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CONTENTS
Volume 24, Number 4, February25 2021
 

Abstract
In an earlier publication (Serrano et al. 2014), the theoretical basis for evaluating the shear strength in rock joints was presented and used to derive an equation that governs the relationship between tangential and normal stresses on the joint during slippage between the joint faces. In this paper, the theoretical equation is applied to two non-linear failure criteria by using non-associated flow laws, including the modified Hoek and Brown and modified Mohr-Coulomb equations. The theoretical model considers the geometric dilatancy, the instantaneous friction angle, and a parameter that considers joint surface roughness as dependent variables. This model uses a similar equation structure to the empirical law that was proposed by Barton in 1973. However, a good correlation with the empirical values and, therefore, Barton's equation is necessary to incorporate a non-associated flow law that governs breakage processes in rock masses and becomes more significant in highly fractured media, which can be induced in a rock joint. A linear law of dilatancy is used to assess the importance of the non-associated flow to obtain very close values for different roughness states, so the best results are obtained for null material dilatancy, which considers significant changes that correspond to soft rock masses or altered zones of weakness.

Key Words
rock joint; shear strength; theoretical model; dilatancy; non-linear criterion; non-associated flow law

Address
Ruben Galindo, Jose L. Andres and Antonio Lara: Department of Geotechnical Engineering, Technical University of Madrid, C/ Profesor Aranguren s/n 28040 Madrid, Spain

Bin Xu, Zhigang Cao and Yuanqiang Cai: Department of Civil Engineering, College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, PR China

Abstract
This paper aims to estimate the range of the excavation damaged zone (EDZ) formation caused by the tunnel boring machine (TBM) advancement through dynamic three-dimensional large deformation finite element analysis. Large deformation analysis based on Coupled Eulerian-Lagrangian (CEL) analysis is used to accurately simulate the behavior during TBM excavation. The analysis model is verified based on numerous test results reported in the literature. The range of the formed EDZ will be suggested as a boundary under various conditions – different tunnel diameter, tunnel depth, and rock type. Moreover, evaluation of the integrity of the tunnel structure during excavation has been carried out. Based on the numerical results, the apparent boundary of the EDZ is shown to within the range of 0.7D (D: tunnel diameter) around the excavation surface. Through series of numerical computation, it is clear that for the rock of with higher rock mass rating (RMR) grade (close to 1st grade), the EDZ around the tunnel tends to increase. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional to the magnitude of the EDZ. However, the relationship between the formation of the EDZ and the stability of the tunnel was not found to be consistent. In case where the TBM excavation is carried out in hard rock or rock under high confinement (excavation under greater depth), large range of the EDZ may be formed, but less strain occurs along the excavation surface during excavation and is found to be more stable.

Key Words
excavation damaged zone (EDZ); tunnel boring machine (TBM); 3D finite element method (FEM); large deformation analysis; coupled Eulerian-Lagrangian analysis; rock mass rating (RMR); tunnel surface integrity

Address
Dohyun Kim: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, 02139, MA, U.S.A.

Sangseom Jeong: Department of Civil and Environmental Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea


Abstract
Brillouin Optical Frequency Domain Analysis (BOFDA) is a distributed fiber optic sensing (DFOS) technique that has unique advantages for performance monitoring of piles. However, the complicated production process and harsh operating environment of offshore PHC pipe piles make it difficult to apply this method to pile load testing. In this study, sensing cables were successfully pre-installed into an offshore PHC pipe pile directly for the first time and the BOFDA technique was used for in-situ monitoring of the pile under axial load. High-resolution strain and internal force distributions along the pile were obtained by the BOFDA sensing system. A finite element analysis incorporating the Degradation and Hardening Hyperbolic Model (DHHM) was carried out to evaluate and predict the performance of the pile, which provides an improved insight into the offshore pile-soil interaction mechanism.

Key Words
PHC pipe pile; Brillouin Optical Frequency Domain Analysis (BOFDA); offshore engineering; distributed fiber optic sensing (DFOS); load transfer analysis

Address
Xing Zheng, Bin Shi, Hong-Hu Zhu and Meng-Ya Sun :School of Earth Sciences and Engineering, Nanjing University, 163 Xianlin Ave, Nanjing, China

Cheng-Cheng Zhang: 1.) School of Earth Sciences and Engineering, Nanjing University, 163 Xianlin Ave, Nanjing, China
2.) Yuxiu Postdoctoral Institute, Nanjing University, 163 Xianlin Ave, Nanjing, China

Xing Wang: Nanjing University High-Tech Institute at Suzhou, 150 Renai Rd, Suzhou, China


Abstract
The Brazilian test has been widely used to determine the indirect tensile strength of rock, concrete and other brittle materials. The basic assumption for the calculation formula of Brazilian tensile strength is that the elastic moduli of rock are the same both in tension and compression. However, the fact is that the elastic moduli in tension and compression of most rocks are different. Thus, the formula of Brazilian tensile strength under the assumption of isotropy is unreasonable. In the present study, we conducted Brazilian tests on flat disk-shaped rock specimens and attached strain gauges at the center of the disc to measure the strains of rock. A tension-compression bi-modular model is proposed to interpret the data of the Brazilian test. The relations between the principal strains, principal stresses and the ratio of the compressive modulus to tensile modulus at the disc center are established. Thus, the tensile and compressive moduli as well as the correct tensile strength can be estimated simultaneously by the new formulas. It is found that the tensile and compressive moduli obtained using these formulas were in well agreement with the values obtained from the direct tension and compression tests. The formulas deduced from the Brazilian test based on the assumption of isotropy overestimated the tensile strength and tensile modulus and underestimated the compressive modulus. This work provides a new methodology to estimate tensile strength and moduli of rock simultaneously considering tension-compression bi-modularity.

Key Words
Brazilian test; tensile modulus; compressive modulus; tension-compression bi-modular rock; indirect tensile strength

Address
Jiong Wei: Department of Engineering Mechanics and CNMM, School of Aerospace Engineering, Tsinghua University,
NO. 30, Shuangqing Road, Haidian District, Beijing, Republic of China

Jingren Zhou: State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resources and Hydropower, Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu, Republic of China

Jae-Joon Song:Department of Energy Resources Engineering, Research Institute of Energy and Resources, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, Republic of Korea

Yulong Chen: State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology,
Ding No.11 Xueyuan Road, Haidian District, Beijing, Republic of China

Pinnaduwa H.S.W. Kulatilake: School of Resources and Environmental Engineering, Jiangxi University of Science and Technology, No.86, Hongqi Avenue, Ganzhou, Republic of China



Abstract
Joint roughness is combination of primary and secondary roughness. Ordinarily primary roughness is a geostatistical part of a joint surface that has a periodic nature but secondary roughness or unevenness is a statistical part of that which have a random nature. Using roughness generating algorithms is a useful method for evaluation of joint roughness. In this paper after determining geostatistical parameters of the joint profile, were presented two roughness generating algorithms using Mount-Carlo method for evaluation of primary (GJRGAP) and secondary (GJRGAS) roughness. These based on geostatistical parameters (range and sill) and statistical parameters (standard deviation of asperities height, SDH, and standard deviation of asperities angle, SDA) for generation two-dimensional joint roughness profiles. In this study different geostatistical regions were defined depending on the range and SDH. As SDH increases, the height of the generated asperities increases and asperities become sharper and at a specific range (a specific curve) relation between SDH and SDA is linear. As the range in GJRGAP becomes larger (the base of the asperities) the shape of asperities becomes flatter. The results illustrate that joint profiles have larger SDA with increase of SDH and decrease of range. Consequencely increase of SDA leads to joint roughness parameters such Z2, Z3 and Rp increases. The results showed that secondary roughness or unevenness has a great influence on roughness values. In general, it can be concluded that the shape and size of asperities are appropriate parameters to approach the field scale from the laboratory scale.

Key Words
joint roughness; classification; geostatistical method; generation algorithm; JRC

Address
Hojat Nasab and Saeed Karimi-Nasab: Department of Mining Engineering, Shahid Bahonar University of Kerman, 76196-37147 Kerman, Iran

Hossein Jalalifar: Department of Oil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract
A novel flexibility-based beam-foundation model for inelastic analyses of beams resting on foundation is presented in this paper. To model the deformability of supporting foundation media, the Winkler-Pasternak foundation model is adopted. Following the derivation of basic equations of the problem (strong form), the flexibility-based finite beam-foundation element (weak form) is formulated within the framework of the matrix virtual force principle. Through equilibrated force shape functions, the internal force fields are related to the element force degrees of freedom. Tonti's diagrams are adopted to present both strong and weak forms of the problem. Three numerical simulations are employed to assess validity and to show effectiveness of the proposed flexibility-based beam-foundation model. The first two simulations focus on elastic beam-foundation systems while the last simulation emphasizes on an inelastic beam-foundation system. The influences of the adopted foundation model to represent the underlying foundation medium are also discussed.

Key Words
flexibility-based formulation; beam element; Winkler-Pasternak foundation; soil-structure interaction; virtual force principle; finite element; nonlinear analysis

Address
Worathep Sae-Long: Department of Civil Engineering, School of Engineering, University of Phayao, Phayao 56000, Thailand

Suchart Limkatanyu and Woraphot Prachasaree: Department of Civil Engineering, Faculty of Engineering, Prince of Songkla University, Songkhla 90110, Thailand

Chayanon Hansapinyo: Excellence Center in Infrastructure and Transportation Engingeering (ExCITE),Department of Civil Engineering, Chiang Mai University, Chiang Mai 50200, Thailand

Jaroon Rungamornrat: Applied Mechanics and Structures Research Unit, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand

Minho Kwon: Department of Civil Engineering, ERI, Gyeongsang National University, Jinju 660-701, South Korea

Abstract
Pile foundation is a typical form of bridge foundation and viaduct, and large-diameter rock-socketed piles are typically adopted in bridges with long span or high piers. To investigate the effect of a mountain slope with a deep overburden layer on the bearing characteristics of large-diameter rock-socketed piles, four centrifuge model tests of single piles on different slopes (0o, 15o, 30o and 45o) were carried out to investigate the effect of slope on the bearing characteristics of piles. In addition, three pile group tests with different slope (0o, 30o and 45o) were also performed to explore the effect of slope on the bearing characteristics of the pile group. The results of the single pile tests indicate that the slope with a deep overburden layer not only accelerates the drag force of the pile with the increasing slope, but also causes the bending moment to move down owing to the increase in the unsymmetrical pressure around the pile. As the slope increases from 0o to 45o, the drag force of the pile is significantly enlarged and the axial force of the pile reduces to beyond 12%. The position of the maximum bending moment of the pile shifts downward, while the magnitude becomes larger. Meanwhile, the slope results in the reduction in the shaft resistance of the pile, and the maximum value at the front side of the pile is 3.98% less than at its rear side at a 45o slope. The load-sharing ratio of the tip resistance of the pile is increased from 5.49% to 12.02%. The results of the pile group tests show that the increase in the slope enhances the uneven distribution of the pile top reaction and yields a larger bending moment and different settlements on the pile cap, which might cause safety issues to bridge structures.

Key Words
rock-socketed pile; bearing behavior; centrifuge model test; slope degree

Address
Haofeng Xing, Hao Zhang and Liangliang Liu: Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

Yong Luo: Department of Geology Survey and Design,
Guizhou Transportation Planning Survey and Design Academe Co., Ltd., Guiyang, 550001, China

Abstract
It is a key issue in the tunnel design to evaluate the stability of the excavation face. Two efficient analytical models in the context of the limit equilibrium method (LEM) and the limit analysis method (LAM) are used to carry out the deterministic calculations of the safety factor. The safety factor obtained by these two models agrees well with that provided by the numerical modelling by FLAC 3D, but consuming less time. A simple probabilistic approach based on the Mote-Carlo Simulation technique which can quickly calculate the probability distribution of the safety factor was used to perform the probabilistic analysis on the tunnel face stability. Both the cumulative probabilistic distribution and the probability density function in terms of the safety factor were obtained. The obtained results show the effectiveness of this probabilistic approach in the tunnel design.

Key Words
safety factor; tunnel face; limit equilibrium method; limit analysis method; probabilistic analysis; Monte-Carlo simulation

Address
Qiujing Pan, Zhiyu Chen and Yimin Wu: Department of Civil Engineering, Central South University, Changsha, Hunan, China

Daniel Dias: Laboratory 3SR, Grenoble Alpes University, CNRS UMR 5521, Grenoble, France

Pierpaolo Oreste: Department of Environmental, Land and Infrastructural Engineering, Politecnico di Torino, Italy


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