Techno Press
Tp_Editing System.E (TES.E)
Login Search
You logged in as

gae
 
CONTENTS
Volume 28, Number 5, March10 2022
 


Abstract
The hydro-mechanical (HM) two-way sequential coupling in the TOUGH2-FLAC3D linking algorithm is validated completely and successfully in both M to H and H to M directions, which are initiated by mechanical surface loading for geomechanical validation and hydrological groundwater pumping for hydrogeological validation, respectively. For such complete and successful validation, a TOUGH2-FLAC3D linked numerical model is developed first by adopting the TOUGH2-FLAC3D linking algorithm, which uses the two-way (fixed-stress split) sequential coupling scheme and the implicit backward time stepping method. Two geomechanical and two hydrogeological validation problems are then simulated using the linked numerical model together with basic validation strategies and prerequisites. The second geomechanical and second hydrogeological validation problems are also associated with the Mandel effect and the Noordbergum and Rhade effects, respectively, which are three phenomenally well-known but numerically challenging HM effects. Finally, sequentially coupled numerical solutions are compared with either analytical solutions (verification) or fully coupled numerical solutions (benchmarking). In all the four validation problems, they show almost perfect to extremely or very good agreement. In addition, the second geomechanical validation problem clearly displays the Mandel effect and suggests a proper or minimum geometrical ratio of the height to the width for the rectangular domain to maximize agreement between the numerical and analytical solutions. In the meantime, the second hydrogeological validation problem clearly displays the Noordbergum and Rhade effects and implies that the HM two-way sequential coupling scheme used in the linked numerical model is as rigorous as the HM two-way full coupling scheme used in a fully coupled numerical model.

Key Words
geomechanical validation; hydrogeological validation; hydro-mechanical two-way sequential coupling; Mandel effect; Noordbergum effect; Rhade effect; TOUGH2-FLAC3D linking algorithm

Address
Sungho Lee: School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea
Jai-Yong Park: Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea
Jung-Hwi Kihm :Department of Fire and Disaster Prevention, Jungwon University, Goesan-Gun 28024, Republic of Korea
Jun-Mo Kim: School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea;
GeoLab, Seoul 08787, Republic of Korea

Abstract
Numerical assessment of the dynamic stability behavior of nonlocal beams rested on elastic foundation has been provided in the present research. The beam is made of fucntional graded (FG) porous material and is exposed to thermal and humid environments. It is also consiered that the beam is subjected to axial periodic mechanical load which especific exitation frequency leading to its instability behavior. Beam modeling has been performed via a two-variable theory developed for thick beams. Then, nonlocal elasticity has been used to establish the governing equation which are solved via Chebyshev-Ritz-Bolotin method. Temperature and moisture variation showed notable effects on stability boundaries of the beam. Also, the stability boundaries are affected by the amount of porosities inside the material.

Key Words
beam theory; dynamic stability; nonlocal elasticity; porosities; thermal load

Address
Mouayed H.Z. Al-Toki: 1Middle Technical University, Technical College, Baghdad, Iraq
Hayder A.K. Ali, Nadhim M. Faleh and Raad M. Fenjan: Al Mustansiriah University, Engineering Collage P.O. Box 46049, Bab Muadum, Baghdad 10001, Iraq


Abstract
In the mine exploitation stage; one of the critical issues is the stability assessment of post-pillars. The instability of post-pillars leads to serious safety hazards in mining operations. The focus of this study is to assess the stability of post-pillars in the 130# stope in the central ore body at Trepça hard rock mine by employing both conventional (i.e., critical span curve) and numerical methods (i.e., FLAC3D). Moreover, a new numerical based index (i.e., Pillar Yield Ratio-PYR) was proposed. The aim of PYR index is to determine a border line between stable, potentially unstable, and failure state of post-pillars at a specific mine site. The critical value of pillar width to height ratio is 2.5 for deep production stopes (e.g., > 800 m). Results showed that pillar size, mining height and mining depth significantly have affected the post-pillar stability. The reliability of numerical based index (i.e., PYR) is verified based on empirical underground pillar stability graph developed by Lunder, 1994. The proposed pillar yield ratio index and pillar stability graph can be used as a design tool in new mining areas at Trepça hard rock mine and for other situations with similar geotechnical conditions.

Key Words
FLAC3D software; hard rock mine post-pillar design; underground excavation

Address
Gzim Ibishi: Department of Mining Engineering, Faculty of Geosciences,
Mitrovica Isa Boletini University, 40000, Mitrovica, Kosovo
Melih Geniş : Department of Mining Engineering, Faculty of Engineering,
Zonguldak Bülent Ecevit University, 67100, Zonguldak, Turkey
Mahmut Yavuz: Department of Mining Engineering, Faculty of Architecture and Engineering,
Eskişehir Osmangazi University, 26040, Eskişehir, Turkey

Abstract
In the present study, the effects of thermal loading on the buckling and resonance frequency of graphene platelets (GPL) reinforced nano-composites are examined. Functionally graded (FG) material properties are considered in thickness direction for the thermal responses of the composite. The equivalent material properties are obtained using Halphin-Tsai nano-mechanical model for composite layers. Moreover, the effects of nano-scale sizes are taken into account, employing functionally modified couple stress (FMCS) parameter. In this regard, for the first time, it is demonstrated that at certain values of GPL weight fraction, thermal buckling occurs. In obtaining results of vibrational behavior, both analytical solution and deep neural network (DNN) methods are used. The DNN method needs low computational costs to predict the resonance behavior. A comprehensive parametric study is conducted to indicate the effects of several geometrical, material, and loading conditions on the vibrational and buckling behavior of cylindrical shell structures made of GPL-nanocomposites. It is shown that the effect of temperature change on the occurrence of buckling is vital while it has a negligible impact on the resonance frequency of the structure. Moreover, the size-dependency of the results is demonstrated, and it cannot be neglected in nano-scales.

Key Words
graphene nano-platelet; modified couple stress parameter; resonance frequency; thermal buckling; various thermal distributions

Address
Yunrui Yan: College of Material science and Nanoengineering, Rice University, Houston 77005, Texas, USA

Abstract
Cavity expansion is a classical problem in the field of solid mechanics with a wide range of applications in geotechnical and petroleum engineering. A drained solution is developed for cylindrical cavity expansion in anisotropic soils under biaxial in-situ stresses using a K0-based anisotropic modified Cam-clay model (K0-AMCC). The problem is formulated by solving differential equations using an auxiliary variable, which provides analytical expressions for the volume and four stress components of the soil around the cylindrical cavity. The solution is validated by comparisons with existing well-developed solutions. The results show that the present solution well captures the cavity expansion responses in anisotropic soils under biaxial in-situ stresses, and removes limiting assumptions that the cylindrical cavity expands under uniform in-situ stress in isotropic soils. The elastic-plastic boundary of the expanding cylindrical cavity in K0-consolidated anisotropic soils under biaxial in-situ stresses is a circle rather than an ellipse in isotropic soils, and the mathematical proof is provided in detail.

Key Words
anisotropic; biaxial in-situ stresses; circle; drained; elastic-plastic boundary; K0-consolidated

Address
Xiaobing Cao: Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China
Junran Zhang: Henan Province Key Laboratory of Geomechanics and Structural Engineering, North China University of Water Resources and Electric Power, Zhengzhou, Henan 450046, China
De'an Sun: Department of Civil Engineering, Shanghai University, Shanghai 200444, China

Abstract
In recent years, geotextile-encased gravel columns (usually called stone columns) have become a popular method to increasing soil shear strength, decreasing the settlement, acceleration of the rate of consolidation, reducing the liquefaction potential and increasing the bearing capacity of foundations. The behavior of improved loose base-soil with gravel columns under shear loading and the shear stress-horizontal displacement curves got from large scale direct shear test are of great importance in understanding the performance of this method. In the present study, by performing 36 large-scale direct shear tests on sandy base-soil with different fine-content of zero to 30% in both not improved and improved with gravel columns, the effect of the presence of gravel columns in the loose soils were investigated. The results were used to predict the shear stress-horizontal displacement curve of these samples using support vector machines (SVM). Variables such as the non-plastic fine content of base-soil (FC), the area replacement ratio of the gravel column (Arr), the geotextile encasement and the normal stress on the sample were effective factors in the shear stress-horizontal displacement curve of the samples. The training and testing data of the model showed higher power of SVM compared to multilayer perceptron (MLP) neural network in predicting shear stress- horizontal displacement curve. After ensuring the accuracy of the model evaluation, by introducing different samples to the model, the effect of different variables on the maximum shear stress of the samples was investigated. The results showed that by adding a gravel column and increasing the Arr, the friction angle (o) and cohesion (c) of the samples increase. This increase is less in base-soil with more FC, and in a proportion of the same Arr, with increasing FC, internal friction angle and cohesion decreases.

Key Words
geotextile; gravel columns; shear strength; silty-sand; support vector machines

Address
Reza Dinarvand and Alireza Ardakani: Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran

Abstract
This research work deals with the development of air pluviation method for preparing uniform sand specimens for conducting large scale laboratory testing. Simulating real field conditions and to get reliable results, air pluviation method is highly desirable. This paper presents a special technique called air pluviation or sand raining technique for achieving uniform relative density. The apparatus is accompanied by a hopper, shutters with different orifice sizes and numbers and set of sieves. Before using this apparatus, calibration curves are drawn for relative density against different height of fall (H) and shutter sizes. From these calibration curves, corresponding to the desired relative density of 60%, the shutter size of 13mm and height of fall of 457.2 mm, are selected and maintained throughout the pluviation process. The density obtained from the mobile pluviator is then verified using the Dynamic Cone Penetrometer (DCP) test where the soil is poured in the box using defined shutter size and fall height. The results obtained from the DCP test are averaged as 60+0.5 which was desirable. The mobile pluviator used in this research is also capable of obtaining relative densities up to 90%. The instrument is validated using experimental and numerical approach. In numerical study, Plaxis 3D software is used in which the soil mass is defined by 10-Node tetrahedral elements and 6-Node plate is used to simulate plate behavior in the validation phase. The results obtained from numerical approach were compared with that of experimental one which showed very close correlation.

Key Words
cohesionless soil; DCP; mobile pluviator; relative density

Address
Irfan Jamil, Irshad Ahmad, Wali Ullah, Muhammad Junaid and Shahid Ali Khan: Department of Civil Engineering, University of Engineering & Technology, Peshawar, Pakistan

Abstract
Ground displacements caused by the construction of overlapping twin shield tunnels with small turning radius are complex, especially under special geological conditions of construction. To investigate the ground displacements caused due to shield machines in the unique calcareous sand layers in Israel for the first time and determine the main factors affecting the ground displacements, field monitoring, laboratory geological analysis, theoretical calculations, and parameter studies were adopted. By using rod extensometers, inclinometers, total stations, and automatic segment-displacement monitors, subsurface tunneling-induced displacement, surface settlement, and displacement of the down-track tunnel segments caused by the construction of an up-track tunnel were analyzed. The up-track tunnel and the down-track tunnel pass through different stratum, resulting in different construction parameters and ground displacements. The laws of variation of thrust and torque, soil pressure in the chamber, excavated soil quantity, synchronous grouting pressure, and grout volume of the two tunnels from parallel to fully overlapping orientations were compared. The thrust and torque of the shield in the fine sand are larger than those in the Kurkar layer, and the grouting amount in fine sand is unstable. According to fuzzy statistics and Gaussian curve fitting of the shield tunneling speed, the tunneling speed in the Kurkar stratum is twice that in the fine-sand stratum.

Key Words
calcareous sand stratum; geological characteristics; ground displacement; parametric study; shield tunneling

Address
Weiqiang Qi, Zhiyong Yang, Yusheng Jiang, Xing Yang and Xiaokang Shao: School of Mechanics and Civil Engineering, China University of Mining and Technology-Beijinig, Ding, No. 11 Xueyuan Road,
Haidian District, Beijing, 100083, P.R. China
Hongbin An: China Railway 12th Bureau Group Co., Ltd., No. 19 Renmin South Road, Xiaodian District, Taiyuan, Shanxi, 030000, P.R. China


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2022 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-2-736-6800 (SCS, EAS, WAS, ANR) +82-42-828-7995 (GAE, SEM, SSS, CAC) Fax : +82-2-736-6801, Email: info@techno-press.com