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CONTENTS
Volume 27, Number 2, October25 2021
 


Abstract
An environmentally friendly improvement method with using biopolymer stabilization of soil has been currently paid more attention for geotechnical engineering practices. And the existing concerns focused on the performance of biopolymers treated clay due to the occurrence of electrical interaction. Therefore, the effect of biopolymer types and water content on the behaviors of biopolymer-clay mixture should be firstly explored in terms of biopolymer applications. In this study, fall cone tests were conducted to evaluate the consistency variations of eight types of biopolymers treated clay, e.g., carrageenan kappa gum (KG), locust bean gum (LBG), xanthan gum (XG), agar gum (AG), guar gum (GG), sodium alginate (SA), gellan gum (GE) and chitosan (CH) at various biopolymer concentrations (e.g., between 0.1% to 5% biopolymer to soil mass ratio). The results indicated that neutral biopolymers (e.g., LBG and GG) significantly caused the increase of liquid limit and undrained shear strength regardless of biopolymer concentration. And the liquid limit and undrained shear strength of negative charged biopolymers (e.g., KG, SA, GE and XG) treated clay decreased firstly following increased, while AG and CH had limit effect on soil consistency. In addition, the trend of plasticity index was similar to liquid limit altering the USCS classification of biopolymer treated clay as silt or clay. Moreover, empirical equations determining undrained shear strength and shear viscosity of biopolymer-treated clay were also established.

Key Words
biopolymer treated clay; shear viscosity; soil classification; soil consistency; undrained shear strength

Address
Zhanbo Cheng and Xueyu Geng: School of Engineering, University of Warwick, Coventry CV47AL, U.K.

Abstract
This paper presents a simplified modelling strategy to simulate the soil-foundation-structure interaction under seismic loadings. The interaction of soil and structure is modeled by a macro-element with the coupling of geometric and material non-linearities. The model consists of 4 degrees of freedom in which the superstructure is lumped as a single degree of freedom (DOF) while the soil-foundation is modeled by 3 DOFs. The dynamic equilibrium equations are solved by a Newmark time integration scheme and implemented in Matlab. To verify the numerical model, an experimental investigation based on shaking table method has been conducted in the present study. Five series of earthquake motions with maximum acceleration increased from 0.1 m/s^2 to 1.4 m/s^2were applied and the results of time-dependent accelerations and displacements are extracted. Based on the result comparisons, it is found that the numerical results were well validated against the experimental results.

Key Words
experimentation; macro-element; seismic loading; shaking table test; soil-structure interaction

Address
Van Quan Huynh: Campus in Ho Chi Minh city, University of Transport and Communications, Ho Chi Minh City, Vietnam

Trung Kien Nguyen and Xuan Huy Nguyen: Research and Application Center for Technology in Civil Engineering (RACE), University of Transport and Communications, Hanoi,

Abstract
Thin layers have substantial effects on the ultimate bearing capacity, despite their seeming insignificant. In this research, the effects of a thin layer on the ultimate bearing capacity of a circular footing on the sand bed are investigated by small-scale physical models. The investigations were carried out by varying the material type, thickness, and depth of the thin layer. The results indicate that the weak thin layer decreases both the ultimate bearing capacity and stiffness of the soil-footing system and the strong thin layer increases both the ultimate bearing capacity and the soil-footing system stiffness. The amount of this effect depends on the thickness, depth of deposition, and the material type of the thin layer. According to the results, the weak layer for the critical depth of 1B led to the most reduction in ultimate bearing capacity by 26% (from 183 kPa to 135 kPa), while no effects were observed at the depth of 2B. The strong layer is also for the state where this layer is just below the footing, had the highest increase in ultimate bearing capacity by 329% (from 183 kPa to 603 kPa), but at a depth of about 1.25B, it was ineffective.

Key Words
physical model; stiffness; strong thin layer; ultimate bearing capacity; weak thin layer

Address
Morteza Askari, Ahad Bagherzadeh Khalkhali and Navid Ganjian: Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

Abstract
Brazilian tensile strength (BTS) is a critical mechanical parameter of rock; and the measurement of BTS performed on core samples is a cumbersome procedure. Thus, rock index properties including point load, P-wave velocity and Schmidt hammer tests have been widely used to estimate BTS. The correlations between BTS and index properties are rock-type, grain size and anisotropy dependent, but, how the correlations related to the variation of grain size or anisotropy remain unexplained. In this study, the impact of grain size or anisotropy on those correlations is respectively examined using sandstone (fine or coarse grain size) and gneiss (0o, 45o, 90o inclined anisotropy) samples. Several significant equations for predicting BTS through index properties were established for different types of samples. The finding implies that either grain size variation or multidirectional anisotropy reduces not only the correlated degree between BTS and index properties, but also the BTS estimation reliability of those empirical equations. All three index properties should be used with much care for coarse-grained rock and respectively performed on samples with unidirectional anisotropy. Using an empirical equation between BTS and index properties ignoring grain size or anisotropy can yield considerable discrepancies of estimated BTS. Among three index properties, point load test is the first choice for predicting BTS as the small discrepancies of estimated results. As the invalid correlation, P-wave velocity test should not be performed at 45o angle to the anisotropy in the BTS estimation; and this recommendation is also appropriate for Schmidt hammer test conducted parallel to anisotropy.

Key Words
anisotropy; Brazilian tensile strength; correlations; grain size; rock index properties

Address
Fanmeng Kong, Yiguo Xue, Daohong Qiu, Zhiqiang Li, Qiqi Chen and Qian Song: Geotechnical and Structural Engineering Research Center, Shandong University, No. 17923 of Jingshi Road, Jinan City, China

Abstract
Selecting suitable simulation methods for complex problems requires a careful balance between the predicted accuracy and computational effort. This research comparatively investigated the effects of adjacent loaded pile row on an existing tunnel in terms of tunnel deformation and lining force, displacement of soil surrounding between tunnel and pile and load transfer of the pile. Simulations were carried out by eight simulation models consisting of 3D finite element (FE) full models (model 1-2); 3D FE symmetry models (model 3-4); and a pile wall in 2D FE models (models 5-8). In loaded pile row simulation, simulations were performed with two pile types: volume pile and embedded pile. In 2D simulation, the 3D pile row was converted into 2D pile wall under plane strain condition by using three transformation methods. The results show that the predicted tunnel responses are adequately accurate as long as the reasonable soil movement behavior can be reproduced. The 2D equivalent dimensions and 2D equivalent axial rigidity are recommended since they provide conservative estimation on both tunnel deformation and lining forces. The 2D equivalent flexural rigidity is not recommended if the pile response is also of concern. The novelty of this research lies in the use and discussion on the applicability of various 2D and 3D models to simulate the effects of adjacent loaded pile row on the existing tunnel, as opposed to previous studies which focused on one or two simulation models.

Key Words
2D Finite element method; 3D Finite element method; adjacent loaded pile row; existing tunnel; tunnel response

Address
Narunat Heama,Prateep Lueprasert and Suchatvee Suwansawat: Department of Civil Engineering, School of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok, Thailand

Pornkasem Jongpradist: Construction Innovations and Future Infrastructures Research Center, Department of Civil Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi, Bangkok, Thailand

Pitthaya Jamsawang: Soil Engineering Research Center, Department of Civil Engineering, King Mongkut's University of Technology North Bangkok, Thailand


Abstract
This paper focuses on the use of a certain punched and drawn geogrid to increase the bearing capacity of a circular shallow foundation subjected to a combination of static and repeated loads. In the experiments, the foundation is first subjected to a prespecified static load, afterwards, a repeated load derived in different proportions of the applied static load is superimposed to that static load. The variables investigated in the tests are the number of geogrid layers, the amplitude of repeated load, and the number of load cycles. The effect of these variables is also investigated by a finite element numerical modeling approach verified with one-dimensional site response analysis, and as a consequence of this effort that refers to the innovation of the study, the consistency between the results obtained from both methods is observed. The test results show that the displacements of the shallow foundation increase rapidly in the first 100 load cycles in all cases. After that, the rate of increase is reduced until about 2000 load cycles and the displacements become negligible. From the experiments, 2 geogrid layers were found to be quite effective in reducing displacements due to both static and dynamic loading cases. In other respects, finite element simulations of the physical experiment have produced numerical results in good agreement with the test results. Plus, the main contribution of the numerical simulation is to indicate the deformed mesh outputs of the model including the geogrids for the foregoing variables.

Key Words
finite element method; geogrid-reinforcement; large-scale test; repeated loading; shallow foundation

Address
Mustafa Tolun: Department of Civil Engineering, Adana Alparslan Turkes Science and Technology University, 01250, Adana, Turkey

Sefer E. Epsileli: 6th Regional Directorate, Republic of Turkey General Directorate of Highways, 38060, Kayseri, Turkey

Buse Emirler and Abdulazim Yildiz: Department of Civil Engineering, Cukurova University, 01250, Adana, Turkey

Erol Tutumluer: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Illinois, 61801, U.S.A.

Abstract
The artificial ground freezing technique has been widely adopted in tunnel construction in order to impede heavy water flow and to reinforce weak sections during excavation. While liquid nitrogen is one of common cryogenic refrigerants particularly for rapid freezing, it has a serious potential risk of suffocation due to an abrupt increase in nitrogen content in the atmosphere after being vaporized. This paper introduces a novel cryogenic refrigerant, liquid air, and addresses the applicability of it by performing a series of laboratory chamber experiments. The key parameters for the application of artificial freezing using liquid air in subsea tunnel construction are freezing time and energy consumption, which were evaluated and discussed in this paper. The comparative study of these parameters between the use of liquid air and liquid nitrogen demonstrates that liquid air with no risk of suffocation can be a potential substitute for liquid nitrogen delivering the equivalent performance. In addition, the theoretical model was adopted to evaluate the chamber experiments in an effort to estimate the freezing time and the energy consumption ratio (energy consumption for maintaining the frozen state to the energy consumption for freezing soil specimens).

Key Words
artificial ground freezing; energy consumption ratio; freezing time; heat transfer; liquid air; refrigerant

Address
Youngjin Son: Eco Infra Solutions Team2, SK Ecoplant, Seoul, 03149, Republic of Korea

Tae Young Ko: Department of Energy and Resources Engineering, Kangwon National University, Kangwon, 24341, Republic of Korea

Dongseop Lee: POSCO, Incheon, 21998, Republic of Korea

Jongmuk Won: Department of Civil Engineering, University of Ulsan, Ulsan, 44610, Republic of Korea

In-Mo Lee and Hangseok Choi: School of Civil, Environmental, & Architectural Engineering, Korea University, Seoul, 02841, Republic of Korea

Abstract
This paper adopts the kinematic theorem of limit analysis to assess the seismic stability of a two-stage slope. The seismic effect is taken into account by using the pseudo-static approach. The failure mechanism for the slope is extended to include below-toe failure, toe failure and face failure. Validation of this approach is conducted by comparing the factor of safety with the data in the existing literatures. The stability charts are presented based on the graphical method for reading the factor of safety readily. Parametric study involving the effect of slope geometry, internal friction angle, seismic effect as well as depth coefficient on the stability of a two-stage slope is carried out. The critical failure surfaces with various parameters are plotted. The results obtained reveal the significant influence of slope geometry on the failure mechanism of a two-stage slope under static and seismic condition.

Key Words
critical failure surface; limit analysis; safety factor; seismic stability; two-stage slope

Address
Pingping Rao and Jian Wu: Department of Civil Engineering, University of Shanghai for Science and Technology, Shanghai 20093, China

Ganyou Jiang: Guangxi Luqiao Engineering Group Co., Ltd., Nanning 530011, China

Yunwei Shi: School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiaotong University, Shanghai 200240, China

Qingsheng Chen: Hubei Provincial Ecological Road Engineering Technology Research Center, Hubei University of Technology, Wuhan, 430068, China

Sanjay Nimbalkar: School of Civil and Environmental Engineering, University of Technology Sydney, 15 Broadway Ultimo NSW 2007, Australia


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