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CONTENTS
Volume 27, Number 1, October10 2021
 

Abstract
In some construction works such as multi-basement buildings, subways, deep excavation problems are encountered. In such cases, the shoring walls are used to to prevent damage to the structures next to the excavation area and to provide a safe working environment in the excavation area. In cases where a temporary excavation support is required, sheet pile walls can be more economical comparing to the other walls in the long run due to their reusability. In the present study the analyses were carried out by changing various parametric components such as the number of anchors in vertical row, horizontal and vertical spacing amongst the anchors, anchor angle and excavation depth in LARSSEN type sheet piles constructed temporarily in medium-dense sand. In the analyses, the trapezoidal horizontal earth pressure envelope recommended by FHWA (1999) since the stress concentration occured at the anchor locations. Besides the limit values recommended by FHWA (1999) and BS (1989) was used in the analyses. In total 35488 different sheet pile wall geometry configurations were investigated. According to research results, the lowest costs occur when the horizontal spacing amongst the anchors is 3 m and the angle of the anchors with the horizontal is 150. The lowest costs were obtained when the vertical distance of the uppermost anchor to the ground surface is 3 m. Sheet pile sections with optimum cost were modeled in Plaxis 2D to run displacement analyses. Findings showed that the wall displacements were within the allowable limits commonly used in the literature.

Key Words
earth pressure; finite element analysis; multi-anchored sheet pile; optimum design; temporary wall

Address
Mehmet F. Yazici and Siddika N. Keskin: Department of Civil Engineering, Suleyman Demirel University Graduate School of Natural and Applied Sciences,Suleyman Demirel Street, Cunur, 32260 Isparta, Turkey


Abstract
Microbial induced calcium carbonate precipitation (MICP), a sustainable and effective soil improvement method, has experienced a burgeoning development in recent years. It is a bio-mediated method that uses the metabolic process of bacteria to cause CaCO3 precipitation in the pore space of the soil. This technique has a large potential in the geotechnical engineering field to enhance soil properties, including mitigation of liquefaction, control of suffusion, etc. Multi-scale studies, from microstructure investigations (microscopic imaging and related rising techniques at micron-scale), to macroscopic tests (lab-based physical, chemical and mechanical tests from centimeter to meter), to in-situ trials (kilometers), have been done to study the mechanisms and efficiency of MICP. In this article, results obtained in recent years from various testing methods (conventional tests including unconfined compression tests, triaxial and oedometric tests, centrifuge tests, shear wave velocity and permeability measurements, as well as microscopic imaging) were selected, presented, analyzed and summarized, in order to be used as reference for future studies. Though results obtained in various studies are rather scattered, owning to the different experimental conditions, general conclusions can be given: when the CaCO3 content (CCC) increases, the unconfined compression strength increases (up to 1.4 MPa for CCC=5%) as well as the shear wave velocity (more than 1-fold increase in V_s for each 1% CaCO3 precipitated), and the permeability decreases (with a drop limited to less than 3 orders of magnitude). Concerning the mechanical behavior of MICP treated soil, an increase in the peak properties, an indefinite increase in friction angle and a large increase in cohesion were obtained. When the soil was subjected to cyclic/dynamic loadings, lower pore pressure generation, reduced strains, and increasing number of cycles to reach liquefaction were concluded. It is important to note that the formation of CaCO3 results in an increase in the dry density of the samples, which adds to the bonding of particles and may play a major part in the improvement of the mechanical properties of soil, such as peak maximum deviator, resistance to liquefaction, etc.

Key Words
biocementation; engineering properties; microstructures; MICP

Address
Tong Yu and Jean-Marie Fleureau: Laboratoire de mécanique des Sols, Structures et Matériaux, CNRS UMR 8579, Université Paris Saclay, CentraleSupelec, 8-10 Rue Joliot Curie, 91190 Gif-sur-Yvette, France

Hanene Souli: Laboratoire de Tribologie et Dynamique des Systemes, CNRS UMR 5513, Universite de Lyon, CentraleLyon-ENISE, 58 Rue Jean Parot, 42023 Saint Etienne Cedex, France

Yoan Pechaud:Laboratoire Géomatériaux et Environnement, Université Gustave Eiffel, 77454 Marne-la-Vallée Cedex 2, France

Abstract
The force change characteristics of gravel side support structures during gangue heaping can provide useful information about roadway stability in a new non-pillar-mining approach—noncoal pillar mining with automatically formed gob-side entry (NMAFG). Considering the dynamic shock and static stacking phenomena during gangue heaping, the coefficient of restitution and Janssen model are introduced into the theoretical analysis. Analytical results show that the impact force decreased with increasing gangue heaping height under dynamic shock, while under static stacking, the gangue extrusion force first increased sharply, then increased slowly and stabilized, and the final force was unrelated to the gangue heaping height. Field monitoring was conducted to verify the rationality of the pattern obtained from theoretical analysis. The gangue support structure lateral stress from field monitoring can be divided into two periods. In Period I, the peak value at the lower monitoring point was greater than that at any other point. The lowest sensor was subjected to the greatest impact, at 59.09 kN. In Period II, the stress value first rapidly increased, then slowly increased and stabilized. The final force was unrelated to the gangue height. The sensors at #2 (highest position), #4 (middle position), and #6 (lowest position) measured 31.91 kN, 44.82 kN and 38.19 kN, respectively. The analysis confirmed the variation characteristics of the impact force and extrusion force.

Key Words
extrusion force; gangue heaping; impact force; non-pillar-mining approach

Address
Jianning Liu: 1.) State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology - Beijing, Beijing, 100083, China
2.) ShanXiYinFeng S&T CO., LTD, Taiyuan, 030000, China
3.) Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya, Barcelona Tech, 08034, Spain

Manchao He, Shilin Hou and Jun Yang: State Key Laboratory for Geomechanics and Deep Underground Engineering,
China University of Mining and Technology - Beijing, Beijing, 100083, China

Zhen Zhu: 1.)State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology - Beijing, Beijing, 100083, China
2.) School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China


Abstract
The present paper is aimed at studying the effect of gravity on the general model of the equations of generalized magneto-thermo-micro-stretch for a homogeneous isotropic elastic half-space solid. The problem is in the context of the Green-Lindsay (G-L) theories, as well as the coupled theory (CT). Finite element method is used to obtain the expressions for the displacement components, the force stresses, the temperature, the couple stresses, and the micro-stress distribution. Comparisons are made with the results in the presence and absence of gravity and magnetic field of a particular case for the generalized micropolar thermo-elasticity elastic medium (without micro-stretch constants) between the three theories.

Key Words
finite element method; gravity; magnetic field; thermo-microstretch; thermal relaxation

Address
Mohamed I. A. Othman: Department of Mathematics, Faculty of Science, Zagazig University, P.O. Box 44519, Zagazig, Egypt

Ibrahim A. Abbas: 1.) Nonlinear Analysis and Applied Mathematics Research Group (NAAM), King Abdulaziz University, Saudi Arabia
2.) Department of Mathematics, Faculty of Science, Sohag University, Sohag, Egypt

S. M. Abo-Dahab: 1.) Department of Mathematics, Faculty of Science, South Valley University, Qena 83523, Egypt
2.) Department of Computer Science, Faculty of Computers and Information, Luxor University, Egypt


Abstract
The movement and collapse of roof strata in underground longwall mining is a key trigger factor for the occurrence of dynamic disasters. An accuracy estimation of roof strata mechanical state is critical for the prediction and control of dynamic disaster, such as coal burst and coal-and-gas outburst. An analytical approach is proposed in this work to estimate the mechanical state of roof strata in underground longwall mining. To do so, the unit width of roof strata is considered as a beam structure. A system of 4 simulations differential equations is proposed with 4 local slope data as input parameters to derive the mechanical expression of suspending roof strata. A differential evolution algorithm is further adapted to solve the equation system. In addition, a set of verification tests is carried out to showcase the feasibility and robustness of the proposed method. The results show that the average relative errors of 10 independent tests reach a high accuracy, which is less than 1% for the strata mechanical state control parameters. By using the estimated results, the slope, bending moment and shear force of suspending strata are derived. Moreover, the slope data sampling strategy is also devised. The parameters bound determination method is also proposed to ensure the calculation convergence. The local slope based analytical method proposed in this paper is a feasible approach to estimate the mechanical state of suspended roof strata before first weighting.

Key Words
analytical model; beam slope; differential evolution; local acceleration monitoring; longwall miningstrata mechanical state

Address
Jie Zhang, Yansong Zhang, Wenzhou Du and Houwang Wang: College of Safety and Environmental Engineering, Shandong University of Science and Technology, Qingdao, 266590, China

Mehdi Serati: School of Civil Engineering, The University of Queensland, Brisbane, QLD, 4072, Australia

Abstract
ased on concept of Pareto-optimal solution and game theory associated with Nash non-cooperative and cooperative solution, a mathematical procedure is presented for optimum design of axially loaded pile structure. The decision making situation is formulated as a constrained optimization problem with two objectives of contradictory in nature. The factor of safety is taken as the design variable. Geometric constraints are considered by imposing a lower and upper bound on the design variable. Two objectives considered are: maximization of ultimate load carrying capacity of pile and minimization of associated cost. The generation of Pareto-optimal solution and methodology based on game theory concept is described. The design problem is mathematically formulated as two-person game. To obtain the starting point of game, Nash non-cooperative solution or Nash equilibrium solution is evaluated for an irrational play. For cooperative game, a negotiation model is developed for overall benefit of all players. Game is terminated when the optimal trade-off between two objectives is reached with maximization of supercriterion. Two numerical examples of practical interest are solved to demonstrate the methodology.

Key Words
game theory; Nash cooperative game; Nash non-cooperative solution; pareto-optimal; pile structure; supercriterion

Address
Shantanu Hati and Sarat K. Panda: Department of Civil Engineering, Indian Institute of Technology (ISM) Dhanbad, India

Abstract
Considering the continuous development of gob side entry driving technology, the influence of roof fracture on coal pillar is difficult to be accurately predicted. In order to explore the fracture structure characteristics of the overlying multi thick hard rock strata and its influence on coal pillars, the stress analysis tests of coal pillars under different roof fracture positions were designed. Different fracture positions of immediate roof and high-level thick hard rock were simulated by different corresponding positions of goaf, coal pillar edge line and rotary fixture line. According to four experimental design schemes, the strain distribution of coal mine goaf under different roof fracture combination positions was obtained. By analyzing the results of digital speckle pattern experiment, the distribution range and form of stress above coal pillar and low level thick hard rock are obtained, which provides theoretical basis for studying the whole process of coal pillar fracture.

Key Words
coal pillar; digital speckle; gob-side entry driving; roof fracture

Address
Shankun Zhao and Yin Wang: 1.) School of Energy and Mining Engineering, China University of Mining and Technology Beijing,Ding 11, Xueyuan Road, Haidian District, Beijing, PR China
2.) Safety Technology Branch, CCTEG China Coal Research Institute, # 5, Qingniangoudong Road, Chaoyang District, Beijing, PR China

Qiru Sui, Cong Cao, Xuecheng Wang, Chunlai Wang and Daming Zhao: School of Energy and Mining Engineering, China University of Mining and Technology Beijing,Ding 11, Xueyuan Road, Haidian District, Beijing, PR China

Yang Zhao:Safety Technology Branch, CCTEG China Coal Research Institute, # 5, Qingniangoudong Road, Chaoyang District, Beijing, PR China

Abstract
Discontinuities are known to have a significant impact on the engineering characteristics of the rock masses, governing their potential failure pattern, increasing their deformation, and reducing their strength. In particular, the impact of non-persistent joints on the strength and failure mechanism of rock mass needs to be investigated further. The impact of different flaw geometrical characteristics such as flaw inclination, flaw length, flaw aperture, and flaw filling on uniaxial compressive strength of specimens has not been investigated thoroughly. In this paper, a series of uniaxial compression tests were conducted on cylindrical specimens containing an open central flaw. The effect of different parameters such as flaw inclination, flaw length, flaw aperture, and filling on the uniaxial compressive strength of specimens have been investigated through laboratory experiments. Response Surface Methodology (RSM) is adopted to analyze the impact of flaw parameters on the compressive strength of the constructed samples. The results of the experiments show that flaw inclination and flaw length have a significant impact on the peak strength of the samples, meaning that strength increases by growing of flaw angle and decreases by increasing of flaw length. In addition, at a low flaw length, aperture affects the UCS significantly, while by increasing flaw length, its effect decreases dramatically, and strength drops at a flaw inclination of 45 degrees. Conversely, at a higher flaw length, by increasing flaw inclination, the UCS increases constantly. It also has been observed that changing the flaw aperture had no important effect on the peak strength.

Key Words
filling material; open flaw; RSM; strength anisotropy; UCS

Address
Javad Karimi: School of Mining Engineering, College of Engineering, University of Tehran, 1439957131 Tehran, Iran

Mostafa Asadizadeh:1.) Department of Mining Engineering, Hamedan University of Technology, Mardom Street, Hamedan, 65155 -579, Iran
2.) Department of Mining and Nuclear Engineering, Missouri University of Science and Technology, Rolla, MO 65409, U.S.A

Mohammad Farouq Hossaini: School of Minerals and Energy Resources Engineering, University of New South Wales, Sydney, Australia

Samuel Nowak and Taghi Sherizadeh: Department of Mining and Nuclear Engineering, Missouri University of Science and Technology, Rolla, MO 65409, U.S.A.

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