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CONTENTS
Volume 20, Number 6, March25 2020
 

Abstract
The prediction of the ground conditions ahead of a tunnel face is very important, especially for tunnel boring machine (TBM) tunneling, because encountering unexpected anomalies during tunnel excavation can cause a considerable loss of time and money. Several prediction techniques, such as BEAM, TSP, and GPR, have been suggested. However, these methods have various shortcomings, such as low accuracy and low resolution. Most studies on electrical resistivity tomography surveys have been conducted using numerical simulation programs, but laboratory experiments were just a few. Furthermore, most studies of scaled model tests on electrical resistivity tomography were conducted only on the ground surface, which is a different environment as compared to that of mechanized tunneling. This study performed a laboratory experimental test to extend and verify a prediction method proposed by Lee et al., which used electrical resistivity tomography to predict the ground conditions ahead of a tunnel face in TBM tunneling environments. The results showed that the modified dipole-dipole array is better than the other arrays in terms of predicting the location and shape of the anomalies ahead of the tunnel face. Having longer upper and lower borehole lengths led to better accuracy of the survey. However, the number and length of boreholes should be properly controlled according to the field environments in practice. Finally, a modified and verified technique to predict the ground conditions ahead of a tunnel face during TBM tunneling is proposed.

Key Words
electrical resistivity tomography; experimental test; electrode array; prediction method; tunnel boring machine

Address
Kang-Hyun Lee: Research Institute, Korea Expressway Corporation, 208-96, Dongbu-daero 922beon-gil, Hwaseong-si, Gyeonggi-do, Korea

Jin-Ho Park and In-Mo Lee: School of Civil, Environmental and Architectural Engineering, Korea University, 02841 145 Anam-ro, Seongbuk-gu, Seoul, 02841, Korea

Jeongjun Park: Korea Railroad Research Institute,176, Cheoldobangmulgwan-ro, Uiwang-si, Gyeonggi-do, Korea

Seok-Won Lee: Division of Civil and Environmental Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Korea


Abstract
Based on the movement characteristics of overlying strata with gangue backfilling, the compression test of gangue is designed. The deformation characterristics of gangue is obtained based on the different Talbot index. The deformation has a logarithmic growth trend, including sharp deformation stage, linear deformation stage, rheological stage, and the resistance to deformation changes in different stages. The more advantageous Talbot gradation index is obtained to control the surface subsidence. On the basis of similarity simulation test with gangue backfilling, the characteristics of roof failure and the evolution of the supporting force are analyzed. In the early stage of gangue backfilling, beam structure damage directly occurs at the roof, and the layer is separated from the overlying rock. As the working face advances, the crack arch of the basic roof is generated, and the separation layer is closed. Due to the supporting effect of filling gangue, the stress concentration in gangue backfilling stope is relatively mild. Based on the equivalent mining height model of gangue backfilling stope, the relationship between full ratio and mining height is obtained. It is necessary to ensure that the gradation of filling gangue meets the Talbot distribution of n=0.5, and the full ratio meets the protection grade requirements of surface buildings.

Key Words
mining under village; compression test of filling gangue; Talbot gradation index; gangue backfilling similarity simulation test; full ratio

Address
Changxiang Wang, Baotang Shen, Juntao Chen, Weixin Tong, Zhe Jiang, Yin Liu and Yangyang Li: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.) State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, China


Abstract
In the Kingdom of Saudi Arabia, the shallower depth of the earth\'s crust is composed of loose dune or beach sand with soluble salts. The expansive behavior of salt bearing soil, fluctuation of ground water table and extreme environmental conditions offer a variety of geotechnical problems affecting safety and serviceability of the infrastructure built on it. Despite spending money, time and other resources on repair and rehabilitation, no significant attention is paid to explore the root causes of excessive differential settlement and cracking to these facilities. The scientific solution required to ensure safety and serviceability of the constructed infrastructure is to improve the strength and durability properties of the supporting ground. In this study, shredded plastic is employed as a low cost and locally available additive to improve strength characteristics of the desert sand. The study shows a remarkable increase in the shear strength and normal settlement of the soil. A seven (07) degree increase in angle of internal friction is achieved by adding 0.4 percent of the shredded plastic additive. The effect of different proportions and sizes of the plastic strips is also investigated to obtain optimum values. Such a long-lived solution will seek to reduce maintenance and repair costs of the infrastructure facilities laid on problematic soil along with reduction of environmental pollutants.

Key Words
loose sand; geotechnical investigation; shredded plastic; shear strength; angle of internal friction

Address
Zaheer Abbas Kazmi: Department of Civil & Construction Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia

Abstract
In recent years, Nano-technology significantly invaded the field of Geotechnical engineering, particularly in soil stabilisation techniques. Stabilisation of weak soil is envisioned to modify various soil characteristics by the addition of natural or synthetic materials into the virgin soil. In the present study, laboratory experiments were executed to investigate the influence of nano-silica particles in the consistency limits, compressive strength of the soft clay blended with cement. The results revealed that the high compressibility behaviour of soft clay modified to medium-stiff condition with fewer dosages of cement and nano-silica. The mechanism behind the strength development is verified with the previous researches as well as from Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction test (XRD) and Scanning Electron Microscopy (SEM) analysis. Based on the results, the presence of nano-silica in soft clay blended with cement has a positive effect on the behaviour of soil. This technique proves to be very economical and less detrimental to the environment.

Key Words
cement; nano-silica; soil stabilisation; soft clay; strength improvement

Address
Geethu Thomas and Kodi Rangaswamy: Department of Civil Engineering, National Institute of Technology, Calicut, Kerala, India

Abstract
The long-term stability of rock engineering is significantly affected by the time-dependent deformation behavior of rock, which is an important mechanical property of rock for engineering design. Although the hard rocks show small creep deformation, it cannot be ignored under high-stress condition during deep excavation. The inner mechanism of creep is complicated, therefore, it is necessary to investigate the relationship between microscopic creep mechanism and the macro creep behavior of rock. Microscopic numerical modeling of sandstone creep was performed in the investigation. A numerical sandstone sample was generated and Parallel Bond contact and Burger\'s contact model were assigned to the contacts between particles in DEM simulation. Sensitivity analysis of the microscopic creep parameters was conducted to explore how microscopic parameters affect the macroscopic creep deformation. The results show that the microscopic creep parameters have linear correlations with the corresponding macroscopic creep parameters, whereas the friction coefficient shows power function with peak strength and Young\'s modulus, respectively. Moreover, the microscopic parameters were calibrated. The creep modeling curve is in good agreement with the verification test result. Finally, the creep curves under one-step loading and multi-step loading were compared. This investigation can act as a helpful reference for modeling rock creep behavior from a microscopic mechanism perspective.

Key Words
hard sandstone; creep simulation; particle flow code; parallel bond model; Burger\'s model

Address
Wen-Bin Guo: 1.) Inner Mongolia Key Laboratory of Mining Pressure and Strata Control, Hulunbeir University, Hulunbeir 021008, China
2.) College of Engineering and Technology, Hulunbeir University, Hulunbeir 021008, China

Bo Hu: 1.)Inner Mongolia Key Laboratory of Mining Pressure and Strata Control, Hulunbeir University, Hulunbeir 021008, China
2.) State Key Laboratory for Geomechanics and Deep Underground Engineering,
China University of Mining and Technology, Xuzhou 221116, China

Jian-Long Cheng: State Key Laboratory of Geohazard Prevention and Geoenvironment Protection,
Chengdu University of Technology, Chengdu 610059, China

Bei-Fang Wang: State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing 100011, China


Abstract
The paper represents an optimization algorithm for reinforced concrete retaining wall design. The proposed method, called Rao-3 optimization algorithm, is a recently developed algorithm. The total weight of the steel and concrete, which are used for constructing the retaining wall, were chosen as the objective function. Building Code Requirements for Structural Concrete (ACI 318-05) and Rankine\'s theory for lateral earth pressure were considered for structural and geotechnical design, respectively. Number of the design variables are 12. Eight of those express the geometrical dimensions of the wall and four of those express the steel reinforcement of the wall. The safety against overturning, sliding and bearing capacity failure were regarded as the geotechnical constraints. The safety against bending and shear failure, minimum and maximum areas of reinforcement, development lengths of steel reinforcement were regarded as structural constraints. The performance of proposed algorithm was evaluated with two design examples.

Key Words
design optimization; Rao-3 algorithm; retaining wall; metaheuristic; weight optimization

Address
Elif N. Kalemci and S. Banu Ikizler: Department of Civil Engineering, Karadeniz Technical University, Trabzon, 61080, Turkey

Abstract
Oil and natural gas reserves have been recognised abundantly in clayey rich rock formations in deep costal reservoirs. It is necessary to understand the sedimentary history of those reservoir rocks to well explore these natural resources. This work designs a group of laboratory experiments to mimic the physical process of the sedimentary clay-rich rock formation. It presents characterisation results of the physical properties of the artificial clayey rocks synthesized from illite clay, quartz sand and brine water by high-pressure consolidation tests. Special focus is given on the effects of illite clay content and high-stress consolidation on the physical properties. Multi-step loaded consolidation experiments were carried out with stress up to 35 MPa on mixtures constituting of the illite clay, quartz sand and brine water with five initial illite clay contents (w=85%, 70%, 55%, 40% and 25%). Compressibility and void ratio were characterised throughout the physical compaction process of the mixtures constituting of five illite clay contents and their water permeability was measured as well. Results show that the applied stress induces a great reduction of clayey rock void ratio. Illite clay contents has a significant influence on the compressibility, void ratio and the permeability of the physically synthesized clayey rocks. There is a critical illite clay content w=70% that induces the minimum void ratio in the physically synthesised clayey rocks. The SEM study indicates, in the high-pressure synthesised clayey rocks with high illite clay contents, the illite clay minerals are located in layers and serve as the material matrix, and the quartz minerals fill in the inter-mineral pores or are embedded in the illite clay matrix. The arrangements of the minerals in microscale originate the structural anisotropy of the high-pressure synthesised clayey rock. The test findings can give an intuitive physical understanding of the deep-buried clayey rock basins in energy reservoirs.

Key Words
artificial clayey rocks; property characterisation; low permeability; clay content; porosity reduction

Address
Taogen Liu: 1.) School of Civil Engineering and Architectural Engineering, Nanchang Institute of Technology, 330029 Nanchang, China
2.) Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, College of Resources and Civil Engineering, Northeastern University, Shenyang, 110819, China
3.) University of Lille, LaMcube (FR2016), 59650, Villeneuve d\'Ascq, France

Ling Li: 1.) School of Civil Engineering and Architectural Engineering, Nanchang Institute of Technology, 330029 Nanchang, China
2.) University of Lille, LaMcube (FR2016), 59650, Villeneuve d\'Ascq, France

Zaobao Liu, Shouyi Xie and Jianfu Shao: 1.) Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines,
College of Resources and Civil Engineering, Northeastern University, Shenyang, 110819, China
2.) University of Lille, LaMcube (FR2016), 59650, Villeneuve d\'Ascq, France

Abstract
An understanding of the influence of MR (Magmatic Rock) thickness on the surrounding rock behaviors is essential for the prevention and management of dynamic disasters in coal mining. In this study, we used FLC3D to study the breaking and instability laws of surrounding rock with different MR thicknesses in terms of strata movement, stress and energy. The mechanism of dynamic disasters was revealed. The results show that the thicker the MR is, (1) the smaller the subsidence of the overlying strata is, but the subsidence span of the overlying strata become wider, and the corresponding displacement deformation value of the basin edge become smaller. (2) the slower the growth rate of abutment pressure in front of the working face is, but the peak value is smaller, and the influence range is larger. The peak value decreases rapidly after the breaking, and the stress concentration coefficient is maintained at about 1.31. (3) the slower the peak energy in front of coal wall, but the range of energy concentration increases (isoline \"O\" type energy circle). Finally, a case study was conducted to verify the disaster-causing mechanism. We anticipate that the research findings presented herein can assist in the control of dynamic hazards.

Key Words
strata behaviors; dynamic hazards; numerical simulation; rock break; coal mine

Address
Yanchao Xue: School of Resources & Civil Engineering, Northeastern University, Shenyang 110819, China

Wenbin Sun: College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

Quansen Wu: Department of Chemistry and Chemical Engineering, Jining University, Qufu 273100, China


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