Journal of the Civil Engineering Forum

Excess Pore Pressure Migration Analysis Due to High Embankment Construction – Case Study East Kalimantan

Edwin Lie — 2024-03-05

A 42-inch pipeline traverses a predominantly flat right-of-way (ROW), running from south to north in East Kalimantan. Adjacent to the ROW, a coal mine concession was located on the western side, while the Mahakam River lies a further 3 km to the east. A mining waste dump has been constructed since 2010, situated in an area underlain by soft alluvium soil (Q_a). The waste was stacked, reaching heights of up to 75 meters, with its toe approximately 200 m from the edge of the ROW. In 2016, a failure occurred in the ROW, causing the 42-inch pipeline to shift a maximum of 6.8 m horizontally, and rise by 2.0 m within a 300 m span. A geotechnical investigation was then conducted, consisting of 7 CPTu with dissipation testing. The CPTu results indicated high pore pressure, with a layer of soft clay ranging from 15 to 32 m thickness found in the ROW area. A hypothesis was formulated suggesting that the soft clay was not fully consolidated. Hence, the failure of the pipeline was possibly caused by the migration of excess pore water pressure accumulated during the construction of the waste dump. Results of the investigation indicated that the permeability coefficient was 2.5 times greater in the horizontal direction compared to the vertical ones (k_h/k_v = 2.5), allowing the pore water pressure to migrate more easily in the horizontal direction. This study aims to elucidate how the migration of excess pore water pressure in the horizontal direction influences ground stability. The analysis was conducted using finite element software MIDAS GTS NX, with the k_h/k_v varying from 2.5 to 100 times to explore excess pore pressure movement behaviors. The results of this study confirm that excess pore pressure migration can occur horizontally if the horizontal permeability coefficient is larger than its vertical counterpart. Thus, this study highlights that the greater the permeability coefficient and the larger the ratio, the further the excess pore pressure travels. Moreover, the horizontal displacement increases with the permeability coefficient ratio.

Structural Health Assessment of Kretek II Bridge using Enhanced Frequency Domain Decomposition

Didib Astalis Ulul Absor — 2024-03-15

The development of infrastructure is growing rapidly in Indonesia. Kretek II bridge is one of the infrastructures built in the country. Dynamics aspects are one of the very important aspects used to validate structural analysis model or being linked to Structural Health Monitoring (SHM) of the bridge. Dynamics properties such as natural frequency, damping ratio, and mode shape also referred as modal parameters. The objective of this research is to determine the modal parameters of Kretek II bridge using Enhanced Frequency Domain Decomposition (EFDD) which is commonly used to extract modal parameters from the acceleration data recorded. Compared to the conventional method, EFDD is very practical and robust in structural health assessment because of its user-friendly uses in the ARTeMIS Modal software. To make sure that the results from EFDD are accurate, numerical modeling is necessary to validate it. This research was conducted using dynamics load test results as data for the modal extraction with EFDD method assisted by ARTeMIS Modal software. Dynamics load test was performed by placing 8 accelerometers in the span and exciting it with impact load from dropped truck on ramp. Modal parameters from the EFDD results are then compared to the numerical modeling results. The first two modes of the EFDD and numerical modeling results consecutively are 3.09 Hz, 3.745 Hz and 3.06 Hz, 3.49 Hz. The EFDD and numerical modeling results are both in agreement with both results having similar mode shape on their first two mode and low error percentage with only 0.89% and 7.17% respectively.

The Impact of Fiber Density and Layering in NFRP on Confined Concrete Compressive Strength

Zahra Amalia — 2024-03-15

Strengthening columns holds a crucial role in structural engineering and is frequently called for due to a range of factors, including heightened load requirements, structural degradation, design flaws, or the need for seismic retrofitting. Natural Fiber-Reinforced Polymers (NFRP) in concrete reinforcement has gained significant attention in recent years as a sustainable and eco-friendly alternative to strengthened reinforced concrete. NFRP jacketing presents an adaptable option, as it delivers an improved load-carrying capability as a confining effect. This paper explores the fundamental reasons behind the need for column strengthening and the advantages of employing NFRP jacketing as a preferred method. The study examined the influence of varying fiber densities and the number of fiber layers in NFRP on the mechanical properties of concrete, with a specific focus on its confined concrete compressive strength. The test specimen was a cylinder with a diameter of 150mm and a height of 300mm. NFRP, made from abaca fiber and resin, was attached around the specimen’s circumference to provide a confinement effect. Axial load was applied to the test specimen. The findings indicated that introducing abaca fiber as an NFRP material increased confined concrete compressive strength by up to 37% compared to unconfined concrete. Moreover, the application of three layers of NFRP fibers results in a 15% rise in confined concrete stress, especially when higher-density fiber types are utilized. Study findings suggest that natural fiber density and the number of layers play a role in enhancing concrete strength, however, their influence may not be significantly pronounced.

Mapping the Lava Flood Hazard Using the Flood Discharge Approach and 2D Hydrodynamic Modeling at the Rejali River, Mount Semeru

Akbar Bagus Prawira — 2024-03-22

In December 2021, Mount Semeru experienced an eruption accompanied by extreme rainfall, which resulted in lava floods, known as lahars or debris flows. The lava flood destroyed infrastructure, resulting in loss of life. Various rivers surrounding Mount Semeru, including the Rejali River, experienced the effects of this phenomenon. To address this, a study is needed to analyze the occurrence and frequency of lava floods over specific time intervals through the creation of a hazard map. This study aims to map the hazard of lava floods for various return periods using a coupled HEC-HMS and HEC-RAS software alongside a lava flood discharge approach. The HEC-HMS software is used to simulate hydrological processes, to obtain the lava flood discharge, while the HEC-RAS is used to model a two-dimensional (2D) lava flood hazard map. The input parameters of the modeling in this study are rainfall intensity, soil type, land cover, river distance, slope, and elevation. The results show that the flood area covers 9.55% of the total study area by 2 year return period (Q2), 11.80% by Q10, 14.10% by Q50, and 15.72% by Q200 with an overall validation Root Mean Square Error (RMSE) of 0.16. These changes are determined by the discharge volume from each return phase and the river's shallow depth, which causes overflow beyond the river's ability to accommodate the flow. Thus, this study suggests that the models successfully generated a reliable model for mapping the risk of lava floods on the Rejali River. These findings can help the government reduce disaster losses through adequate adaptation and mitigation initiatives.

Water Quality Modelling with Industrial and Domestic Point Source Pollution : a Study Case of Cikakembang River, Majalaya District

Steven Kent — 2024-03-28

Rapid industrial development is one of the leading causes of environmental degradation. The textile industries and the domestic activities in Majalaya District produce wastewater directly discharged into the Cikakembang River. As a result, the Cikakembang River’s water quality has decreased to the point that the water quality cannot be used for daily needs. This study modeled three main parameters in water quality modelling, namely Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), and Chemical Oxygen Demand (COD). Using MATLAB, the three-water quality governing equations originating from the Advection-Dispersion Equation were solved using the Runge Kutte-4 discretization scheme. The numerical modelling was carried out along 2.36 km of the Cikakembang River. All water quality coefficients, such as the DO Saturation (DO_sat), the Reaeration Rate (k_a), the Dispersion Coefficient (D), the Deoxygenation Rate (k_d), and the Decomposition Rate (k_c), for the Cikakembang River were estimated using equations developed by existing studies. The estimation of k_a and D coefficients requires hydraulic parameters, which in this study were estimated using the HEC-RAS simulation. Meanwhile, k_d and k_c values were obtained from the calibration and verification process. The Relative Root Mean Square Error (RRMSE) objective function was used to evaluate the results of water quality modelling at three sampling points. In the calibration process, the results
of water quality modelling produced RRMSE values for the DO, BOD, and COD parameters of 1.99%, 0.36% and 0.92%, respectively. Meanwhile, for the verification process, the RRMSE values for the DO, BOD, and COD parameters are 1.95%, 1.02% and 1.86%. All water quality parameters produce small RRMSE values in the calibration and verification processes. Hence, the water quality model created has good accuracy and stability.

Optimization of Pengga Reservoir in The Mandalika Special Economic Zone for Irrigation and Water Supply

Dewandha Mas Agastya — 2024-04-04

Mandalika Special Economic Zone is tourism area that is expected to improve the economy in West Nusa Tenggara Province. To support these activities, an allocation of domestic water needs of 200 liters second -1 is needed. The potential availability of water in the Pengga Reservoir is planned to be a source of domestic water needs in the Mandalika Special Economic Zone. Pengga Reservoir has an effective storage volume of 17.26 MCM. Potential water resources in Pengga Reservoir are obtained from reservoir outflow upstream and lateral inflow from several tributaries. The study was carried out to determine the reservoir storage capacity to meet domestic water needs and irrigation water needs covering an area 3189 ha. The cropping pattern used in the Pengga irrigation area is Paddy – Paddy/Secondary Crops – Paddy/Secondary Crops. To optimize the potential of water resources in the Pengga Reservoir, a linear programming optimization method is used. Indicators of the success of optimization calculations are indicated by the value of cropping intensity, k factor and reliability that have met the minimum limit value. The k factor value for irrigation water needs is 0.70 and domestic water needs is 0.85. Based on the optimization results, it is known the largest annual cropping intensity value occurs in the November I planting season. This conclusion can be seen from the comparison of annual cropping intensity values for the November I and November II planting schedules for the dry year inflow discharge scenario of 99.98% and 97.22% respectively. The cropping intensity value in the November I planting season is greater than November II, namely 100% and 97.25%, for the normal year discharge inflow scenario. This study provides an information for policy makers can use the November I planting schedule to obtain values for maximum cropping intensity and domestic water requirements.

Numerical Study on the Shear Failure and Load Transfer Mechanism of Helical Piles in Cohesionless Soils under Axial Compressive Loading

Ignatius Tommy Pratama — 2024-04-04

The methods employed to calculate the axial bearing capacity of a helical pile depends on the shear failure model around the pile, which is also influenced by the spacing and diameter of the helical plates. However, studies on the transition of the failure mode and the load transfer mechanism with the change of helical plate spacing and diameter in cohesionless soil subjected to axial compressive load have been limited. Thus, this paper investigated the effects of helix diameter and spacing on the axial compressive load-bearing capacity, shear failure model, and load transfer mechanism of helical piles with two helical plates embedded in the homogeneous medium and dense sands, as well as in the stratified medium to very dense sand. Axial loading tests on helical piles with various helix diameters and spacings were simulated using a two-dimensional finite element program with axisymmetric modeling to obtain the load-settlement curve, which was later used to estimate the ultimate bearing capacity of the helical piles. The ultimate bearing capacity of the helical piles was also computed using the conventional methods, i.e., the individual bearing and cylindrical shear methods, and then compared to the numerical-based axial bearing capacity. The stress-strain behaviors of pile and soil were modeled using the Linear Elastic and Mohr-Coulomb material models, respectively. The results show that the numerical-based ultimate bearing capacity of a helical pile increased with increasing the diameter and spacing of the helix. However, the ultimate bearing capacity computed using conventional methods did not show this trend. Then, the transition from the cylindrical shear to the individual bearing failure mechanism occurred at a spacing ratio (i.e., helical plate spacing divided by its diameter) of about two. Ultimately, the load transfer curves indicate that the helical plates mainly supported the applied load.

Analysis of Chloride Contaminant Transport in Tailings Storage Facility Dam (Case Study: Gold Mine in Sumatra)

Devina Pascayulinda — 2024-04-04

In the practice of gold mining industry, hazardous waste known as tailings is produced during the ore extraction process. These tailings are typically stored in a dam structure called a Tailings Storage Facility (TSF). The planning and construction of a TSF are critical considerations, as the failure of a TSF can have substantial environmental impacts, pose risks to human safety, and result in industrial losses. Therefore, strict control is necessary in the development of TSFs to minimize the potential negative consequences. This research focuses on the transport of contaminants within a TSF, specifically examining the concentration of chloride contaminants and conducting particle movement analysis. The study utilizes modeling through the GeoStudio SEEP/W program to simulate groundwater flow profiles and the GeoStudio CTRAN/W program to understand contaminant movement over a 100-year period. GeoStudio modeling employs 10 materials: impermeable clay soil, filter sandy soil, transition gravel rock, three mine waste types (Fine, Rockfill, and Rockfill with fine), hard rock bedrock layer, in-situ soil representing the original layer, landslide with colluvial soil, and the tailings itself. Back analysis is employed to iterate model parameters and ensure modeling accuracy against field data, including comparisons with water quality test results and readings from vibrating wire piezometer (VWP) instrumentation. The contaminant transport is influenced by advection-dispersion processes and tends to concentrate within the TSF boundary toward the dam toe over a 100-year timeframe. The analysis emphasizes the influence of advection in contaminant transport and underscores the importance of particle position relative to the groundwater level, with Particle Tracking Analysis shows significant movement within the groundwater flow area. This research provides crucial insights into the dynamics of contaminant concentration, informing better decision-making in TSF planning and management. The findings underscore the imperative of strict control measures to minimize environmental impacts and human safety risks associated with TSFs, thereby advancing knowledge in gold mining waste management.

Seismic Vulnerability Assessment of Regular and Vertically Irregular Residential Buildings in Nepal

Satish Paudel — 2024-04-20

The need to assess the vulnerability of non-engineered residential RCC buildings in Nepal has become urgent, especially considering the ongoing modifications and additions to these structures without understanding their susceptibility to seismic events. Many residential buildings, particularly those up to three stories, did not fully comply to the guidelines outlined in Nepal Building Code NBC 105:2020. Therefore, there is a necessity to assess the seismic performance of these structures. This study aims to quantify the seismic vulnerability of such buildings by focusing on three distinct types: regular two and three-story structures, and irregular three-story structures. Using finite element modeling, the analysis of the buildings’ seismic capacity was performed through pushover analysis. Subsequently, linear time history analysis is conducted to determine the seismic demand. Two software were utilized to conduct the analyses, namely SAP2000 and STERA_3D. The study also includes the matching eleven strong ground motion inputs to Nepal’s site characteristics and response spectrum to ensure the relevance of the local context. Furthermore, fragility curves are constructed to compare the probability of structural failure, by first conducting the nonlinear dynamic analyses on the building specimens. The result showed that the probability of complete failure rises rapidly when an additional story is constructed with vertical irregularity, increasing from 1.8% to 5.7% in a non-engineered two-story building. The study also observes variations in top displacement across all three buildings due to differences in earthquake duration and frequency. From the findings, it is revealed that a significant increase in seismic vulnerability for vertically irregular buildings compared to regular ones

Effect of the Specimen’s Height on the Split-Tensile Strength of the Fibers Reinforced Clay- Lime - Rice Husk Ask Mixture

Edi Hartono — 2024-04-22

Various studies on the effect of specimen size on splitting tensile strength. However, geotechnical codes lack consensus regarding the recommended specimen diameter and height-to-diameter (H/D) ratio for the split tensile strength test. Hence, it is imperative to study the effect of the height-to-diameter ratio of the specimen on the outcomes of the split tensile strength test, especially for stabilized and fiber-reinforced soil. This research examines the effect of adding lime-rice husk ash and plastic fiber and the effect of specimen size on splitting tensile strength. The height of the specimen is varied, using a height-to-diameter ratio (H/D), namely 0.5, 1.0, 1.5, 2.0, and 2.5, in which the diameter is 70 mm. Two groups of specimens were prepared as stabilized clay without fibers and stabilized clay with 0.1% fibers. The lime required for stabilization is 10% of the dry weight of the soil. In this research, the lime and rice husk ash ratio was designed as 1:1. The splitting tensile strength test was carried out after the specimen was cured for seven days. The investigation indicates that the splitting tensile strength of the specimen without fibers reduces from 217 kPa to 150 kPa as the H/D ratio grows from 0.5 to 2.5. Conversely, the tensile strength of the specimen with fibers increases from 284 kPa to 357 kPa. The findings suggest that the fiber inclusion enhances the splitting tensile strength of the stabilized clay. The specimen size affects the splitting tensile strength, but the effect becomes less noticeable when the H/D ratio exceeds 2.5. From a fracture mechanism perspective, the specimen experiences mode II (shearing) due to
a probable “flexural action” along its height. It remains challenging to conclude the dimensions of the test specimen or, at the very least, estimate the correction factor for the size-to-tensile strength ratio.