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Volume 22, Number 2, July25 2020

The present article is concerned about the study of disturbances in a homogeneous nonlocal magneto-thermoelastic medium under the combined effects of hall current, rotation and two temperatures. The model under assumption has been subjected to normal force. Laplace and Fourier transform have been used for finding the solution to the field equations. The analytical expressions for conductive temperature, stress components, normal current density, transverse current density and displacement components have been obtained in the physical domain using a numerical inversion technique. The effects of hall current and nonlocal parameter on resulting quantities have been depicted graphically. Some particular cases have also been figured out from the current work. The results can be very important for the researchers working in the field of magneto-thermoelastic materials, nonlocal thermoelasticity, geophysics etc.

Key Words
thermoelasticity; nonlocality; nonlocal theory of thermoelasticity; normal force; hall current; rotation; Laplace and Fourier transform

Parveen Lata: Department of Basic and applied Sciences, Punjabi University Patiala, India

Sukhveer Singh: Punjabi University APS Neighbourhood Campus, Dehla Seehan, India

In this study a new innovative three unknowns trigonometric shear deformation theory is proposed for the buckling and vibration responses of exponentially graded sandwich plates resting on elastic mediums under various boundary conditions. The key feature of this theoretical formulation is that, in addition to considering shear deformation effect, it has only three unknowns in the displacement field as in the case of the classical plate theory (CPT), contrary to five as in the first shear deformation theory (FSDT) and higher-order shear deformation theory (HSDT). Material characteristics of the sandwich plate faces are considered to vary within the thickness direction via an exponential law distribution as a function of the volume fractions of the constituents. Equations of motion are obtained by employing Hamilton\'s principle. Numerical results for buckling and free vibration analysis of exponentially graded sandwich plates under various boundary conditions are obtained and discussed. Verification studies confirmed that the present three -unknown shear deformation theory is comparable with higher-order shear deformation theories which contain a greater number of unknowns.

Key Words
functionally graded materials; sandwich plates; a 3-unknown theory; various boundary conditions; elastic; foundations; free vibration; buckling loads

Mohamed Rabhi, Kouider Halim Benrahou and Abdeldjebbar Tounsi: Department of Civil Engineering, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria

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

Mohammed Sid Ahmed Houari: Faculty of Science and Technology, Mascara University, Mascara 29000, Algeria

Fouad Bourada: 1.) Department of Civil Engineering, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
2.) Department of Science and Technology, Tissemsilt University Center, BP 38004 Ben Hamouda, Algeria

Abdelmoumen Anis Bousahla: Multi-scale Modeling and Simulation Laboratory, University of Sidi Bel Abbes, Algeria

E.A. Adda Bedia: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia

S.R. Mahmoud: GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia

Abdelouahed Tounsi: 1.) Department of Civil Engineering, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
2.) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

The evolution of the mining-induced fracture network formed during longwall top coal caving (LTCC) has a great influence on the gas drainage, roof control, top coal recovery ratio and engineering safety of aquifers. To reveal the evolution of the mining-induced stress and fracture network formed during LTCC, the fracture network in front of the working face was observed by borehole video experiments. A discrete element model was established by the universal discrete element code (UDEC) to explore the local stress distribution. The regression relationship between the fractal dimension of the fracture network and mining stress was established. The results revealed the following: (1) The mining disturbance had the most severe impact on the borehole depth range between approximately 10 m and 25 m. (2) The distribution of fractures was related to the lithology and its integrity. The coal seam was mainly microfractures, which formed a complex fracture network. The hard rock stratum was mainly included longitudinal cracks and separated fissures. (3) Through a numerical simulation, the stress distribution in front of the mining face and the development of the fracturing of the overlying rock were obtained. There was a quadratic relationship between the fractal dimension of the fractures and the mining stress. The results obtained herein will provide a reference for engineering projects under similar geological conditions.

Key Words
longwall top coal caving; fracture network; mining-induced stress; fractal dimension; fracture connectivity

Cong Li, Jing Xie, Zhiqiang He, Guangdi Deng, Bengao Yang and Mingqing Yang: 1.) State Key Laboratory of Hydraulics and Mountain River Engineering,
College of Water Resource and Hydropower, Sichuan University, Chengdu, 610065, China
2.) MOE Key Laboratory of Deep Underground Science and Engineering, Sichuan University, Chengdu 610065, China

In this research, soil samples of the Kerman sedimentary basin, Iran, were investigated through laboratory tests such as petrography (Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF) and X-Ray Diffraction (XRD)), physical and mechanical characteristics tests. The soil in this area is dominantly CL. The petrography results showed that the dominant clay mineral is Illite. This soil has made some problems in the earth dams due to the low shear strength. In this study, a set of samples were prepared by adding different amounts of lime. Next, the petrography and strength tests at the optimum moisture content were performed. The results of SEM analysis showed substantial changes in the soil structure after the addition of lime. The primary structure was porous and granular that was changed to a uniform and solid after the lime was added. According to XRD results, dominant mineral in none stabilized soil and stabilized soil are Illite and calcite, respectively. The pozzolanic reaction resulted in the reduction of clay minerals in the stabilized samples and calcite was known as the soil hardener material that led to an increase in soil strength. An increase in the hydrated lime leads to a decrease in their maximum dry unit weight and an increase in their optimum moisture content. Furthermore, increasing the hydrated lime content enhanced the Unconfined Compressive Strength (UCS) and soil\'s optimum moisture. An increase in the strength is significantly affected by the curing time and hydrated lime contents, as the maximum compressive strength is achieved at 7% hydrated lime. Moreover, the maximum increase in the California Bearing Ratio (CBR) achieved in clay soils mixed with 8% hydrated lime.

Key Words
petrography; illite clay; physical and mechanical properties; lime additive

Ahmad Rastegarnia: Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran

Seyed Mehdi Seyed Alizadeh: Department of Petroleum Engineering, Australian College of Kuwait, West Mishref, Kuwait

Mohammad Khaleghi Esfahani: Department of Engineering Geology, University of Isfahan, Isfahan, Iran

Omid Amini: Faculty of Civil and Surveying Engineering, Graduate University of Advanced Technology, Kerman, Iran

Anatolij Sergeevich Utyuzh: I.M. Sechenov First Moscow State Medical University, Moscow, Russia

Laboratory experiments were conducted with two different soil conditions to investigate rainfall infiltration characteristics. The soil layer materials that were tested were weathered granite soil and weathered gneiss soil. Artificial rainfall of 80 mm/hr was reproduced through the use of a rainfall device, and the volumetric water content and matric suction were measured. In the case of the granite soil, the saturation velocity and the moving direction of the wetting front were fast and upward, respectively, whereas in the case of the weathered gneiss soil, the velocity and direction were slow and downward, respectively. Rainfall penetrated and saturated from the bottom to the top as the hydraulic conductivity of the granite soil was higher than the infiltration capacity of the artificial rainfall. In contrast, as the hydraulic conductivity of the gneiss soil was lower than the infiltration capacity of the rainfall, ponding occurred on the surface: part of the rainfall first infiltrated, with the remaining rainfall subsequently flowing out. The unsaturated hydraulic conductivity function of weathered soils was determined and analyzed with matric suction and the effective degree of saturation.

Key Words
infiltration; rainfall intensity; unsaturated hydraulic conductivity; weathered gneiss soil; weathered granite soil

Young-Suk Song: Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea

Seongwon Hong: Department of Safety Engineering, Korea National University of Transportation, Chungju-si, Chungbuk 27469, Korea

Laboratory determination of strength and deformation behavior of clean sands and gravels has always been challenging due to the difficulty in obtaining their undisturbed samples. An alternative solution to this problem is to develop correlations between mechanical properties of cohesionless soils and their gradation characteristics. This study presents database of 3 natural sands with 11 varying particle size gradation curves to allow investigating relationships between mean particle size, maximum and minimum void ratio, relative density and shear strength of the test soils. Direct shear tests were performed at relative densities of 50, 75 and 95% to explore the effects of gradation and density on the angle of internal friction of the modeled sand samples. It is found that the mean grain size D50 bears good correlations with void ratio range (emax - emin) and peak angle of internal friction Φ\'peak. The generated regression models are in good agreement with published literature and can be considered as reliable for natural sands in Pakistan. These empirical correlations can save considerable time and efforts involved in laboratory and field testing.

Key Words
natural sands; gradation; relative density; void ratio; direct shear test; friction angle

Mubashir Aziz: Department of Civil Engineering, National University of Computer and Emerging Sciences, Lahore, Pakistan

Calcareous soil is originated from marine biogenic sediments and weathering of carbonate rocks. The formation history for calcareous sediment includes complex physical, biological and chemical processes. It is preferably selected as the major fill materials for hydraulic reclamation and artificial island construction. Calcareous sands possess inter pores and complex shape are liable to be damaged at normal working stress level due to its fragile nature. Thus, the engineering properties of calcareous soil are greatly affected by its high compressibility and crushability. A series of triaxial shear tests were performed on calcareous sands derived from South China Sea under different test conditions. The effects of confining pressure, particle size, grading, compactness, drainage condition, and water content on the total amount of particle breakage for calcareous soil were symmetrically investigated. The test results showed that the crushing extent of calcareous sand with full gradation was smaller than that a single particle group under the same test condition. Large grains are cushioned by surrounding small particles and such micro-structure reduces the probability of breakage for well-graded sands. The increasing tendency of particle crushing for calcareous sand with a rise in confining pressure and compactness is confirmed. It is also evident that a rise in water content enhances the amount of particle breakage for calcareous sand. However, varying tendency of particle breakage with grain size is still controversial and requires further examination.

Key Words
shear strength; particle breakage; water content; triaxial test; gradation

Xinzhi Wang, Qingshan Meng and Changqi Zhu:State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics,
Chinese Academy of Sciences, Wuhan, Hubei 430071, China

Huagang Shan: Shaoxing Traffic Investment Group Co., Ltd., Shaoxing, Zhejiang 312000, China

Yang Wu:School of Civil Engineering, Guangzhou University, Guangzhou, Guangdong 510006, China

The changeable stress environment directly affect the propagation law of a stress wave. Stress wave propagation tests in sandstone with different axial stresses were carried using a modified split Hopkinson Pressure bar (SHPB) assuming the sandstone has a uniform pore distribution. Then the waveform and stress wave energy dissipation were analyzed. The results show that the stress wave exhibits the double peak phenomenon. With increasing axial stress, the intensity difference decreases exponentially and experiences first a dramatic decrease and then gentle development. The demarcation stress is σ/σc=30%, indicating that the closer to the incident end, the faster the intensity difference attenuates. Under the same axial stress, the intensity difference decreases linearly with propagation distance and its attenuation intensity factor displays a quadratic function with axial stress. With increasing propagation distance, the time difference decays linearly and its delay coefficient reflects the damage degree. The stress wave energy attenuates exponentially with propagation distance, and the relations between attenuation rate, attenuation coefficient and axial stress can be represented by the quadratic function.

Key Words
sandstone; axial stress; stress wave; waveform characterization

Yun Cheng: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China

Zhanping Song and Tong Wang: 1.) School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China
2.) Shaanxi Key Laboratory of Geotechnical and Underground Space Engineering, Xi\'an 710055, China

Jiefang Jin: School of Architectural and Surveying Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China

Tengtian Yang: 1.) Shaanxi Key Laboratory of Geotechnical and Underground Space Engineering, Xi\'an 710055, China
2.) China Railway Bridge Engineering Bureau Group Co. Ltd., Tianjin 300300, China

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