Indonesian Geotechnical Journal

Influence of Underconsolidating Soil on Effective Stress Path in a Deep Excavation Case

Albert Sebastian — 2025-12-31

This study investigates the influence and impact of clay soil that is presumed to be undergoing consolidation process on an unbraced shallow excavation system. The excavation geometry spans up to 160 meters with a maximum depth of 5.25 meters. A concrete sheet pile wall was installed at the front side of the excavation, supported by additional tie beams connected to square precast piles behind the wall. Based on soil investigation data, residual excess pore water pressures were identified within the underconsolidating clay layer at depths between 3 to 12 meters. These residual pore pressures contribute additional loading to the retaining wall system. A back analysis was conducted to obtain appropriate soil parameters to be used for PLAXIS 2D modelling. The finite element analysis results were compared with inclinometer data to validate the back analysis. Modeling of the underconsolidating condition was performed by manually inputting the pore water pressure into the initial condition. Results show that under underconsolidating conditions, the maximum wall deflection reached 190 mm, whereas under hydrostatic conditions, it was only 100 mm. Additionally, a parametric study was carried out to examine the relationship between the degree of consolidation and wall deflection. The findings indicate that a higher degree of consolidation leads to reduced wall deflection. To investigate the stress changes on the wall due to underconsolidating soil, a stress path analysis was performed to understand the stress history around the excavation. It was found that in underconsolidating conditions, the average effective stress tends to be lower and the deviatoric stress higher, resulting in a stress path that is closer to the failure line.

Analysis and Design of a High-Risk Tiered Retaining Wall Using a Geosynthetic Reinforcement System

Valdy Kosalim — 2025-12-31

Infrastructure development in Indonesia often faces rugged terrain and high seismicity, requiring advanced geotechnical solutions. One of the challenges lies in ensuring that an embankment can effectively withstand heavy loading conditions. Mechanically stabilized earth (MSE) walls provide a safe and efficient option to address these RSS with a total height of 26.95 meters based on a previous project. The structure is designed to withstand a large static surcharge load (up to 375 kPa) and a seismic load with a peak horizontal ground acceleration (kh) of 0.225g. The method employed is a limit equilibrium stability analysis using Janbu's simplified method of slices for non-circular failure surfaces, referring to the SNI 8460:2017 standard, and utilizing TensarSlope software. The selected system is the SierraScape System, which combines high-strength uniaxial geogrid primary reinforcement with a flexible welded wire for facing. The analysis results show that the retaining wall design meets the required factors of safety for both static (FS = 1.301 > 1.300) and seismic (FS = 1.163 > 1.100) conditions. In conclusion, this case study demonstrates that the application of modern geosynthetic reinforcement systems is a reliable and effective solution for addressing geotechnical challenges in high-risk projects in Indonesia, contributing a design reference for similar conditions.

Determination of Bentonite’s Flow Limit Using Cylinder Strength Test and Suspension Settling Model

Samuel Jemmy Setiadjie — 2025-12-31

Cohesive soils exhibit complex behavior characterized by distinct transitional boundaries between different states. One of the boundaries is the flow limit (FL), which is the transition between the viscous liquid and suspension states. Currently, there are no specific standard tests to determine the flow limit. Most previous studies have used the undrained shear strength (c_u) value to determine the FL value. This study employed two different approaches to obtain the FL value: first, using the cylinder strength test (CST), which approaches from the viscous state, and second, using the suspension settling model, which approaches from the suspension state. There are five variations of samples for each test: 100% bentonite, 90% bentonite and 10% sand, 80% bentonite and 20% sand, 70% bentonite and 30% sand, and 60% bentonite and 40% sand. The cylinder test was conducted with three different cylinder diameters: 30 mm, 40 mm, and 50 mm. For the suspension settling model, five solid concentrations were used, namely 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%, for each sample. The results show that the CST for bentonite suspension gave higher results than the other; meanwhile, the suspension settling model is the most conservative. The FL value from the CST test ranges from 3.33 to 4.9 times higher than the liquid limit (LL); the suspension settling model yielded values of 1.9 to 2.6 times higher than LL. The results are higher than those in previous studies, which can be attributed to differences in apparatus capacities used to determine the c_u value, variations in bentonite mineral compositions, and different estimation approaches. Although in this research the range of FL values is still vast, this study has provided insights from two different approaches. This research still has various development opportunities, such as mineralogy effect and new method development to divine the FL value.

Microbial Enzyme Extract Evaluation for Calcium Carbonate Biocementation: Implications for Ground Improvement

Lutfian Rusdi Daryono — 2025-12-31

Microbially Induced Carbonate Precipitation (MICP) has emerged as a promising technique for slope surface stabilization or other ground improvements. However, its effectiveness in fine-grained soils is limited due to challenges associated with bacterial cell transport. This study explores the feasibility of an alternative approach Enzyme Induced Carbonate Precipitation (EICP) from microbial bacteria itself for stabilizing fine-grained slope soils. In this study, urease was extracted from whole-cell cultures of Lysinibacillus xylanilyticus (LyXy) which developed under Hokkaido University and using cyclic sonication. The extracted enzyme solution was then applied to a precipitation test using fine-grained sand and/or soil samples. The performance of enzyme extract was evaluated in comparison to traditional MICP with a focus on the adaptability to precipitate the fine-grained sand/soil and the effectiveness of the enzyme. Results indicated that the urease extract exhibited higher enzymatic activity than the original bacterial culture and maintained better stability at 15°C. The observation verified that the effectiveness of enzyme-induced and MICP would vary depending on the soil to be treated. The enzyme-induced resulted in unconfined compressive strength around 4 MPa and deeper cementation in the finest sand. Microscopic analysis revealed that while enzyme-induced produced smaller calcium carbonate crystals compared to MICP, it generated a significantly higher quantity of crystals, leading to enhanced particle bonding and improved soil stabilization.

Characterization of Sepaku Clay Shale with Slaking Test, X-Ray Diffraction and Scanning Electron Microscopy: Potential Stabilization Using Bacillus Subtilis

Yuswal Subhy — 2025-12-31

Clay shale in the Sepaku region exhibits geotechnical vulnerability (slaking, cohesion loss, saturation expansion) that threatens slope stability and road foundations. Conventional stabilization methods (cement/lime) can cause negative environmental impact; therefore, alternatives with low environmental impact such as microbially induced carbonate precipitation (MICP) are sought for. MICP has the potential to improve the mechanical properties of clay shale. MICP utilizes microbial activity (urease enzyme or alternative pathways) to trigger CaCO₃ precipitation that binds soil particles and fills pores. In order to optimize the stabilization effects of MICP on Sepaku clay shale, it is first necessary to characterize the clay shale properties. Slaking test, X-Ray diffraction and scanning electron microscopy were conducted on clay shales samples obtained from Sepaku region. The SPT tests from two boreholes show NSPT values of above 60 for the shale, which is expected for unweathered shale. The disturbed samples were then subjected to slaking tests, which the results categorize the shale to be low durability after one cycle of wetting and drying, and very low durability after two cycles of wetting and drying. The unconfined compressive strength was found to be 2.53 MPa, categorizing the Sepaku clay as weak rock. The XRD and SEM results of Sepaku clay revealed consistent values and characteristics as other clay shales. This research serves as preliminary investigation to optimize the stabilization of Sepaku clay shale using MICP method, in particular Bacillus Subtilis bacteria.