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CONTENTS
Volume 29, Number 5, June10 2022
 


Abstract
Most of the pile's vertical static load tests in construction sites are the proof load tests, which is difficult to accurately estimate the ultimate bearing capacity and analyze the reliability of piles. Therefore, a reliability analysis method based on the proof load-settlement (Q-s) data is proposed in this study. In this proposed method, a simple ultimate limit state function based on the hyperbolic model is established, where the random variables of reliability analysis include the model factor of the ultimate bearing capacity and the fitting parameters of the hyperbolic model. The model factor M = RuR / RuP is calculated based on the available destructive Q-s data, where the real value of the ultimate bearing capacity (RuR) is obtained by the complete destructive Q-s data; the predicted value of the ultimate bearing capacity (RuP) is obtained by the proof Q-s data, a part of the available destructive Q-s data, that before the predetermined load determined by the pile test report. The results demonstrate that the proposed method can easy and effectively perform the reliability analysis based on the proof Q-s data.

Key Words
model factor; pile; reliability analysis; ultimate bearing capacity; vertical static load test

Address
Xiaole Dong, Xiaohui Tan, Xin Lin, Xuejuan Zhang, Xiaoliang Hou and Daoxiang Wu:School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China

Abstract
Tailings fluidization (i.e., tailings behave as being fluidized) under cyclic loading is one concern during the construction of tailings dams, especially in the shallow tailings layers. The primary goal of this study is to evaluate the responses of tailings under cyclic loadings and the tailings potential for fluidization. A series of cyclic triaxial undrained and drained tests were performed on medium and dense tailings samples under various cyclic stress ratios (CSR). The results indicated that axial strain and excess pore water pressure accumulated over time due to cyclic loading. However, the accumulations were dependent on CSR values, densities, and drainage conditions. The fluidization potential analysis in this study was then evaluated based on the obtained cyclic axial strain and excess pore water pressure. As a result, tailings samples were stable (unfluidized) under small CSR values, and the critical CSR values, where the tailings fluidized, varied depending on the density of tailings samples. Tailings fluidization is triggered as cyclic stress ratios reach critical values. In this study, the critical CSR values were found to be 0.15 and 0.40 for medium and dense samples, respectively.

Key Words
critical cyclic stress ratios; cyclic characteristics; tailings fluidization

Address
Tan Manh Do: Department of Civil, Environmental and Natural Resources Engineering, Luleå university of technology, Luleå, Sweden;
Department of Civil Engineering, University of Mining and Geology, Hanoi, Vietnam
Jan Laue, Hans Mattson and Qi Jia: Department of Civil, Environmental and Natural Resources Engineering, Luleå university of technology, Luleå, Sweden

Abstract
Tail-grouting is an effective measure in shield engineering for filling the gap at the shield tail to reduce ground deformation. However, the gap-filling ratio affects the value of the gap parameters, leading to different surface settlements. It is impossible to adjust the fill ratio indiscriminately to study its effect, because the allowable adjustment range of the grouting quantity is limited to ensure construction site safety. In this study, taking the shield tunnel section between Chaoyanggang Station and Shilihe Station of Beijing Metro Line 17 as an example, the correlation between the tail-grouting parameter and the surface settlement is investigated and the optimal grouting quantity is evaluated. This site is suitable for conducting field tests to reduce the tail-grouting quantity of shield tunneling over a large range. In addition, the shield tunneling under different grouting parameters was simulated. Furthermore, we analyzed the evolution law of the surface settlement under different grouting parameters and obtained the difference in the settlement parameters for each construction stage. The results obtained indicate that the characteristics of the grout affect the development of the surface settlement. Therefore, reducing the setting time or increasing the initial strength of the grout could effectively suppress the development of surface subsidence. As the fill ratio decreases, the loose zone of the soil above the tunnel expands, and the soil deformation is easily transmitted to the surface. Meanwhile, owing to insufficient grout support, the lateral pressure on the tunnel segments is significantly reduced, and the segment moves considerably after being removed from the shield tail.

Key Words
grout hardening properties; grouting quantity; shield tunnel; surface settlement; tail-grouting

Address
Xiaokang Shao, Zhiyong Yang, Yusheng Jiang, Xing Yang and Weiqiang Qi: School of Mechanics and Civil Engineering, China University of Mining and Technology-Beijing, Ding, No. 11 Xueyuan Road,
Haidian District, Beijing 100083, P.R. China

Abstract
Several prediction model of penetration rate (PR) of tunnel boring machines (TBMs) have been focused on applying to design stage. In construction stage, however, the expected PR and its trends are changed during tunneling owing to TBM excavation skills and the gap between the investigated and actual geological conditions. Monitoring the PR during tunneling is crucial to rescheduling the excavation plan in real-time. This study proposes a sequential prediction method applicable in the construction stage. Geological and TBM operating data are collected from Gunpo cable tunnel in Korea, and preprocessed through normalization and augmentation. The results show that the sequential prediction for 1 ring unit prediction distance (UPD) is R2 R2>0.79; whereas, a one-step prediction is R2<0.30. In modeling algorithm, a gradient boosted regression tree (GBRT) outperformed a least square-based linear regression in sequential prediction method. For practical use, a simple equation between the R2 and UPD is proposed. When UPD increases R2 decreases exponentially; In particular, UPD at R2=0.60 is calculated as 28 rings using the equation. Such a time interval will provide enough time for decision-making. Evidently, the UPD can be adjusted depending on other project and the R2 value targeted by an operator. Therefore, a calculation process for the equation between the R2 and UPD is addressed.

Key Words
construction stage; gradient boosted regression tree; penetration rate; sequential prediction; tunnel boring machine

Address
Hang-Lo Lee: Disposal Performance Demonstration Research Division, Korea Atomic Energy Research Institute, Daejeon, 34057, Republic of Korea
Ki-Il Song: Department of Civil Engineering, Inha University, Incheon 22212, Republic of Korea
Chongchong Qi: School of Resources and Safety Engineering, Central South University, Changsha, 410083, China
Kyoung-Yul Kim: Next Generation Transmission & Substation Laboratory, KEPCO Research Institute, Daejeon, 34057, Republic of Korea

Abstract
Recently, the construction industry has focused on eco-friendly materials instead of traditional materials due to their harmful effects on the environment. To this end, biopolymers are among proper choices to improve the geotechnical behavior of problematic soils. In the current study, serish biopolymer is introduced as a new binder for the purpose of sand improvement. Serish is a natural polysaccharide extracted from the roots of Eremurus plant, which mainly contains inulins. The effect of serish biopolymer on sand treatment has been investigated through performing unconfined compressive strength (UCS), California bearing ratio (CBR), as well as wind erosion tests. The results demonstrated that serish increased the compressive strength of dune sand in both terms of UCS and CBR. Also, wind erosion resistance of the sand was considerably improved as a result of treatment with serish biopolymer. A microstructural study was also conducted via SEM images; it can be seen that serish coated the sand particles and formed a strong network.

Key Words
biopolymer; sand; SEM; soil improvement; sustainable materials; unconfined compressive strength

Address
Khosro Shabani: Department of civil engineering, K. N. Toosi University of Technology, Tehran, Iran
Maysam Bahmani: Department of Civil, Construction, and Environmental Engineering, University of Alabama, Tuscaloosa, AL 35487, USA
Hadi Fatehi: School of Engineering & Built Environment, Griffith University, Nathan, QLD 4111, Australia
Ilhan Chang: Department of Civil Systems Engineering, Ajou University, Republic of Korea

Abstract
Severe acid rains can be a major source for geotechnical and environmental problems in any soil depending on the acid type and concentration. Hence, this study investigates the individual severe effects of sulfuric, hydrochloric and nitric acids on the geotechnical properties of real field soil through a series of experimental laboratory tests. The laboratory program consists of experimental tests such as consistency, compaction, unconfined compression, pH determination, electrical conductivity, total dissolved salts, total suspended solids, gypsum and carbonates contents. The experimental tests have been performed on the untreated soil and individual acid treated soil for acid concentrations range of 0% to 20% by weight. In addition, a unique hyperbolic mathematical model has been used to predict significant geotechnical characteristics for acid treated soil. The plastic and liquid limits and optimum moisture content have been increased under the effect of all the used acids whereas the maximum dry density and unconfined stress-strain behavior have been decreased with increasing the acid concentrations. Moreover, the used hyperbolic mathematical model has predicted all the geotechnical characteristics very well with a very high coefficient of determination (R2) value and lowest root mean square error (RMSE) estimate.

Key Words
acid rain; chemical acids; electrical conductivity; geotechnical experimental tests; hyperbolic model; mathematical modeling; pH value

Address
Aram M. Raheem and Shno M. Ali:Department of Civil Engineering, College of Engineering, University of Kirkuk, Al-Sayada Street, Kirkuk, Iraq

Abstract
In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

Key Words
dynamic loads; failure behavior; flawed roadway tunnel models; mixed-mode crack; static loads

Address
Lei Zhou: Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province,
Southwest University of Science and Technology, Mianyang 621010, Sichuan, China;
Key Laboratory of Deep Earth Science and Engineering (Ministry of Education), College of Architecture and Environment,
Sichuan University, Chengdu 610065, China;
Failure Mechanics & Engineering Disaster Prevention and Mitigation, Key Laboratory of Sichuan Province,
College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Jianxing Chen, Zheming Zhu, Yuqing Dong and Hanbing Wang: Failure Mechanics & Engineering Disaster Prevention and Mitigation, Key Laboratory of Sichuan Province,
College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Changlin Zhou: Chengdu Surveying Geotechnical Research Institute Co., Ltd. of MCC, Chengdu, 610023, China

Abstract
The Compaction effect is important for evaluating the subgrade construction. However, there is little research exploring the compaction quality of deep soil using hydraulic compaction. According to reinforcement effect analysis, dimensional analysis is adopted in this work to analyze subgrade compactness within the effective reinforcement depth, and a prediction model is obtained. A hydraulic compactor is then employed to carry out an in-situ reinforcement test on gravel soil subgrade, and the subgrade parameters before and after reinforcement are analyzed. Results show that a reinforcement difference exists inside the subgrade, and the effective reinforcement depth is defined as increasing compactness to 90% in the depth direction. Layered compactness within the effective reinforcement depth is expressed by parameters including the drop distance of the rammer, peak acceleration, tamping times, subgrade settlement, and properties of rammer and filler. Finally, a field test is conducted to verify the results.

Key Words
compactness; dimensional analysis; gravel soil subgrade; hydraulic compaction; road engineering

Address
Dandan Han: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing,
Jiangsu, 210098, The People's Republic of China;
School of Highway, Chang'an University, Xi'an, Shaanxi, 710064, The People's Republic of China
Zhijun Zhou and Haochen Zhan: School of Highway, Chang'an University, Xi'an, Shaanxi, 710064, The People's Republic of China
Jiangtao Lei: Division of Geotechnical Engineering and Geosciences, Department of Civil and Environmental Engineering,
Polytechnic University of Catalonia (UPC), Spain
Minguo Lin: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing,
Jiangsu, 210098, The People's Republic of China


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