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CONTENTS
Volume 11, Number 6, December 2016
 

Abstract
The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c') and tangent of effective friction angle (tanφ') in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c' and tanφ' may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (σ1σ3)f, secant modulus of elasticity (Es) and c' while little influence on φ'. Hence, conventional SSRFEM which reduces c' and tanφ' equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c' is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.

Key Words
wetting-drying cycles; shear strength reduction finite element method; modification; factor of safety; soil slope

Address
(1) Yiliang Tu, Zuliang Zhong, Weikun Luo, Xinrong Liu, Sui Wang:
College of Civil Engineering, Chongqing University, Chongqing 400045, China;
(2) Yiliang Tu, Zuliang Zhong, Weikun Luo, Xinrong Liu, Sui Wang:
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China;
(3) Zuliang Zhong
Department of Architecture and Civil Engineering, Logistical Engineering University, Chongqing, 400041, China.

Abstract
Rail support modulus is an important parameter for analysis and design of ballasted railway tracks. One of the challenges in track stiffness assessment is its dynamic nature under the moving trains which differs it from the case of standing trains. So the present study is allocated to establish a relation between the dynamic and static stiffness of ballasted tracks via field measurements. In this regard, two different sites of ballasted tracks with wooden and concrete sleepers were selected and the static and dynamic stiffness were measured based on Talbot – Wasiutynski method. In this matter, the selected tracks were loaded by two heavy and light car bodies for standing and moving conditions and consequently the deflection basins were evaluated in both sites. Knowing the deflection basins respect to light and heavy loading conditions, both of static and dynamic stiffness values were extracted. Finally two definite relations were obtained for ballasted tracks with wooded and concrete sleepers.

Key Words
ballasted railway track; field investigation; rail support modulus; concrete and wooden sleeper; light and heavy car bodies

Address
School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran.

Abstract
The thermal conductivity of soils is an important property in energy-related geotechnical structures, such as underground heat pumps and underground electric power cable tunnels. This study explores the effects of geotechnical engineering properties on the thermal conductivity of soils. The thermal conductivities of quartz sands and Korean weathered silty sands were documented via a series of laboratory experiments, and its variations with effective stress, porosity, and water saturation were examined. While thermal conductivity was found to increase with an increase in the effective stress and water saturation and with a decrease in porosity, replacing air by water in pores the most predominantly enhanced the thermal conductivity by almost one order of magnitude. In addition, we have suggested an improved model for thermal conductivity prediction, based on water saturation, dry thermal conductivity, saturated thermal conductivity, and a fitting parameter that represents the curvature of the thermal conductivity-water saturation relation.

Key Words
thermal conductivity; quartz sand; silty sand; weathered soil; effective stress; water saturation; correlation

Address
(1) So-Jung Lee:
Korea Institute of Civil Engineering and Building Technology (KICT), Daejeon, Korea;
(2) Kyoung-Yul Kim:
Principle Researcher, Structural and Seismic Technology Group, Power Transmission Laboratory, Korea Electric Power Research Institute (KEPRI), Daejeon, Korea;
(3) Jung-Chan Choi:
Norwegian Geotechnical Institute (NGI), Oslo, Norway;
(4) Tae-Hyuk Kwon:
Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea.

Abstract
DDARF (Discontinuous Deformation Analysis for Rock Failure) is a numerical algorithm for simulating jointed rock masses' discontinuous deformation. While its reinforcement simulation is only limited to endanchorage bolt, which is assumed to be a linear spring simply. Here, several new reinforcement modes in DDARF are proposed, including lining reinforcement, full-length anchorage bolt and equivalent reinforcement. In the numerical simulation, lining part is assigned higher mechanical strength than surrounding rock masses, it may include multiple virtual joints or not, depending on projects. There must be no embedding or stretching between lining blocks and surrounding blocks. To realize simulation of the full-length anchorage bolt, at every discontinuity passed through the bolt, a set of normal and tangential spring needs to be added along the bolt's axial and tangential direction. Thus, bolt's axial force, shearing force and full-length anchorage effect are all realized synchronously. And, failure criterions of anchorage effect are established for different failure modes. In the meantime, from the perspective of improving surrounding rock masses' overall strength, a new equivalent and tentative simulation method is proposed, it can save calculation storage and improve efficiency. Along the text, simulation algorithms and applications of these new reinforcement modes in DDARF are given.

Key Words
DDARF; lining reinforcement; full-length anchorage bolt; failure criterion; equivalent reinforcement

Address
(1) Yunjuan Chen, Xin Zhang:
Shandong Provincial Key Laboratory of Appraisal and Retrofitting in Building Structures, Shandong Jianzhu University, Ji'nan 250101, Shandong, China;
(2) Weishen Zhu, Shucai Li:
Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China.

Abstract
A fully coupled non-linear effective stress response finite difference (FD) model is built to survey the counter-intuitive recent findings on the reliance of pore water pressure ratio on foundation contact pressure. Two alternative design scenarios for a benchmark problem are explored and contrasted in the light of construction emission rates using the EFFC-DFI methodology. A strain-hardening effective stress plasticity model is adopted to simulate the dynamic loading. A combination of input motions, contact pressure, initial vertical total pressure and distance to foundation centreline are employed, as model variables, to further investigate the control of permanent and variable actions on the residual pore pressure ratio. The model is verified against the Ghosh and Madabhushi high acceleration field test database. The outputs of this work are aimed to improve the current computer-aided seismic foundation design that relies on ground

Key Words
liquefaction; dynamic; finite difference; effective stress; surcharge; non-linear; carbon

Address
(1) Saeid Ardeshiri-Lajimi, Mahmoud Yazdani:
School of Civil and Environmental Engineering, Tarbiat Modares University, Iran;
(2) Arya Assadi-Langroudi:
School of Architecture, Computing and Engineering, University of East London, England, UK.

Abstract
Extensive researches on distribution of earthquake induced damages in different regions have shown that geological and geotechnical conditions of the local soils significantly influence behavior of alluvial areas under seismic loading. In this article, the site of Babol city which is formed up of saturated fine alluvial soils is considered as a case study. In order to reduce the uncertainties associated with earthquake resistant design of structures in this area (Babol city), the required design parameters have been evaluated with consideration of site\'s dynamic effects. The utilized methodology combines experimental ground ambient noise analysis, expressed in terms of horizontal to vertical (H/V) spectral ratio, with numerical one-dimensional response analysis of soil columns using DEEPSOIL software. The H/V spectral analysis was performed at 60 points, experimentally, for the region in order to estimate both the fundamental period and its corresponding amplification for the ground vibration. The investigation resulted in amplification ratios that were greater than one in all areas. A good agreement between the proposed ranges of natural periods and alluvial amplification ratios obtained through the analytical model and the experimental microtremor studies verifies the analytical model to provide a good engineering reflection of the subterraneous alluviums.

Key Words
site effect; Babol; amplification; DEEPSOIL; microtremor

Address
Department of Civil Engineering, Babol Noushirvani University of Technology, Babol, Iran.

Abstract
In this study, a series of geotechnical centrifugal tests were conducted to investigate the effectiveness of settlement control of two types of rigid pile structure embankments (PRSE) in collapsible loess under high-speed railway embankments. The research results show that ground reinforcement is required to reduce the postconstruction settlement and settlement rate of the embankments. The rigid pile structure embankments using rigid piles can substantially reduce the embankment settlement in the construction of embankments on collapsible loess, and the efficiency in settlement reduction is affected by the pile spacing. The pile-raft structure embankments (PRSE) have much stronger ability in terms of the effectiveness of settlement control, while the pile-geogrid structure embankments (PGSE) provides rapid construction as well as economic benefits. Rational range of pile spacing of PRSE and PGSE are suggested based on the requirements of various railways design speeds. Furthermore, the time effectiveness of negative skin friction of piles and the action of pile-cap setting are also investigated. The relevant measures for improving the bearing capacity and two parts of transition zone forms as positive control mean have been suggested.

Key Words
high-speed railways; embankment engineering; rigid pile structure embankment (RPSE); centrifuge model test; settlement controlling; collapsible loess

Address
(1) Changdan Wang, Shunhua Zhou, Binglong Wang:
Key Laboratory of Road and Traffic Engineering of the Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai, 201804 China;
(2) Peijun Guo, Hui Su:
Department of Civil Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4L6 Canada.

Abstract
Collapse shape of tunnel roof in layered Hoek-Brown rock media is investigated within the framework of upper bound theorem. The traditional collapse mechanism for homogeneous stratum is no longer suitable for the present analysis of roof stability, and it would be necessary to propose a curve failure mode to describe the velocity discontinuity surface in layered media. What is discussed in the paper is that the failure mechanism of tunnel roofs, consisting of two different functions, is proposed for layered rock media. Then it is employed to investigate the impending roof failure. Based on the nonlinear Hoek-Brown failure criterion, the collapse volume of roof blocks are derived with the upper bound theorem and variational principle. Numerical calculations and parametric analysis are carried out to illustrate the effects of different parameters on the shape of failure mechanism, which is of overriding significance to the stability analysis of tunnel roof in layered rock media.

Key Words
layered rock; nonlinear failure criterion; tunnel roof

Address
School of Civil Engineering, Central South University, Hunan 410075, China.

Abstract
A new earth pressure equation considering the arching effect in c-Χ soils was proposed for the accurate calculation of earth pressure on circular vertical shafts. The arching effect and the subsequent load recovery phenomenon occurring due to multi-step excavation were quantitatively investigated through laboratory tests. The new earth pressure equation was verified by comparing the test results with the earth pressures predicted by new equation in various soil conditions. Resulting from testing by using multi-step excavation, the arching effect and load recovery were clearly observed. The test results in c-Χ soil showed that even a small amount of cohesion can cause the earth pressure to decrease significantly. Therefore, predicting earth pressure without considering such cohesion can lead to overestimation of earth pressure. The test results in various ground conditions demonstrated that the newly proposed equation, which enables consideration of cohesion as appropriate, is the most reliable equation for predicting earth pressure in both Χ soil and c-Χ soil. The comparison of the theoretical equations with the field data measured on a real construction site also highlighted the best-fitness of the theoretical equation in predicting earth pressure.

Key Words
active earth pressure; arching effect; vertical shaft; cohesion; wall friction

Address
(1) In-Mo Lee:
School of Civil, Environmental, and Architectural Engineering, Korea University, Seoul, Korea;
(2) Do-Hoon Kim:
Hyundai Eng. and Construction Co., Ltd., Seoul, Korea (former Ph.D. Student in Korea University);
(3) Kyoung-Yul Kim:
Korea Electric Power Research Institute, Deajeon, Korea;
(4) Seok-Won Lee:
Department of Civil and Environmental System Engineering, Konkuk University, Seoul, Korea.


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