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CONTENTS
Volume 13, Number 5, November 2017
 

Abstract
Earth berms are often left in place to support retaining walls or piles in order to eliminate horizontal struts in excavations of soft soil areas. However, if the excavation depth is relatively large, an earth berm-supported retaining system may not be applicable and could be replaced by a multi-bench retaining system. However, studies on multi-bench retaining systems are limited. The goal of this investigation is to study the deformation characteristics, internal forces and interaction mechanisms of the retaining structures in a multi-bench retaining system and the failure modes of this retaining system. Therefore, a series of model tests of a two-bench retaining system was designed and conducted, and corresponding finite difference simulations were developed to back-analyze the model tests and for further analysis. The tests and numerical results show that the distance between the two rows of retaining piles (bench width) and their embedded lengths can significantly influence the relative movement between the piles; this relative movement determines the horizontal stress distribution in the soil between the two rows of piles (i.e., the bench zone) and thus determines the bending moments in the retaining piles. As the bench width increases, the deformations and bending moments in the retaining piles decrease, while the excavation stability increases. If the second retaining piles are longer than a certain length, they will experience a larger bending moment than the first retaining piles and become the primary retaining structure. In addition, for varying bench widths, the slip surface formation differs, and the failure modes of two-bench retained excavations can be divided into three types: integrated failure, interactive failure and disconnected failure.

Key Words
multi-bench retained excavation; model test; finite difference method; strain softening; failure mechanism; earth berm

Address
Gang Zheng, Dongqing Nie, Yu Diao, Jie Liu and Xuesong Cheng:
1)MOE Key Laboratory of Coast Civil Structure Safety, Tianjin University, 92 Weijin Rd., Nankai District, Tianjin 300072, China

2)Department of Civil Engineering, Tianjin University, 92 Weijin Rd., Nankai District, Tianjin 300072, China

Abstract
Laboratory investigation reveals that rockfills exhibit significant stress-path-dependent behavior during shearing, therefore realistic prediction of deformation of rockfill structures requires suitable constitutive models to properly reproduce such behavior. This paper evaluates the capability of a strain hardening model proposed by the authors, by comparing simulation results with large-scale triaxial stress-path test results. Despite of its simplicity, the model can simulate essential aspects of the shear behavior of rockfills, including the non-linear stress-strain relationship, the stress-dependence of the stiffness, the non-linear strength behavior, and the shearing contraction and dilatancy. More importantly, the model is shown to predict the markedly different stress-strain and volumetric behavior along various loading paths with fair accuracy. All parameters required for the model can be derived entirely from the results of conventional large triaxial tests with constant confining pressures.

Key Words
rockfills; stress path; shear behavior; strain hardening; volumetric change

Address
Ming Xu, Erxiang Song and Dehai Jin: Department of Civil Engineering, Tsinghua University, Beijing 100084, China


Abstract
The subgrade reaction modulus of a large mat foundation was investigated by using a numerical analysis and a field case study. The emphasis was on quantifying the appropriate method for determining the subgrade reaction modulus for the design of a flexible mat foundation. A series of 3D non-linear FE analyses are conducted with special attention given to the subgrade reaction modulus under various conditions, such as the mat width, mat shape, mat thickness, and soil condition. It is shown that the distribution of the subgrade reaction modulus is non-uniform and that the modulus of subgrade reaction at both the corners and edges should be stiffer than that at the center. Based on the results obtained, a simple modification factor for the subgrade reaction modulus is proposed depending on the relative positions within the foundation in weathered soil and rocks.

Key Words
subgrade reaction modulus; mat foundation; numerical analysis; non-uniform; modification factor

Address
Sangseom Jeong, Jongjeon Park and Moonhyun Hong: School of Civil and Environmental Engineering, Yonsei University, Seoul, 120-749, Republic of Korea
Jaehwan Lee: Road Infrastructure Maintenance Office, KISTEC, Gyongsangnam-do, 52852, Republic of Korea

Abstract
Surface wave techniques are widely used as non-invasive method for geotechnical site characterization. Field surface wave data are collected and analyzed using different processing techniques to generate the dispersion curves, which are further used to extract the shear wave velocity profile by inverse problem solution. Characteristics of a dispersion curve depend on the subsurface layering information of a vertically heterogeneous medium. Sometimes soft layer can be found between two stiff layers in the vertically heterogeneous media, and it can affect the wave propagation dramatically. Now most of the surface wave techniques use the fundamental mode Rayleigh wave propagation during the inversion, but this may not be the actual scenario when a soft layer is present in a vertically layered medium. This paper presents a detailed and comprehensive study using finite element method to examine the effect of soft layers which sometimes get trapped between two high velocity layers. Determination of the presence of a soft layer is quite important for proper mechanical characterization of a soil deposit. Present analysis shows that the thickness and position of the trapped soft layer highly influence the dispersion of Rayleigh waves while the higher modes also contribute in the resulting wave propagation.

Key Words
dispersion; surface wave; finite element; frequency-wave number analysis; soft layer; Rayleigh wave

Address
Narayan Roy, Ravi S. Jakka and H.R. Wason: Department of Earthquake Engineering, Indian Institute of Technology Roorkee, Roorkee, India

Abstract
Regularities of temperature variation were determined in points of subgrade of the highway. Measurement of temperature was performed by special sensors, based on the effect of thermal resistance. Regular measurements of temperature were performed for two sections of the highway with asphalt concrete and cement concrete pavements for continuous period from November 2010 to March 2016. Multi-year experimental data, which we obtained, allowed establishing of peculiarities for temperature variation in points of subgrade in time and temperature distribution in the depth for annual cycle. Characteristics were determined for winter period-depth, duration and freezing rate, duration and defreezing rate for pavement and subgrade of the highway.

Key Words
highway; subgrade; sensor; temperature; temperature gradient; freezing; defreezing

Address
Bagdat B. Teltayev and Elena A. Suppes: Kazakhstan Highway Research Institute, 2A, Nurpeissov St., Almaty City, 050061, Republic of Kazakhstan

Abstract
This paper describes lab test results of artificial rock-like material samples having a plane joint. Cyclic shear tests were performed under different normal loads and different shear displacement amplitudes. For this purpose, multi-stage normal loading tests (30 kN, 60 kN, 90 kN, 180 kN, 360 kN and 480 kN) with cyclic excitation at frequency of 1.0 Hz and different shear displacement amplitudes (0.5 mm, 1.0 mm, 2.0 mm, 4.0 mm, 5.0 mm, and 8.0 mm) were conducted using the big shear box device GS-1000. Experimental results show, that shear forces increase with the increase of normal forces and quasi-static friction coefficient is larger than dynamic one. With the increase of normal loads, approaching the peak value of shear forces needs larger shear displacements. During each cycle the normal displacements increase and decrease (rotational behavior in every cycle). Peak angle of inclination increases with the increase of normal load. A phase shift between maximum shear displacement and maximum shear force is observed. The corresponding time shift decreases with increasing normal load and increases with increasing shear displacement amplitudes.

Key Words
joint; cyclic loading; shear box device; direct shear test; lab testing

Address
Wengang Dang: 1)State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University,
No. 8 Donghu South Road, Wuhan 430072, China
2)State Key Laboratory for GeoMechanics and Deep Underground Engineering,
China University of Mining and Technology, Beijing, China
3)Institute of Geotechnics, TU Bergakademie Freiberg, Gustav-Zeuner-Stra

Abstract
This study aimed to find out the pullout capacity of inclined strip anchor plate embedded in anisotropic and nonhomogeneous fully saturated cohesive soil in undrained condition. The ultimate pullout load has been found out by using numerical lower bound finite element analysis with linear programming. The undrained pullout capacity of anchor plate of width B is determined for different embedment ratios (H/B) varying from 3 to 7 and various inclination of anchor plates ranging from 0o to 90o with an interval of 15o. In case of anisotropic fully saturated clay the variation of cohesion with direction has been considered by varying the ratio of the cohesion along vertical direction (cv) to the cohesion along horizontal direction (ch). In case of nonhomogeneous clay the cohesion of the undrained clay has been considered to be increased with depth below ground surface keeping cv/ch=1. The results are presented in terms of pullout capacity factor (Fc0=pu/cH) where pu is the ultimate pullout stress along the anchor plate at failure and cH is the cohesion in horizontal direction at the level of the middle point of the anchor plate. It is observed that the pullout capacity factor increases with an increase in anisotropic cohesion ratio (cv/ch) whereas the pullout capacity factor decreases with an increase in undrained cohesion of the soil with depth.

Key Words
inclined anchor plate; anisotropic clay; nonhomogeneous clay; limit analysis; pullout capacity

Address
Paramita Bhattacharya: Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur-721302, India

Abstract
It is very important to study displacement prediction in geotechnical engineering. Nowadays, the grey system method, time series analysis method and artificial neural network method are three main methods. Based on the brief introduction, the three methods are analyzed comprehensively. Their merits and demerits, applied ranges are revealed. To solve the shortcomings of the artificial neural network method, a new prediction method based on new evolutionary neural network is proposed. Finally, through two real engineering applications, the analysis of three main methods and the new evolutionary neural network method all have been verified. The results show that, the grey system method is a kind of exponential approximation to displacement sequence, and time series analysis is linear autoregression approximation, while artificial neural network is nonlinear autoregression approximation. Thus, the grey system method can suitably analyze the sequence, which has the exponential law, the time series method can suitably analyze the random sequence and the neural network method almostly can be applied in any sequences. Moreover, the prediction results of new evolutionary neural network method is the best, and its approximation sequence and the generalization prediction sequence are all coincided with the real displacement sequence well. Thus, the new evolutionary neural network method is an acceptable method to predict the measurement displacements of geotechnical engineering.

Key Words
displacement prediction; geotechnical engineering; grey system; time series analysis; artificial neural network; evolutionary neural network

Address
Wei Gao and T.Y. He: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China


Abstract
Coal and gas outburst is a serious dynamic disaster that occurs during coal mining and threatens the lives of coal miners. Currently, coal and gas outburst is commonly predicted using single indicator and its critical value. However, single indicator is unable to fully reflect all of the factors impacting outburst risk and has poor prediction accuracy. Therefore, a more accurate prediction method is necessary. In this work, we first analyzed on-site impacting factors and precursors of coal and gas outburst; then, we constructed a Fisher discriminant analysis (FDA) index system using the gas adsorption index of drilling cutting h2, the drilling cutting weight S, the initial velocity of gas emission from borehole q, the thickness of soft coal h, and the maximum ratio of post-blasting gas emission peak to pre-blasting gas emission Bmax; finally, we studied an FDA-based multiple indicators discriminant model of coal and gas outburst, and applied the discriminant model to predict coal and gas outburst. The results showed that the discriminant model has 100% prediction accuracy, even when some conventional indexes are lower than the warning criteria. The FDA method has a broad application prospects in coal and gas outburst prediction.

Key Words
coal and gas outburst; prediction; fisher discriminant analysis; indicator

Address
Liang Chen: 1) School of Energy & Environment Engineering, Zhongyuan University of Technology, 450007 Zhengzhou,
Henan, China
2) Key Laboratory of Safety and High-efficiency Coal Mining, Ministry of Education
Anhui University of Science and Technology, 232001 Huainan, Anhui, China

Enyuan Wang, Junjun Feng, Xiaoran Wang and Xuelong Li:Key Laboratory of Coal Methane and Fire Control, Ministry of Education,
China University of Mining and Technology, 221116 Xuzhou, Jiangsu, China


Abstract
Design and management of concrete slabs in concrete-faced rock-fill dams are crucial issues for stability and overall dam safety since cracks in the concrete face induced by stress, shrinkage, and deterioration can cause severe leakage from the reservoir into the dam. Especially, the increase of dam height to a certain level to enhance the storage capacity and to improve hydraulic stability can lead to undesirable deformation behavior and stress distribution in the existing dam body and in the concrete slabs. In such conditions, simulation of a concrete slab with a numerical method should involve the use of an interface element because the behavior of the concrete slab does not follow the behavior of the dam body when the dam body settles due to the increase of dam height. However, the interfacial properties between the dam body and the concrete slab have yet to be clearly defined. In this study, construction sequence of a 125 m high CFRD in South Korea is simulated with commercial FDM software. The proper interfacial properties of the concrete slab are estimated based on a comparison to monitored vertical displacement history obtained from the concrete slab. Possibility of shear strength failure under the critical condition is investigated based on the simplified model. Results present the significance of the interfacial properties of the concrete slab.

Key Words
CFRD; concrete slab; back analysis; interface element; numerical analysis

Address
Seung-Hyung Baak and Gye-Chun Cho: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea

Ki-Il Song: Department of Civil Engineering, Inha University, Incheon, 22212, Republic of Korea


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