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CONTENTS
Volume 26, Number 6, September25 2021
 

Abstract
The study focuses on the characterization of asphalt pavement mechanical properties containing two different sizes of irradiated plastic waste polyethylene terephthalate (IP) using gamma irradiation technique as fine aggregate substitutes in a 14mm asphaltic concrete wearing (ACW14). Response Surface Methodology (RSM) was employed in this study to determine the relationships between three independent factors (IP6, IP16, and bitumen content) on mix volumetric and Marshall Characteristics. To fabricate the samples, 0 to 1%, 1 to 2.5%, and 4 to 6% all by weight of aggregate particles were used as percentages for IP6, IP16, and bitumen contents, respectively. RSM statistical analysis demonstrates a high coefficient of correlation (R2) of 0.9700, 0.9896, 0.9869, and 0.8946 for the responses bulk density (BSD), void in the mix (VIM), stability, and flow, respectively. The high correlation coefficient shows that the models developed are in reasonable agreement with the analyzed experimental outcomes. Investigation of the individual effect of the independent factors elucidates that interactions between the three factors influenced all the responses. In view of the outcomes accomplished 0.55%, 1.77%, and 4.63% were observed to be the optimized contents for IP6, IP16, and bitumen contents, respectively.

Key Words
asphalt concrete; gamma irradiation; mechanical properties; pavement; plastic waste; response surface methodology (RSM)

Address
Aliyu Usman: 1.) Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia
2.) Department of Civil Engineering, Ahmadu Bello University, Zaria, P.M.B 1045 Zaria, Kaduna State, Nigeria

Muslich H. Sutanto: 1.) Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia
2.) Institute of Self-Sustainable Building, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia

Madzlan Napia and bdulnaser M. Al-Sabaeei: Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia

Salah E. Zoorob: Construction and Building Materials Program, Kuwait Institute for Scientific Research, P. O. Box 24885 Safat, 13109 Kuwait

Abstract
The mechanical coupling between a fiber-optic cable and surrounding soil is a significant concern in distributed strain sensing-based geotechnical monitoring. In this study, the cable–soil mechanical coupling is quantitatively evaluated using elastoplastic pullout interaction modeling. Data from a laboratory pullout test performed on a 2-mm-diameter tight-buffered cable buried in a sand–gravel–clay mixture are used to validate a documented elastoplastic pullout model. By using cable axial strain profiles and cable–soil relative displacement measurements, two new indices are proposed to quantify the cable–soil mechanical coupling based on this model, in addition to the common interface shear strength proxy. A parametric study is conducted to investigate how the geometrical and mechanical properties of the cable and the cable–soil interface characteristics affect the two indices. Relating the parametric analysis to practical considerations, recommendations are made as to the design of strain-sensing cables for use in field and laboratory scenarios. Furthermore, modification to the elastoplastic pullout model is discussed to better simulate cable–soil pullout interactions. This study demonstrates that the elastoplastic pullout model can be effective in assessing cable–soil interface behavior and mechanical coupling.

Key Words
distributed strain sensing; elastoplastic model; geotechnical monitoring; interface behavior; pullout test

Address
Su-Ping Liu: 1.) School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
2.) School of Civil Engineering, University of Leeds, Leeds LS2 9JT, U.K.

Bin Shi and Kai Gu: School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China

Cheng-Cheng Zhang: 1.)School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
2.) Nanjing University High-Tech Institute at Suzhou, Suzhou 215123, China

Pei-Zhi Zhuang: 1.) School of Civil Engineering, University of Leeds, Leeds LS2 9JT, U.K.
2.) School of Civil Engineering, University of Leeds, Leeds LS2 9JT, U.K.

Abstract
Attempt has been proved to be effective that surrounding rock reinforcement is emphasized simultaneously considering displacement release in weak rock tunnels. In this study, the calculation formulas for mechanical parameters of bolt-reinforced rocks are provided using the homogenization method and the supporting characteristic curve is divided into three stages with proposing the corresponding stiffness equations. The mechanical model for bolted-reinforced rock-yielding supports interaction is then established and coupled solutions for displacements and stresses around tunnels considering bolt reinforcement and yielding effects are provided. Furthermore, parametric investigations on the influences of rockbolts and yielding supports are carried out. Results show that (1) rock displacement gradually decreases as the rockbolt length increases. However, when rockbolt length becomes large enough, the further improvement of rock displacement will not be obvious by still increasing their length. (2) Both rock displacement and plastic zone of tunnel decrease with the increase of rockbolt radius. There exists the highest utilization of rockbolts corresponding to a certain rockbolt radius. (3) Also, the rock displacement and plastic zone of tunnel decrease as installation density of rockbolts including circumferential space and longitudinal space increases. Under the condition prescribed, this decreasing trend becomes sharper and the improvement is more evident. (4) Larger yielding displacement or stiffness parameter leads to smaller support pressure, but greater plastic radius of tunnel. The optimal yielding displacement and stiffness parameters need to be determined through a comprehensive investigation combining rock properties, support characteristics and tunnel design requirements.

Key Words
analytical solution; deep tunnel; novel supporting concept; rockbolt reinforcement; yielding supports

Address
Su Qin, Kui Wu and Zhushan Shao: 1.) Xi'an University of Architecture and Technology, Xi'an 710055, China
2.) Shaanxi Key Lab of Geotechnical and Underground Space Engineering (XAUAT), Xi'an 710055, China


Abstract
Fracture characteristics and damage mechanism of rock mass under cyclic loading and unloading is one of the basic research topics of rock mechanics. To study the deformation and fracture response characteristics of brittle hard rock under cyclic disturbance loading, cyclic loading and unloading tests were carried out at different loading and unloading rates, and the stress-strain curve shapes, modulus elastic, critical damage value, fracture characteristics and fractal dimension laws were analyzed. The results show that the loading and unloading effect has significant influence on stress-strain curve shape and fatigue life. The hysteresis loop is overdistributed from sparse to dense with increasing loading and unloading rate and fatigue life is significantly reduced. The loading and unloading action has a phased control effect on peak strength with a first increases and then decreases. The rock has a stable rupture type with a brittle strength about 1.16~31.07% of peak strength, and brittle strength indicates a brittle fracture. With increasing cycle number, loading elastic modulus and unloading elastic modulus firstly increase sharply then increase linearly and finally decrease gradually. The critical damage factor has an approximately linear relationship with loading and unloading rates. The rock mainly occurs oblique shear through and tension through ruptures, and the failure types changes from shear failure to tension failure excessively with increasing loading and unloading rate. The increased loading and unloading rate weakens the end constraint effect, the greater the loading and unloading rate, the more obvious the fragmentation degree, and the more significant the fragments uniformity. The fractal dimension is logarithmic function related to loading and unloading rate.

Key Words
fractal dimension; fracture response characteristic; hard rock; loading and unloading effect; peak strength

Address
Yun Cheng and Zhanping Song: 1.) School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China
2.) Shaanxi Key Lab of Geotechnical and Underground Space Engineering, Xi'an 710055, China

Wanxue Song, Zekun Zhang, Tong Wang and Kuisheng Wang: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China

Shuguang Li: 1.) Shaanxi Key Lab of Geotechnical and Underground Space Engineering, Xi'an 710055, China
2.) Post-Doctoral Research Workstation, China Railway 20th Bureau Group Co. Ltd., Xi'an, 710016, China

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

Abstract
The distribution pattern of flaws has a significant impact on the mechanical behavior of the rock. To understand the cracking mechanism of the rock with intersecting flaws, the cracking behavior of sandstone containing two intersecting flaws under uniaxial compression was investigated through laboratory tests and particle flow code (PFC2D). The strength and failure characteristics of sandstone with intersecting flaws were studied. Subsequently, the evolution of the stress fields and displacement fields were analyzed, and the cracking mechanism of intersecting flaws was discussed. The results showed that the peak stress and average modulus decrease with increasing intersecting angle α of intersecting flaws in both experiments and numerical simulation. The experimental peak stress shows an increasing tendency, while the experimental average modulus first increases and then decreases with increasing direction angle β, which is slightly different from simulation results. The cracking mode of the intersecting flaws was determined by angles α and β. Specifically, when α and β were small, the main fracture surfaces formed at the inner and outer tips of one flaw. When α and β were large, the main fracture surfaces formed at the outer tips of the two flaws. The variation in the high tensile stress zone with α and β is the essential reason for the change in cracking modes with α and β. In addition, a new type of displacement field (defined as DF_IV) related to crack initiation was found. In this type of displacement field, the displacement difference is the main cause of cracking.

Key Words
damage evolution; displacement field; intersecting flaws; PFC2D; sandstone; stress field

Address
Fei Xiong: 1.)School of Civil Engineering, Chongqing University, Chongqing 400045, China
2.) State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China

Xinrong Li and Xiaohan Zhou: 1.) School of Civil Engineering, Chongqing University, Chongqing 400045, China
2.) State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
3.) National Joint Engineering Research Center of Geohazards Prevention in The Reservoir Areas,Chongqing University, Chongqing 400045, China

Dongshuang Liu, Bin Xu, Yafeng Han: School of Civil Engineering, Chongqing University, Chongqing 400045, China

Chunmei He: College of Architectural Engineering, Neijiang Normal University, Neijiang 641100, China

Zijuan Wang: School of Management Science and Engineering, Chongqing Technology and Business University, Chongqing 400067, China

Abstract
Laboratory tests were carried out to study the effect of temperature on the long-term strength of rock salt, the creep modulus was defined and the evolution equation of creep thermal damage of rock salt was established. Based on the creep test results of rock salt, a nonlinear thermal visco-plastic damage model considering the influence of temperature damage and expressing the accelerated creep behavior of rock salt is established. According to the construction method of nonlinear creep model, a new nonlinear visco-elastic-plastic creep damage model considering the influence of temperature (nonlinear T-VEPD creep model) is established by concatenating the nonlinear thermal visco-plastic damage model with the Burgers creep model. And then the parameter inversion identification of the model, the results show that the model can well describe the creep properties of rock salt. The finite difference expression of nonlinear T-VEPD creep model is derived by using finite difference theory. The dynamic link calculation program (.dll) of the model is obtained by using the programming and FLAC3D secondary development interface, and then the creep model is verified by laboratory test simulation.

Key Words
creep; damage; nonlinear creep model; rock salt

Address
Tianzhu Huang, Jianlin Li: 1.) College of Civil Engineering and Architecture, China Three Gorges University, Yichang City, Hubei Province, 443002, China
2.) Key Laboratory of Geological Hazards on Three Gorges Reservoir Area of Ministry of Education, China Three Gorges University, Yichang City, Hubei Province, 443002, China

Baoyun Zhao: 1.) Graduate Office, Chongqing University of Science and Technology, Chongqing, 401331, China
2.) School of Civil Engineering and Architecture, Chongqing University of Science and Technology, Chongqing, 401331, China


Abstract
Crack initiation, propagation and coalescence, induced by mining stress disturbance are the direct causes of engineering geological hazards which posed a great threat to the safety of coal mining and the stability of engineering rock mass. With the aid of Mining-Induced Stress Test System and Acoustic Emission(AE) monitoring system, the uniaxial compression test of prefabricated large-size double-hole specimens were constructed. The field mining height, the borehole diameter and borehole spacing were reduced in equal proportion. The strength, AE characteristics and fracture evolution process of specimens under different conditions were systematically studied and the dimensionless damage risk coefficient was constructed based on the current research. The formula for the theoretical calculation of reasonable borehole spacing for pressure relief is further revised. Results show that: compared with the complete specimen, the peak strength, elastic modulus and crack initiation stress of the double-hole specimens are significantly decreased. Basically the increase of the hole spacing shows an increasing trend first and then it is decreased. The first tensile crack in the specimen with holes, is initiated close to the hole and it is propagated along the direction of the maximum principal stress. The secondary tensile crack and shear crack are produced with the increase of load and finally the tensile failure mode is formed. An obvious corresponding relationship is shown by the stress curve and AE energy curve. The shear crack always accompanied with a large energy emission rate. The specimens show obvious brittle failure, and internal cracks of the specimens create sudden changes in the rate of AE energy curve and energy accumulation curve. The dimensionless damage risk coefficient can quantitatively characterize the stability of surrounding rock, the revised calculation formula accomplished the field requirements. The research results strengthen the understanding of the mechanism of crack initiation and provide theoretical support for improving the reliability of engineering disaster prediction.

Key Words
crack initiation stress; dimensionless damage risk coefficient; fracture evolution; large-size double-hole specimens; strength characteristics

Address
Fanbao Meng, Zhijie Wen, uolin Jing, Pubudu Dilan Welgama and Jing Huang: 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

Baotang Shen: 1.) 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
2.) CSIRO Energy, QCAT, 1 Technology Court, Pullenvale, Qld 4069, Australia

Abstract
Considering the modified power function form of material parameters, the wave equation of porous functionally graded material plate was established according to Hamilton principle based on the concept of physical medium surface and Reddy high-order shear deformed plate theory. The dispersion relations of five different elastic waves were obtained by using eigenvalue method. Then, the effects of functional gradient index and porosity on the propagation characteristics of five kinds of elastic waves are discussed. Finally, it is found that the pore volume fraction can simultaneously characterize the stiffness strengthening effect and stiffness softening effect, which depends on the power law index.

Key Words
functionally graded material; physical neutral surface concept; wave propagation; porosity

Address
Hang Xiao: College of Mechanical and Electrical Engineering, Changsha University, Changsha 410022, China

Kunming Yan: China Aviation Changsha Design and Research Co. Ltd, Changsha, 410018, China

Guilin She: College of Mechanical and Vehicle Engineering, Chongqing University, Chongqing 400044, China

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