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Volume 22, Number 5, September10 2020

In this study, the application of conventional cubic law to a deep depth condition was experimentally evaluated. Moreover, a modified equation for estimating the rock permeability at a deep depth was suggested using precise hydraulic tests and an effect analysis according to the vertical stress, pore water pressure and fracture roughness. The experimental apparatus which enabled the generation of high pore water pressure (< 10 MPa) and vertical stress (< 20 MPa) was manufactured, and the surface roughness of a cylindrical rock sample was quantitatively analyzed by means of 3D (three-dimensional) laser scanning. Experimental data of the injected pore water pressure and outflow rate obtained through the hydraulic test were applied to the cubic law equation, which was used to estimate the permeability of rock fracture. The rock permeability was estimated under various pressure (vertical stress and pore water pressure) and geometry (roughness) conditions. Finally, an empirical formula was proposed by considering nonlinear flow behavior; the formula can be applied to evaluations of changes of rock permeability levels in deep underground facility such as nuclear waste disposal repository with high vertical stress and pore water pressure levels.

Key Words
deep depth; rock permeability; high vertical stress; high pore water pressure; roughness; nonlinear flow; underground facility; nuclear waste disposal repository

Hangbok Lee and Chan Park: Center for Deep Subsurface Research, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea

Tae-Min Oh: Department of Civil and Environmental Engineering, Pusan National University, Busan 46241, Republic of Korea

A uniaxial compression test was performed to analyse the mechanical properties and macroscale and mesoscale failure mechanisms of sandstone with pyrite concretions. The effect of the pyrite concretions on the evolution of macroscale cracks in the sandstone was further investigated through numerical simulations with Particle Flow Code in 2D (PFC2D). The results revealed that pyrite concretions substantially influence the mechanical properties and macroscale and mesoscale failure characteristics of sandstone. During the initial loading stage, significant stress concentrations occurred around the edges of the pyrite concretion accompanied by the preferential generation of cracks. Meanwhile, the events and cumulative energy counts of the acoustic emission (AE) signal increased rapidly because of friction sliding between the concretion and sandstone matrix. As the axial stress increased, the degree of the stress concentration remained relatively unchanged around the edges of the concretions. The cracks continued growing rapidly around the edges of the concretions and gradually expanded toward the centre of the sample. During this stage, the AE events and cumulative energy counts increased quite slowly. As the axial stress approached the peak strength of the sandstone, the cracks that developed around the edges of the concretion started to merge with cracks that propagated at the top-left and bottom-right corners of the sample. This crack evolution ultimately resulted in the shear failure of the sandstone sample around the edges of the pyrite concretions.

Key Words
pyrite concretion; mechanical properties; failure mechanics; acoustic emission; discrete element method

Shao J. Chen, Meng Z. Ren and Da W. Yin: College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, China

Feng Wang: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, China
2.) Key Laboratory of Safety and High-efficiency Coal Mining, Ministry of Education,
Anhui University of Science and Technology, Huainan, Anhui 232001, China

Deng H. Chen: Key Laboratory of Safety and High-efficiency Coal Mining, Ministry of Education, Anhui University of Science and Technology, Huainan, Anhui 232001, China

In this paper, practical predictive models for soil shear strength parameters are proposed. As cohesion and internal friction angle are of essential shear strength parameters in any geotechnical studies, we try to predict them via artificial neural network (ANN) and neuro-imperialism approaches. The proposed models was based on the result of a series of consolidated undrained triaxial tests were conducted on reinforced sandy soil. The experimental program surveys the increase in internal friction angle of sandy soil due to addition of polypropylene fibers with different lengths and percentages. According to the result of the experimental study, the most important parameters impact on internal friction angle i.e., fiber percentage, fiber length, deviator stress, and pore water pressure were selected as predictive model inputs. The inputs were used to construct several ANN and neuro-imperialism models and a series of statistical indices were calculated to evaluate the prediction accuracy of the developed models. Both simulation results and the values of computed indices confirm that the newly-proposed neuro-imperialism model performs noticeably better comparing to the proposed ANN model. While neuro-imperialism model has training and test error values of 0.068 and 0.094, respectively, ANN model give error values of 0.083 for training sets and 0.26 for testing sets. Therefore, the neuro-imperialism can provide a new applicable model to effectively predict the internal friction angle of fiber-reinforced sandy soil.

Key Words
shear strength; reinforced-soil; artificial neural network; neuro-imperialism

Danial Jahed Armaghani: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam

Fatemeh Mirzaei: Department of Civil Engineering, Bu-Ali Sina University, Hamedan, Iran

Ali Toghroli: Department of Civil Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran

Ali Shariati: 1.) Division of Computational Mathematics and Engineering, Institute for Computational Science,
Ton Duc Thang University, Ho Chi Minh City 758307, Vietnam
2.) Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City 758307, Vietnam

In this study, dynamics responses of advanced composite plates resting variable elastic foundations via a quasi-3D theory are developed using an analytical approach. This higher shear deformation theory (HSDT) is included the shear deformation theory and effect stretching that has five unknowns, which is even inferior to normal deformation theories found literature and other theories. The quasi-three-dimensional (quasi-3D) theory accounts for a parabolic distribution of the transverse shear deformation and satisfies the zero traction boundary conditions on the surfaces of the advanced composite plate without needing shear correction factors. The plates assumed to be rest on two-parameter elastic foundations, the Winkler parameter is supposed to be constant but the Pasternak parameter varies along the long side of the plate with three distributions (linear, parabolic and sinusoidal). The material properties of the advanced composite plates gradually vary through the thickness according to two distribution models (power law and Mori-Tanaka). Governing differential equations and associated boundary conditions for dynamics responses of the advanced composite plates are derived using the Hamilton principle and are solved by using an analytical solution of Navier\'s technique. The present results and validations of our modal with literature are presented that permitted to demonstrate the accuracy of the present quasi-3D theory to predict the effect of variables elastic foundation on dynamics responses of advanced composite plates.

Key Words
dynamics responses; advanced composite plates; quasi-3D theory; variables elastic foundations

Mokhtar Nebab and Hassen Ait Atmane: 1.) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
2.) Department of Civil Engineering, Faculty of Civil Engineering and Architecture, University Hassiba Benbouali of Chlef, Algeria

Soumia Benguediab: 1.) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
2.) Department of Civil and Hydraulic Engineering, Faculty of Technology, Dr. Tahar Moulay University of Saida,
BP 138 Cité En-Nasr 20000 Saida, Algeria

Fabrice Bernard: NSA Rennes, France

Tunnels are one of the most important constructions in civil engineering. The damage to these structures caused enormous costs. Therefore, the safe and economic design of these structures has long been considered. However, both applied loads on the tunnels as well as the resistance of the structural members are naturally uncertain parameters, hence, the design of these structures requires considering the probabilistic approaches. This study aims to determine the load and resistant factors of lining tunnels concerning the earthquake extreme events limit state function. For this purpose, tunnels that have been designed according to the previous design codes (AASHTO Tunnel LRFD 2017) and using reliability analysis, the optimum reliability of these structures for different loading scenarios is determined. In this paper, the tunnel is considered circular. Finally, the proper load and resistance factors are calculated corresponding to the obtained target reliability. Based on the performed calibration earthquake extreme events limit state function, the result of this study can be recommended to AASHTO Tunnel LRFD 2017.

Key Words
structural reliability; tunnel; load and resistance factor design (LRFD); code calibration; seismic design

Mohammad Azadi and Mohammadreza Mohammadi: Department of Civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin 1477893855, Iran

S. Hooman Ghasemi: 1.) Department of Civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin 1477893855, Iran
2.) Department of Civil and Environmental Engineering, Washington State University, U.S.A.

This paper presents a study on the undrained shear strength (su) of various sands treated with a biopolymer by employing an extensive series of laboratory fall-cone penetration values covered a range of about 15 mm to 25 mm. In the tests, two sizes (0.15 mm-0.30 mm, and 1.0 mm-2.0 mm) and shapes (rounded, angular) of sand grains, Xanthan gum (XG), and distilled water were used. The XG biopolymer in 0.0%, 1.0%, 2.0%, and 3.0% by dry weight were mixed separately with four different sands, and water. The tests results obtained at the same water content revealed an increase in the su values at different levels with an increase in the XG content. Treating the sands with the XG biopolymer addition was concluded to have a greater efficacy on finer and more angular grains than coarser and more rounded grains in the samples. Overall, the present study indicates that different amount of the XG biopolymer has an important potential to be utilized for increasing the su values of samples with various size/shape of sand grains and water content.

Key Words
fall-cone; xanthan gum; sand; size; shape

Ali Firat Cabalar: Department of Civil Engineering, University of Gaziantep, Gaziantep 27310, Turkey

Suleyman Demir: Department of Civil Engineering, Kilis 7 Aralik University, Kilis 79000, Turkey

The double-lane arrangement model is frequently used in underground coal mines because it is beneficial to improve the mining efficiency of the working face. When the double-lane arrangement is used, the service time of the reserved roadway increases by twice, which causes several difficulties for the maintenance of the roadway. Given the severe non-uniform deformation of the reserved roadway in the Buertai Coal Mine, the stress distribution law in the mining area, the failure characteristics of roadway and the control effect of support resistance (SR) were systematically studied through on-site monitoring, FLAC 3D numerical simulation, mechanical model analysis. The research shows that the deformation and failure of the reserved roadway mainly manifested as asymmetrical roof sag and floor heave in the region behind the working face, and the roof dripping phenomenon occurred in the severe roof sag area. After the coal is mined out, the stress adjustment around goaf will happen to some extent. For example, the magnitude, direction, and confining pressure ratio of the principal stress at different positions will change. Under the influence of high-stress rotation, the plastic zone of the weak surrounding rock is expanded asymmetrically, which finally leads to the asymmetric failure of roadway. The existing roadway support has a limited effect on the control of the stress field and plastic zone, i.e., the anchor cable reinforcement cannot fully control the roadway deformation under given conditions. Based on obtained results, using roadway grouting and advanced hydraulic support during the secondary mining of the panel 22205 is proposed to ensure roadway safety. This study provides a reference for the stability control of roadway with similar geological conditions.

Key Words
reserved roadway; asymmetric deformation; stress distribution; plastic zone; surrounding rock control

Chen Li, Zheng Wu and Wenlong Zhang: School of Energy & Mining Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

Yanhua Sun: School of Civil Engineering, Guizhou University of Engineering Science, Bijie, 551700, China

Chun Zhu: School of Earth Sciences and Engineering, Hohai University, Nanjing, 210098, China

Xiaohu Zhang: 1.)School of Civil Engineering, Guizhou University of Engineering Science, Bijie, 551700, China
2.) State Key Laboratory for Geomechanics & Deep Underground Engineering, Beijing, 100083, China

Natural rock mass contains defects of different shapes, usually filled with inclusions such as clay or gravel. The presence of inclusions affects the failure characteristics and mechanical properties of rock mass. In this study, the strength and failure characteristics of rock with inclusions were studied using the particle flow code under uniaxial compression. The results show that the presence of inclusions not only improves the mechanical properties of rock with defects but also increases the bearing capacity of rock. Circular inclusion has the most obvious effect on improving model strength. The inclusions affect the stress distribution, development of initial crack, change in crack propagation characteristics, and failure mode of rock. In defect models, concentration area of the maximum tensile stress is generated at the top and bottom of defect, and the maximum compressive stress is distributed on the left and right sides of defect. In filled models, the tensile stress and compressive stress are uniformly distributed. Failing mode of defect models is mainly tensile failure, while that of filled models is mainly shear failure.

Key Words
inclusions; different shapes; strength characteristics; fracture evolution; numerical simulation

Zhi G. Xia and Shao J. Chen: State Key Laboratory of Mine Disaster Prevention and Control,
Shandong University of Science and Technology, Qingdao, 266590, China

Xing Z. Liu: School of Civil Engineering, Ludong University, Yantai, 264025, China

Run Sun: Yantai Institute of Metrology, Yantai, 264025, China

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