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CONTENTS
Volume 27, Number 3, November10 2021
 

Abstract
The present work focuses on analysing the displacement of a shallow foundation due to sudden change in state of loading. When a dynamic load hits the foundation, before attaining steady state, the foundation undergoes sudden displacement. This displacement is a function of soil properties viz. modulus of elasticity, Poisson's ratio, loading conditions and the static load already applied on the foundation. A Finite Element based numerical model that considers soil structure interaction is simulated to generate a data set. After verification of model results, the dataset is analysed using five different methods including Levenberg Marquardt Neural Network (LMNN), Bayesian Regularization Neural network (BRNN), Support Vector Machines (SVM), Multivariate Adaptive Regression Splines (MARS) and Multi Gene Genetic Programming (MGGP). A comparative analysis of all the methods has been presented to find out the most effective method. In addition to these, sensitivity analysis is performed to find out the most influencing input parameter. The BRNN method is found to be the most efficient method and the static load on the foundation is the most influencing parameter as revealed from the rigorous statistical analysis. The outcomes will be helpful in quick analysis of shallow strip foundations.

Key Words
artificial intelligence; displacement; sensitivity analysis; shallow strip foundations; soil structure interaction; statistical analysis

Address
Suvendu K. Sasmal:Department of Civil Engineering, National Institute of Technology Rourkela, India

Rabi N. Behera:Department of Civil Engineering, National Institute of Technology Rourkela, India

Abstract
The vertical uplift resistance of circular plate anchors buried in undrained two-layered clays was studied by means of finite element method. Anchors with immediate breakaway (vented) and no breakaway (bonded) are taken into account. The numerical results are given in the form of the breakout factors accounting for the anchor embedment depth, top layer thickness, clay strength ratio, and clay overburden (clay self-weight), which are compared with existing empirical and analytical solutions.It is found that the breakout factors for strong-over-soft clays are greater than those for soft-over-strong clays. Also, the breakout factors of bonded anchors are identical to those of vented anchors with large overburden pressure. Failure patterns are examined for the cases of soft-over-strong clay and strong-over-soft clay, depending on anchor embedment depth and top layer thickness.

Key Words
clays; layered soil; numerical analysis; plate anchors; uplift resistance

Address
Su Han Park:Department of Civil Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul, 02504, Republic of Korea

Joon Kyu Lee:Department of Civil Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul, 02504, Republic of Korea

Abstract
Granular mixtures are often encountered in civil engineering, but the micromechanical implications of their packing and shear characteristics are still unclear. In this study, the packing and shear characteristics of binary mixtures were studied using a three-dimensional discrete element method (DEM). The binary mixtures contained realistic gravel-shaped coarse particles and one of two tested fine particle shapes (namely, spherical or elongated particles). The densest isotropic samples were generated by using a frictionless condition. The initial void ratio and particle contacts of the packed samples were examined. This study shows that the particle shape of the fines affects the relationship between the initial void ratio and fines content (FC). The contact types in binary mixtures can be classified as coarse particle-coarse particle (CC contacts), coarse particle-fine particle (CF contacts) and fine particle-fine particle (FF contacts). A microscopic investigation of the particle contacts indicated that the coarse and fine particle shapes influenced the partial coordination numbers of the CC and CF contacts and the CF and FF contacts, respectively. All the samples were then subjected to numerical triaxial compression tests. The results show that the particle shape of the fines affected the magnitudes and evolutions of the peak (φp) and critical (φc) friction angles of the binary mixtures. Finally, an anisotropic analysis was performed to highlight the microscopic mechanisms that cause the shear strength to be dependent on the particle shape and FC.

Key Words
discrete element method; granular mixtures; fines content; fine particle shape; packing characteristics; shear strength

Address
Jian Gong:1)College of Civil Engineering and Architecture, Guangxi University, Guangxi, China 2)School of Civil Engineering, Central South University, Hunan, China

Lipo Cheng:College of Civil Engineering and Architecture, Guangxi University, Guangxi, China

Lianheng Zhao:School of Civil Engineering, Central South University, Hunan, China

Liang Li:School of Civil Engineering, Central South University, Hunan, China

Zhihong Nie:School of Civil Engineering, Central South University, Hunan, China

Abstract
In order to study the damage features and mechanical properties of rock-coal-rock combination (RCR) models with defects and filling material, the 2-Dimensional Particle Flow Code (PFC2D) is used for the numerical simulation models. The variations of stress-strain, caused by uniaxial compression, are investigated. The distribution of the stress and displacement fields in horizontal and vertical directions of the models after failure is analyzed. The damage characteristics are discussed from the microscopic aspects of crack development, acoustic emission and contact force distribution. The results show the following: (1)The defects significantly affect the mechanical properties, the propagation of internal cracks, the evolution of displacement and stress and the distribution of stress concentration area. The peak stress-strain and elastic modulus of RCR models with defects decrease as the number of square holes increases. The more defects, the earlier new cracks appear in the coal body and the easier the defective models fail. (2) After filling the holes of the defective models, the number of cracks, crack initiation stress, elastic modulus and peak stress-strain are significantly larger than those of the corresponding model with holes, meaning that they can sustain larger load. The displacement and stress fields of the filled models are similar to the ones of the complete combination model. Hence, the filling material can enhance the mechanical properties of the defective RCR combination models.

Key Words
damage; flaw filling; mechanical properties; PFC2D simulation; Rock-Coal-Rock combination; weak interlayer

Address
Han D. Liu:Henan Key Laboratory of Geomechanics and Structural Engineering, North China University of Water Resourcesand Electric Power, Zhengzhou, 450045, China

Shuai Liu: 1)Henan Key Laboratory of Geomechanics and Structural Engineering, North China University of Water Resourcesand Electric Power, Zhengzhou, 450045, China
2)College of Geosciences and Engineering, North China University of Water Resources and Electric Power, Zhengzhou, 450045, China

Zhi G. Xia:School of Mining Engineering, University of Science and Technology Liaoning, Anshan, 114051, China

Jing J. Liu: College of Geosciences and Engineering, North China University of Water Resources and Electric Power, Zhengzhou, 450045, China

Hao Guo: Liaoning Metallurgical Geological Exploration Team 405 Co., Ltd, Liaoyang, 111000, China

Yong T. Yuan:Hami energy security monitoring center of Xinjiang Uygur Autonomous Region, Hami, 839000, China

Abstract
As the curing process proceeds, both the strength and electrical resistivity (pmix) of cement-based (or cement-grouted) materials increase, leading to the nondestructive pmix measurement technique is very appealing in the assessment/monitoring of the quality of cement-grouted materials. However, the strength gain of cement-grouted sands with time differs from the increase in pmix with time. Thus, the relationship between unconfined compressive strength (UCS) and pmix can be affected by the curing time. This study evaluated the effect of curing time on the relationship between pmix and UCS of sands grouted with microcement. The ultimate goal of this study is to estimate UCS over time of cement-grouted sands based on pmix. Three silica sands with different median particle sizes were grouted with microcement at different water-to-cement ratios (wc) of 1.0, 1.5, and 2.0. Both unconfined compression test and electrical resistivity measurement test were conducted. Results demonstrate that curing time, particle size, and wc influenced both pmix and UCS of tested grouted sands in a similar manner; therefore, a direct relationship between pmix and UCS can be established. However, the complex impact of curing time on the relation between UCS and pmix and the nonlinear increase in UCS with time hinder the capture of adequate interplay between UCS, pmix, and curing time. Because a nonlinear increase in UCS with time can be represented by hyperbolic model, an estimation method for hyperbolic model parameters is newly suggested in this study based on pmix at early curing days.

Key Words
curing time; electrical resistivity; hyperbolic mode; microcement; unconfined compressive strength

Address
Hyunwook Choo:Department of Civil and Environmental Engineering, Hanyang University, Seoul 04763, Republic of Korea

Woojin Lee:School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Republic of Korea

Changho Lee:Department of Civil Engineering, Chonnam National University, Gwangju 61184, Republic of Korea

Abstract
Soil particles may be blocked at the pores of geotextiles even if the diameter of the soil particle is smaller than the size of the pores, and then a soil bridge is formed. To design a reasonable filter, it is vital to understand the formation of bridges at the soil-geotextile interface. The two-dimensional Distinct-Element Method was used to explore bridge formation at the cohesionless sand-geotextile interface. To realistically reflect the geological environment of cohesionless sand, the hydraulic gradient, confining pressure, multiple openings and inherent characteristics of cohesionless sand were covered in the simulations. It is found that both the number of openings of the filter and the uniformity coefficient of cohesionless sand had a substantial influence on the formation of a soil bridge. The bridge coefficient substantially decreased when there was more than one opening, because the narrower walls decreased the support of the bridge foot. When the confining pressure was greater than zero, the bridge coefficient was larger than that when there was no confining pressure. With the continual increase in the confining pressure, the confining pressure began to have an unfavourable effect on the formation of a soil bridge. The hydraulic gradient slightly decreased the bridge coefficient when the uniformity coefficient was 1.

Key Words
bridge formation; cohesionless sand; DEM method; geotextile; two-dimensional

Address
Sheng Liu:College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China

Yuan Wang:College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China

Di Feng:College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China

Abstract
This paper investigates the relative influences of backfill particle properties and imposed stress path on the response of retained granular assemblies. The characteristics considered are particle shape, backfill density, and gradation. For this purpose, Discrete Element Modelling (DEM) is employed to simulate the development of passive and active states in a cohesionless soil. Particle shape is assessed first through restraining the rotational freedoms of spherical particles (i.e. assigning rolling resistance), and the next by joining spherical particles (i.e. multisphere). The obtained results show that it is not possible to capture realistic response using a contact-independent rolling resistance model. Then, using backfill models composed of particles with various angularities, which are prepared at two alternative densities, backfill deformation towards passive and active states are simulated. Results are used to judge the relative weights of the influences of particle angularity, backfill density and gradation on back behaviour, employing both qualitative and quantitative methods. For densely packed clump particles varying particle angularity influences backfill density, shear band characteristics, geometries of the resulting failure wedges, and distribution of lateral backfill pressure. In addition, the effect of shape complexity is evaluated for packings with identical initial density, which are relatively loose. Overall, comparing the results from packings with different densities revealed the idea that particle shape effect is density and stress-path dependent.

Key Words
active state; density; Discrete Element Modelling (DEM); particle shape; passive state; retaining wall

Address
Adlen Altunbas:Department of Civil Engineering, Medipol University, Istanbul, Turkey

Behzad Soltanbeigi:Van Oord Dredging and Marine Contractors, Rotterdam, The Netherlands

Ozer Cinicioglu:Department of Civil Engineering, Bogazici University, Istanbul, Turkey

Abstract
The bench method is widely used in the construction of underground oil storage caverns. From the perspective of single caverns, a large amount of work has been performed on the cavern stability, assuming that the influence of the auxiliary tunnels can be ignored. This paper reevaluates the necessity of auxiliary tunnels for the stability analysis. First, the equivalent continuum model is established based on a cavern group that includes auxiliary tunnels, and the space-time evolution of the displacement field after excavation in a practical sequence is studied. Then, the field monitoring time series are collected to compare the differences in deformation characteristics between the intersection and non-intersection of auxiliary tunnels and caverns. The results show that the crown settlement is significantly increased at the intersection of the caverns affected by the auxiliary tunnels. When the three-cavern group design is adopted, the stability of the middle cavern is worse, and these intersections must be reinforced. The crown settlement before excavation accounts for approximately 40%–50% of the total. As different construction stages proceed, the convergence characteristics of different feature points in a whole section are different, which is helpful for improving the understanding of the deformation space-time evolution of the excavation.

Key Words
sequential excavation method; space-time evolution; stability evaluation; field monitoring; underground oil storage caverns

Address
Zexu Ning:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Maoxin Su:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Yiguo Xue:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Daohong Qiu:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Zhiqiang Li:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

Kang Fu:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China

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