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CONTENTS
Volume 39, Number 6, December25 2024
 

Abstract
Organic soil is often encountered in seasonally frozen areas in China. Before construction, the organic soil is required to be treated to improve its engineering performance due to the high moisture content and low bearing capacity. Cement and fly ash were adopted in this study to treat organic soil subjected to natural freeze-thaw cycles. The influences of freeze-thaw cycles on the stress-strain behavior and microstructure of cement and fly ash-stabilized organic soil (C-F-S-O-S) were evaluated using unconsolidated undrained triaxial (U-U), mercury intrusion porosimetry (MIP) and CT experiments. With and without freeze-thaw cycles, results indicate that the specimen with 20% cement and 5.0% fly ash content performed the best in strength and was selected to evaluate the influence of freeze-thaw cycles on C-F-S-O-S mechanical and microstructure characteristics. The strength, elastic modulus (E-M), cohesion, and internal friction angle of the specimen show the largest decrease of 9.27%, 13.97%, 3.45%, 5.19% after the first freeze-thaw cycle and then slow decreased with further increase of the number of freeze-thaw cycles. The strain corresponding to the peak stress increased with increasing freeze-thaw cycles, and the increase was the largest with a value of 10.19% after the first freeze-thaw cycle. Relationships between the number of freeze-thaw cycles and above parameters were established. A generalized model was also established to predict the stress-strain curve of the C-F-S-O-S. The applicability of the proposed model was validated with published experiment data. The specimen porosity increased first (by 11.03%) and then gradually stabilized after a series of freeze-thaw cycles as revealed by the MIP. Consequently, MIP and CT analysis reveals the soil structural variation since the freeze-thaw cycle is the main reason of the reduction of the specimen strength after the freeze-thaw cycle.

Key Words
freeze thaw cycles; peak strain; peak stress; stabilized organic soil; stress-strain

Address
Jiling Zhao: College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, Jiangsu, China;
School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China
Ping Yang, Lin Li, Ting Zhang and Haibo Wang: College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, Jiangsu, China

Abstract
Backbreak, a recurring issue in blasting operations, causes mine wall instability, equipment failure, inappropriate disintegration, lower drilling efficiency, and increased cost of mining operations. This study aims to address these issues by developing a hybrid LSSVM-GWO model for predicting blast-induced backbreak in open pit mines. To evaluate the effectiveness of the proposed model, its predictive performance was compared with three convolutional models, such as the support vector machine, K-nearest neighbor, and the least square support vector machine. Results demonstrated that the LSSVM-GWO model outperformed the other three models, achieving coefficient of determination values of 0.998 and 0.997, mean absolute error values of 0.0068 and 0.1209, root mean squared error values of 0.0825 and 0.1936, and a20-index values of 0.99 and 1.01 for training and testing datasets, respectively. Furthermore, the SHAP machine learning technique was applied to evaluate the feature importance, revealing that the powder factor had the highest influence, while the burden exhibited the least impact on backbreak. Sensitivity analysis confirmed these findings, highlighting the robustness of the hybrid model. The study concludes that the LSSVM-GWO model significantly enhances the prediction and evaluation of backbreak in open pit mines, providing critical insights to improve blasting operations, reduce costs, and ensure mine safety.

Key Words
backbreak; blasting environmental issue; fracture mechanics; LSSVM- GWO; open-pit mines

Address
Niaz Muhammad Shahani: School of Mines, China University of Mining and Technology, Xuzhou, 221116, Jiangsu Province, China;
Shanxi Guxian Jingu Coal Industry Co., Ltd Linfen, 041000, Shanxi Province, China
Xigui Zheng: School of Mines, China University of Mining and Technology, Xuzhou, 221116, Jiangsu Province, China;
Shanxi Guxian Jingu Coal Industry Co., Ltd Linfen, 041000, Shanxi Province, China;
School of Mines and Civil Engineering, Liupanshui Normal University, Liupanshui 553004, China;
Guizhou Guineng Investment Co., Ltd., Liupanshui 553600, China
Patrick Siarry: Université Paris-Est Creteil, LiSSi Lab, France
Danial Jahed Armaghani: School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia
Cancan Liu: School of Mines, China University of Mining and Technology, Xuzhou, 221116, Jiangsu Province, China

Abstract
The residual coal pillar and roof strata of strip mining in coal mine constitute a joint bearing body, which can be simplified into " T " shaped unequal size rock-coal combination sample in laboratory test. In this paper, the uniaxial compression test of the composite specimen is carried out to explore its mechanical properties. The results show that both sides of the specimen sandstone can share part of the load. As the width ratio h of rock and coal increases, the peak load of the composite increases, but the effect is limited. When h reaches 2.0, the " bending " deformation on both sides of the sandstone is prominent, which aggravates the damage of the combined coal sample and reduces the bearing capacity. The acoustic emission characteristic signal of the rock-coal composite sample can be divided into four stages : calm, fluctuating rise, growth and steep increase. With the increase of h, the acoustic emission signal is more obvious, the failure time of the composite sample is prolonged, and the failure mode of the sample is changed from spalling failure to spalling-ejection mixed failure.

Key Words
bending deformation; coal-rock interactions; dynamic b-value; failure mechanism; rock-coal assemblage

Address
Dawei Yin and Xuelong Li: Mine Disaster Prevention and Control-Ministry of State Key Laboratory Breeding Base,
Shandong University of Science and Technology, Qingdao, China
Yu Sun and Xiaotian Yuan: College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao, China
Shaojun Xuan and Zhen Zhang: Shandong Kangge Energy Technology Co., Ltd., Jining 272000, China

Abstract
Lignosulfonate (LS), an environmentally friendly and non-toxic material, has attracted attention as a non-traditional soil stabilizer. However, LS could be easily washed out from soil due to its high water-solubility, which leads to the consequent loss of strength. Therefore, an additional admixture is needed to overcome this limitation. In this study, polyethyleneimine (PEI) was mixed with LS to stabilize silica sand. The consequent improvements in the water-resistant and strength characteristics of LS-treated soil were investigated through the unconfined compressive strength (UCS) test, triaxial test, and cyclic wetting-drying tests. The results demonstrated that the UCS had an increasing trend with a rise in LS content. Moreover, the UCS was influenced by the drying out of the water from the specimen related to the LS concentration and the curing time: a higher concentration and a longer curing duration improve the UCS. According to the triaxial test, the deviatoric stress also increased with the LS content. In addition, both the soil's cohesion and secant elastic modulus were improved in a more ductile manner than typical cemented soil. In the cyclic wetting-drying test, no disintegration of the specimen was observed. Although the UCS of the treated soil in wet condition revealed a notable decrease, after re-dry for seven days in a controlled room, its strength recovered to about 86% of that in its initial dry condition.

Key Words
lignosulfonate; polyethyleneimine; unconfined compressive strength; wetting-drying cycle

Address
Sopharith Chou: Zachry Department of Civil and Environmental Engineering, Texas A&M University, College Station, TX, USA 77840
Boyoung Yoon: School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA 30332-0355
Woojin Lee: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, Republic of Korea 02841
Hyunwook Choo: Department of Civil and Environmental Engineering, Hanyang University, Seoul, Republic of Korea 04763
Junghee Park: Department of Civil and Environmental Engineering, Incheon National University, Incheon, Republic of Korea 22012
Changho Lee: Department of Civil Engineering, Chonnam National University, Gwangju, Republic of Korea 61186

Abstract
Nowadays, nailed retaining structures are one of the most practical methods of stabilizing pit walls in urban environments and slopes. This study evaluates the optimal distance and placement length of nails in various conditions using Plaxis and GeoSlope software, taking advantage of the findings of other studies to increase the reliability and stability of the pits. In this study, three examples of common urban pits with a height of 4, 8, and 12 meters were selected, and the variable distances of the nails were evaluated as 0.5, 1, 1.5, 2, and 2.5 meters in each pit. The results of various modeling are presented in 3-dimensional forms, taking into account the state of stability and the maximum displacement, to achieve the minimum amount of the total length of nails used (economic efficiency) in different conditions. For example, the three-dimensional results of the simultaneous investigation of safety factor and displacement along with the total length of nails in an 8-meter pit show that the most suitable safety factor is 1.4 for nails with a distance of 1.5 meters (5 rows of nails with lengths of 10, 9, 8, 6, 4 meters) and with a maximum displacement of 10 mm. In the best case, the total length of nails is 37 meters. Also, the second priority is nails with a distance of 1 meter with a total length of nails of 45 meters, which is not economical. Although shorter distances of nails produce better results, special attention should be given to the parameter of the total length of used nails. In addition, there is a good agreement between the results of the finite element method (FEM - Plaxis) and Limit Equilibrium Method (LEM – GeoSlope/w). Furthermore, a relationship is proposed to relate the response parameters of the pit (i.e., maximum displacement, optimal length of nails, and factor of safety) to the input parameters, such as pit height and nails distance. The results show that the proposed formula has good accuracy and efficiency in predicting the response parameters and gives reliable estimates in comparison to finite element simulations.

Key Words
GeoSlope; nailing; optimum length and space; pit; plaxis; safety factor

Address
Mohammad Momeni: Department of Civil Engineering, Faculty of Engineering, Fasa University, Fasa, Iran
Elham Moghimi: Department of Civil Engineering, Khazar University, Mazandaran, Iran
Mehri Nassiri: Department of Civil Engineering, Maziar University, Mazandaran, Iran
Fateme Hajari: School of architecture and design, University of Camerino, Camerino, Italy
Sohrab Mirassi: Department of Civil Engineering, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran

Abstract
An essential component of designing geosynthetic reinforced soil walls (GRSW) is deformation analysis. Nonetheless, research highlights how artificial intelligence techniques may be used to solve geotechnical engineering problems. This study's primary goal was to investigate the potential use of machine learning-based techniques for GRSW deformation (Dis) estimate. This paper presents and validates new methods that combine random forests (RF) with the ant lion optimization (AnOA), the chimp optimization algorithm (ChnO), and the gannet optimization algorithm (GAOA). The dataset for this purpose was created by combining 166 finite element studies that have been done in the literature. The findings presented that the RF(AnOA), RF(ChOA), and RF(GaOA) methods have a significant ability to accurately predict the 𝐷𝑖𝑠 of GRSW with R2 values larger than 0.976. The value of Theil inequality coefficient (TIC) was 0.0463 and 0.0282 in the learning and examining sections for 𝑅𝐹(𝐺𝑎𝑂𝐴), remarkably smaller than those of RF(ChOA) at 0.0523 and 0.063, and RF(AnOA) by 0.0564 and 0.0799, respectively. In conclusion, the results suggest that the suggested models may be used to evaluate the effectiveness of geosynthetic reinforced soil structures. This research provides a significant contribution by establishing a scalable and efficient framework for evaluating the deformation performance of GRSW structures, bridging the gap between computational geomechanics and machine learning. The proposed RF models can replace or complement traditional numerical methods for estimating GRSW deformation, saving time and computational resources. Using these models, engineers can predict GRSW deformations with high precision, enabling more accurate design and better safety assessments of geotechnical structures.

Key Words
displacement; estimation; geogrid; 𝐺𝑅𝑆 wall; hyperparameter; random forests; sensitivity analysis

Address
Jiaman Li: School of Architecture and Surveying Engineering, Shaanxi College of Communication Technology, Xi'an 710018, Shaanxi, China
Xing Gao: Capital Construction Department, Yantai Yuhuangding Hospital, Yantai 264000, Shandong, China

Abstract
This study focuses on enhancing structural strength in flood-prone regions by utilizing industrial waste under varying temperature conditions. Industrial waste's increasing usage and its environmental implications require deeper comprehension. The escalating adoption of industrial waste as an alternative construction material underscores this shift. The research employs fly ash (F), ground-granulated blast-furnace slag (G), and lime (L) to augment geotechnical properties and bolster the flood resistance of stabilized soil. Various clay, lime, GGBS, and 2% fly ash mixtures are tested under optimal moisture and maximum dry density conditions. The curing spans 1, 7, 14, 28, 56, and 90 days at ambient temperature and 3C. Subsequent unconfined compressive strength (UCS), durability, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and field emission scanning electron microscopy (FE-SEM) analyses are conducted. Results highlight a 257% UCS increase at 14 days' curing for the 8% GGBS + 6% Lime + 2% Fly ash mixture at ambient temperature, while the mix of 6% GGBS + 8% Lime + 2% Fly ash records a 686% UCS enhancement after 90 days' curing at 3C. Lime concentration affects the plasticity index and maximum dry unit weight (MDU). Upon water immersion, durability testing indicates an 11-17% strength reduction for lime, GGBS, and fly ash samples. The microstructural evaluation identifies hydration products like calcium aluminate silicate-hydrate and calcium silicate hydrate. According to the findings, using industrial waste can be a promising solution to pavement sustainability, especially after the flood, and it can reduce related costs and decrease CO2 emissions.

Key Words
durability; fly ash; lime; microstructural analysis; road engineering; temperature condition

Address
Navid Khayat and Hadis Nasiri: Department of Civil Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
Ahad Nazarpour: Department of Geology, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
Anil Kumar Sharma: Department of Civil Engineering, National Institute of Technology Patna, Patna, Bihar, India

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