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CONTENTS
Volume 22, Number 3, August10 2020
 

Abstract
Reutilization of solid waste such as Tire Derived Aggregate (TDA) and mixing it with soft soil for backfill material not only reduces the required volume of backfill soil (i.e., sand-mining procedures; reinforcement), but also preserves the environment from pollution by recycling. TDA is a widely-used material that has a good track record for improving sustainable construction. This paper attempted to investigate the performance of Kaolin-TDA mixtures as a backfill material underneath a strip footing and close to a retaining wall. For this purpose, different types of TDA i.e., powdery, shredded, small-size granular (1-4 mm) and large-size granular (5-8 mm), were mixed with Kaolin at 0, 20, 40, and 60% by weight. Static surcharge load with the rate of 10 kPa per min was applied on the strip footing until the failure of footing happened. The behaviour of samples K80-G (1-4 mm) 20 and K80-G (5-8 mm) 20 were identical to that of pure Kaolin, except that the maximum footing stress had grown by roughly three times (300-310 kPa). Therefore, it can be concluded that the total flexibility of the backfill and shear strength of the strip footing have been increased by adding the TDA. The results indicate that, a significant increase in the failure vertical stress of the footing is observed at the optimum mixture content. In addition, the TDA increases the elasticity behaviour of the backfill.

Key Words
kaolin; tire derived aggregate (TDA); strip foundation; optimum mixture; backfill settlement; wall displacement

Address
Ali Arefnia: 1.) Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran
2.) Department of Geotechnics & Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia

Ali Dehghanbanadaki: 1.) Department of Civil Engineering, Damavand Branch, Islamic Azad University, Damavand, Iran
2.) Research Center of Concrete and Asphalt, Damavand Brach, Islamic Azad University, Damavand, Iran

Khairul Anuar Kassim and Kamarudin Ahmad: Department of Geotechnics & Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia


Abstract
Slope reliability analysis and risk assessment for spatially variable soils under rainfall infiltration are important subjects but they have not been well addressed. This lack of study may in part be due to the multiple and diverse evaluation indexes and the low computational efficiency of Monte-Carlo simulations. To remedy this, this paper proposes a highly efficient computational method for investigating random field problems for slopes. First, the probability density evolution method (PDEM) is introduced. This method has high computational efficiency and does not need the tens of thousands of numerical simulation samples required by other methods. Second, the influence of rainfall on slope reliability is investigated, where the reliability is calculated from based on the safety factor curves during the rainfall. Finally, the uncertainty of the sliding mass for the slope random field problem is analyzed. Slope failure consequences are considered to be directly correlated with the sliding mass. Calculations showed that the mass that slides is smaller than the potential sliding mass (shallow surface sliding in rainfall). Sliding mass-based risk assessment is both needed and feasible for engineered slope design. The efficient PDEM is recommended for problems requiring lengthy calculations such as random field problems coupled with rainfall infiltration.

Key Words
slope risk assessment; rainfall-induced slope failure; random fields; spatially variable soil; probability density evolution method

Address
Liuyuan Zhao: 1.) Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China
2.) PowerChina Huadong Engineering Corporation Limited, Hangzhou 311122, China

Yu Huang and Guanbao Ye: 1.) Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China
2.) Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, Shanghai 200092, China

Min Xiong: Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
Unconfined compression test (UCT) is widely conducted in laboratories to evaluate the mechanical behavior of frozen soils. However, its results are sensitive to the initial conditions of sample creation by freezing as well as the end-surface conditions during loading of the specimen into the apparatus for testing. This work compared ice samples prepared by three-dimensional and one-dimensional freezing. The latter created more-homogenous ice samples containing fewer entrapped air bubbles or air nuclei, leading to relatively stable UCT results. Three end-surface conditions were compared for UCT on ice specimens made by one-dimensional freezing. Steel disc cap with embedded rubber was found most appropriate for UCT. Three frozen materials (ice, frozen sand, and frozen silt) showed different failure patterns, which were classified as brittle failure and ductile failure. Ice and frozen sand showed strain-softening, while frozen silt showed strain-hardening. Subsequent investigation considered the influence of fines content on the unconfined compression behavior of frozen soil mixtures with fines contents of 0-100%. The mixtures showed a brittle-to-ductile transition of failure patterns at 10%-20% fines content.

Key Words
unconfined compression test; one-dimensional freezing; ice; frozen soil mixture; stress-strain behavior; fines content

Address
Hyunwoo Jin, Jangguen Lee, Li Zhuang and Byung Hyun Ryu: Extreme Engineering Research Center, Korea Institute of Civil Engineering and Building Technology 283, Goyangdae-ro, Ilsanseo-Gu, Goyang-Si, Gyeonggi-Do, 10223, Republic of Korea


Abstract
Expansive soils are renowned for their swelling-shrinkage property and these volumetric changes resultantly cause huge damage to civil infrastructures. Likewise, subgrades consisting of expansive soils instigate serviceability failures in pavements across various regions of Pakistan and worldwide. This study presents the use of polypropylene fibers to improve the engineering properties of a local swelling soil. The moisture-density relationship, unconfined compressive strength (UCS) and elastic modulus (E50), California bearing ratio (CBR) and one-dimensional consolidation behavior of the soil treated with 0, 0.2, 0.4, 0.6 and 0.8% fibers have been investigated in this study. It is found that the maximum dry density of reinforced soil slightly decreased by 2.8% due to replacement of heavier soil particles by light-weight fibers and the optimum moisture content remained almost unaffected due to non-absorbent nature of the fibers. A significant improvement has been observed in UCS (an increase of 279%), E50 (an increase of 113.6%) and CBR value (an increase of 94.4% under unsoaked and an increase of 55.6% under soaked conditions) of the soil reinforced with 0.4% fibers, thereby providing a better quality subgrade for the construction of pavements on such soils. Free swell and swell pressure of the soil also significantly reduced (94.4% and 87.9%, respectively) with the addition of 0.8% fibers and eventually converting the medium swelling soil to a low swelling class. Similarly, the compression and rebound indices also reduced by 69.9% and 88%, respectively with fiber inclusion of 0.8%. From the experimental evaluations, it emerges that polypropylene fiber has great potential as a low cost and sustainable stabilizing material for widespread swelling soils.

Key Words
swelling soils; polypropylene fiber; soil improvement; unconfined compressive strength; California bearing ratio; free swell; swell pressure; compressibility

Address
Muhammad Ali and Muhammad Hamza: Department of Technology, The University of Lahore, Lahore, Pakistan

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

Muhammad Faizan Madni: Department of Civil Engineering, The University of Lahore, Lahore, Pakistan

Abstract
To achieve a wide suction range, the low suction was imposed on compacted silt specimens by the axis translation technique and the high suction was imposed by the vapor equilibrium technique with saturated salt solutions. Firstly, the results of soil water retention tests on compacted silt show that the soil water retention curves in terms of gravimetric water content versus suction relation are independent of the dry density or void ratio in a high suction range. Therefore, triaxial tests on compacted silt with constant water content at high suctions can be considered as that with constant suction. Secondly, the results of triaxial shear tests on unsaturated compacted silt with the initial void ratio of about 0.75 show a strain-hardening behavior with a slightly shear contraction and then strain-softening behavior with an obviously dilation. As the imposed suction increases, the shear strength increases up to a peak value and then decreases when the suction is beyond a special value corresponding to the peak shear strength. The residual strength increases to fair value and those at high suctions are almost independent of imposed suctions. In addition, the contribution of suction to the strength of compacted silt would not diminish even in a high suction range.

Key Words
unsaturated soil; soil water retention behavior; triaxial test; high suction

Address
Bo Chen and De\'an Sun: College of Civil Engineering and Architecture, Quzhou University, 78 Jiuhua Road, Quzhou 324000, China

Xiuheng Ding: Shanghai Civil Engineering Co. LTD of CREC, 237 Yangjiangsan Road, Shanghai 200436, China

You Gao: School of Civil and Environmental Engineering, Ningbo University, 818 Fenghua Road, Ningbo 315211, China

Haihao Yu:Laboratory of Geomechnics and Geotechnical Engineering, Guilin University of Technology, 12 Jian Gan Road, Guilin, 541004, China

Abstract
The interaction between the frozen soil and building structures deteriorates with the increasing temperature. A nuclear magnetic resonance (NMR) stratification test was conducted with respect to the unfrozen water content on the interface and a shear test was conducted on the frozen soil-structure interface to explore the shear characteristics of the frozen soil-structure interface and its failure mechanism during the thawing process. The test results showed that the unfrozen water at the interface during the thawing process can be clearly distributed in three stages, i.e., freezing, phase transition, and thawing, and that the shear strength of the interface decreases as the unfrozen water content increases. The internal friction angle and cohesive force display a change law of \"as one falls, the other rises,\" and the minimum internal friction angle and maximum cohesive force can be observed at -1oC. In addition, the change characteristics of the interface strength parameters during the freezing process were compared, and the differences between the interface shear characteristics and failure mechanisms during the frozen soil-structure interface freezing-thawing process were discussed. The shear strength parameters of the interface was subjected to different changes during the freezing–thawing process because of the different interaction mechanisms of the molecular structures of ice and water in case of the ice-water phase transition of the test sample during the freezing-thawing process.

Key Words
frozen soil-structure interface; freezing-thawing; NMR; unfrozen water content

Address
Liyun Tang, Yang Du and Liujun Yang: Architecture and Civil Engineering School, Xi\'an University of Science and Technology, Xi\'an, China

Lang Liu: 1.) Energy School, Xi\'an University of Science and Technology, Xi\'an 710054, China
2.) Key Laboratory of Western Mine Exploitation and Hazard Prevention with Ministry of Education, Xi\'an University of Science and Technology, Shaanxi, Xi\'an 710054, China

Long Jin: CCCC First Highway Consultants Co. Ltd. Shaanxi, Xi\'an 710000, China

Guoyu Li: State Key Laboratory of Frozen Soil Engineering,
Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, China

Abstract
With the ongoing development of deep mining of coal resources, some coal mine dynamic disasters have exhibited characteristics of both coal-gas outbursts and rockbursts. Therefore, research is required on the mechanism of rockburst-outburst coupling disaster. In this study, the failure characteristics of coal-rock combination structures were investigated using lab-scale physical simulation experiments. The energy criterion of the rockburst-outburst coupling disaster was obtained, and the mechanism of the disaster induced by the gas-solid coupling instability of the coal-rock combination structure was determined. The experimental results indicate that the damage of the coal-rock structure is significantly different from that of a coal body. The influence of the coal-rock structure should be considered in the study of rockburst-outburst coupling disaster. The deformation degree of the roof is controlled by the more significant main role of the gas pressure and the difference in the strength between the rock body and the coal body. The outburst holes and spall characteristics of the coal body after the failure of the coal-rock structure are strongly affected by the difference in strength between the roof and the coal body. The research results provide an in-depth understanding of the mechanism of rockburst-outburst coupling disasters in deep mining.

Key Words
coal-rock combination structure; coal-gas outburst; rockburst; coupling dynamic disaster; damage and failure; gas-solid coupling

Address
Feng Du, Kai Wang and Yangyang Guo: 1.) Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology (Beijing), Beijing 100083, China
2.) State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology (Beijing), Beijing 100083, China
3.) School of Emergency Management and Safety Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China

Gongda Wang: School of Civil and Resources Engineering, University of Science and Technology Beijing, Beijing 100083, China

Liang Wang and Yanhai Wang: 1.) Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology (Beijing), Beijing 100083, China
2.) State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology (Beijing), Beijing 100083, China

Abstract
As a flexible supporting structure, the anchoring frame structure is widely adopted to support multistage slopes in high earthquake-intensity area for its effectiveness and practicality. The previous study indicates that the anchor of anchoring frame structure is the most likely to be damaged during earthquakes. It is crucial to determine the pull-out capacity of anchor against seismic force for the seismic design of anchoring frame structure. In this study, an analytical model of a three-stage slope supported by anchoring frame structure is established, and the upper bound method of limit analysis is applied to deduce the seismic anchor force of anchoring frame structure. The pull-out capacity of anchor against seismic force of anchoring frame structure at each stage is obtained by computer programming. The proposed method is proved to be reasonable and effective compared with the existing published solution. Besides, the influence of main parameters on the pull-out capacity of anchor against seismic force is analyzed to provide some recommendations for the seismic design of anchoring frame structure.

Key Words
upper bound limit analysis; seismic anchor force; anchoring frame structure; three-stage slope

Address
Yu-liang Lin: 1.) School of Civil Engineering, Central South University, Changsha 410075, China
2.) MOE Key Laboratory of Engineering Structures of Heavy Haul Railway, Central South University, Changsha 410075, China
3.) Joint International Research Laboratory of Key Technology for Rail Traffic Safety, Central South University, Changsha 410075, China

Li Lu, Ying-xin Li and Guo-lin Yang: School of Civil Engineering, Central South University, Changsha 410075, China

Yuan Xue, Zhi-jun Feng and Zhi-meng Wang: China Railway Eryuan Engineering Group Co. Ltd., Chengdu 610031, China

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