Abstract
Undrained shear strength (Su) is a critical parameter for geo-structural design, conventionally evaluated at
an arbitrary 20% axial strain threshold. However, this ultimate capacity also reflects post-failure residual strength and
fails to capture early-stage instability. To address this gap, this study investigates the initial failure mechanics of
Bangkok soft clay using a dual-methodology framework on 86 undisturbed samples. Initial failure was quantified by
coupling observation of physical changes during an unconfined compressive strength test by image-processing
detection (Fiji software) and calculation of tangent stiffness degradation with mathematical analysis (Google
Colaboratory). This approach objectively identifies the initial failure, the transition from homogeneous deformation
to localized strain. Statistical analysis confirmed a direct physical causality between the two methods, revealing that
failure initiates earlier than the ultimate Su, typically at axial strain between 4.6% and 10.8%. The initial failure
threshold averages 0.637 times the ultimate Su, secured by a tight 95% Confidence Interval of 0.618 to 0.656 and a
lower-bound safety threshold of 0.52. Furthermore, correlations between initial failure and sample depth, dry density,
Liquidity Index (LI), and Plasticity Index (PI) were evaluated. An independent 10-specimen validation dataset was
used to verify the proposed empirical models, yielding an average error of 4.2% and 100% envelope compliance.
This study provides a reliable reduction factor of 0.637 times the ultimate Su, with a 4.6% axial strain, for initial
failure assessment in the limit-state design of Bangkok soft clay under a dry density range of 0.82 to 1.02 t/m and in
a plastic state condition.
Address
Anubud Liangsunthonsit, Salisa Chaiyaput: Department of Civil Engineering, School of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand
Jiratchaya Ayawanna: School of Ceramic Engineering, Institute of Engineering, Suranaree University of Technology,Nakhon Ratchasima 30000, Thailand
Lindung Zalbuin Mase: Department of Civil Engineering, Faculty of Engineering, University of Bengkulu, Bengkulu 38371, Indonesia
Trong Nghia-Nguyen: Faculty of Engineering, Vietnamese-German University, Ho Chi Minh City 75000, Vietnam
Abstract
The dynamic evolution of plastic zones in roadway surrounding rock controls large deformation and
structural instability. This study systematically investigates the effects of roof strata combinations on plastic zone
development under varying stress conditions through theoretical analysis, numerical simulations, laboratory
experiments, and an engineering case study. The evolution of plastic zones and deformation characteristics in three
representative composite roof roadways with different soft-hard roof configurations were analyzed to elucidate the
nonlinear regulatory mechanism of roof strata combinations on plastic zone evolution. Results indicate that, as the
stress level and stress anisotropy increase, the plastic zones in the three roadway types progressively evolve into
composite butterfly-shaped morphologies, with distinct expansion characteristics governed by roof stratification.
However, different roof layer arrangements produce distinct expansion patterns of the plastic zones. In roadways with
soft-hard interbedded and thick hard composite roofs, segmentation and jumping behaviors are observed, indicating
that, under high deviatoric stress, hard rock layers act both as stress barriers and as pathways for stress redistribution
or concentration. This demonstrates the nonlinear regulatory role of rock mass structure in stress transfer and
distribution within the surrounding rock mass. A pronounced asynchrony exists between plastic zone expansion and
surrounding rock deformation. Increasing the lateral pressure coefficient causes the deviatoric stress field to evolve
into a composite butterfly shape, closely corresponding to the morphology of the plastic zone and confirming its
dominant role in controlling failure extent and deformation patterns. Experimental results further show that the
strength of coal-rock composites is primarily controlled by weak rock layers, while hard rock layers provide
reinforcement. Field application in the No. 5 coal roadway, whose roof exhibits characteristics intermediate between
Type I and Type II, confirms that reinforced roof–sidewall support can effectively control surrounding-rock
deformation. The findings advance the understanding of plastic zone evolution and failure mechanisms in composite
roof roadways, refine the theoretical framework for surrounding rock stability control, and provide a theoretical basis
for the differentiated support design of composite roof roadways with diverse roof structures.
Key Words
composite roof; deviatoric stress; laboratory experiments; plastic zone; surrounding rock
deformation
Address
Sha Ge: School of Resources Environment and Safety Engineering, Hunan University of Science and Technology,
Xiangtan 411201, China;
Hunan Urban Construction College, Xiangtan 411100, China
Wei-jun Wang, Chao Yuan, Xin-yu Tian, Shi-hai Shu, Rong-jie Du, Cheng-hao Cui: School of Resources Environment and Safety Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
Chang Liu: State Key Laboratory of Safety Technology of Metal Mines, Changsha Institute of Mining Research Co., Ltd., Changsha 410012, China
Abstract
A utility tunnel is a facility that integrally manages electricity, telecommunications, water supply, gas, and
waste. Integrated management offers advantages such as efficient operation, economic efficiency in maintenance,
and enhanced safety. However, utility tunnels can cause greater damage than single purpose ducts in situations such
as fire, condensation, gas leaks, flooding, unauthorized intrusion, and structural failure. In South Korea, the
installation of utility tunnels is mandatory in development areas exceeding 2,000,000 m2, and fires within the tunnels
must be detected at 1.0 m intervals. Additionally, since utility tunnels are designated as sealed facilities, hazardous
gases must be continuously monitored. However, detecting fires within a utility tunnel at 1.0 m intervals imposes a
significant economic burden on managers, and currently, there are no regulations for installing sensors required for
continuous hazardous gas monitoring, meaning fires are monitored solely through temperature changes. Therefore,
this study simulated fires inside a utility tunnel using computational fluid dynamics (CFD) analysis. The utility tunnel
was modeled into 12 cases according to the presence and location of vertical shafts and their open or closed states
(natural ventilation conditions), and the increase in temperature and gas diffusion during a fire were compared and
analyzed using temperature sensors and gas sensors. In this case, to ensure the results are applicable to all utility
tunnels, the modeling included only the minimum infrastructure necessary for the fire simulation. Based on the
simulation results, an appropriate gas sensor installation interval (40–50 m) was proposed to supplement the current
regulation that mandates fire detection at 1.0 m intervals. These results can be commonly applied to various utility
tunnels in Korea, providing a foundational guideline for basic gas sensor installation.
Key Words
computational fluid dynamics; fire; gas; sensor; utility tunnels
Address
Suk-Min Kong, Ah-Ram Kim, Yoseph Byun,
Gi-Jun Lee, Seong-Won Lee: Department of Geotechnical Engineering Research, Korea Institute of Civil Engineering and Building Technology, 283, Goyang-daero, Ilsanseo-gu, Goyang 10223, Republic of Korea
Abstract
Rainfall-induced slope failure is a common geohazard, particularly in shallow unsaturated soil slopes.
However, its reliable prediction remains challenging because slope responses are influenced by variable rainfall
conditions, initial hydraulic states, and soil properties. This study investigates the relationships among the factor of
safety (FOS), matric suction, and suction stress during rainfall infiltration and proposes reference suction stress (RSS)
as a local hydraulic–mechanical indicator of global slope stability. Numerical analyses were conducted under
different rainfall conditions, reference locations, soil-water retention characteristics, and slope inclinations. The results
showed that the FOS–RSS relationships exhibited broadly similar piecewise trends across the conditions
investigated, although the threshold RSS and the corresponding linear relationships remained dependent on soil
properties and reference location. A supplementary assessment of the reconstructed Hadong slope-failure case also
showed a transition from a stable response zone to a linear zone before the FOS reached 1.0. These findings suggest
that RSS has potential as a simplified indicator for monitoring the evolution of rainfall-induced slope stability.
Nevertheless, site-specific calibration and further validation through laboratory testing and synchronous field
monitoring are required before the proposed framework can be applied to operational landslide early-warning
systems.
Key Words
early warning system; rainfall-induced slope failure; reference suction stress; unsaturated soil
Address
Depu Hu: CCCC Second Highway Consultants Co., Ltd., No. 18 Chuangye Road, Wuhan Economic and Technological Development Zone, Wuhan, Hubei Province, 430056, China
Yeong-Ung Han, Byeong-Su Kim: Department of Civil and Environmental Engineering, Dankook University
152, Jukjeon-ro, Suji-gu, Yongin-si, Gyeonggi-do, 16890, Korea
Abstract
Anti-slide piles are widely adopted as an effective measure to stabilize unstable slopes. However, current
research primarily focuses on global stability assessment, while the mechanisms governing crack initiation and
propagation within piles during the sequential collapse process remain insufficiently understood. A numerical
framework simulating the interaction between the pile and slope is constructed based on the Finite–Discrete Element
Method (FDEM), with the objective of revealing the coupled evolution between macroscopic slope deformation and
localized pile response. By comparing scenarios with and without piles, the characteristics of displacement fields,
strain distribution, and earth pressure variation are systematically analyzed. The results reveal that, during the
progressive failure of the slope, localized cracking and deformation concentration develop near the potential sliding
surface and then evolve progressively. Simultaneously, localized stress concentrations develop around the pile–soil
contact region, producing arching-like stress redistribution that modifies crack propagation and delays the
development of global instability. Through the analysis of macroscopic stress redistribution and dynamic fracture
evolution, the collapse sequence from crack initiation to macroscopic instability is simulated. This study enhances the
understanding of pile–slope interaction mechanisms and provides a reliable mechanical basis for the rational layout
and design of anti-slide pile support structures.
Key Words
crack propagation; FDEM; pile–slope system; progressive failure
Address
Yanyan Li, Zixin Zhang, Yaoyao Zhang, Xuxi Zhang: College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124, China
Xudong Han: Center for Hydrogeology and Environmental Geology Survey, China Geological Survey,
Tianjin 300309, China
Abstract
Although conventional vegetated geomat slope protection can reduce surface erosion, its long-term
effectiveness is affected by the variability of vegetation development. This study presents a composite slope
protection system that integrates enzyme-induced carbonate precipitation (EICP) with vegetated geomats. To
evaluate the performance of the proposed system, a series of model-scale rainfall simulation tests were conducted.
The results show that the EICP-enhanced vegetated geomat slope exhibited no visible surface erosion or toe
undercutting under rainfall scouring, whereas the three-dimensional geomat slope experienced severe rill erosion and
toe undercutting, and the vegetated geomat slope showed moderate toe undercutting. Compared with the threedimensional
geomat slope and the vegetated geomat slope, the EICP-enhanced system reduced toe displacement by
97.8% and 96.7%, respectively, and reduced the cumulative eroded sediment mass by 92.3% and 62.5%. Moreover,
wedge stability analysis revealed that its post-rainfall safety factor increased by 57.9% and 15.4%, confirming a
remarkable improvement in slope stability. Overall, the proposed technology provides an innovative, eco-friendly,
and mechanically robust solution for sustainable slope protection with strong potential for engineering applications.
Address
Xiaojuan Yu, Xingyu Wu, Chao Liu,Zhongbing Cai: School of Civil Engineering, Yancheng Institute of Technology, Yancheng, 224005, Jiangsu, China
Guizhong Xu: School of Architecture and Engineering, Yancheng Polytechnic College, Yancheng 224005, Jiangsu, China
Zhanlei Liu: School of Civil Engineering and Architecture, University of Jinan, Jinan 250022, Shandong, China
open access