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CONTENTS
Volume 16, Number 5, December10 2018
 

Abstract
In offshore engineering, lateral cyclic loading may induce excessive lateral movement and bending strain in pile foundations. Previous studies mainly focused on deformation mechanisms of single piles due to lateral cyclic loading. In this paper, centrifuge model tests were conducted to investigate the response of a 2x2 pile group due to lateral cyclic loading in clay. After applying each loading-unloading cycle, the pile group cannot move back to its original location. It implies that residual movement and bending strain are induced in the pile group. This is because cyclic loading induces plastic deformation in the soil surrounding the piles. As the cyclic load increases from 62.5 to 375 kN, the ratio of the residual to the maximum pile head movements varies from 0.30 to 0.84. Moreover, the ratio of the residual to the maximum bending strains induced in the piles is in a range of 0.23 to 0.82. The bending strain induced in the front pile is up to 3.2 times as large as that in the rear pile. Thus, much more protection measures should be applied to the front piles to ensure the serviceability and safety of pile foundations.

Key Words
centrifuge modeling; cyclic loading; pile group; lateral movement; bending strain

Address
Jiangwei Shi and Long Chen: 1.) Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210024, China
2.) Jiangsu Research Center for Geotechnical Engineering Technology, Hohai University, Nanjing 210024, China

Yuting Zhang: Tianjin Research Institute for Water Transport Enginnering, M.O.T., China

Zhongzhi Fu: Nanjing Hydraulic Research Institute, Geotechical Engineering Department, Nanjing 210029, China


Abstract
A flat-jointed bonded-particle model (BPM) has been proved to be an effective tool for simulating mechanical behaviours of intact rocks. However, the tedious and time-consuming calibration procedure imposes restrictions on its widespread application. In this study, a systematic approach is proposed for simplifying the calibration procedure. The initial relationships between the microscopic, constitutive parameters and macro-mechanical rock properties are firstly determined through dimensionless analysis. Then, sensitivity analyses and regression analyses are conducted to quantify the relationships, using results from numerical simulations. Finally, four examples are used to demonstrate the effectiveness and robustness of the proposed systematic approach for the calibration procedure of BPMs.

Key Words
discrete element method; bonded-particle model; flat-jointed model; micro-parameters; macro-rock properties; intact rocks

Address
Changtai Zhou and Murat Karakus: School of Civil, Environmental and Mining Engineering, The University of Adelaide, Adelaide, Australia

Chaoshui Xu: 1.) School of Civil, Environmental and Mining Engineering, The University of Adelaide, Adelaide, Australia
2.) School of Resource and Environmental Engineering, Wuhan University of Science and Technology, Wuhan, China

Jiayi Shen: Institute of Port, Coastal and Offshore Engineering, Zhejiang University, Hangzhou, China

Abstract
Experimental study of the deterioration of high-temperature rock subjected to rapid cooling is essential for thermal engineering applications. To evaluate the influence of thermal shock on heated granite with different temperatures, laboratory tests were conducted to record the changes in the physical properties of granite specimens and the dynamic mechanical characteristics of granite after rapid cooling were experimentally investigated by using a split Hopkinson pressure bar (SHPB). The results indicate that there are threshold temperatures (500-600oC) for variations in density, porosity, and P-wave velocity of granite with increasing treatment temperature. The stress-strain curves of 500-1000oC show the brittle-plastic transition of tested granite specimens. It was also found that in the temperature range of 200-400oC, the through-cracks induced by rapid cooling have a decisive influence on the failure pattern of rock specimens under dynamic load. Moreover, the increase of crack density due to higher treatment temperature will result in the dilution of thermal shock effect for the rocks at temperatures above 500oC. Eventually, a fitting formula was established to relate the dynamic peak strength of pretreated granite to the crack density, which is the exponential function.

Key Words
rapid cooling; thermal stress; physical properties; rock dynamic; crack density

Address
Tubing Yin, Shuaishuai Zhang, Xibing Li and Lv Bai: School of Resources and Safety Engineering, Central South University, Changsha, Hunan, China

Abstract
Geogrid application that has proved to be an effective and economic method of reinforcing particles, is widely used in geotechnical engineering. The discrete element method (DEM) has been used to investigate the micro mechanics of the geogrid deformation and also the interlocking mechanism that cannot be easily studies in laboratory tests. Two types of realistically shaped geogrid models with square and triangle apertures were developed using parallel bonds in PFC3D. The calibration test simulations have demonstrated that the precisely shaped triangular geogrid model is also able to reproduce the deformation and strength characteristics of geogrids. Moreover, the square and triangular geogrid models were also used in DEM pull-out test simulations with idealized shape particle models for validation. The simulation results have been shown to provide good predictions of pullout force as a function of displacement especially for the initial 30 mm displacement. For the granular material of size 40 mm, both the experimental and DEM results demonstrate that the triangular geogrid of size 75 mm outperforms the square geogrid of size 65 mm. Besides, the simulations have given valuable insight into the interaction between particle and geogrid and also revealed similar deformation behavior of geogrids during pullout. Therefore, the DEM provides a tool which enable to model other possible prototype geogrid and investigate their performance before manufacture.

Key Words
DEM, geogrid; aperture shape; deformation behavior; interlocking mechanism; pullout test

Address
Cheng Chen and Rui Rui: School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan, 430070 China

Glenn McDowell: Nottingham Center for Geomechanics, University of Nottingham, Nottingham, U.K.

Abstract
sources of energy. The storage of solar thermal energy is a crucial aspect for implementing the solar energy for space heating in high latitudes, where solar insolation is high in summer and almost negligible in winter when the domestic heating demand is high. To use the solar heating during winter thermal energy storage is required. In this paper, equations representing the single U-tube heat exchanger are implemented in weak form edge elements in COMSOL Multiphysics to speed up the calculation process for modelling of a borehole storage layout. Multiple borehole seasonal solar thermal energy storage scenarios are successfully simulated. After 5 years of operation, the most efficient simulated borehole pattern containing 168 borehole heat exchangers recovers 69% of the stored seasonal thermal energy and provides 971 MWh of thermal energy for heating in winter.

Key Words
solar thermal energy, borehole thermal energy storage, numerical modelling, COMSOL, weak form, rock

Address
Mateusz Janiszewski, Topias Siren, Lauri Uotinen, Harm Oosterbaan and Mikael Rinne: Department of Civil Engineering, School of Engineering, Aalto University, P.O. Box 12100, FI-00076 AALTO, Finland

Abstract
Slope stability of sensitive clayey soils is particularly important when subjected to strength loss and deformation. Except for progressive failure, for most sensitive and insensitive slopes, it is important to review the feasibility of conventional analysis methods based on peak strength since peak strength governs slope stability before yielding. In this study, as a part of efforts to understand the behavior of sensitive clay slopes, a total of 12 centrifuge tests were performed for artificially sensitive and insensitive clay slopes using San Francisco Bay Mud (PI = 50) and Yolo Loam (PI = 10). In terms of slope stability, the results were analyzed using the updated instability factor (NI). NI using equivalent unit weight to cause a failure is in reasonable agreement shown in the Taylor\'s chart (NI ~ 5.5). In terms of dynamic deformation, it is shown that two-way sliding is a more accurate approach than conventional one-way sliding. Two-way sliding may relate to diffused shear surfaces. The outcome of this study is contributable to analyzing stability and deformation of steep sensitive clay slopes.

Key Words
sensitive clay; slope stability; sensitivity; cement treated; centrifuge model; limit equilibrium

Address
Dong Soon Park: K-water Convergence Research Institute, Korea Water Resources Corporation,125, 1689beon-gil, Yuseong-daero, Yuseong-gu, Daejeon 34045, Republic of Korea


Abstract
The study on the performance of the nonlinear friction tuned mass dampers (FTMD) for the mitigation of the seismic responses of the structures is a topic that still inspires the efforts of researchers. The present paper aims to carry out a numerical study on the optimum tuning of TMD and FTMD parameters using a multi-objective particle swarm optimization (MOPSO) algorithm including soil-structure interaction (SSI) effects for seismic applications. Considering a 3-story structure, the performances of the optimized TMD and FTMD are compared with the uncontrolled structure for three types of soils and the fixed base state. The simulation results indicate that, unlike TMDs, optimum tuning of FTMD parameters for a large preselected mass ratio may not provide a best and optimum design. For low mass ratios, optimal selection of friction coefficient has an important key to enhance the performance of FTMDs. Consequently, a free parameter search of all FTMD parameters provides a better performance in comparison with considering a preselected mass ratio for FTMD in the optimum design stage of the FTMD. Furthermore, the SSI significant effects on the optimum design of the TMD and FTMD. The simulation results also show that the FTMD provides a better performance in reducing the maximum top floor displacement and acceleration of the building in different soil types. Moreover, the performance of the TMD and FTMD decrease with increasing soil softness, so that ignoring the SSI effects in the design process may give an incorrect and unrealistic estimation of their performance.

Key Words
seismic-excited structures; tuned mass damper; friction tuned mass damper; multi-objective particle swarm optimization; soil-structure interaction

Address
Sadegh Etedali: Department of Civil Engineering, Birjand University of Technology, P.O. Box 97175-569, Birjand, Iran

Abstract
Longitudinal Displacement Profile (LDP) is an appropriate tool for determination of the displacement magnitude of the tunnel walls as a function of the distance to the tunnel face. Some useful formulations for calculation of LDP have been developed based on the monitoring data on site or by 3D numerical simulations. However, the presented equations are only based on the tunnel dimensions and for different quality of rock masses proposed a unique LDP. In the present study, it is tried to present a new formulation, for calculation of LDP, on the basis of Rock mass quality. For this purpose, a comprehensive numerical simulation program was developed to investigate the effect of rock mass quality on the LDP. Results of the numerical modelling were analyzed and the least square technique was used for fitting an appropriate curve on the derived data from the numerical simulations. The proposed formulation in the present study, is a logistic function and the constants of the logistic function were predicted by rock mass quality index (GSI). Results of this study revealed that, the LDP curves of the tunnel surrounded by rock masses with high quality (GSI>60) match together; because the rock mass deformation varies over an elastic range.

Key Words
: longitudinal displacement profile (LDP); logistic function; least square technique; rock mass quality

Address
Ali Rooh, Hamid Reza Nejati and Kamran Goshtasbi: Rock Mechanics Division, School of Engineering, Tarbiat Modares University

Abstract
Studies of soil dynamic properties in Malaysia are still very limited. This study aims to investigate the dynamic properties of two selected tropical residual soils (i.e., Sandy Clay and Sandy Silt) and a sand mining trail (Silty Sand) in Peninsular Malaysia using 1g shaking table test. The use of 1g shaking table test for soil dynamic testing is often constrained to large strain level and small confining pressure only. Three new experimental setups, namely large laminar shear box test (LLSBT), small chamber test with positive air pressure (SCT), and small sample test with suction (SSTS) are attempted with the aims of these experimental setups are capable of evaluating the dynamic properties of soils covering a wider range of shear strain and confining pressure. The details of each experimental setup are described explicitly in this paper. Experimental results show that the combined use of the LLSBT and SCT is capable of rendering soil dynamic properties covering a strain range of 0.017%-1.48% under confining pressures of 5-100 kPa. The studied tropical residual soils in Malaysia behaved neither as pure sand nor clay, but show a relatively good agreement with the dynamic properties of residual soils in Singapore. Effects of confining pressure and plasticity index on the studied tropical residual soils are found to be insignificant in this particular study.

Key Words
residual soil; 1g shaking table test; secant shear modulus; damping ratio; confining pressure

Address
Jun X. Lim and Yasuo Tanaka:Department of Civil Engineering, Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Selangor, Malaysia

Min L. Lee:Department of Civil Engineering, Faculty of Engineering, University of Nottingham Malaysia, Selangor, Malaysia

Abstract
Technological innovations in sustainable materials for soil improvement have attracted considerable interest due to energy crisis and environmental concerns in recent years. This study presents results of a comprehensive investigation on utilization of nanocarbons in reinforcement of a residual soil mixed with 0, 10 and 20% bentonite. Effects of adding proportionate quantities (0, 0.05, 0.075, 0.1 and 0.2%) of carbon nanotubes and carbon nanofibers to soil samples of different plasticities were evaluated. The investigation revealed that the inclusion of nanocarbons into the soil samples significantly improved unconfined compressive strength, Young\'s modulus and indirect tensile strength. It was observed that carbon nanofibers showed better performance as compared to carbon nanotubes. The nanosized diameter and high aspect ratio of nanocarbons make it possible to distribute the reinforcing materials on a much smaller scale and bridge the inter-particles voids. As a result, a better \'soil-reinforcing material\' interaction is achieved and desired properties of the soil are improved at nanolevel.

Key Words
soft soils; nanocarbons; soil improvement; unconfined compression; elastic modulus; indirect tensile strength

Address
Mohd R. Taha: 1.) Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor, Malaysia
2.) Institute for Environment and Development (LESTARI), Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor, Malaysia

Jamal M. A. Alsharef and Maryam Gaber: Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor, Malaysia

Tanveer A. Khan: Department of Civil Engineering, Bahauddin Zakariya University, Multan, Pakistan

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


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