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CONTENTS
Volume 31, Number 5, December10 2022
 


Abstract
A forecast of slope behavior during catastrophic events, such as earthquakes is crucial to recognize the risk of slope failure. This paper endeavors to eliminate the significant supposition of predefined slip surfaces in the slope stability analysis, which questions the relevance of simple conventional methods under seismic conditions. To overcome such limitations, a methodology dependent on the slip line hypothesis, which permits an automatic generation of slip surfaces, is embraced to trace the extreme slope face under static and seismic conditions. The effect of earthquakes is considered using the pseudo-static approach. The current outcomes developed from a parametric study endorse a non-linear slope surface as the extreme profile, which is in accordance with the geomorphological aspect of slopes. The proposed methodology is compared with the finite element limit analysis to ensure credibility. Through the design charts obtained from the current investigation, the stability of slopes can be assessed under seismic conditions. It can be observed that the extreme slope profile demands a flat configuration to endure the condition of the limiting equilibrium at a higher level of seismicity. However, a concurrent enhancement in the shear strength of the slope medium suppresses this tendency by offering greater resistance to the seismic inertial forces induced in the medium. Unlike the traditional linear slopes, the extreme slope profiles mostly exhibit a steeper layout over a significant part of the slope height, thus ensuring a more optimized solution to the slope stability problem. Further, the susceptibility of the Longnan slope failure in the Huining-Wudu seismic belt is predicted using the current plasticity approach, which is found to be in close agreement with a case study reported in the literature. Finally, the concept of equivalent single or multi-tiered planar slopes is explored through an example problem, which exhibits the appropriateness of the proposed non-linear slope geometry under actual field conditions.

Key Words
earthquake; failure; numerical analyses; plasticity; slope stability

Address
Shibsankar Nandi and Priyanka Ghosh: Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur – 208 016, India
G. Santhoshkumar: School of Infrastructure, Indian Institute of Technology Bhubaneswar, Argul, Khordha, Odhisha – 752 050, India

Abstract
It is essential for geotechnical engineers to conduct studies and make predictions about the stability of slopes, since collapse of a slope may result in catastrophic events. The Gaussian process regression (GPR) approach was carried out for the purpose of predicting the factor of safety (FOS) of the slopes in the study that was presented here. The model makes use of a total of 327 slope cases from Iran, each of which has a unique combination of geometric and shear strength parameters that were analyzed by PLAXIS software in order to determine their FOS. The K-fold (K = 5) technique of cross-validation (CV) was used in order to conduct an analysis of the accuracy of the models' predictions. In conclusion, the GPR model showed excellent ability in the prediction of FOS of slope stability, with an R2 value of 0.8355, RMSE value of 0.1372, and MAPE value of 6.6389%, respectively. According to the results of the sensitivity analysis, the characteristics (friction angle) and (unit weight) are, in descending order, the most effective, the next most effective, and the least effective parameters for determining slope stability.

Key Words
factor of safety; feature selection;Gaussian process; machine learning;regression;slope stability

Address
Arsalan Mahmoodzadeh andid Reza Nejati: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Tehran, Iran
Nafiseh Rezaie: Department of Civil Engineering, Faculty of Engineering, University of Qom,Qom, Iran
Adil Hussein Mohammed: Department of Communication and Computer Engineering, Faculty of Engineering, Cihan University-Erbil, Kurdistan Region, Iraq
Hawkar Hashim Ibrahim: Department of Civil Engineering, College of Engineering, Salahaddin University-Erbil, 44002 Erbil, Kurdistan Region, Iraq
Mokhtar Mohammadi: Department of Information Technology, College of Engineering and Computer Science, Lebanese French University, Kurdistan Region, Iraq
Shima Rashidi: Department of Computer Science, College of Science and Technology, University of Human Development, Sulaymaniyah,
Kurdistan Region, Iraq



Abstract
Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confinements ranging from 0 to 15 MPa. Peak strength tends to grow from smaller to standard-size samples (54 mm) and then diminishes for larger values at low confinement. However, a slight change in strength is observed at higher confinements. Residual strength is observed to be much less size-dependent. Additionally, this study introduces preliminary modelling approaches of these laboratory observations with the help of three-dimensional particle flow code (PFC3D) simulations based on bonded particle models (BPM). Based on previous studies, two modelling approaches have been followed. In the first one, the maximum and minimum particle diameter (Dmax and Dmin) are kept constant irrespective of the sample size, whereas in the second one, the resolution (number of particles within the sample or v) was kept constant. Neither of these approaches properly represent the observations in actual laboratory tests, even if both of them show some interesting capabilities reported in this document. Eventually, some suggestions are provided to proceed towards improving modelling approaches to represent observed scale effects.

Key Words
flat joint; Hoek-Brown criterion; intact granite samples; numerical methods; PFC; size effects

Address
Xian Estévez-Ventosa, Uxía Castro-Filgueira, Manuel A. González-Fernández,Fernando García-Bastante and Leandro R. Alejano: CINTECX, GESSMin group, Department of Natural Resources and Environmental Engineering, University of Vigo, Campus Lagoas,
Vigo, Pontevedra, 36.310, Spain
Diego Mas-Ivars: Swedish Nuclear Fuel and Waste Management Company (SKB), Evenemangsgatan 13, Box 3091, SE-169 03 Solna, Stockholm, Sweden;
Division of Soil and Rock Mechanics, Royal Institute of Technology (KTH), Brinellvägen 23, 100 44 Stockholm, Sweden

Abstract
Pile composite foundation (PCF) has been commonly applied in practice. Existing research has focused primarily on semi-infinite media having equal pile lengths with little attention given to the effects of inclined bedrock and dissimilar pile lengths. This investigation considers the effects of inclined bedrock on vertical loaded PCF with dissimilar pile lengths. The pile-soil system is decomposed into fictitious piles and extended soil. The Fredholm integral equation about the axial force along fictitious piles is then established based on the compatibility of axial strain between fictitious piles and extended soil. Then, an iterative procedure is induced to calculate the PCF characteristics with a rigid cap. The results agree well with two field load tests of a single pile and numerical simulation case. The settlement and load transfer behaviors of dissimilar 3-pile PCFs and the effects of inclined bedrock are analyzed, which shows that the embedded depth of the inclined bedrock significantly affects the pile-soil load sharing ratios, non-dimensional vertical stiffness N0/wdEs, and differential settlement for different length-diameter ratios of the pile l/d and pile-soil stiffness ratio k conditions. The differential settlement and pile-soil load sharing ratios are also influenced by the inclined angle of the bedrock for different k and l/d. The developed model helps better understand the PCF characteristics over inclined bedrock under vertical loading.

Key Words
boundary element method; inclined bedrock; fictious pile; pile composite foundation; vertical loading

Address
Kaiyu Jiang: Key of Laboratory for RC and PRC Structure of Education Ministry, Southeast University, Nanjing 211189, China;
School of Civil Engineering, Southeast University, Nanjing 211189, China;
School of Civil Engineering, Chongqing Three Gorges University, Chongqing, 404100, China
Weiming Gong and Guoliang Dai:Key of Laboratory for RC and PRC Structure of Education Ministry, Southeast University, Nanjing 211189, China;
School of Civil Engineering, Southeast University, Nanjing 211189, China
Jiang Xu: College of Civil Science and Engineering, Yangzhou University, Yangzhou, 225000, China
Xia Guo: Nuclear Industry Huzhou Survey Planning & Design Institute Co., Ltd. , Zhejiang, 313002, China

Abstract
A 1257-m-long irregular deep foundation pit located in the central of Nanjing, China was constructed using the combined full-width and half-width top-down method. Based on the long-term field monitoring data, this study analyzed the evolution characteristics of the vertical movement of the columns, internal force of the struts, and axial force of the structural beam and slab. The relevance of the three mentioned above and their relationship with the excavation process, structural system, and geological conditions were also investigated. The results showed that the column uplift was within the range of 0.08% to 0.22% of the excavation depth, and the embedded depth ratio of the diaphragm wall and the bottom heave affected significantly on the column uplift. The differential settlement between the column and diaphragm wall remained unchanged after the base slab was cast. The final settlement of the diaphragm wall was twice the column uplift. The internal force of the struts did not varied monotonically but was related to numerous factors such as the excavation depth, number of struts, and environmental conditions. Additionally, the dynamic force and deformation of the columns, beams, and slabs were analyzed to investigate the inherent relationship and variation patterns of the responses of different parts of the structure.

Key Words
field monitoring; internal force variation; internal structure; irregular foundation pit; top-down method

Address
Yang Sun, Yufei Che and Ruicai Wang: College of Harbour, Coastal and Offshore Engineering, Hohai University, No. 1 Xikang Road, Nanjing, Jiangsu, P.R. China
Zhenxue Gu: Shanghai Shen Yuan Geotechnical Engineering Co., Ltd, No. 1368 Tibet South Road, Shanghai, P.R. China
Yawen Fan: College of Telecommunications and Information Engineering, Nanjing University of Posts and Telecommunications,
No. 66 New Model Road, Nanjing, Jiangsu, P.R. China

Abstract
This study introduces soil resistance multipliers at locations encompassed by the zone of influence of the helix plate to consider the added lateral resistance provided to the helical pile. The zone of influence of a helix plate is a function of its diameter and serves as a boundary condition for the modified soil resistance springs. The concept is based on implementing p-multipliers as a reduction factor for piles in group action. The application of modified p-y springs in the analysis of helical piles allows for better characterization and understanding of the lateral behavior of helical piles, which will help further the development of design methods. To execute the proposed method, a finite difference program, HPCap (Helical Pile Capacity), was developed by the authors using Matlab. The program computes the deflection, shear force, bending moment, and soil resistance of the helical pile and allows the user to freely input the value of the zone of influence and (a coefficient that affects the value of the p-multiplier). Results from ten full-scale lateral load tests on helical piles embedded at depths of 3.0 m with varying shaft diameters, shaft thicknesses, and helix configurations were analyzed to determine the zone of influence and the magnitude of the p-multipliers. The analysis determined that the value of the p-multipliers is influenced by the ratio between the pile embedment length and the shaft diameter (Dp), the effective helix diameter (Dh-Dp), and the zone of influence. Furthermore, the zone of influence is recommended to be 1.75 times the helix diameter (Dh). Using the numerical analysis method presented in this study, the predicted deflections of the various helical pile cases showed good agreement with the observed field test results.

Key Words
finite difference method; helical piles; lateral load test; p-multiplier; p-y springs

Address
Hyeong-Joo Kim: Department of Civil Engineering, Kunsan National University, 558 Daehak-ro, Miryong-dong, Gunsan 54150, Republic of Korea
James Vincent Reyes, Peter Rey Dinoy Hyeong-Soo Kim and Jun-Young Kim: Department of Civil and Environmental Engineering, Kunsan National University, 558 Daehak-ro,
Miryong-dong, Gunsan 54150, Republic of Korea
Tae-Woong Park: Renewable Energy Research Institute, Kunsan National University, 558 Daehak-ro,
Miryong-dong, Gunsan 54150, Republic of Korea

Abstract
Shear failure in soil is the primary cause of most geotechnical structure failures or instability. Soil water content is a significant factor affecting soil shear strength. In this study, the shear strength of samples with different water contents was tested. The shear strength, cohesion, and internal friction angle decreased with increasing water content. Based on the variation of cohesion and internal friction angle, the water content zone was divided into a high-water content zone and low-water content zone with a threshold water content of 15.05%. Cohesion and internal friction angle have a good linear relationship with water content in both zones. Environmental Scanning Electron Microscopy (ESEM) test presented that the aggregates size of the compacted loess gradually increases with increasing water content. Meanwhile, the clay in the compacted loess forms a matric that envelops around the surface of the aggregates and fills the inter-aggregates pores. A quantitative analysis of bound water and free water under different water contents using a nuclear magnetic resonance (NMR) test was carried out. The threshold water content between bound water and free water was slightly below the plastic limit, which is consistent with the results of shear strength parameters. Combined with the T2 distributions obtained by NMR, one can define a T2 relaxation time of 1.58 ms as the boundary point for bound water distribution without free water. Finally, the effects of bound water and free water on shear strength parameters were analyzed using linear regression analysis.

Key Words
bound water; ESEM; linear regression analysis; loess; shear strength

Address
Kang-ze Yuan: Department of Geological Engineering, College of Geological Engineering and Surveying and Mapping,
Chang'An University, No.126 Yanta Road, Xi'an, Shaanxi 710054, P.R. China;
Department of Civil and Environmental Engineering, Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milano, Italy
Wan-kui Ni, Xiang-fei Lü and Hai-man Wang: Department of Geological Engineering, College of Geological Engineering and Surveying and Mapping,
Chang'An University, No.126 Yanta Road, Xi'an, Shaanxi 710054, P.R. China


Abstract
The lattice-spring-based synthetic rock mass model (LS-SRM) technique has been extensively employed in large open-pit mining and underground projects in the last decade. Since the LS-SRM requires a complex and time-consuming calibration process, a robust approach was developed using the Response Surface Methodology (RSM) to optimize the calibration procedure. For this purpose, numerical models were designed using the Box–Behnken Design technique, and numerical simulations were performed under uniaxial and triaxial stress states. The model input parameters represented the models' micro-mechanical (lattice) properties and the macro-scale properties, including uniaxial compressive strength (UCS), elastic modulus, cohesion, and friction angle constitute the output parameters of the model. The results from RSM models indicate that the lattice UCS and lattice friction angle are the most influential parameters on the macro-scale UCS of the specimen. Moreover, lattice UCS and elastic modulus mainly control macro-scale cohesion. Lattice friction angle (flat joint fiction angle) and lattice elastic modulus affect the macro-scale friction angle. Model validation was performed using physical laboratory experiment results, ranging from weak to hard rock. The results indicated that the RSM model could be employed to calibrate LS-SRM numerical models without a trial-and-error process.

Key Words
lattice-spring-based synthetic rock mass; LS-SRM model; response surface method; SRMTools

Address
Mariam Al-E' Bayat: Department of Geosciences and Geological and Petroleum Engineering,
Missouri University of Science and Technology, Rolla, MO 65409, USA
Taghi Sherizadeh, Dogukan Guner and Mostafa Asadizadeh: Department of Mining and Explosives Engineering, Missouri University of Science and Technology, Rolla, MO 65409, USA


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