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CONTENTS
Volume 23, Number 1, October10 2020
 

Abstract
To give a solution for seismic stability of tunnel faces subjected to earthquake ground shakings, the pseudo-dynamic approach is originally introduced to analyze tunnel face stability in this study. In the light of the upper-bound theorem of limit analysis, an advanced three-dimensional mechanism combined with pseudo-dynamic approach is proposed. Based on this mechanism, the required support pressure on tunnel face can be obtained by equaling external work rates to the internal energy dissipation and implementing an optimization searching procedure related to time. Both time and space feature of seismic waves are properly accounted for in the proposed mechanism. For this reason, the proposed mechanism can better represent the actual influence of seismic motion and has a remarkable advantage in evaluating the effects of vertical seismic acceleration, soil amplification factor, seismic wave period and initial phase difference on tunnel face stability. Furthermore, the pseudo-dynamic approach is compared with the pseudo-static approach. The difference between them is illustrated from a new but understandable perspective. The comparison demonstrates that the pseudo-static approach is a conservative method but still could provide precise enough results as the pseudo-dynamic approach if the value of seismic wavelengths is large or the height of soil structures is small.

Key Words
limit analysis; tunnel face; seismic; pseudo-dynamic; cohesive soils

Address
Qi Huang, Jin-feng Zou and Ze-hang Qian: School of Civil Engineering, Central South University, No.22, Shaoshan South Road, Changsha, Hunan Province, People\'s Republic of China


Abstract
The probabilistic bearing capacity of a strip footing placed on the edge of a purely cohesive reinforced soil slope is computed by combining lower bound finite element limit analysis technique with random field method and Monte Carlo simulation technique. To simulate actual field condition, anisotropic random field model of undrained soil shear strength is generated by using the Cholesky-Decomposition method. With the inclusion of a single layer of reinforcement, dimensionless bearing capacity factor, N always increases in both deterministic and probabilistic analysis. As the coefficient of variation of the undrained soil shear strength increases, the mean N value in both unreinforced and reinforced slopes reduces for particular values of correlation length in horizontal and vertical directions. For smaller correlation lengths, the mean N value of unreinforced and reinforced slopes is always lower than the deterministic solutions. However, with the increment in the correlation lengths, this difference reduces and at a higher correlation length, both the deterministic and probabilistic mean values become almost equal. Providing reinforcement under footing subjected to eccentric load is found to be an efficient solution. However, both the deterministic and probabilistic bearing capacity for unreinforced and reinforced slopes reduces with the consideration of loading eccentricity.

Key Words
strip footing; reinforced slope; vertical and eccentric load; lower bound limit analysis; anisotropic random model; monte-carlo simulation

Address
Koushik Halder and Debarghya Chakraborty: Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India

Abstract
Soil-cement stabilization is a type of ground improvement method which has been used to improve the engineering properties of soil. The unconfined compression test is the commonly used method to evaluate the quality of the stabilized soil due to its simplicity, reliability, rapidity and cost-effectiveness. The main objective of this study was to evaluate the effect of recovered carbon black (rCB) on the strength characteristic of cement-stabilized sand. Various rCB contents and water to cement ratios (w/c) were examined. The unconfined compression test on stabilized sand with different curing times was also conducted for a reconstituted specimen. From the test result, it was found that the compressive strength of cement-stabilized sand increased with the increase of the rCB content up to 3% and the curing time and with the decrease of the w/c ratio, showing that the optimum rCB concentration of the tested stabilized sand was around 3%. In addition, a prediction equation was suggested in this study for cement-stabilized sand with rCB as a function of the w/c ratio and rCB concentration at 14 and 28 days of curing.

Key Words
cement stabilization; recovered carbon black; microfine cement; compressive strength; unconfined compression test

Address
Kean Thai Chhun,Panyabot Kaothon and Chan-Young Yune: Department of Civil Engineering, Gangneung-Wonju National University, Jukheon-gil 7, Gangneung-si, Gangwon-do, 25457, Republic of Korea

Hyunwook Choo: Department of Civil Engineering, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin-si, 17104, Republic of Korea


Abstract
In order to understand the shear mechanical properties of the interface between clay and structure and better serve the practical engineering projects, it is critical to conduct shear tests on the clay-structure interface. In this work, the direct shear test of clay-concrete slab with different joint roughness coefficient (JRC) of the interface and different normal stress is performed in the laboratory. Our experimental results show that (1) shear strength of the interface between clay and structure is greatly affected by the change of normal stress under the same condition of JRC and shear stress of the interface gradually increases with increasing normal stress; (2) there is a critical value JRCcr in the roughness coefficient of the interface; (3) the relationship between shear strength and normal stress can be described by the Mohr Coulomb failure criterion, and the cohesion and friction angle of the interface under different roughness conditions can be calculated accordingly. We find that there also exists a critical value JRCcr for cohesion and the cohesion of the interface increases first and then decreases as JRC increases. Moreover, the friction angle of the interface fluctuates with the change of JRC and it is always smaller than the internal friction angle of clay used in this experiment; (4) the failure type of the interface of the clay-concrete slab is type I sliding failure and does not change with varying JRC when the normal stress is small enough. When the normal stress increases to a certain extent, the failure type of the interface will gradually change from shear failure to type II sliding failure with the increment of JRC.

Key Words
JRC; shear test; clay-concrete interface; shear strength; cohesion; friction angle

Address
Wendong Yang and Ling Wang: College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao, Shandong, 266580, China

Jingjing Guo: China Construction Second Engineering Bureau Ltd, Beijing, 100160, China

Xuguang Chen: College of Engineering, Ocean University of China, Qingdao, Shandong, 266100, China

Abstract
In this paper, the WEKA platform was used to mine and analyze measured data of floor failure depth and a prediction system of floor failure depth was developed with Java. Based on the standardization and discretization of 35-set measured data of floor failure depth in China, the grey correlation degree analysis on five factors affecting the floor failure depth was carried out. The correlation order from big to small is: mining depth, working face length, floor failure resistance, mining thickness, dip angle of coal seams. Naive Bayes model, neural network model and decision tree model were used for learning and training, and the accuracy of the confusion matrix, detailed accuracy and node error rate were analyzed. Finally, artificial neural network was concluded to be the optimal model. Based on Java language, a prediction system of floor failure depth was developed. With the easy operation in the system, the prediction from measured data and error analyses were performed for nine sets of data. The results show that the WEKA prediction formula has the smallest relative error and the best prediction effect. Besides, the applicability of WEKA prediction formula was analyzed. The results show that WEKA prediction has a better applicability under the coal seam mining depth of 110 m~550 m, dip angle of coal seams of 0o~15o and working face length of 30 m~135 m.

Key Words
floor failure depth; WEKA platform; the grey relational degree; optimal model; prediction system

Address
Yao Lu, Juntao Chen and Weixin Tong: 1.) College of Energy and Mining Engineering, College of Safety and Environmental 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

Liyang Bai: Lvliang University, Lvliang, 033000, Shanxi, China

Zhe Jiang: 1.) College of Energy and Mining Engineering, College of Safety and Environmental Engineering,
Shandong University of Science and Technology, Qingdao 266590, China
2.) Lvliang University, Lvliang, 033000, Shanxi, China

Abstract
The uniaxial compressive strength (UCS) of rock is a basic parameter in underground engineering design. The disadvantages of this commonly employed laboratory testing method are untimely testing, difficulty in performing core testing of broken rock mass and long and complicated onsite testing processes. Therefore, the development of a fast and simple in situ rock UCS testing method for field use is urgent. In this study, a multi-function digital rock drilling and testing system and a digital core bit dedicated to the system are independently developed and employed in digital drilling tests on rock specimens with different strengths. The energy analysis is performed during rock cutting to estimate the energy consumed by the drill bit to remove a unit volume of rock. Two quantitative relationship models of energy analysis-based core drilling parameters (ECD) and rock UCS (ECD-UCS models) are established in this manuscript by the methods of regression analysis and support vector machine (SVM). The predictive abilities of the two models are comparatively analysed. The results show that the mean value of relative difference between the predicted rock UCS values and the UCS values measured by the laboratory uniaxial compression test in the prediction set are 3.76 MPa and 4.30 MPa, respectively, and the standard deviations are 2.08 MPa and 4.14 MPa, respectively. The regression analysis-based ECD-UCS model has a more stable predictive ability. The energy analysis-based rock drilling method for the prediction of UCS is proposed. This method realized the quick and convenient in situ test of rock UCS.

Key Words
core drilling; energy analysis; drilling parameter; rock; uniaxial compressive strength; relationship model; prediction method

Address
Wang Qi, Xu Shuo, Gao Hong Ke, Zhang Peng and Liu Bo Hong: 1.) State Key Laboratory for Geo-mechanics and Deep Underground Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
2.) Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China

Jiang Bei: 1.) State Key Laboratory for Geo-mechanics and Deep Underground Engineering,
China University of Mining & Technology (Beijing), Beijing 100083, China
2.) Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China
3.) School of Civil Engineering and Architecture, University of Jinan, Jinan 250022, China

Abstract
Cantilever sheet pile walls are subjected to surcharge loading located on the backfill soil and at different distances from the top of the wall. The response of cantilever sheet pile walls to surcharge loadings at varying distances under seismic conditions is scarce in literature. In the present study, the influence of uniform surcharge load on cantilever sheet pile wall at varying distances from the top of the wall under seismic conditions are analyzed using finite difference based computer program. The results of the numerical analysis are presented in non-dimensional form like variation of bending moment and horizontal earth pressure along the depth of the sheet pile walls. The numerical analysis has been conducted at different magnitudes of horizontal seismic acceleration coefficient and vertical seismic acceleration coefficients by varying the magnitude and position of uniform surcharge from the top of the wall for different embedded depths and types of soil. The parametric study is conducted with different embedded depth of sheet pile walls, magnitude of surcharge on the top of the wall and at a distance from the top of the wall for different angles of internal friction. It is observed that the maximum bending moment increases and more mobilization of earth pressure takes place with increase in horizontal seismic acceleration coefficients, magnitude of uniform surcharge, embedded depth and decrease in the distance of surcharge from the top of the wall in loose sand.

Key Words
seismic; surcharge; finite difference; sheet pile; embedded depth

Address
Akshay Pratap Singh and Kaustav Chatterjee: Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee 247 667, India

Abstract
This study adopted soil test and laboratory physical model experiments to simulate the tailings impoundment accumulation process according to the principle of similarity. Relying on the practical engineering, it analyzed the tailings deposition characteristics on dry beach surface during the damming process, as well as the variation rules of dam saturation line. Results suggested that, the tailings particles gradually became finer along the dry beach surface to inside the impoundment. The particle size suddenly changed at the junction between the deposited beach and the water surface, which displayed an obvious coarsening phenomenon. Besides, the deposited beach exhibited the vertical feature of coarse upward and fine downward on the whole. Additionally, in the physical model, the saturation line elevated with the increase in dam height, and its amplitude was relatively obvious within the range of 1.0-4.5 m away from the initial dam. Under flood condition, the saturation line height was higher than that under normal condition on the whole, with the maximum height difference of 4 cm. This study could provide an important theoretical basis for further studies on dam failure experiments and the evolution rules of leaked tailings flow.

Key Words
geotechnical slope; taings dam stability; deposition characteristics; saturation line; physical model

Address
Guangjin Wang, Sen Tian and Xiangyun Kong: Engineering Research Center for Green Comprehensive Utilization of Metal Ore Tailings Resources, Faculty of Land Resources Engineering, Kunming University of Science and Technology, Kunming 650093, China

Bin Hu: Hubei Key Laboratory for Efficient Utilization and Agglomeration of Metallurgic Mineral Resources, School of Resources and Environmental Engineering, Wuhan University of Science and Technology, Wuhan 430081, China

Jie Chen: State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China



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