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Volume 11, Number 2, August 2016

To secure the stability of geotechnical infrastructures and minimize failures during the construction process, a number of support systems have been introduced in the last several decades. In particular, stabilization methods using steel bars have been widely used in the field of geotechnical engineering. Rock bolt system is representative support system using steel bars. Pre-stressing has been applied to enhance reinforcement performance but can be released because of the failure of head or anchor sections. To overcome this deficiency, this paper proposes an innovative support system that can actively reinforce the weak ground along the whole structural element by introducing an active tension bolt containing a spring unit to the middle of the steel bar to increase its reinforcement capacity. In addition, the paper presents the support mechanism of the active tension bolt based on a theoretical study and employs an experimental study to validate the performance of the proposed active tension bolt based on a down-scaled model. To examine the feasibility of the active tension unit in a pillar, the paper considers a pullout test and a small-scale experimental model. The experimental results suggest the active tension bolt to be an effective support system for pillar reinforcement.

Key Words
active tension bolt; tunnel pillar reinforcement; support mechanism; experimental study

(1) Sang-Hwan Kim:
Hoseo University, Department of Civil Engineering, 20, Hoeo-ro 79 Beon-gil, Baebang-eup, Asan-si, 31499, Republic of Korea;
(2) Ki-Il Song:
Inha University, Department of Civil Engineering,100 Inha-ro, Nam-gu, Incheon, 22212, Republic of Korea;
(3) Jae-Hyun Park:
Hankook 2 Arch, 78 Jangmi-ro, Bundang-gu, Seongnam-si, Gyeonggi-do, 13496, Republic of Korea.

Clayey rock has large clay mineral content. When in contact with water, this expands considerably and may present a significant hazard to the stability of the rock in geotechnical engineering applications. This is particularly important in the present work, which focused on mitigating some unwelcomed properties of clayey rock. Changes in its physical properties were simulated by subjecting the rock to a low voltage direct current (DC) using copper, steel and aluminum electrodes. The modified mechanism of the coupled electrical and chemical fields acting on the clayey rock was analyzed. It was concluded that the essence of clayey rock electrochemical modification is the electrokinetic effect of the DC field, together with the coupled hydraulic and electrical potential gradients in finegrained clayey rock, including ion migration, electrophoresis and electro-osmosis. The aluminum cathodes were corroded and generated gibbsite at the anode; the steel and copper cathodes showed no obvious change. The electrical resistivity and uniaxial compressive strength (UCS) of the modified specimens from the anode, intermediate and cathode zones tended to decrease. Samples taken from these zones showed a positive correlation between electric resistivity and UCS.

Key Words
clayey rock; modified mechanism; electrokinetic effect; physical simulation; long-term stability

(1) Zhaoyun Chai, Yatiao Zhang:
Mining Technology Institute, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China;
(2) Zhaoyun Chai Alexander Scheuermann:
School of Civil Engineering, the University of Queensland, Brisbane, 4067, Australia.

A total of 99 full-scale field load tests at 22 sites were compiled for this study to elucidate several issues related to the load-displacement behaviour of belled piers under axial uplift loading, including (1) interpretation criteria to define various elastic, inelastic, and "failure" states for each load test from the load-displacement curve; (2) generalized correlations among these states and determinations to the predicted ultimate uplift resistances; (3) uncertainty in the resistance model factor statistics required for reliability-based ultimate limit state (ULS) design; (4) uncertainty associated with the normalized load-displacement curves and the resulting model factor statistics required for reliability-based serviceability limit state (SLS) design; and (5) variations of the combined ULS and SLS model factor statistics for reliability-based limit state designs. The approaches discussed in this study are practical and grounded realistically on the load tests of belled piers with minimal assumptions. The results on the characterization and uncertainty of uplift load.displacement behaviour of belled piers could be served as to extend the early contributions for reliability-based ULS and SLS designs.

Key Words
belled piers; uplift; load tests; reliability-based design; model uncertainty; normalized load-displacement curve; hyperbolic curve-fitting parameters

(1) Xian-long Lu, Wei-feng Zheng, Wen-zhi Yang:
China Electric Power Research Institute, No. 15, Xiaoying East Road, Haidian District, Beijing, 100192, China;
(2) Zeng-zhen Qian:
School of Engineering and Technology, China University of Geosciences, No. 29 Xueyuan Road, Haidian District, Beijing, 100083, China.

This paper presents a new numerical solution of the ultimate lateral capacity of rectangular piles in clay. The two-dimensional plane strain finite element was employed to determine the limit load of this problem. A rectangular pile is subjected to purely lateral loading along either its major or minor axes. Complete parametric studies were performed for two dimensionless variables including: (1) the aspect ratios of rectangular piles were studied in the full range from plates to square piles loaded along either their major or minor axes; and (2) the adhesion factors between the soil-pile interface were studied in the complete range from smooth surfaces to rough surfaces. It was found that the dimensionless load factor of rectangular piles showed a highly non-linear function with the aspect ratio of piles and a slightly non-linear function with the adhesion factor at the soil-pile interface. In addition, the dimensionless load factor of rectangular piles loaded along the major axis was significantly higher than that loaded along the minor axis until it converged to the same value at square piles. The solutions of finite element analyses were verified with the finite element limit analysis for selected cases. The empirical equation of the dimensionless load factor of rectangular piles was also proposed based on the data of finite element analysis. Because of the plane strain condition of the top view section, results can be only applied to the full-flow failure mechanism around the pile for the prediction of limiting pressure at the deeper length of a very long pile with full tension interface that does not allow any separation at soil-pile interfaces.

Key Words
numerical analysis; plane strain; finite element; limit analysis; rectangular piles

Geotechnical Research Unit, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, Thailand.

The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and KI and KII of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compressionshear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that σ3 changes linearly with the change of σ1. And the change rate is related to β, angle between the cracks and σ1. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.

Key Words
instability mechanism; nearly horizontal stratum; macro failure; micro fracture; comprehensive failure criteria

(1) Shu-cai Li, Jian-hua Wang, Wei-zhong Chen, Li-ping Li, Qian-qing Zhang, Peng He:
Research Center of Geotechnical and Structural Engineering, Shandong University, Ji'nan 250061, Shandong, China;
(2) Wei-zhong Chen:
State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, Hubei, China.

The jointed rock mass behavior often plays a major role in the design of underground excavation, and their failures during excavation and in operation, are usually closely related to joints. This research attempts to evaluate the effects of two basic geometric factors influencing tunnel behavior in a jointed rock mass; joints spacing and joints orientation. A hybridized indirect boundary element code known as TFSDDM (Two-dimensional Fictitious Stress Displacement Discontinuity Method) is used to study the stress distribution around the tunnels excavated in jointed rock masses. This numerical analysis revealed that both the dip angle and spacing of joints have important influences on stress distribution on tunnel walls. For example the tensile and compressive tangential stresses at the boundary of the circular tunnel increase by reduction in the joint spacing, and by increase the dip joint angle the tensile stress in the tunnel roof decreases.

Key Words
boundary element method; dip; spacing; joint; tunnel

Department of Mine Exploitation Engineering, Faculty of Mining and Metallurgy, Yazd, Iran.

A simple hyperbolic shear deformation theory taking into account transverse shear deformation effects is proposed for the free flexural vibration analysis of thick functionally graded plates resting on elastic foundations. By considering further supposition, the present formulation introduces only four unknowns and its governing equations are therefore reduced. Hamilton\'s principle is employed to obtain equations of motion and Navier-type analytical solutions for simply-supported plates are compared with the available solutions in literature to check the accuracy of the proposed theory. Numerical results are computed to examine the effects of the power-law index and side-to-thickness ratio on the natural frequencies.

Key Words
shear deformation theory; vibration; functionally graded plate

(1) Hayat Saidi, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Abdelouahed Tounsi, Abdelmoumen Anis Bousahla:
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria;
(3) Abdelouahed Tounsi:
Algerian National Thematic Agency of Research in Science and Technology (ATRST), Algeria;
(4) Abdelmoumen Anis Bousahla:
Département de Génie Civil, Centre Universitaire de Relizane, Algeria.

As the forefront of structural design method, capacity spectrum method can be applied conveniently, and through this method, deformation demand of structure can be considered. However, there is no research for the seismic application in the structure of sheet pile retaining wall to report. Therefore, focusing on laterally loaded stabilizing sheet pile wall, which belongs to flexible cantilever retaining structure and meets the applying requirement of capacity spectrum method from seismic design of building structure, this paper studied an approach of seismic design of sheet pile wall based on capacity spectrum method. In the procedure, the interaction between soil and structure was simplified, and through Pushover analysis, seismic fortification standard was well associated with performance of retaining structure. In addition, by comparing the result of nonlinear time history analysis, it suggests that this approach is applicable.

Key Words
capacity spectrum method; pushover analysis; sheet pile wall; interaction between soil and structure

(1) Honglue Qu:
School of Geoscience and Technology, Southwest Petroleum University, No. 8 of Xindu Avenue, Chengdu 610500, China;
(2) Ruifeng Li, Huanguo Hu:
School of Civil Engineering and Architecture, Southwest Petroleum University, No. 8 of Xindu Avenue, Chengdu 610500, China;
(3) Hongyu Jia, Jianjing Zhang:
School of Civil Engineering, Southwest Jiaotong University, No. 111, North 1st Section of Second Ring Road, Chengdu 610031, China.

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