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CONTENTS
Volume 41, Number 2, April25 2025 (Special Issue)
 

Abstract
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Key Words
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Address
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Abstract
The long-term disposal of high-level radioactive waste (HLW) in deep geological repositories requires the reliable performance of engineered barrier systems (EBS). Compacted bentonite, widely used for its high swelling capacity, low permeability, and self-sealing properties, plays a critical role in these barriers. However, understanding the complex coupled thermo-hydro-mechanical (THM) behavior governing water infiltration dynamics remains a significant challenge, especially when gap spaces (or technological voids) are present. This study investigates water infiltration dynamics in bentonite-based EBS using a novel laboratory-scale experimental setup. Time-lapse photography was employed to monitor the evolution of hydration and swelling under thermal gradients and varying gap sizes, simulating repository conditions. The experimental program was designed to compare the effects of two gap sizes on infiltration rates, swelling behavior, and desiccation cracking. Results demonstrated that larger void spaces accommodated greater swelling, leading to lower dry density and higher permeability, while smaller gaps restricted desiccation cracking due to mechanical constraints. The correlation between pixel intensity and water content allowed the derivation of a linear calibration model, enabling real-time, non-destructive estimation of moisture distribution in bentonite. Findings in this study highlight the interplay between gap size, water infiltration, and thermal effects, emphasizing the need for optimized EBS designs to balance mechanical integrity and hydraulic performance. It is anticipated that the insights provided by this study contribute to the refinement of predictive models and advancing the safe and effective containment of HLW over geological timescales.

Key Words
bentonite; engineered barrier systems; gap space; high-level radioactive waste disposal; THM behavior; water infiltration

Address
Jinwoo Kim: Disposal Performance Demonstration Research Division, Korea Atomic Energy Research Institute (KAERI),
Daejeon 34057, Republic of Korea;
Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST),
Daejeon 34141, Republic of Korea
Hwan-Hui Lim: Department of Structural Systems & Site Safety Evaluation, Korea Institute of Nuclear Safety(KINS), Daejeon 34045, Republic of Korea
Jin-Seop Kim: Disposal Performance Demonstration Research Division, Korea Atomic Energy Research Institute (KAERI),
Daejeon 34057, Republic of Korea
Tae-Hyuk Kwon: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST),
Daejeon 34141, Republic of Korea


Abstract
Understanding the dynamic properties of soils—particularly their behavior under cyclic or dynamic loading conditions, such as those induced by seismic events or construction activities—is critical for designing resilient geotechnical structures and foundations. This study investigates well-graded sand with silt soils from Astana, Kazakhstan, using the Resonant Column (RC) and Cyclic Torsional Shear (CTS) tests, to characterize their dynamic behavior under varying confining pressures (o𝑐). Although seismic activity in Astana is generally low, aftershocks from distant earthquakes highlight the importance of understanding site-specific seismic risks. This study provides site-specific shear modulus reduction (G) and material damping ratio (D) curves, essential for evaluating seismic hazards and mitigating disasters. These findings address significant gaps in the dynamic characterization of well-graded sand with silt and have practical applications in seismic risk mitigation, foundation design, and urban planning, contributing to safer and more resilient infrastructure in earthquake-prone regions.

Key Words
cyclic torsional shear testing; damping ratio; dynamic soil characterization; resonant column apparatus; shear modulus; well-graded sand with a silt

Address
Nuraiym Paiyz, Sung-Woo Moon, Alfrendo Satyanaga and Jong Kim: Department of Civil and Environmental Engineering, School of Engineering and Digital Sciences
Nazarbayev University, 53, Kabanbay batyr Ave., Astana, 010000, Republic of Kazakhstan

Abstract
In Korea, most people live in metropolitan areas. Social infrastructure is concentrated in a small area based on the demands of many people. The development of underground space in urban areas using deep tunnels for roads, railways, subways, communication facilities, and waterway facilities is expanding. This underground space is composed of weathered rock ground with geological joints, and many tunnels have been excavated in such ground. The effect of discontinuity on the behavior of the tunnel must be considered during the design and construction stages. Therefore, in this study, a ground model with three dip angles was created using concrete blocks to analyze the relaxation behavior of the surrounding ground when excavating a tunnel in a rock mass with joints. In addition, a trapdoor tester capable of creating linear and nonlinear settlement was manufactured, and the stress distribution and settlement occurrence tendency of the tunnel top and surrounding ground were analyzed when different settlement shapes occurred. The experimental results showed that the behavior of the top of the trapdoor and the surrounding ground varied depending on the displacement shape of the trapdoor and the inclination of the joint surface of the rock. The results of this experiment suggest a displacement shape that is advantageous to the arching effect depending on the inclination of the joint surface of the upper ground during tunnel excavation. In addition, the loosened ground zone of the upper ground can be identified by considering the friction angle of the rock and the dip angle during excavation.

Key Words
fragmental rocks; joint angle; load transfer; non-linear deformation; trapdoor; tunnel excavation

Address
Yong-eun Roh, Hyungbin Park, Munkyeong Baek and Ilhan Chang: Department of Civil Systems Engineering, Ajou university, 206 World cup-ro, Yeongtong-gu,
Suwon-si 16499, Republic of Korea

Abstract
Crosslinked xanthan gum (CrXG) has been introduced to enhance the mechanical stability of biopolymer–soil composites under hydrated conditions. However, its effects on the small-strain stiffness and deformation behavior of granular soils remain underexplored. This study examines the evolution of small-strain shear stiffness, vertical deformation behavior, and shear wave velocity (Vs) in CrXG-treated soils using bender element testing. The results indicate that CrXG treatment improves shear stiffness through a time-dependent gel stiffening mechanism. Higher CrXG concentrations yield greater initial stiffness, with stabilization occurring after approximately 7 days. Additionally, the vertical deformation behavior of CrXG-treated soils is stress-dependent. Increased CrXG concentrations lead to higher Vs values, an elevated a-factor, and a reduced b-exponent, trends that are comparable to those observed in cemented soils. These effects are attributed to the formation of an intergranular hydrogel matrix that enhances particle bonding. These findings provide insights into the mechanical behavior of CrXG-treated soils and their potential applications in geotechnical engineering, particularly for improving soil stiffness and stability.

Key Words
biopolymer; crosslinking; curing time; shear wave; stiffness; vertical stress

Address
Dong-Yeup Park, Jeong-Uk Bang and Gye-Chun Cho: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology,
291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Minhyeong Lee: Disposal Safety Evaluation Research Division, Korea Atomic Energy Research Institute,
111 Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea
Ilhan Chang: Department of Civil Systems Engineering, Ajou University, 206 World cup-ro, Yeongtong-gu, Suwon, 16499,
Gyeonggi-do, Republic of Korea

Abstract
Geogrid pullout is a critical failure mode in mechanically stabilized earth (MSE) walls and must be thoroughly assessed to ensure stability. Pullout resistance consists of skin friction between the soil and geogrid and bearing (passive) resistance generated by the transverse ribs. Due to the nonlinear and complex soil–geogrid interactions, pullout tests are recommended by design and construction guidelines. This study examined the potential of encapsulating geogrids within a biopolymer-based soil treatment (BPST) layer to enhance pullout resistance. Laboratory pullout tests, conducted using an independently developed apparatus, assessed geogrid performance encapsulated in xanthan gum biopolymer hydrogel under initial (wet) and dehydration (dry) conditions across varying normal pressure levels. Results showed that under the initial (wet) condition, pullout resistance increased by at least 10% at low normal pressure levels (<-50 kPa) due to improved adhesion. Under dehydration (dry) conditions, pullout resistance significantly increased, exceeding the geogrid's tensile strength at low normal pressure levels (25 kPa), attributed to enhanced bonding and particle–geogrid interlocking. The apparent friction coefficient and interaction coefficient ratio (ICR) were introduced as metrics to evaluate pullout resistance performance. The BPST method proved effective in addressing challenges where compaction is unsuitable, reinforcement length is constrained in narrow backfill areas, or fine-grained soils are required. This eco-friendly method provides a sustainable alternative for MSE wall applications, offering improved mechanical performance and versatility.

Key Words
Biopolymer-based soil treatment (BPST); geogrid; pullout resistance; soil-geogrid interaction

Address
Gi-Yun Kim, Hwijae Lee, Suhyuk Park and Ilhan Chang: Department of Civil Systems Engineering, Ajou university, 206 World cup-ro, Yeongtong-gu, Suwon-si 16499, Republic of Korea
Junghoon Kim and Tae Sup Yun: Department of Civil and Environmental Engineering, Yonsei university, 50 Yonsei-ro, Seodaemun-gu, Seoul-si 03722, Republic of Korea

Abstract
The recycling and reuse of construction and demolition materials offer significant environmental and economic benefits. This study investigated the performance of aggregates with varying proportions of recycled concrete aggregate (RCA) and natural aggregate (NA) as base materials. Key parameters, such as compaction behaviour, California bearing ratio (CBR), and resilient modulus, were evaluated. The findings revealed that the mixture with 50% RCA and 50% NA exhibited the highest CBR and resilient modulus values. Small-scale cyclic loading tests were then conducted on the samples of NA, RCA, and a 50% RCA-50% NA mixture to assess the suitability of RCA as a base material. Additionally, RCA and NA samples were reinforced with biaxial geogrids for material optimisation. The results showed that the 50% RCA-50% NA mixture exhibited the smallest permanent deformation, and the geogrid, placed at the middle depth of the base, significantly reduced rut depth. Findings of this experimental study suggest that RCA can be used as an alternative base material to partially replace NA in road construction. The results can help conserve natural resources, promote sustainability through the reuse of waste materials, and reduce the environmental impact associated with the use of NA in road construction.

Key Words
geosynthetics; granular materials; ground improvement; reinforced soil; road engineering

Address
Jiacheng Qiu, Yuekai Xie, Yue Chen, Ben Reissenweber,
Chen Wang, Ziheng Wang and Jianfeng Xue: School of Engineering and Technology, The University of New South Wales, Canberra, Australia

Abstract
In recent years, ground disasters such as the collapse of unsaturated river levees have frequently occurred due to the seepage and erosion of rainwater during heavy rain. Applying water repellent soil to engineered slopes can be one of the solutions to prevent rainwater infiltration. For this, previous studies have verified the effects of rainfall intensity, layer thickness, and grain size distribution of geomaterials through water infiltration head (WIH) tests. In this study, to objectively verify the applicability of the impermeable layer of hydrophobic materials to field slopes, a series of laboratory embankment model tests were conducted on these three influences. Like the trend of the results of the previous WIH test, the water-shielding performance of the hydrophobic geomaterial could be determined through the results obtained from the model tests. As a result, it can be said that the application of hydrophobic geomaterials to engineered slopes could be a good alternative to maintain slope stability against rainwater infiltration.

Key Words
hydrophobic material; laboratory embankment model test; rainwater infiltration; water infiltration test

Address
Byeong-Su Kim: Department of Civil & Environmental Engineering, Dankook University,
152, Jukjeon-ro, Suji-gu, Yongin City, Gyeonggi-do 16890, Korea
Shoji Kato: Graduate School of Engineering, Kobe University,
Rokkodai-cho, Nada-ku, Kobe City, Hyogo 657-8501, Japan

Abstract
Abrasive waterjet technology offers high efficiency in drilling high-strength materials such as rock and concrete, and is utilized in various fields such as precision machining, geotechnical engineering and mining engineering. Previous studies have analyzed the jet flow characteristics in air through experimental, analytical, and numerical approaches; however, they were primarily limited to short standoff distances and single-sized abrasive particles, limiting their application to large-scale geotechnical and mining engineering sites. To overcome these limitations, this study performed a numerical analysis considering various standoff distances and abrasive particle sizes. This study observed jet flow characteristics in the axial and radial directions and evaluated the abrasive velocity and kinetic energy. In addition, the critical energy for rock drilling was derived to be approximately 0.36 J from the simulation results based on the minimum critical pressure for hard rock excavation. Based on this value, an effective jet diameter that considers the number of abrasive particles was proposed for various standoff distances and abrasive particle sizes. The abrasive particle size significantly affected the effective jet diameter when the standoff distance was greater than 100 mm. This study aims to expand the applicability of abrasive waterjet technology in geotechnical and mining fields and provide essential guidelines for optimizing an efficient system design and abrasive selection strategy under various field conditions.

Key Words
abrasive waterjet; effective jet diameter; jet flow characteristics; numerical method; rock drilling

Address
Hyun-Joong Hwang: Applied Science Research Institute, Korea Advanced Institute of Science and Technology (KAIST),
291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Yohan Cha: Disposal Performance Demonstration R&D Division, Korea Atomic Energy Research Institute (KAERI),
111 Daedeok-daero, 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea
Joohyun Park and Gye-Chun Cho: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST),
291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

Abstract
This paper presents a new method to address subgrade settlement and alignment deviations in double-block ballastless tracks for high-speed railways. The method focuses on minimizing damage to the track structure during the lifting and rectification of the double-block ballastless track in short-length subgrade sections. A finite element model (FEM) was developed to analyze key construction parameters, including jack spacing and dissociation length. Numerical simulations determined that a 3 m jack spacing is optimal, as increasing it to 5 m results in a 20%–32% increase in jacking force. Additionally, a 31 m dissociation length effectively reduces stress on the track structure while maintaining construction efficiency. The multi-point horizontal thrust correction method was validated, achieving a maximum lift of 39.5 mm and a maximum deviation correction of 4 mm, without inducing structural cracking. Post-construction evaluations confirmed significant enhancements in track smoothness and alignment. Dynamic inspection data indicated a >60% reduction in peak-to-valley values, horizontal displacement, and vertical acceleration. Furthermore, real-time displacement monitoring verified that lateral and vertical movements remained below 0.2 mm and 0.3 mm, respectively, ensuring compliance with high-speed railway safety standards. These findings demonstrate that the proposed mechanical lifting and chemical grouting technique effectively mitigates subgrade settlement and track misalignment. The proposed method has been successfully applied to the Beijing-Guangzhou railway, demonstrating effective solutions for subgrade settlement and alignment deviations in the maintenance phase. As a result, the track smoothness was successfully restored, meeting the operational requirements for increased train speed.

Key Words
ballastless track; correction; high-speed railway; lifting

Address
Zhipeng Su and Junhua Xiao: Shanghai Key Laboratory of Rail Infrastructure Durability and System Safety, Tongji University, No.1239, Siping Road, Yangpu District, Shanghai, China
Xi Yang and Lingzi Zhao: Shanghai Shen Yuan Geotechnical Engineering Co., Ltd, No.1368, South Xizang Road, Huangpu District, Shanghai, China

Abstract
Soil suction and the degree of saturation influence the resilient modulus, which should be considered when designing road and railway foundations. To reasonably account for these factors, a suction stress model incorporating both suction and degree of saturation was established for application in transportation design. In this study, the suction stress was considered by categorizing water into bulk and meniscus water and applying cyclic loading to the samples. The soil water characteristic curve (SWCC) was generated using discrete element method (DEM) analysis. Additionally, the resilient modulus was observed to vary with both deviator stress and the degree of saturation. The trends observed in this study are consistent with the results of laboratory tests conducted by other researchers. These findings demonstrated that the water division and cyclic loading algorithm effectively represented the unsaturated soil state. Furthermore, DEM analysis revealed that the suction stress was influenced the resilient modulus, with the resilient modulus increasing as suction stress increased.

Key Words
discrete element method; resilient modulus; suction stress; unsaturated soil state

Address
Hyun-Su Park, Byeong-Su Kim and Seong-Wan Park: Departement of Civil and Environmental Engineering, Dankook University, 152, Jukjeon-ro, Sugi-gu, Gyeonggi-do, 16890, Republic of Korea

Abstract
Biopolymer-based soil treatment (BPST) enhances soil strength through biofilm matrix formation within soil voids. This study investigates the effects of biopolymer concentration, porosity, and soil packing conditions on biopolymer distribution and connectivity after dehydration. Laboratory experiments assessed the degree of biopolymer filling (DoBF), final condensed biopolymer concentration, and biopolymer film connectivity under simple cubic and rhombohedral packing conditions. The results show that higher initial biopolymer concentrations increase final biopolymer volume, though not proportionally due to threshold effects. Rhombohedral packing results in higher final condensed biopolymer concentrations than simple cubic packing, despite having lower DoBF values, while biopolymer connectivity peaks at an optimal porosity (n ≈ 0.35). Further analysis revealed a strong correlation between biopolymer matrix formation and soil mechanical properties, including uniaxial compressive strength (UCS), cohesion, and friction angle. UCS was found to decrease with increasing porosity, and a predictive model was developed using experimental data. The rhombohedral and simple cubic packing conditions respectively define the upper and lower bounds of the shear parameters. A back-calculation approach confirmed that DoBF provides the most accurate estimation of friction angle and UCS, reinforcing its importance as a key parameter in soil stabilization. These findings emphasize the need for optimized biopolymer concentration and soil structure adjustments to enhance reinforcement efficiency. The study offers valuable guidance for geotechnical applications, enabling the development of optimized biopolymer injection strategies that enhance mechanical performance and promote efficient material utilization.

Key Words
biopolymer; biopolymer-based soil treatment (BPST); geotechnical engineering; Xanthan gum

Address
Sojeong Lee: Korea Standard Construction Center, Korea Institute of Civil engineering and Building Technology, Goyang 10223, Korea
Ilhan Chang: Department of Civil Systems Engineering, Ajou University, Suwon, 16499, Korea

Abstract
Transmission tower foundations play a critical role in supporting and preventing the collapse of tower structures. In Korea, 12,000 tower foundations require additional reinforcement due to the recent design standard changes for wind speed pressure as a result of climate change. However, several challenges arise when attempting to determine appropriate methods of reinforcement, especially in the case of approximately 1,500 towers that lack any records of foundation specifications. In this study, the electrical resistivity survey, one of the non-destructive testing methods, is employed to accurately determine foundation specifications, which can in turn be used to strategically develop reinforcement plans. Using electrical resistivity survey data obtained through both laboratory and field experiments, an algorithm capable of extracting foundation specifications was developed. The system was then applied to 47 transmission tower foundations. According to the results, the electrical resistivity survey achieved a prediction accuracy of 91.5% for depth of the tower foundation, 98.6% for width of the base slab, and 95.6% for thickness of the base slab. These findings suggest that the method is particularly effective at predicting the width and thickness of the base slab, with width predictions being the most accurate. This research is expected to aid in the creation of maintenance and reinforcement plans for transmission tower foundations while also enabling cost-effective specification assessments for various buried civil engineering structures.

Key Words
electrical resistivity survey; foundation; non-destructive test; specification; transmission tower

Address
Hee-Hwan Ryu and Shin-Kyu Choi: Power System Research Laboratory, Korea Electric Power Research Institute,105 Munji-ro, Yuseong-gu, Daejeon 34056, Republic of Korea
Suyoung Choi: Department of Mathematics, Ajou University, 206 World cup-ro, Yeongtong-gu, Suwon 16499, Republic of Korea
Eun-Soo Hong: Harmony Blending and Creativity (HBC), 138 Dunsanjung-ro, Seo-gu, Daejeon 35209, Republic of Korea

Abstract
This research investigates the development of a porous geopolymer cement grout for soil grouting applications, aiming to reduce carbon emissions associated with Portland cement while maintaining critical performance characteristics such as strength and permeability. Class F fly ash and metakaolin were used as aluminosilicate precursors, activated by sodium silicate and sodium hydroxide solutions. The addition of hydrogen peroxide served as a foaming agent to introduce porosity. Compressive strength and porosity were evaluated, with results showing that metakaolin significantly increased compressive strength due to its smaller particle size and higher reactivity. A higher molarity of sodium silicate enhanced strength by reducing the water-to-solid ratio, creating a denser matrix. In contrast, increasing hydrogen peroxide content raised porosity but reduced compressive strength by generating gas bubbles. X-ray diffraction (XRD) analysis revealed the ongoing formation of hydration products and a growing amorphous structure in the geopolymer matrix, contributing to strength development over time. The study concludes that the geopolymer grout can be optimized for a wide range of soil stabilization applications by adjusting material composition, foaming agent concentration, and activator molarity, offering an environmentally sustainable alternative to traditional cement grouts.

Key Words
coal fly ash; grouts; metakaolin; porous geopolymer; sinkhole remediation

Address
Karla Sierra, Chu-Lin Cheng: Department of Civil Engineering, the University of Texas at Rio Grande Valley, Texas, U.S.A
Philip Park and Jinwoo An: Department of Civil Engineering, the University of Texas at Rio Grande Valley, Texas, U.S.A;
Institute for Advanced Manufacturing (IAM), Texas, U.S.A
Yong Je Kim: Department of Civil Engineering, the University of Texas at El Paso, Texas, U.S.A
Jae-Hoon Hwang: Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Canada
Bubryur Kim: School of Space Engineering Sciences, Kyungpook National University, Daegu, South Korea;
Department of Robot and Smart System Engineering, Kyungpook National University, Daegu, South Korea;
Department of Safety Convergence, Kyungpook National University, Daegu, South Korea
Boo Hyun Nam: Department of Civil Engineering, Kyung Hee University, Suwon, South Korea

Abstract
The pulp and paper industry has grown and created tremendous volumes of byproducts (e.g., fly ash) via combustion process. Unfortunately, most of them are being landfilled; in the meantime, environmental regulations restrict the disposal in landfill because of high disposal cost and reduced land due to urbanization. Therefore, the pulp and paper industries urgently seek for its beneficial reuse and one of the most cost-effective applications is a building and construction sector, particularly its reuse as geomaterials such as stabilizing soils. This paper provides a comprehensive review of the beneficial use of the paper sludge ash (PSA) in geotechnical engineering applications. Specifically, the paper explored the state-of-the-art knowledge in the areas of physical, chemical, and mineralogical properties of PSA, geotechnical engineering properties (e.g., strength, stiffness, shear strength parameters, etc.) and field applications of the PSA. In addition, the paper looks into geo-environmental applications such as PSA' s water absorption and retention performance and its performance as adsorbent for environmental contaminants.

Key Words
incineration; paper sludge ash; soil stabilization; strength

Address
Kyungwon Park, Hoyoung Lee,Byounghooi Choi and Boo Hyun Nam: Department of Civil Engineering, College of Engineering, Kyung Hee University, Yongin, Republic of Korea
Junwoo Shin: Department of Civil Engineering, Kumoh National Institute of Technology, Republic of Korea
Jinwoo An: Department of Civil Engineering, University of Texas at Rio Grande Valley, USA
Jiannan Chen: Department of Civil, Environmental, and Construction Engineering, University of Central Florida, USA

Abstract
Full scale field tests were performed on test piles installed based on a typical installation procedure of a precast bored piles, with various cement layer thickness and water-cement ratio of the cement slurry along the pile shaft. The results of the field test were compared to the test conducted on test pile following the installation procedure of driven piles. Simultaneously, large deformation finite element analysis was carried out to verify the effectiveness of precast bored piles under lateral loadings. Lateral displacement of the pile head was reduced as the thickness of the cement layer along the pile shaft increases, up to a certain thickness. Also, lower water-cement ratio also decreased the pile head displacement, but was found to have less effect compared to the cement layer thickness. Overall, the results show that the application of precast bored piles was found to be more effective in reducing the lateral displacement of the pile head under higher lateral loading.

Key Words
full-scale test; large deformation analysis; lateral displacement; lateral load; precast bored piles

Address
Dohyun Kim: Department of Civil and Environmental Engineering, Hanbat National University, Daejeon 34158, Korea

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