Journal of the Civil Engineering Forum

Development of a Numerical Model for the Formation of Complete and Incomplete Channel Blockages and Their Influences on River Flow

Takashi Wada, Hiroshi Miwa, Naoto Aoki, Yusei Fujii — Tue, 08 Jul 2025 08:24:38 +0700

Large landslides, triggered by torrential rain or earthquakes, can slide down mountainous slopes and block river channels at the lower end of the slopes. In cases where the landslide volume is relatively small compared to the river discharge, or when the distance between the landslide slope and the river channel is long, incomplete channel blockages may occur due to an insufficient supply of landslide material to fully block the river flow. Since the shape of the channel blockage is the final result obtained through the temporal changes in landslide material movement, river flow, and topography, considering their interactions, it is necessary to investigate the blockage shape by numerical analysis that accounts for these interactions. Therefore, we developed a numerical model to predict the formation of various channel blockages by incorporating the combined conditions of topography, landslide volume, and river discharge. The developed model is a two-dimensional (2-D) model, which can connect several one-dimensional calculation areas for mountainous streams at any selected point in the 2-D area. In addition, the model can consider landslide material movements represented by cylindrical blocks. To verify our model and identify appropriate values for the associated parameters, we investigated the MAE (mean absolute error) for the deposit thickness distribution and the PWO (percentage of the area where the actual and calculated waterlogged areas overlapped) between the actual and calculated results using our model for two previous channel blockages of different sizes. Although our model and the associated parameters still need to be improved by considering the loss of landslide material, they are useful for estimating the magnitude and area of damage caused by large-scale landslides and the associated channel blockage and waterlogging in various river channels with steep side slopes. The calculated results can be utilized in investigating disaster countermeasures for landslides in the area.

Probabilistic Seismic Hazard Analysis Assessment in Cianjur Following the Mw 5.6, 2022 Earthquake

Yusufa Kholifa Ardha, Iman Satyarno, Gayatri Indah Marliyani — Tue, 08 Jul 2025 08:38:42 +0700

On November 21, 2022, a M_w 5.6 earthquake struck Cianjur, West Java, Indonesia, causing extensive damage to buildings, infrastructure, and public facilities, and resulting in 602 fatalities and thousands of injuries. The earthquake’s hypocenter was located near the Cugenang Sub-District, leading to the identification of the previously unmapped Cugenang Fault as its source. This discovery highlights the need to reassess seismic hazards in the region, as it reveals the existence of previously unrecognized active faults. This study conducts a probabilistic seismic hazard analysis (PSHA) for Cianjur using an updated seismic source model that incorporates the Cugenang Fault. We apply updated ground motion prediction equations (GMPEs) and utilize the logic tree method to account for uncertainties in attenuation equations and source parameters. Ground motion is expressed as peak ground acceleration (PGA) on both bedrock and surface conditions for return periods of 100, 150, 250, 500, 1,000, 2,500, 5,000, and 10,000 years. These return periods capture the hazard levels associated with both frequent low-magnitude and rare high-magnitude earthquakes. Our findings indicate that high PGA values in the Cianjur area are concentrated around crustal faults, exceeding 1.0 g for return periods of 2,500 years and beyond. The Cugenang Fault has a localized impact, with its influence extending up to approximately 10 km from the fault line. A seismic hazard disaggregation analysis confirms that crustal faults are the dominant seismic sources in the region. The results of this study provide valuable insights for updated seismic risk in Cianjur and support future mitigation strategies, urban planning, and infrastructure design to enhance earthquake resilience in the affected area.

Sustainable Lightweight Concrete Using Candlenut Shell as Coarse Aggregate: The Impact of Water-Cement Ratios on Strength and Density

Thu, 17 Jul 2025 00:00:00 +0700

This study explores the promising potential of Candlenut Shell Aggregate (CSA) as a sustainable and innovative alternative for lightweight concrete production. Derived from Aleurites moluccanus, CSA is an agricultural by-product characterized by its low density, moderate abrasion resistance, and high water absorption make it suitable for non-structural applications like wall panels and flooring. However, integrating CSA into concrete mixes requires careful management of the water-cement (w/c) ratio which significantly affects compressive strength, density, and workability. Concrete mixes were prepared using the absolute volume method, with w/c ratios ranging from 0.65 to 0.30, to identify the optimal balance. The absolute volume principle was applied for all mix designs. Our results indicate that an optimal w/c ratio of 0.55 yields the most favorable balance, achieving the highest compressive strength of 14.3 MPa and a maximum density of approximately 1850 kg/m3. This specific ratio strikes an ideal equilibrium between adequate cement hydration and effective void minimization within the concrete matrix. Conversely, higher w/c ratios lead to increased porosity, diminishing both strength and density, while lower ratios impair workability, hindering compaction and hydration, ultimately degrading performance. These findings resonate strongly with existing prior research, further emphasizing the crucial need for pre-treatment of CSA, such as soaking or the strategic incorporation of admixtures, to effectively mitigate its inherent high absorption and enhance overall mix performance. In conclusion, this study robustly confirms the feasibility of utilizing CSA as a lightweight aggregate. This represents a significant step towards developing an eco-friendly solution that not only contributes to global sustainability goals by repurposing agricultural waste but also actively reduces reliance on conventional, resource-intensive aggregates. Future research should explore the long-term durability of CSA-based concrete and investigate advanced admixtures to further enhance its properties for broader applications.

Impact of Tree Canopy Elevation on Rainfall Attenuation and Soil Erosion Dynamics for Enhanced Erosion Control

Fri, 18 Jul 2025 00:00:00 +0700

Afforestation harvesting operations and the interception processes of tree canopies profoundly impact rainfall intensity attenuation, thereby altering both the magnitude and intensity of rainfall, which leads to changes in the production of runoff and sediment. Concurrently, the kinetic energy (KE) of raindrops is moderated by the presence of the canopy, with heightened attenuation observed during the canopy’s full leaf-out phase. This attenuation of rainfall intensity under different tree canopy elevations, resulting from the dynamic interaction between rainfall and the tree canopy, is a fundamental component of the interception process, influencing water distribution and soil stability. This study evaluates the impact of rainfall interception by canopies of six trees of the same species at varying elevations (H1=5.90 m, H2=5.68 m, M1=4.02 m, M2=4.04 m, L1=2.19 m, L2=2.33 m) on soil erosion dynamics. A controlled experiment in the woodland of Ritsumeikan University involved plastic boxes (37 cm25 cm) placed under each canopy, filled with decomposed granite and silica sand, and set on a 20° slope. The experiment measured soil displacement within a designated erosion area (6 cm 15 cm) in the boxes following three rainfall events with different durations and precipitation levels. Results showed that the eroded soil mass (measured in grams) in the boxes was lower at the lower elevation sites (L1 and L2) compared to the medium and higher canopy elevations (M1, M2, H1, and H2). Lower tree canopies not only attenuate raindrop KE but also enhance rainfall redistribution, increase litter-induced surface roughness, improve infiltration, and reduce runoff-driven erosion. Their proximity to the soil enhances microclimatic regulation, minimizing sediment detachment and transport.

Building Distribution and Spatial Constraints from Perspectives of Tsunami Inundation at a Small Island Context: A Study Case of Sabang-Aceh, 20 Years after the 2004 Aceh Tsunami

Fri, 18 Jul 2025 00:00:00 +0700

In the aftermath of the devastating 2004 Indian Ocean tsunami, the Indonesian government implemented disaster mitigation measures through improved spatial planning, particularly in settlement areas. These efforts focused on reconstruction and sustainable development strategies to enhance safety while aligning with national and regional regulations. Sabang City, located in a tsunami-prone region, was also affected by the 2004 tsunami, necessitating further evaluation of its building resilience and spatial planning. This study aims to assess the spatial distribution of buildings in Sabang City to evaluate their suitability in tsunami-prone areas and their potential for residential development. A field survey was conducted between February and June 2023, identifying and classifying 14,104 building units based on the HAZUS methodology developed by FEMA (Federal Emergency Management Agency, USA). The buildings were categorized into six structural types: Reinforced Concrete (C1-La, C1-Lb, C1-M), Concrete Frame with Unreinforced Masonry (C3-L), Steel Frame (S1-M), and Wood Frame (W1-L). Spatial analysis examined settlement patterns in relation to land capability and disaster mitigation requirements. Findings reveal significant constraints in land development for residential purposes, particularly in tsunami-prone and low-capability areas. Of the total surveyed buildings, 6,726 units (47.7%) are located in low-capability zones, primarily influenced by the dominance of protected forests and buffer zones that restrict land availability. Moreover, Sabang’s rugged topography, characterized by steep slopes and hilly terrain, exacerbates land development challenges. These findings underscore the urgent need for strategic interventions, including relocating settlements from high-risk tsunami zones, updating spatial planning policies, and integrating tsunami risk assessments into urban development strategies. Strengthening these measures will enhance urban resilience and promote sustainable growth in Sabang City.