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CONTENTS
Volume 23, Number 3, November10 2020
 

Abstract
The accurate modeling of boundary conditions is important in simulations of the discrete element method (DEM) and can affect the numerical results significantly. In conventional triaxial compression (CTC) tests, the specimens are wrapped by flexible membranes allowing to deform freely. To accurately model the boundary conditions of CTC, new flexible boundary algorithms for 2D and 3D DEM simulations are proposed. The new algorithms are computationally efficient and easy to implement. Moreover, both horizontal and vertical component of confining pressure are considered in the 2D and 3D algorithms, which can ensure that the directions of confining pressure are always perpendicular to the specimen surfaces. Furthermore, the boundaries are continuous and closed in the new algorithms, which can prevent the escape of particles from the specimens. The effectiveness of the proposed algorithms is validated by biaxial and triaxial simulations of granular materials. The results show that the algorithms allow the boundaries to deform non-uniformly on the premise of maintaining high control accuracy of confining pressure. Meanwhile, the influences of different lateral boundary conditions on the numerical results are discussed. It is indicated that the flexible boundary is more appropriate for the models with large strain or significant localization than rigid boundary.

Key Words
discrete element method; conventional triaxial compression; flexible boundary; granular materials; localization

Address
Donghai Liu and Jiaqi Yang: State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 3003550, China

Abstract
This paper presents a kinematic limit analysis for passive earth pressure of rigid retaining structures considering the unsaturation of the backfill. Particular emphasis in the current work is focused on the effects of the spatial change in the degree of saturation on the passive earth pressure under different steady-infiltration/evaporation conditions. The incorporation of change of effective unit weight with degree of saturation is the main contribution of this study. The problem is formulated based on the log-spiral failure model rather than the linear wedge failure model, in which both the spatial variations of suction and soil effective unit weight are taken into account. Parametric studies, which cover a wide range of flow conditions, soil types and properties, wall batter, back slope angle as well as the interface friction angle, are performed to investigate the effects of these factors on the passive pressure and the corresponding shape of potential failure surfaces in the backfill. The results reveal that the flow conditions have significant effects on the suction and unit weight of the clayey backfill, and hence greatly impact the passive earth pressure of retaining structures. It is expected that present study could provide an insight into evaluation of the passive earth pressure of retaining structures with unsaturated backfills.

Key Words
passive earth pressure; retaining structure; unsaturation; suction; log spiral failure model

Address
Li Zheng, Lin Li and Jingpei Li: Department of Civil Engineering, Tongji University, Shanghai 200092, China

De'an Sun: Department of Civil Engineering, Shanghai University, Shanghai 200444, China

Abstract
In this paper, the thermoelastic interactions in a two-dimension porous body are studied. This problem is solved by using the Green and Lindsay (GL) generalized thermoelasticity model under fractional time derivative. The derived approaches are estimated. with numeral results which are applied to the porous mediums in simplifying geometrical. The bounding plane surface of the present half-space continuum is subjected to a pulse heat flux. We use the Laplace-Fourier transforms methods with the eigenvalues approach to solve the problem. The numerical solutions for the field functions are obtained numerically using the numerical Laplace inversion technique. The effects of the fractional parameter and the thermal relaxation times on the temperature field, the displacement field, the change in volume fraction field of voids distribution and the stress fields have been calculated and displayed graphically and the obtained results are discussed.

Key Words
Laplace-Fourier transforms; Green and Lindsay model; porous medium; eigenvalues approach; fractional derivative

Address
Faris S. Alzahrani: Nonlinear Analysis and Applied Mathematics Research Group (NAAM), Department of Mathematics, King Abdulaziz University, Jeddah, Saudi Arabia

Ibrahim A. Abbas: 1.) Nonlinear Analysis and Applied Mathematics Research Group (NAAM), Department of Mathematics, King Abdulaziz University, Jeddah, Saudi Arabia
2.) Department of mathematics, Faculty of Science, Sohag University, Sohag, Egypt


Abstract
Earthen structures have an excellent bioclimatic performance, but they are vulnerable against earthquakes. In order to investigate the edification process and costs, a full-scale rammed soil house was constructed in 2004. In 2016-2019, it was studied its seismic damage, durability and degradation process. During 2004-2016, the house presented a relatively good seismic performance (Mw=5.6-6.4). The damaged cover contributed in the fast deterioration of walls. In 2018 it was observed a partial collapse of one wall due to recent seismicity (Mw=5.6-6.1). The 15-year-old samples presented a reduced compressive strength (0.040 MPa) and a minimum moisture (1.38%). It is estimated that the existing house has approximately a remaining 20% of compressive strength with a degradation of about 5.4% (0.0109 MPa) per year (considering a time frame of 15 years) if compared to the new soil samples (0.2028 MPa, 3.52% of moisture). This correlation between moisture and compressive strength degradation was compared with the study of new soil samples at the same construction site and compared against the extracted samples from the 15-year-old house. At 7-14-days, the specimens presented a similar compressive strength as the degraded ones, but different moisture. Conversely, the 60-days specimens shown almost five times more strength as the existing samples for a similar moisture. It was observed in new rammed soil that the lower the water content, the higher the compressive/shear strength.

Key Words
earthquakes; rammed soil; self-construction; decay; in-situ and laboratory testing; failure mechanisms; moisture content

Address
Adolfo Preciado and Juan Carlos Santo: Department of Habitat and Urban Development,Western Institute of Technology and Higher Education (ITESO), 45604, Tlaquepaque, Jalisco, Mexico

Alejandro Ramirez-Gaytan: Department of Computational Sciences (CUCEI), University of Guadalajara (UdeG), 44430 Guadalajara, Jalisco, Mexico

Karla Ayala: Departament of Architecture, Technological Institute of Colima (ITC), 28979, Villa de Alvarez, Mexico

Jose de Jesus Garcia: Labconstru Maza, S.A. de C.V., 82134, Mazatlan, Sinaloa, Mexico

Abstract
Tunnels have become an indispensable part of metro cities. Blast resistance design of tunnel has attracted the attention of researchers due to numerous implosion event. Present paper deals with the non-linear finite element analysis of rock tunnel having shear zone subjected to internal blast loading. Abaqus Explicit schemes in finite element has been used for the simulation of internal blast event. Structural discontinuity i.e., shear zone has been assumed passing the tunnel cross-section in the vertical direction and consist of Highly Weathered Granite medium surrounding the tunnel. Mohr-Coulomb constitutive material model has been considered for modelling the Highly Weathered Granite and the shear zone material. Concrete Damage Plasticity (CDP), Johnson-Cook (J-C), Jones-Wilkins-Lee (JWL) equation of state models are used for concrete, steel reinforcement and Trinitrotoluene (TNT) simulation respectively. The Coupled-Eulerian-Lagrangian (CEL) method of modelling for TNT explosive and air inside the tunnel has been adopted in this study. The CEL method incorporates the large deformations for which the traditional finite element analysis cannot be used. Shear zone orientations of 0o, 15o, 30o, 45o, 60o, 75o and 90o, with respect to the tunnel axis are considered to see their effect. It has been concluded that 60o orientation of shear zone presents the most critical situation.

Key Words
rock; tunnel; blast; abaqus; finite element method; coupled Eulerian Lagrangian; Jones Wilkins Lee-equation of state; granite

Address
Mohammad Zaid, Md. Rehan Sadique, M. Masroor Alam: Department of Civil Engineering, Zakir Husain College of Engineering and Technology, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India

Manojit Samanta: CSIR-Central Building Research Institute, Roorkee-247667, Uttrakhand, India

Abstract
This paper presents an efficient method utilizing user-defined computer functional codes to determine the reliability of an embankment slope with spatially varying soil properties in real time. The soils'mechanical properties varied with the soil layers that had different degrees of compaction and moisture content levels. The Latin Hypercube Sampling (LHS) for the degree of compaction and Kriging simulation of moisture content variation were adopted and programmed to predict their spatial distributions, respectively, that were subsequently used to characterize the spatial distribution of the soil shear strengths. The shear strength parameters were then integrated into the Geostudio command file to determine the safety factor of the embankment slope. An explicit metamodal for the performance function, using the Kriging method, was established and coded to efficiently compute the failure probability of slope with varying moisture contents. Sensitivity analysis showed that the proposed method significantly reduced the computational time compared to Monte Carlo simulation. About 300 times LHS Geostudio computations were needed to optimize precision and efficiency in determining the failure probability. The results also revealed that an embankment slope is prone to high failure risk if the degree of compaction is low and the moisture content is high.

Key Words
soil; embankment; compaction; moisture content; slope stability; reliability

Address
Tao Bai: School of Civil Engineering and Architecture, Wuhan Institute of Technology, Wuhan, China

Han Yang: 1.) School of Civil Engineering and Architecture, Wuhan Institute of Technology, Wuhan, China
2.) Wuhan Hengtong Highway Survey and Design Co., Ltd, Wuhan, China

Xiaobing Chen: School of Transportation, Southeast University, China

Shoucheng Zhang: Wuhan Municipal Engineering Design & Research Institute Co., Ltd., Wuhan 430072, China

Yuanshang Jin: Liaoning Zhixin Highway Engineering Technology Consulting Corporation, Shenyang, 110000, China

Abstract
Rectangular barrettes have been increasingly used as foundations for many infrastructure projects, but the vertical vibration of a barrette has been rarely addressed theoretically. This paper presents an analysis method of dynamic response for a rectangular barrette subjected to a time-harmonic vertical force with the aid of a modified Vlasov foundation model in multilayered viscoelastic soil. The barrette-soil system is modeled as a continuum, the vertical continuous displacement model for the barrette and soil is proposed. The governing equations of the barrette-soil system and the boundary conditions are obtained and the vertical shaft resistance of barrette is established by employing Hamilton's principle for the system and thin layer element, respectively. The physical meaning of the governing equations and shaft resistance is interpreted. The iterative solution algorithm flow is proposed to obtain the dynamic response of barrette. Good agreement of the analysis and comparison confirms the correctness of the present solution. A parametric study is further used to demonstrate the effects of cross section aspect ratio of barrettes, depth of soil column, and module ratio of substratum to the upper soil layers on the complex barrette-head stiffness and the resistance stiffness.

Key Words
barrette; multilayered viscoelastic soil; continuum; Hamilton's principle; dynamic response

Address
Geng Cao, Ming X. Zhu, Wei M. Gong and Guo L. Dai: 1.) Key of Laboratory for RC and PRC Structure of Education Ministry, Southeast University, Nanjing 211189, China
2.) School of Civil Engineering, Southeast University, Nanjing 211189, China

Xiao Wang: School of Civil Engineering, Southeast University, Nanjing 211189, China

Abstract
With the rapid development of the distributed strain sensing (DSS) technology, the strain becomes an alternative monitoring parameter to analyze slope stability conditions. Previous studies reveal that the horizontal strain measurements can be used to evaluate the deformation pattern and failure mechanism of soil slopes, but they fail to consider various influential factors. Regarding the horizontal strain as a key parameter, this study aims to investigate the stability condition of a locally loaded slope by adopting the variable-controlling method and conducting a strength reduction finite element analysis. The strain distributions and factors of safety in different conditions, such as slope ratio, soil strength parameters and loading locations, are investigated. The results demonstrate that the soil strain distribution is closely related to the slope stability condition. As the slope ratio increases, more tensile strains accumulate in the slope mass under surcharge loading. The cohesion and the friction angle of soil have exponential relationships with the strain parameters. They also display close relationships with the factors of safety. With an increasing distance from the slope edge to the loading position, the transition from slope instability to ultimate bearing capacity failure can be illustrated from the strain perspective.

Key Words
soil strain; slope stability; finite element analysis (FEA); strength reduction method (SRM)

Address
Jia-Chen Wang and Bin Shi: School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China

Hong-Hu Zhu: 1.) School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
2.) Key Laboratory of Mountain Hazards and Earth Surface Processes, Chinese Academy of Sciences, Chengdu 610041, China

Ankit Garg: 1.) Department of Civil and Environmental Engineering, Shantou University, Shantou 515063, China
2.) Guangdong Engineering Center for Structure Safety and Health Monitoring, Shantou University, Shantou 515063, China


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