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CONTENTS
Volume 17, Number 4, March20 2019
 

Abstract
This paper presents the results of parametric analyses to compute the axial capacity of a suction pile using 2D and 3D finite element approaches. The study is intended to simplify the process of analyzing suction piles from 3D to 2D model. The research focuses on obtaining the coefficient to be applied into the 2D model in order to obtain results that are as close as possible to the 3D model. Two 2D models were used in the analysis, namely the plane strain and axisymmetric models. The analyses were performed using two actual offshore soil data of the North and West Java Indonesia. The study reveals that the simplification of model through 2D Finite Element is achievable by applying the appropriate coefficient to the stiffness parameters. The results show that the simplified model of the 2D FEA provides more conservative results (with the difference between 2% to 7%) than the 3D FEA.

Key Words
suction pile; 3D FEA; 2D FEA; simplification analysis

Address
Hendriyawan, M. Abby Primananda and Anisa Dwi Puspita: Faculty of Civil and Environmental Engineering, Institut Teknologi Bandung Jalan Ganesha 10, Bandung 40132 Indonesia

Chao Guo: 1.)Shanxi Lu\'an Mining (Group) Co.,Ltd., Changzhi, Shanxi, 046204, China
2.)College of Mining Engineering, Liaoning Technical University, Fuxin, Liaoning, 123000, China

Indra Noer Hamdhan: Faculty of Civil and Planning Engineering, Institut Teknologi Nasional Bandung, 40132, Indonesia

M. M. Tahir: UTM Construction Research Centre, Institute for Smart Infrastructure and Innovative Construction (ISIIC), Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia

Binh Thai Pham: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam

M.A. Mu\'azu: Civil Engineering Department, University of Hafr Al-Batin, Al-Jamiah, 39524, Hafr Al-Batin, Eastern Province, Kingdom of Saudi Arabia

Majid Khorami: Universidad UTE, Facultad de Arquitectura y Urbanismo, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador

Abstract
The presence of defects in nature changes the physical parameters of the rock. In this paper, by studying the rock-like specimens with conjugated fractures, the horizontal angle and length are changed, and the physical parameters and failure modes of the specimens under uniaxial compression test are analyzed and compared with the results of simulation analysis. The experimental results show that the peak strength and failure mode of the rock-like specimens are closely related to the horizontal angle. When the horizontal angle is 45o, the maximum value is reached and the tensile failure mode is obtained. The fracture length affects the germination and propagation path of the cracks. It is of great significance to study the failure modes and mechanical properties of conjugated fracture rock-like specimens to guide the support of fractured rock on site.

Key Words
rock-like material; conjugate fractures; failure mode; uniaxial compression; cracks propagation

Address
Wenbin Sun: 1.) State Key Laboratory of Mining Disaster Prevention and Control, College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, People\'s Republic of China
2.) Key Laboratory of Modern Mining Engineering, AnHui Province (Anhui University of Science and Technology),
Huainan, 232001, People\'s Republic of China

Houqian Du, Fei Zhou and Jianli Shao: State Key Laboratory of Mining Disaster Prevention and Control, College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, People\'s Republic of China

Abstract
Geological dynamic hazards during coal mining can be caused by the failure of a composite system consisting of roof rock and coal layers, subject to different loading rates due to different advancing velocities in the working face. In this paper, the uniaxial compression test simulations on the composite rock-coal layers were performed using PFC2D software and especially the effects of loading rate on the stress-strain behavior, strength characteristics and crack nucleation, propagation and coalescence in a composite layer were analyzed. In addition, considering the composite layer, the mechanisms for the advanced bore decompression in coal to prevent the geological dynamic hazards at a rapid advancing velocity of working face were explored. The uniaxial compressive strength and peak strain are found to increase with the increase of loading rate. After post-peak point, the stress-strain curve shows a steep stepped drop at a low loading rate, while the stress-strain curve exhibits a slowly progressive decrease at a high loading rate. The cracking mainly occurs within coal, and no apparent cracking is observed for rock. While at a high loading rate, the rock near the bedding plane is damaged by rapid crack propagation in coal. The cracking pattern is not a single shear zone, but exhibits as two simultaneously propagating shear zones in a \"X\" shape. Following this, the coal breaks into many pieces and the fragment size and number increase with loading rate. Whereas a low loading rate promotes the development of tensile crack, the failure pattern shows a V-shaped hybrid shear and tensile failure. The shear failure becomes dominant with an increasing loading rate. Meanwhile, with the increase of loading rate, the width of the main shear failure zone increases. Moreover, the advanced bore decompression changes the physical property and energy accumulation conditions of the composite layer, which increases the strain energy dissipation, and the occurrence possibility of geological dynamic hazards is reduced at a rapid advancing velocity of working face.

Key Words
composite rock-coal layer; loading rate; stress-strain behavior; strength and failure characteristics; advanced bore decompression

Address
Shao J. Chen, Da W. Yin, N. Jiang, F. Wang and Wei J. Guo: College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwanggang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

Abstract
The present study demonstrates the application of seismic petrophysics and amplitude versus angle (AVA) forward modeling to identify the reservoir fluids, discriminate their saturation levels and natural gas composition. Two case studies of the Lumshiwal Formation (mainly sandstone) of the Lower Cretaceous age have been studied from the Kohat Sub-basin and the Middle Indus Basin of Pakistan. The conventional angle-dependent reflection amplitudes such as P converted P (RPP) and S (RPS), S converted S (RSS) and P (RSP) and newly developed AVA attributes (deltaRPP, deltaRPs, deltaRSS and deltaRSP) ) are analyzed at different gas saturation levels in the reservoir rock. These attributes are generated by taking the differences between the water wet reflection coefficient and the reflection coefficient at unknown gas saturation. Intercept (A) and gradient (B) attributes are also computed and cross-plotted at different gas compositions and gas/water scenarios to define the AVO class of reservoir sands. The numerical simulation reveals that deltaRPP, deltaRPS, deltaRSS and deltaRSP are good indicators and able to distinguish low and high gas saturation with a high level of confidence as compared to conventional reflection amplitudes such as P-P, P-S, S-S and S-P. In A-B cross-plots, the gas lines move towards the fluid (wet) lines as the proportion of heavier gases increase in the Lumshiwal Sands. Because of the upper contacts with different sedimentary rocks (Shale/Limestone) in both wells, the same reservoir sand exhibits different response similar to AVO classes like class I and class IV. This study will help to analyze gas sands by using amplitude based attributes as direct gas indicators in further gas drilling wells in clastic successions.

Key Words
AVO modeling; fluid moduli; Indus basin; Zoeppritz equations; intercept-gradient; rock physics

Address
Mubasher Ahmad, Nisar Ahmed, Perveiz Khalid, Muhammad A. Badar, Sohail Akram, Muhammad A. Anwar and Shahid Ali: Institute of Geology, University of the Punjab, Lahore 54590, Pakistan

Mureed Hussain: Department of Marine Geology, Lasbela University of Agriculture, Water and Marine Sciences, Uthal, Lasbela, Pakistan

Azhar Mahmood: Petrophysics, Software Integrated Solution (SIS) Data Services Schlumberger, Pakistan

Anees U. Rehman: Department of Earth Sciences, Quaid-I-Azam University, Islamabad, Pakistan

Abstract
It is normal to observe the presence of numerous cracks in coal body. And it has significantly effective on the mechanical characteristics and realistic failure models of coal mass. Therefore, this paper is to investigate the influence of crack parameters on coal body by comprehensive using theoretical analysis, laboratory experiments and numerical simulation through prepared briquette specimens. Different from intact coal body possessing single peak in stress-strain curve, other specimens with crack angle can be illustrated to own double peaks. Moreover, the unconfined compressive strength (UCS) of specimens decreases and follow by increasing with the increase of crack angle. It seems to like a parabolic shape with an upward opening. And it can be demonstrated that the minimum UCS is obtained in crack angle 45o. In terms of failure types, it is interesting to note that there is a changing trend from tensile failure to tensile-shear mixing failure with tension dominant follow by shear dominant with the increase of crack angle. However, the changing characteristics of UCS and failure forms can be explained by elastic-plastic and fracture mechanics. Lastly, the results of numerical simulations are good consistent with the experimental results. It provides experimental and theoretical foundations to reveal fracture mechanism of coal body with non-penetrating single crack further.

Key Words
unconfined compressive strength; non-penetrating single crack; crack angle; failure form

Address
Huayong Lv: 1.) School of Resource and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
2.) State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China
3.) Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China

Yuesong Tang, Lingfei Zhang and Yaning Zhang: .) School of Resource and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
2.) Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China

Zhanbo Cheng: 1.) School of Resource and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
2.) Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China
3.) School of Engineering, University of Warwick, Coventry CV47AL, U.K.

Abstract
This study concluded the results of a research on the features of cement based permeation grout, based on some important grout parameters, such as the rheological properties (yield stress and viscosity), coefficient of permeability to grout (kG) and the inject ability of cement grout (N and Nc assessment), which govern the performance of cement based permeation grouting in porous media. Due to the limited knowledge of these important grout parameters and other influencing factors (filtration pressure, rate and time of injection and the grout volume) used in the field work, the application of cement based permeation grouting is still largely a trial and error process in the current practice, especially in the local construction industry. It is seen possible to use simple formulas in order to select the injection parameters and to evaluate their inter-relationship, as well as to optimize injection spacing and times with respect to injection source dimensions and in-situ permeability. The validity of spherical and cylindrical flow model was not verified by any past research works covered in the literature review. Therefore, a theoretical investigation including grout flow models and significant grout parameters for the design of permeation grouting was conducted in this study. This two grout flow models were applied for three grout mixes prepared for w/c=0.75, w/c=1.00 and w/c=1.25 in this study. The relations between injection times, radius, pump pressure and flow rate for both flow models were investigated and the results were presented. Furthermore, in order to investigate these two flow model, some rheological properties of the grout mixes, particle size distribution of the cement used in this study and some geotechnical properties of the sand used in this work were defined and presented.

Key Words
permeation grout; spherical flow model; cylindrical flow model; inject ability of grout; rate of injection

Address
Fatih Celik: Department of Civil Engineering, Faculty of Engineering, Nigde Omer Halisdemir University, 51240 Nigde, Turkey

Abstract
In underground retreating longwall coal mining, hard roof collapse is one of the most challenging safety problems for mined-out areas. Identifying precursors for hard roof collapse is of great importance for the development of warning systems related to collapse geohazards and ground control. In this case study, the Xinhe mine was chosen because it is a standard mine and the minable coal seam usually lies beneath hard strata. Real-time monitoring of hard roof collapse was performed in longwall face 5301 of the Xinhe mine using support resistance and microseismic (MS) monitoring; five hard roof collapse cases were identified. To reveal the characteristics of MS activity during hard roof collapse development and to identify its precursors, the change in MS parameters, such as MS event rate, energy release, bursting strain energy, b value and the relationships with hard roof collapse, were studied. This research indicates that some MS parameters showed irregularity before hard roof collapse. For the Xinhe coalmine, a substantial decrease in b value and a rapid increase in MS event rate were reliable hard roof collapse precursors. It is suggested that the b value has the highest predictive sensitivity, and the MS event rate has the second highest.

Key Words
hard roof collapse; microseismic monitoring; precursory parameter; support pressure

Address
Jun Wang, Jianguo Ning, Pengqi Qiu, Shang Yang and Hefu Shang: 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,579 Qianwangang Road, Qingdao, China

Abstract
The present fractional-order plasticity models for granular soil are mainly established under the triaxial compression condition, due to its difficult in analytically solving the fractional differentiation of the third stress invariant, e.g., Lode\'s angle. To solve this problem, a three dimensional fractional-order elastoplastic model based on the transformed stress method, which does not rely on the analytical solution of the Lode\'s angle, is proposed. A nonassociated plastic flow rule is derived by conducting the fractional derivative of the yielding function with respect to the stress tensor in the transformed stress space. All the model parameters can be easily determined by using laboratory test. The performance of this 3D model is then verified by simulating multi series of true triaxial test results of rockfill.

Key Words
fractional plastic flow rule; 3d stress state; transformed stress; state dependence

Address
Shunxiang Song, Yufeng Gao and Yifei Sun: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China


Abstract
The cycling impact test of red sandstone soil under different axial pressure and different impact loads are conducted to reveal the mechanical properties and energy consumption mechanism of red sandstone soil with static-dynamic coupling loading. The results show that: Under the action of different axial pressure and different impact loads, the peak stress of the specimen increases, and then tends to be stable with the times of impact. With the increase of impact times, the specific energy absorption value of the red sandstone soil specimen is increased first and then gentle development trend. When the impact loads are certain, the larger the axial pressure is, the smaller the peak value of energy absorption, which indicates that the energy utilization rate is not high under the condition of large axial pressure. Through the analysis of energy utilization, it is found that the smaller the impact load, the higher the energy utilization rate. The greater the axial pressure, the lower the energy utilization rate. when the axial pressure is large, the impact loads corresponding to the maximum values of reflectivity, transmissivity and absorptivity are the same. The relationship between reflectivity and transmissivity is negatively correlated.

Key Words
red sandstone soil; static-dynamic coupling loading; stress-strain; specific energy absorption value; energy utilization rate

Address
Tong Wang: 1.)School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China
2.) School of Resources and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China

Zhanping Song and Junbao 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

Jianyong Yang:School of Resources and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China

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

Abstract
A significant influence of the particle size distribution on the resilient behaviour of granular aggregates was usually observed in laboratory tests. However, the mechanisms underlying this phenomenon were rarely reached. In this study, a mechanistic model considering particle breakage is proposed. It is found to be the combined effects of the coefficient of uniformity and the size range between maximum and minimum particle sizes that influences the resilient modulus of granular aggregates. The resilient modulus is found to undergo reduction with evolution of particle breakage by shifting the initial particle size distribution to a broader one.

Key Words
fractional plastic flow rule; 3d stress state; transformed stress; state dependence

Address
Yifei Sun and Yufeng Gao: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,
College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China

Zhongtao Wang: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China


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