Indonesian Geotechnical Journal

Case Study of Double-Wall Retaining Wall System for Deep Excavation in Jakarta, Indonesia

2024-11-22T03:07:20+00:00

This paper presents a case study of diaphragm wall behavior in a deep excavation project under double-wall condition. A double-wall condition occurs when two layers of diaphragm wall, either side by side or with gaps between them, are used as a retaining wall system. The project discussed in this paper is located in a soft clay area of Jakarta, Indonesia, with a main excavation depth of approximately 33 meter and a side excavation depth of 23 meter. The project utilizes the top-down construction method, where the retaining walls for both the main and side structures are initially built before the excavation begins, creating the double wall condition. However, due to site issues, main excavation activities commenced after the construction of the main structure wall but before the side structure wall was completed, changing the plan to a single-wall condition. The behavior of the main structure wall under both single-wall and double-wall condition is studied. The study simulated two separate FEM models to evaluate the sequence of construction up to the final excavation level of the main station. According to the analysis result, single wall condition has relatively larger deformation than double wall condition. However, the wall bending moment did not change much, meaning that double-wall did not contribute effectively towards providing higher stiffness. The results contradict the initial assumption that the double-wall condition would be more advantageous for the main structure wall design than single-wall condition. Several critical parameters were found to significantly influence the outcome. The findings of this case study can provide valuable insights for the preliminary design of future excavation projects.

Evolution of Crushing Surface of Ta-d Pumice in Triaxial Compression Tests

2024-11-27T19:16:36+00:00

Crushable porous granular materials like volcanic pumice, distributed worldwide, cause various engineering problems, including slope hazards. These materials are often classified as problematic soils due to their complex mechanical properties, which arise from high compressibility and changes in grain size due to particle crushing. Consequently, their behaviour is typically discussed on a case-by-case basis, and a systematic understanding has yet to be established. This study aims to elucidate the relationship between the mechanical properties and particle crushing of porous granular materials through a series of tests on natural volcanic pumice. The intra-particle void ratio was measured alongside isotropic consolidation and CD/CU triaxial compression tests, with particle crushing assessed before and after the experiments. The results indicate that the intra-particle void ratio correlates with particle size, with larger particles generally having higher porosity. Additionally, the mechanical behaviour of these materials shows high compressibility, and their stress paths resemble those obtained from undrained triaxial tests on loose sand, ultimately reaching the critical state. The relationship between the amount of particle crushing and mean effective stress at the end of the tests can be represented by a single curve for isotropic consolidation tests, CD, and CU triaxial tests, respectively. The amount of crushing generally increases with the progression of axial strain during the compression process, and in CU tests, when reaching the critical state, no further increase in crushing occurs with increased axial strain. Furthermore, critical state and isotropic consolidation state of each material can be represented on its own unique surface, each referred to as a "Crushing Surface," defined by the crushing volume, void ratio, and mean effective stress for that specific soil.

Influence of Sugarcane Bagasse Biochar Amendment on Low Plastic Clay Soil Performance: A Novel Approach for Geotechnical and Geo-environmental Applications

2024-11-28T01:57:20+00:00

The application of biochar in geotechnical and geoenvironmental engineering remains relatively understudied, particularly concerning its impact on soil properties when mixed with sugarcane bagasse. This study investigates the influence of sugarcane bagasse-derived biochar on the strength and water retention behavior of low plastic clay soil, representing a novel contribution to the field. Biochar, a carbon-rich material produced by the pyrolysis of organic biomass, has garnered attention for its potential to enhance soil properties and mitigate environmental challenges. Five different percentages of bagasse biochar (0%, 1%, 2%, 3.5%, and 5%) were incorporated into the low plastic clay soil to prepare biochar-amended soil specimens. Unconfined compressive strength and water retention tests were conducted to evaluate the mechanical and hydraulic properties of the amended soils. The findings reveal that the water retention capacity of the biochar-amended soil increased with the addition of bagasse biochar. This observation suggests that biochar incorporation enhances the soil's ability to retain moisture, potentially beneficial for mitigating soil moisture fluctuations and supporting plant growth in geoenvironmental applications. Furthermore, the study also highlights a positive impact on the strength properties of the soil with a 22.1% increase for 1% biochar content compared to no-amended after 28 days. This increase in strength was attributed to changes in soil structure, pore distribution, and inter-particle bonding induced by the presence of biochar. In conclusion, Biochar amendment offers potential for enhancing soil water retention and strength properties and the use of sugarcane bagasse-derived biochar in low plastic clay soil presents promising opportunities for geoenvironmental engineering applications.

Physical and Numerical Modelling of Rockwool Insulated Landfill Liner Materials as a Heat Mitigation Method

2024-11-28T01:51:52+00:00

The growing global amount of waste emphasizes the urgency of effective landfill management. The large amount of organic matter in landfill liners undergoes rapid biodegradation, generating significant heat. This heat production can cause various environmental issues, such as the release of volatile organic compounds, an increased risk of groundwater contamination from leachate migration, unpleasant odors, and a reduction in the structural integrity of the landfill liner. Therefore, efficient heat mitigation methods in landfill liners are crucial for minimizing detrimental environmental effects. Utilizing insulation material in landfills can be an effective and novel method in the environmental geotechnical field while promoting material sustainability. This study aims to evaluate the effectiveness of rockwool as an insulation material in reducing heat transfer inside landfill liners. The effectiveness of rockwool was assessed by using both physical and numerical modelling with varying thicknesses of rockwool, moisture conditions, and elevated temperatures in the landfill liner system. The insulated landfill liner system was simulated numerically using ANSYS software. A wooden box prototype was built to simulate a real-life insulated landfill liner system to evaluate the feasibility of insulation material as a heat mitigation method in landfills. The findings suggest that rockwool is effective in mitigating the heat in landfill liners. Overall, rockwool reduced the elevated temperatures up to 48.45% despite the system being wet which reduces the effectiveness of insulation performance. Comparatively, the 20 mm rockwool was efficient in minimizing average level of elevated temperatures, meanwhile, rockwool with thicknesses of 35 mm and 50 mm were needed to attenuate extremely elevated temperatures. These results were demonstrated through numerical simulation and validated by physical modelling results. It can imply an effective method for mitigating heat in landfill liners, which advances the development of environmental geotechnics for sustainable waste management.

Investigation of a Notable Landslide under Complex Hydrogeological Conditions at Pak Tam Road, Sai Kung, Hong Kong

2024-11-28T01:50:44+00:00

On 8 June 2022, an intense rainstorm triggered multiple landslides in the northeastern area of Hong Kong. One of these landslides occurred at the registered soil and rock cut slope adjoining Pak Tam Road in the Sai Kung East Country Park with significant social consequences and widespread media attention. An investigation of this notable landslide was undertaken to study the probable causes and mechanism of the failure, as well as the hydrogeological conditions of the slope. The landslide was a large‑scale rain‑induced sliding failure caused by adversely orientated relict joints within the weathered rock profile. Coupling effects of inadequate slope maintenance, steep slope profile and tension cracks rendered the slope particularly vulnerable to landsliding under severe rainfall. Additionally, heavy seepage was observed from some weep holes within the same slope, which suggested the presence of complex hydrogeological conditions. Field mapping and site‑specific ground investigation revealed preferential flow paths along a network of soil pipes and relict joints in the groundmass that prompted the subsurface flow and the build-up of a transient perched groundwater table. The landslide highlighted the importance of proper and regular slope maintenance of slopes in Hong Kong, and the need of assessing the site holistically when modifying the site with engineering works. A robust design solution is strongly advocated for stabilising slopes.

Shaking Table Tests on Geocell-Based Countermeasures against Pipe Flotation

2024-11-28T01:56:32+00:00

This study investigates the effectiveness of the geocell-based countermeasures against pipe flotation in liquefied ground using shaking table tests. Liquefaction-induced pipe flotation is a significant issue, particularly for agricultural pipelines, which are often installed in areas with high groundwater level. A conventional method, such as using geotextiles combined with gravel, is effective in mitigating this problem. However, the conventional method includes challenges in terms of workability, presenting a need for more efficient solutions. We propose a novel approach that employs geocells to enhance resistance against pipe flotation while potentially reducing labor costs. Geocells, which can be transported in a compact form and expanded on-site, are filled with soil or gravel to form a robust reinforcement around the pipe. This method is expected to offer significant advantages in terms of ease of installation and overall cost-effectiveness. To validate the effectiveness of the proposed method, we conducted shaking table tests using an aluminum pipe buried in saturated sand within a steel container. In this study, four different experimental cases were conducted: an unreinforced case, a case for the conventional geotextile method, and two cases for the geocell reinforcement. For the two cases with geocell reinforcement, the two experimental conditions were varied in the method of fixing the geocells and in the backfill material around the pipe. The results demonstrated that all conventional and geocell-reinforced methods significantly reduced pipe flotation compared to the unreinforced method. Compared to the unreinforced case, the case for the geocell reinforcement reduced pipe flotation by 24.6 times, and the conventional method reduced it by 13.6 times. In conclusion, the proposed method using geocells to prevent pipe flotation in liquefied ground has been confirmed as an effective alternative to the conventional method. This study provides a practical and labor-saving solution for improving the seismic resistance of buried pipelines in earthquake-prone areas.