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CONTENTS
Volume 31, Number 4, November25 2022
 


Abstract
Studying slope stability is an important branch of civil engineering. In this way, engineers have employed machine learning models, due to their high efficiency in complex calculations. This paper examines the robustness of various novel optimization schemes, namely equilibrium optimizer (EO), Harris hawks optimization (HHO), water cycle algorithm (WCA), biogeography-based optimization (BBO), dragonfly algorithm (DA), grey wolf optimization (GWO), and teaching learning-based optimization (TLBO) for enhancing the performance of adaptive neuro-fuzzy inference system (ANFIS) in slope stability prediction. The hybrid models estimate the factor of safety (FS) of a cohesive soil-footing system. The role of these algorithms lies in finding the optimal parameters of the membership function in the fuzzy system. By examining the convergence proceeding of the proposed hybrids, the best population sizes are selected, and the corresponding results are compared to the typical ANFIS. Accuracy assessments via root mean square error, mean absolute error, mean absolute percentage error, and Pearson correlation coefficient showed that all models can reliably understand and reproduce the FS behavior. Moreover, applying the WCA, EO, GWO, and TLBO resulted in reducing both learning and prediction error of the ANFIS. Also, an efficiency comparison demonstrated the WCA-ANFIS as the most accurate hybrid, while the GWO-ANFIS was the fastest promising model. Overall, the findings of this research professed the suitability of improved intelligent models for practical slope stability evaluations.

Key Words
metaheuristic optimizers; neuro-fuzzy model; optimization; safety engineering; slope stability

Address
Yu-tian Gu: College of Geoscience & Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
Yong-xuan Xu: China Construction Second Engineering Bureau LTD., China
Hossein Moayedi and Binh Nguyen Le:Institute of Research and Development, Duy Tan University, Da Nang, Vietnam;
School of Engineering & Technology, Duy Tan University, Da Nang, Vietnam
Jian-wei Zhao: School of Electrical and Information Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China

Abstract
This study presents a hybrid algorithm for classifying the rock joints, where the improved artificial bee colony (IABC) and the fuzzy C-means (FCM) clustering algorithms are incorporated to take advantage of the artificial bee colony (ABC) algorithm by tuning the FCM clustering algorithm to obtain the more reasonable and stable result. A coefficient is proposed to reduce the amount of blind random searches and speed up convergence, thus achieving the goals of optimizing and improving the ABC algorithm. The results from the IABC algorithm are used as initial parameters in FCM to avoid falling to the local optimum in the local search, thus obtaining stable classifying results. Two validity indices are adopted to verify the rationality and practicability of the IABC–FCM algorithm in classifying the rock joints, and the optimal amount of joint sets is obtained based on the two validity indices. Two illustrative examples, i.e., the simulated rock joints data and the field-survey rock joints data, are used in the verification to check the feasibility and practicability in rock engineering for the proposed algorithm. The results show that the IABC–FCM algorithm could be applicable in classifying the rock joint sets.

Key Words
fuzzy C-means clustering algorithm; improved artificial bee colony algorithm; joint set; rock mass

Address
Duofa Ji: Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin, 150090, China;
Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology,
Harbin Institute of Technology, Harbin, 150090, China
Weidong Lei and Wenqin Chen: Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, 518055, China

Abstract
In order to investigate the damage evolution law of rock specimens under cyclic loading, cyclic loading tests under constant loads with different amplitudes were carried out on limestone specimens with high strength and brittleness values using acoustic emission (AE) technology and the energy evolution and AE characteristics were evaluated. Based on dissipated energy density and AE counts, the damage variable of specimen was characterized and two damage evolution processes were analyzed and compared. The obtained results showed that the change of AE counts was closely related to radial deformation. Higher cyclic loading values result in more significant radial strain of limestone specimen and larger accumulative AE counts of cyclic loading segment, which indicated Felicity effect. Regarding dissipated energy density, the damage of limestone specimen was defined without considering the influence of radial deformation, which made the damage value of cyclic loading segment higher at lower amplitude loads. The damage of cyclic loading segment was increased with the magnitude of load. When dissipated energy density was applied to define damage, the damage value at unloading segment was smaller than that of AE counts. Under higher cyclic loading values, rocks show obvious damage during both loading and unloading processes. Therefore, during deep rock excavation, the damages caused by the deformation recovery of unloading rocks could not be ignored when considering the damage caused by abutment pressure.

Key Words
AE counts; cyclic loading; damage variable; energy dissipation; residual strain

Address
Cheng J. Li: State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mine,
Anhui University of Science and Technology, Huainan, Anhui 232001, China;
School of Civil Engineering and Architecture, Anhui University of Science and Technology, Huainan, Anhui 232001, China
Pei J. Lou: School of Civil Engineering and Architecture, Anhui University of Science and Technology, Huainan, Anhui 232001, China;
Engineering Research Center of Underground Mine Construction, Ministry of Education, Anhui University of Science and Technology, Huainan, Anhui 232001, China
Ying Xu: State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mine,
Anhui University of Science and Technology, Huainan, Anhui 232001, China;
School of Civil Engineering and Architecture, Anhui University of Science and Technology, Huainan, Anhui 232001, China;
Engineering Research Center of Underground Mine Construction, Ministry of Education, Anhui University of Science and Technology, Huainan, Anhui 232001, China

Abstract
The variation of the undrained shear strength (cu) is an important consideration for assessing slope stability in engineering practice. Previous studies focused on the three-dimensional (3D) stability of slopes in normally consolidated clays generally assume the undrained shear strength increases linearly with depth but does not vary in the horizontal direction. To assess the 3D stability of slopes with spatially varying undrained shear strength, the kinematic approach of limit analysis was adopted to obtain the upper bound solution to the stability number based on a modified failure mechanism. Three types failure mechanism: the toe failure, face failure and below-toe failure were considered. A serious of charts was then presented to illustrate the effect of key parameters on the slope stability and failure geometry. It was found that the stability and failure geometry of slopes are significantly influenced by the gradient of cu in the depth direction. The influence of cu profile inclination on the slope stability was found to be pronounced when the increasing gradient of cu in the depth direction is large. Slopes with larger width-to-height ratio B/H are more sensitive to the variation of cu profile inclination.

Key Words
3D slope stability; failure mechanism; limit analysis; spatially varying strength

Address
Yunwei Shi, Xianqi Luo and Pingfan Wang: School of Naval Architecture, Ocean & Civil Engineering, Shanghai Jiao Tong University,
800 Dongchuan Road, Minhang District, Shanghai, China

Abstract
Previous studies postulated insignificant capillary rise (hc) effect above the water table (Hw) for unsaturated soils. In addition, these studies utilised dry unit weight above Hw. This paper, therefore, addresses the effect of these postulations on strength where the influence of hc using a modified upper bound approach, Discontinuity Layout Optimization (UNSAT-DLO) for a simulated soil was predicted. Two different parametric studies to model passive earth pressure and bearing capacity problems are carried out to provide an insight into the effect of capillary rise on strength. Significant increase in strength, owing to unsaturated conditions, was obtained where the maximum increase was when suction slightly less or greater than the air entry suction. On the other hand, the results showed a negative effect of hc. For example, up to 8.24% decrease in passive thrust (Pp) was obtained at Hw=0 m when hc rose 1 m from 0 m. To put this into perspective, this was equivalent to a decrease of about 2o in o at Hw=0 m and hc =0 m in order to obtain the same result at hc =1 m. For the bearing capacity problem, the effect was seen to be higher, up to 18.4% decrease in N was obtained when hc rose from 0 m to 2.5 m at Hw =0 m. In addition, the results revealed a negative influence of assigning dry unit weight above Hw or hc.. However, considerable increase in strength was obtained when unsaturated unit weight above hc was assigned.

Key Words
bearing capacity; capillary rise; passive earth pressure; unsaturated soil; upper bound

Address
Bestun J. Shwan: Department of Geotechnical Engineering, Faculty of Engineering, Koya University, Koya KOY45, Kurdistan Region- F.R. Iraq

Abstract
In this paper, cracks with different angles are prefabricated in rock specimens to study the fracture characteristics of rock based on CT images. The rock specimens are prepared for compression tests according to the standard recommended by ISRM (International Society for Rock Mechanics). The effects of different angles on rock mechanical properties and crack propagation fracture modes are analyzed. Then, based on the cohesive element method and CT images, the relationship between porosity and Young's modulus as well as the fracture property is explored by the numerical modelling. In the modelling, the distribution of Young's modulus is determined by the CT image through the field variable method. The results show that prefabricated cracks reduce the mechanical properties of rock. The closer the angles of the prefabricated crack is, the greater the Young 's modulus of the rock sample is. The failure process of each specimen with prefabricated cracks is formed by the initiation and propagation of crack, and the angle of the prefabricated crack will affect the type of extended crack. As part of the numerical model proposed in this paper, the microstructure of rocks is reflected by CT images. The numerical results verify the effectiveness of the cohesive element method in the study of crack propagation for rock. The rock model in this paper can be used to predict engineering disasters such as collapse and landslide caused by rock fracture, which means that the methodology adopted in this paper is comprehensive and important to solve rock engineering problems.

Key Words
cohesive element method; CT; field variables method; fracture; rock

Address
Nan Xiao, Li-Cheng Luo, Fu Huangand Tong-Hua Ling: School of Civil Engineering, Changsha University of Science and Technology, Changsha 410004, Hunan, China

Abstract
The use of calcium sulfoaluminate (CSA) cement as a rapid-hardening cement admixture or eco-friendly alternate for ordinary Portland cement (OPC) has been attempted over the years, but the cost of CSA cement and availability of suitable aluminium resource prevent its wide practical application. To propose an effective ground improvement design in sandy soil, this study aims at blending a certain percentage of CSA with OPC to find an optimum blend that would have fast-setting behavior with a lower carbon footprint than OPC without compromising the mechanical properties of the cemented sand. Compared to the 100% CSA case, initial speed of strength development of blended cement is relatively low as it is mixed with OPC. It is found that 80% OPC and 20% CSA blend has low initial strength but eventually produces equivalent ultimate strength (28 days curing) to that of CSA treated sand. The specific OPC-CSA blend (80:20) exhibits significantly higher strength gain than using pure OPC, thus allowing effective geotechnical designs for sustainable and controlled ground improvement. Further parametric studies were conducted for the blended cement under various curing conditions, cement contents, and curing times. Wet-cured cement treated sand had 33% lower strength than that of dry-cured samples, while the stiffness of wet-cured samples was 25% lower than that of dry-cured samples.

Key Words
blended cement; calcium sulfoaluminate; cement treated sand; ordinary Portland cement; small strain shear modulus

Address
Sathya Subramanian and Wei Zhong Tee: Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576
Juhyuk Moon: Department of Civil and Environmental Engineering, Seoul National University, Seoul 08826, South Korea
Taeseo Ku: Department of Civil and Environmental Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, South Korea

Abstract
The objective of the study is to evaluate the feasibility of the dynamic behavior of slope through both 1 g shaking table test and numerical analysis. Accelerometers were installed in the slope model with different types of seismic waves. The numerical analysis (ABAQUS and DEEPSOIL) was used to simulate 1 g shaking table test at infinite boundary. Similar Acceleration-time history, Spectral acceleration (SA) and Spectral acceleration amplification factor (Fa) were obtained, which verified the feasibility of modeling using ABAQUS and DEEPSOIL under the same size. The influence of the size (1, 2, 5, 10 and 20 times larger than that used in the 1 g shaking table test) of the model used in the numerical analysis were extensively investigated. According to the similitude law, ABAQUS was used to analyze the dynamic behavior of large-scale slope model. The 5% Damping Spectral acceleration (SA) and Spectral acceleration amplification factor (Fa) at the same proportional positions were compared. Based on the comparison of numerical analyses and 1 g shaking table tests, it was found that the 1 g shaking table test result can be utilized to predict the dynamic behavior of the real scale slope through numerical analysis.

Key Words
1 g shaking table test; ABAQUS; amplification; dynamic behavior of soil; infinite boundary; similarity law; slope

Address
Yong Jin, Daehyeon Kim and Sugeun Jeong: Department of Civil Engineering, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju, Republic of Korea
Kyungho Park: Department of Civil Construction Engineering, Chosun College of Science and Technology,
309-1 Pilmun-daero, Dong-gu, Gwangju, Republic of Korea


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