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CONTENTS
Volume 16, Number 1, September20 2018
 

Abstract
In this paper an efficient and simple refined shear deformation theory is presented for the free vibration of Functionally Graded Plates Under Various Boundary Conditions. The theory accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The number of independent unknowns of present theory is four, as against five in other shear deformation theories. The plates are considered of the type having two opposite sides simply-supported, and the two other sides having combinations of simply-supported, clamped, and free boundary conditions. The mechanical properties of functionally graded material are assumed to vary according to power law distribution of the volume fraction of the constituents. Equations of motion are derived using Hamilton\'s principle. The results of this theory are compared with those of other shear deformation theories. Various numerical results including the effect of boundary conditions, power-law index, plate aspect ratio, and side-to-thickness ratio on the free vibration of FGM plates are presented.

Key Words
free vibration; functionally graded materials; boundary conditions; shear deformation theories; Hamilton

Address
Nafissa Zouatnia and Amar Kassoul: Department of Civil Engineering, Laboratory of Structures, Geotechnics and Risks (LSGR), Hassiba Benbouali University of Chlef, Algeria, BP 151, Hay Essalam, UHB Chlef, Chlef (02000), Algeria

Lazreg Hadji: 1.) Department of Civil Engineering, Ibn Khaldoun University, BP 78 Zaaroura, Tiaret (14000), Algeria
2.) Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria


Abstract
Propagation of the generalized Rayleigh waves in an elastic half-space covered by an elastic layer for different initial stress combinations and imperfect contact conditions is investigated. Three-dimensional linearized theory of elastic waves in initially stressed bodies in plane-strain state is employed, the corresponding dispersion equation is derived and an algorithm is developed for numerical solution to this equation. Numerical results on the influence of the initial stress patterns and on the influence of the contact conditions are presented and discussed. The case where the external forces are \"follower forces\" is considered as well. These investigations provide some theoretical foundations for the study of the near-surface waves propagating in layered mechanical systems and can be successfully used for estimation of the degree of the bonded defects between layers, fault characteristics and study of the behavior of seismic surface waves propagating under the bottom of the oceans.

Key Words
generalized Rayleigh waves; initial stresses; imperfect contact conditions; follower forces; wave dispersion

Address
Masoud Negin: Faculty of Engineering and Natural Sciences, Bahcesehir University, Besiktas, 34353, Istanbul, Turkey

Abstract
. Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical parameters of several discontinuity sets related to the surrounding rock mass of Rudbar Lorestan Pumped Storage Power Plant powerhouse cavern making use of the linear and areal (circular and rectangular) sampling methods. Taking into consideration quite a large quantity of scanline and the window samplings used in this research, it was realized that the areal sampling methods are more time consuming and cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties related to four sets of discontinuities were computed. There is an acceptable difference among the mean trace lengths measured using two linear and areal methods for the two joint sets. A 3D discrete fracture network generation code (3DFAM) has been developed to model the fracture network based on the mapped data. The code has been validated on the basis of numerous geometrical characteristics computed by use of the linear, areal sampling methods and volumetric method. Results of the linear sampling method have significant variations. So, the areal and volumetric methods are more efficient than the linear method and they are more appropriate for validation of 3D DFN (Discrete Fracture Network) codes.

Key Words
discontinuity; geometrical characteristics; areal sampling; 3DDFN code; validation

Address
Abbas Kamali Bandpey, Kourush Shahriar and Parviz Marefvand: Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran

Mostafa Sharifzadeh: Department of Mining Engineering and Metallurgy Engineering, Western Australian School of Mines (WASM), Curtin University, Australia

Abstract
This paper investigates the mechanisms of tunnel spalling and massive tunnel failures using fracture mechanics principles. The study starts with examining the fracture propagation due to tensile and shear failure mechanisms. It was found that, fundamentally, in rock masses with high compressive stresses, tensile fracture propagation is often a stable process which leads to a gradual failure. Shear fracture propagation tends to be an unstable process. Several real case observations of spalling failures and massive shear failures in boreholes, tunnels and underground roadways are shown in the paper. A number of numerical models were used to investigate the fracture mechanisms and extents in the roof/wall of a deep tunnel and in an underground coal mine roadway. The modelling was done using a unique fracture mechanics code FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that both tensile and shear fracturing may occur in the vicinity of an underground opening. Shallow spalling in the tunnel wall is believed to be caused by tensile fracturing from extensional strain although no tensile stress exists there. Massive large scale failure however is most likely to be caused by shear fracturing under high compressive stresses. The observation that tunnel spalling often starts when the hoop stress reaches 0.4*UCS has been explained in this paper by using the extension strain criterion. At this uniaxial compressive stress level, the lateral extensional strain is equivalent to the critical strain under uniaxial tension. Scale effect on UCS commonly believed by many is unlikely the dominant factor in this phenomenon.

Key Words
tunnel spalling; fracture propagation; extension strain criterion; shear fracturing; failure mechanism; FRACOD

Address
Baotang Shen: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China
2.0 Commonwealth Scientific and Industrial Research Organization (CSIRO) Energy, P.O. Box 883, Kenmore, Brisbane QLD 4069, Australia

Nick Barton: Nick Barton & Associates, Fjordveien 65c,1363 Hovik, Oslo, Norway

Abstract
Open-mode cracks could be commonly observed in layered rocks. A concept model is firstly used to explore the mechanism of the vertical cracks (VCs) in the top layer. Then the crack behaviour of the two-layer model is simulated based on a cohesive zone model (CZM) for layer interfaces and a plastic-damage model for rocks. The model indicates that the tensile stress normal to the VCs changes to compression if the crack spacing to layer thickness ratio is lower than a threshold. The results indicate that there is a threshold for interfacial shear strength that controls the crack patterns of the layered system. If the shear strength is lower than the threshold, the top layer is meshed by the VCs and interfacial cracks (ICs). When the shear strength is higher than the threshold, the top layer is meshed by the VCs and parallel cracks (PCs). If the shear strength is comparative to the threshold, a combining pattern of VCs, PCs and ICs for the top layer can be formed. The evolutions of stress distribution in the crack-bound block indicate that the ICs and PCs can reduce the load transferred for the substrate layer, and thus leads to a crack saturation state.

Key Words
interface cracks; vertical crack; parallel crack; shear strength; layered rock

Address
Xu Chang: 1.) International Joint Research Laboratory of Henan Province for Underground Space Development and Disaster Prevention, Jiaozuo, China
2.) School of Civil Engineering, Henan Polytechnic University, Jiaozuo, China

Wenya Ma, Zhenhua Li and Hui Wang: School of Civil Engineering, Henan Polytechnic University, Jiaozuo, China


Abstract
This study focused on the mechanical and hydraulic characteristics of underwater tunnels based on Mohr-Coulomb (M-C), Hoek-Brown (H-B) and generalized H-B failure criteria. An improved approach for calculating stress, displacement and plastic radius of the circular tunnel considering hydraulic-mechanical coupling was developed. The innovation of this study was that the radius-incremental-approach was reconstructed (i.e., the whole plastic zone is divided into a finite number of concentric annuli by radius), stress and displacement of each annulus were determined in terms of numerical method and Terzaghi\'s effective stress principle. The validation of the proposed approach was conducted by comparing with the results in Brown and Bray (1982) and Park and Kim (2006). In addition, the Rp-pin curve (plastic radius-internal supporting pressure curve) was obtained using the numerical iterative method, and the plastic radius of the deep-buried tunnel could be obtained by interpolation method in terms of the known value of internal supporting pressure pin. Combining with the theories in Carranza and Fairhurst (2000), the improved technique for assessing the reliability of the tunnel support was proposed.

Key Words
hydraulic-mechanical coupling; strain-softening; safety factor; finite difference method

Address
Jin-Feng Zou and Xing-Xing Wei: School of Civil Engineering, Central South University, No.22, Shaoshan South Road, Central South University Railway Campus,
Changsha, Hunan Province, People

Abstract
Compacted bentonites were chosen as the backfill material and buffer in high level nuclear waste disposal due to its high swelling pressure, high ion adsorption capacity and low permeability. It is essential to estimate the swelling pressure in design and considering the safety of the nuclear repositories. The swelling pressure model of expansive clay colloids was developed based on Gouy-Chapman diffuse double layer theory. However, the diffuse double layer model is effective in predicting low compaction dry density (low swelling pressure) for certain bentonites, and invalidation in simulating high compaction dry density (high swelling pressure). In this paper, the new relationship between nondimensional midplane potential function, u, and nondimensional distance function, Kd, were established based on the Gouy-Chapman theory by considering the variation of void ratio. The new developed model was constructed based on the published literature data of compacted Na-bentonite (MX80) and Ca-bentonite (FoCa) for sodium and calcium bentonite respectively. The proposed models were applied to re-compute swelling pressure of other compacted Na-bentonites (Kunigel-V1, Voclay, Neokunibond and GMZ) and Ca-bentonites (FEBEX, Bavaria bentonite, Bentonite S-2, Montigel bentonite) based on the reported experimental data. Results show that the predicted swelling pressure has a good agreement with the experimental swelling pressure in all cases.

Key Words
bentonite, swelling pressure, expansive soils, nuclear waste disposal

Address
Haiquan Sun: Faculty of Science, Charles University, Albertov 6, 128 43, Prague 2, Czech Republic

Abstract
Water affects the mechanical properties of coal and stress wave propagation. To comprehensively investigate the effect of water content on the properties of coal, laboratory tests including X-Ray Diffraction (XRD) analysis, P-wave test, S-wave test, static and dynamic compression test with different water contents were conducted. The compressive strength, elastic modulus and failure strain and their mechanism of coal specimen under coupled static-dynamic load with the increased water content were observed. Meanwhile, energy transmission and dissipation characteristics of a stress wave in coal specimens with different water contents under dynamic load and its relation with the failure features, such as fragmentation and fractal dimension, of coal was analyzed. Furthermore, the dynamic interpretation of water infusion to prevent coal burst based on water infusion model of coal seam roadway was provided.

Key Words
coal; water content; dynamic mechanical properties; stress wave propagation; failure features

Address
Helong Gu, Ming Tao, Jingxiao Wang and Qiyue Li: School of Resources and Safety Engineering, Central South University, Changsha, Hunan, 410083, People\'s Republic of China

Haibo Jiang: 1.) School of Resources and Safety Engineering, Central South University, Changsha, Hunan, 410083, People\'s Republic of China
2.) Safety Engineering Institute, Hunan Vocational Institute of Safety Technology, Changsha, Henan, 410151, People\'s Republic of China

Wen Wang: School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan, 454003, People\'s Republic of China

Abstract
The finite difference software Flac3D is used to study the influence of tunnel burial depth, tunnel diameter and lateral pressure coefficient of original rock stress on the stress and deformation of tunnel surrounding rock under sandstone condition. The results show that the maximum shear stress, the radius of the plastic zone and the maximum displacement in the surrounding rock increase with the increase of the diameter of the tunnel. When the lateral pressure coefficient is 1, it is most favorable for surrounding rock and lining structure, with the increase or decrease of lateral pressure coefficient, the maximum principal stress, surrounding displacement and plastic zone range of surrounding rock and lining show a sharp increase trend, the plastic zone on the lining increases with the increase of buried depth.

Key Words
water conveyance tunnel; deformation of surrounding rock; numerical simulation; the lateral pressure coefficient; buried depth

Address
Lujun Ding: College of Water Resource and Hydropower, Sichuan University, Chengdu, 610065, China

Yuhong Liu: Sichuan College of Architectural Technology, Deyang, 618000, China

Abstract
This paper presents results of a compressive investigation conducted on weathered soil stabilized with ground bottom ash (GBA) and red mud (RM). The effects of water/binder ratio, RM/GBA ratio, chemical activator (NaOH and Na2SiO3) and curing time on unconfined compressive strength of stabilized soils were examined. The results show that the water/binder ratio of 1.2 is optimum ratio at which the stabilized soils have the maximum compressive strength. For 28 days of curing, the compressive strength of soils stabilized with alkali-activated GBA and RM varies between 1.5 MPa and 4.1 MPa. The addition of GBA, RM and chemical activators enhanced strength development and the rate of strength improvement was more significant at the later age than at the early age. The potential environmental impacts of stabilized soils were also assessed. The chemical property changes of leachate from stabilized soils were analyzed in terms of pH and concentrations of hazardous elements. The observation revealed that the soil mixture with ground bottom ash and red mud proved environmentally safe.

Key Words
soil stabilization; ground bottom ash; red mud; weathered soil; compressive strength; leaching

Address
Youngsang Kim: Department of Civil Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea

My Quoc Dang: Department of Civil Engineering, Nha Trang University, 02 Nguyen Dinh Chieu St., Nha Trang, Khanh Hoa, 650000, Vietnam

Tan Manh Do: Department of Civil Engineering, Hanoi University of Mining and Geology, Duc Thang Ward, North Tu Liem District, Vietnam

Joon Kyu Lee: Department of Civil Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul, 02504, South Korea


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