 < NSPT < 70), the adhesion factor (α) = 0.12~0.18. While for fresh clay shale (NSPT > 70), the adhesion factor (α) = 0.32~0.35. These values are significantly lower than α = 0.55 which is usually applied in practice; as well as some previous studies, including the value recommended by Reese and Wright (1979).

Stabilization of Patimban Marine Soft Clay with Portland Composite Cement: The Effect of Initial Water Content Variations on Soil Bearing Strength

Yosse Triade Pandiangan — 2026-04-30

Marine clay soil generally exhibits poor physical and mechanical properties, such as high plasticity, low bearing capacity, and excessive settlement under pressure. Soil improvement techniques, such as cement stabilization are thus needed to enhance these characteristics. This study investigates the effect of clay water to cement content ratio (w_c/c) and curing time variations on the unconfined compressive strength (q_u) of Patimban dredged marine clay stabilized with Portland Composite Cement. Laboratory tests employed variations in ratio of initial water content to its liquid limit (w₀/LL), i.e., 1, 1.25, 1.5, and 2, as well as variations in cement content of 20% and 30% of the dry soil mass. Unconfined compressive strength (UCS) test was carried out at curing periods of 1, 3, 7, 28, and 56 days. The peak effective cement hydration process occurred in the first 7 days. The results revealed an inverse correlation between the ratio and , where an increase in the ratio caused a decrease in the values. The high-water content resulted in large voids between cement-soil particles, weakening the strength of the binder. The relationship between the ratio and the value indicated a good match yielded an R² value of 0.88-0.94. Further, the unconfined compressive strength of the soil continued to develop with the increasing curing time of 1-56 days. The Average Normalized Difference (A.N.D) value obtained from the relationship between the measured and the estimated compressive strength value was low (11.40%), meaning the estimation equation can be effectively used to estimate the compressive strength of marine clay soil stabilized with Portland Composite Cement at various curing times.

Characterization and Shear Strength Evaluation of Sensitive Volcanic Residual Soils in West Java

Mirna Dwi Lestari Salamah — 2026-04-30

Volcanic residual soils in tropical regions exhibit unique engineering behavior that differs significantly from sedimentary soils. These soils often contain amorphous clay minerals such as allophane and halloysite, which contribute to their sensitivity and unusual strength characteristics. Field observations in West Java revealed near-vertical, free-standing cuts up to 12 meters high, indicating apparent cohesion supported by natural cementation and unsaturated conditions. A geotechnical investigation was carried out using standard penetration tests (SPT), cone penetration tests with pore pressure measurement (CPTu), and laboratory tests including Atterberg limits, index properties, and unconsolidated-undrained triaxial tests. Results show that Su values obtained from CPTu are more consistent with laboratory triaxial data, while SPT correlations tend to underestimate strength due to sample disturbance. Furthermore, particle size analyses confirm the gap-graded nature of volcanic residual soils, reflecting differential weathering processes. This study aims to establish representative undrained shear strength parameters of sensitive volcanic residual soils in West Java by integrating field and laboratory investigations. The findings highlight the importance of careful sample handling, the use of less-disturbing in-situ tests, and the selection of appropriate testing methods to obtain reliable soil parameters for engineering design. These findings provide practical implications for the characterization and modeling of sensitive volcanic residual soils in engineering applications.

Implementation of Sludge-Filled Geotextile Tubes as a Sustainable Coastal Protection Measure in Muddy Coastline

Nastiti Tiasundari — 2026-04-30

Coastal erosion is one of the major challenges faced along the northern shoreline of Java Island. This phenomenon results in degradation of the coastline, threatening not only the local ecosystems but also the livelihoods of coastal communities. The soft, muddy coastal characteristics of this region make conventional hard-engineering structures less effective and unsustainable, prompting the need for alternate solutions. This study aims to evaluate the effectiveness of sludge-filled geotextile tubes (GI-Tubes) as an erosion control measure in muddy coastal areas. A field experiment was conducted using three GI-Tube units, each measuring 1.3 meters in height and 20 meters in length, installed parallel to the shoreline. The GI-Tubes were made from double-layered needle-punched staple fiber polypropylene non-woven geotextile and filled with locally sourced sludge mixed with flocculants to promote effective sediment floc formation within the tubes. The small opening size of the non-woven geotextile facilitated efficient dewatering while retaining the sludge inside. The outer layer of the GI-Tube provided high UV resistance and enhanced sediment-trapping capability, offering additional protection and extended durability. The double-layered design of the geotextile tubes enhances their overall structural integrity, enabling them to withstand hydrodynamic forces such as wave and coastal currents. After five months, a height reduction of approximately 0.4 meters was observed, likely due to settlement of the sludge filling. Monitoring conducted 2 years after installation indicated that the sludge fill remained solid and well-consolidated with no sign of damage, thereby confirming good performance of the structure. Satellite imagery analysis 40 months post installation indicated shoreline accretion accompanied by a significant expansion of mangrove growth, reaching up to 50 m beyond the initial vegetation line. These findings suggest that sludge-filled GI-Tubes can be an effective, low-cost, and sustainable solution for mitigating coastal erosion in soft-soil coastal environments.