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CONTENTS
Volume 14, Number 3, February28 2018
 

Abstract
In this paper, a predictive method accounting for the scaling effects of rockfill materials in the numerical deformation analysis of rockfill dams is developed. It aims to take into consideration the differences of engineering properties of rockfill materials between in situ and laboratory conditions in the deformation analysis. The developed method is based on the modification of model parameters used in the chosen material model, which is, in this study, an elasto-plastic model with double yield surfaces, i.e., the modified Hardening Soil model. Datasets of experimental tests are collected from previous studies, and a new dataset of the Nam Ngum 2 dam project for investigating the scaling effects of rockfill materials, including particle size, particle gradation and density, is obtained. To quantitatively consider the influence of particle gradation, the coarse-to-fine content (C/F) concept is proposed in this study. The simple relations between the model parameters and particle size, C/F and density are formulated, which enable us to predict the mechanical properties of prototype materials from laboratory tests. Subsequently, a 3D finite element analysis of the Nam Ngum 2 concrete face slab rockfill dam at the end of the construction stage is carried out using two sets of model parameters (1) based on the laboratory tests and (2) in accordance with the proposed method. Comparisons of the computed results with dam monitoring data indicate that the proposed method can provide a simple but effective framework to take account of the scaling effect in dam deformation analysis.

Key Words
scaling effects; modified model; coarse-to-fine content; finite element analysis; concrete face rockfill dam

Address
Raksiri Sukkarak, Pornthap Pramthawee, Pornkasem Jongpradist and Warat Kongkitkul: Department of Civil Engineering, King Mongkut

Abstract
In this paper, in order to explain the splitting of cylindrical rock specimen under uniaxial loading, cracks in cylindrical rock specimen are divided into two kinds, the longitudinal crack and the slanting crack. Mechanical behavior of the rock is described by elastic-brittle-plastic model and splitting is assumed to suddenly occur when the uniaxial compressive strength is reached. Expression of the stresses induced by the longitudinal crack in direction perpendicular to the major axis of the crack is deduced by using the Maxwell model. Results show that the induced stress is tensile and can be greater than the tensile strength even before the uniaxial compressive strength is reached. By using the Inglis\'s formula and simplifying the cracks as slender ellipse, the above conclusions that drawn by using the Maxwell model are confirmed. Compared to shearing fracture, energy consumption of splitting seems to be less, and splitting is most likely to occur when the uniaxial loading is great and quick. Besides, explaining the rock core disking occurred under the fast axial unloading by using the Maxwell model may be helpful for understanding that rock core disking is fundamentally a tensile failure phenomenon.

Key Words
rock splitting; uniaxial loading; fast axial unloading; Maxwell model; Griffith\'s criterion

Address
Houxu Huang, Jie Li and Xin Dong: State Key Laboratory of Disaster Prevention and Mitigation of Explosion and Impact,PLA University of Science and Technology,
Nanjing, China

Yiqing Hao: High-Tech Institute, Fan Gong-ting South Street on the 12th, Qingzhou, Shandong, China

Abstract
Pullout tests are usually employed to determine the ultimate bearing capacity of reinforced soil, and the load-displacement curve can be obtained easily. This paper presents an analytical solution for predicting the full-range mechanical behavior of a buried planar reinforcement subjected to pullout based on a bi-linear bond-slip model. The full-range behavior consists of three consecutive stages: elastic stage, elastic-plastic stage and debonding stage. For each stage, closed-form solutions for the load-displacement relationship, the interfacial slip distribution, the interfacial shear stress distribution and the axial stress distribution along the planar reinforcement were derived. The ultimate load and the effective bond length were also obtained. Then the analytical model was calibrated and validated against three pullout experimental tests. The predicted load-displacement curves as well as the internal displacement distribution are in closed agreement with test results. Moreover, a parametric study on the effect of anchorage length, reinforcement axial stiffness, interfacial shear stiffness and interfacial shear strength is also presented, providing insights into the pullout behaviour of planar reinforcements of MSE structures.

Key Words
planar reinforcements; analytical solution; pullout behavior; bond-slip model; parametric study

Address
Feifan Ren and Bin Ye: 1)Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, Shanghai 200092, China

2) Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China

Guan Wang: School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093, China

Abstract
The displacement monitoring data series reconstruction method was developed under equal water level effects based on displacement monitoring data of concrete dams. A dam displacement variation equation was set up under the action of temperature and aging factors by optimized analysis techniques and then the dam displacement hydraulic pressure components can be separated. Through the dynamic adjustment of temperature and aging effect factors, the aging component isolation method of dam displacement was developed. Utilizing the isolated dam displacement aging components, the dam stability model was established. Then, the dam stability criterion was put forward based on convergence and divergence of dam displacement aging components and catastrophe theory. The validity of the proposed method was finally verified combined with the case study.

Key Words
concrete dam; monitoring data; displacement effect factor separation; displacement aging component; stability model and criterion

Address
Xiaofei Huang, Dongjian Zheng, Meng Yang, Hao Gu, Huaizhi Su and Wenhan Cao: 1)College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
2)State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China
3National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, Hohai University, Nanjing 210098, China

Xinbo Cui: Information Center of Bureau of land and resources in Binzhou City, Binzhou 256603, China

Abstract
Soil stabilization can make the soils becoming more stable by using an admixture to the soil. Lime stabilization enhances the engineering properties of soil, which includes reducing soil plasticity, increasing optimum moisture content, decreasing maximum dry density and improving soil compaction. Silica fume is utilized as a pozzolanic material in the application of soil stabilization. Silica fume was once considered non-environmental friendly. In this paper, the materials required are kaolin grade S300, lime and silica fume. The focus of the study is on the determination of the physical properties of the soils tested and the consolidation of kaolin mixed with 6% silica fume and different percentages (3%, 5%, 7% and 9%) of lime. Consolidation test is carried out on the kaolin and the mixtures of soil-lime-silica fume to investigate the effect of lime stabilization with silica fume additives on the consolidation of the mixtures. Based on the results obtained, all soil samples are indicated as soils with medium plasticity. For mixtures with 0% to 9% of lime with 6% SF, the decrease in the maximum dry density is about 15.9% and the increase in the optimum moisture content is about 23.5%. Decreases in the coefficient of permeability of the mixtures occur if compared to the coefficient of permeability of kaolin soft clay itself reduce the compression index (Cc) more than L- SF soil mix due to pozzolanic reaction between lime and silica fume and the optimum percent of lime-silica fume was found to be (5%+6%) mix. The average coefficient of volume compressibility decreases with increasing the stabilizer content due to pozzolanic reaction happening within the soil which results in changes in the soil matrix. Lime content +6% silica fume mix can reduce the coefficient of consolidation from at 3%L+6%SF, thereafter there is an increase from 9%L+6%SF mix. The optimal percentage of lime silica fume combination is attained at 5.0% lime and 6.0% silica fume in order to improve the shear strength of kaolin soft clay. Microstructural development took place in the stabilized soil due to increase in lime content of tertiary clay stabilized with 7% lime and 4% silica fume together.

Key Words
soft clay, stabilization, lime, silica fume, consolidation

Address
Ali Jamal Alrubaye and Muzamir Hasan: Centre for Earth Resources Research and Management (CERRM), Faculty of Civil Engineering and Earth Resources (FKASA),
University Malaysia Pahang (UMP), 26300 Gambang, Kuantan, Pahang, Malaysia

Mohammed Y. Fattah: Building and Construction Engineering Department, University of Technology, Baghdad, Iraq

Abstract
Analysis of slope stability failures, as one of the complex natural hazards, is one of the important research issues in the field of civil engineering. Present paper adopts and investigates four soft computing-based techniques for this problem: Patient Rule-Induction Method (PRIM), M5\' algorithm, Group Method of data Handling (GMDH) and Multivariate Adaptive Regression Splines (MARS). A comprehensive database consisting of 168 case histories is used to calibrate and test the developed models. Six predictive variables including slope height, slope angle, bulk density, cohesion, angle of internal friction, and pore water pressure ratio were considered to generate new models. The results of test studies are used for feasibility, effectiveness and practicality comparison of techniques with each other, and with the other available well-known methods in the literature. Results show that all methods not only are feasible but also result in better performance than previously developed soft computing based predictive models and tools. It is shown that M5\' and PRIM algorithms are the most effective and practical prediction models.

Key Words
slope stability assessment; data mining; PRIM; M5\'; GMDH, MARS

Address
A. Kaveh: Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology, Tehran, Iran

S.M. Hamze-Ziabari: Departmant of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

T. Bakhshpoori: Faculty of Technology and Engineering, Department of Civil Engineering, East of Guilan, University of Guilan, Rudsar-Vajargah, Iran

Abstract
A jointed rock slope stability evaluation was simulated by a discontinuous deformation analysis numerical method to investigate the process and safety factors for different crack distributions and different overloading situations. An optimized method using Discontinuous Deformation Analysis for Rock Failure (DDARF) is presented to perform numerical investigations on the jointed rock slope stability evaluation of the Dagangshan hydropower station. During the pre-processing of establishing the numerical model, an integrated software system including AutoCAD, Screen Capture, and Excel is adopted to facilitate the implementation of the numerical model with random joint network. These optimizations during the pre-processing stage of DDARF can remarkably improve the simulation efficiency, making it possible for complex model calculation. In the numerical investigations on the jointed rock slope stability evaluations using the optimized DDARF, three calculation schemes have been taken into account in the numerical model: (I) no joint; (II) two sets of regular parallel joints; and (III) multiple sets of random joints. This model is capable of replicating the entire processes including crack initiation, propagation, formation of shear zones, and local failures, and thus is able to provide constructive suggestions to supporting schemes for the slope. Meanwhile, the overloading numerical simulations under the same three schemes have also been performed. Overloading safety factors of the three schemes are 5.68, 2.42 and 1.39, respectively, which are obtained by analyzing the displacement evolutions of key monitoring points during overloading.

Key Words
jointed rock mass; slope stability; numerical investigation; DDARF; overloading test

Address
Yong Li: 1)Geotechnical & Structural Engineering Research Center, Shandong University, No. 17923 Jingshi Rd.,Jinan, Shandong Province, P.R. China 250061
2)School of Civil Engineering, Shandong University, No. 17922 Jingshi Rd., Jinan, Shandong Province, P. R. China 250061

Hao Zhou: 1)Geotechnical & Structural Engineering Research Center, Shandong University, No. 17923 Jingshi Rd.,Jinan, Shandong Province, P.R. China 250061
2) Jinan Rail Transit Group Co., Ltd, No. 2000 Shunhua Rd., Jinan, Shandong Province, P. R. China 250101

Zhenxing Dong, Weishen Zhu, Shucai Li, and Shugang Wang: Geotechnical & Structural Engineering Research Center, Shandong University, No. 17923 Jingshi Rd.,Jinan,Shandong Province, P.R. China 250061


Abstract
Cracks in soil provide significant preferential pathways for contaminant transport and rainfall infiltration. Water exchange between the soil matrix and crack is crucial to characterize the preferential flow, which is often quantitatively described by a water exchange ratio. The water exchange ratio is defined as the amount of water flowing from the crack into the clay matrix per unit time. Most of the previous studies on the water exchange ratio mainly focused on cracked sandy soils. The water exchange between cracks and clay matrix were rarely studied mainly due to two reasons: (1) Cracks open upon drying and close upon wetting. The deformable cracks lead to a dynamic change in the water exchange ratio. (2) The aperture of desiccation crack in clay is narrow (generally 0.5 mm to 5 mm) which is difficult to model in experiments. This study will investigate the water exchange between a deformable crack and the clay matrix using a newly developed experimental apparatus. An artificial crack with small aperture was first fabricated in clay without disturbing the clay matrix. Water content sensors and suction sensors were instrumented at different places of the cracked clay to monitor the water content and suction changes. Results showed that the water exchange ratio was relatively large at the initial stage and decreased with the increasing water content in clay matrix. The water exchange ratio increased with increasing crack apertures and approached the largest value when the clay was compacted at the water content to the optimal water content. The effective hydraulic conductivity of the crack-clay matrix interface was about one order of magnitude larger than that of saturated soil matrix.

Key Words
clay; crack; water exchange; wetting front; seepage; hydraulic conductivity

Address
Lei Song and Jinhui Li: Department of Civil and
Environmental Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China

Ankit Garg: Department of Civil Engineering, Indian Institute of Technology, Guwahati Assam, India

Guoxiong Mei: Department of Civil Engineering, Guangxi University, Guangxi, China


Abstract
This paper has the aim of estimating the applicability of a numerical approach to the Hyperstatic Reaction Method (HRM) for the analysis of segmental tunnel linings. For this purpose, a simplified three-dimensional (3D) numerical model, using the FLAC3D finite difference software, has been developed, which allows analysing in a rigorous way the effect of the lining segmentation on the overall behaviour of the lining. Comparisons between the results obtained with the HRM and those determined by means of the simplified 3D numerical model show that the proposed HRM method can be used to investigate the behaviour of a segmental tunnel lining.

Key Words
hyperstatic reaction method; lining response; numerical method; segmental tunnel lining; three-dimensional model

Address
Ngoc Anh Do: Department of Underground and Mining Construction, Hanoi University of Mining and Geology, Faculty of Civil Engineering, Hanoi, Vietnam

Daniel Dias: 1) School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei, China

2)University of Grenoble Alpes, CNRS, Grenoble INP, 3SR, F-38000 Grenoble, France

Pierpaolo Oreste: Department of LEGE, Politecnico of Torino, Torino, Italy

Abstract
Stabilization of clayey soil has been studied from past to present by mixing different additives to the soil to increase its strength and durability. In recent years, there has been an increasing interest in stabilization of soils with natural pozzolans. Despite this, very few studies have investigated the impact of pozzolanic additives under freeze-thaw cycling. This paper presents the results of an experimental research study on the durability behavior of clayey soils treated with lime and perlite. For this purpose, soil was stabilized with 6% lime content by weight of dry soil (optimum lime ratio of the the soil), perlite was mixed with it in 0%, 5%, 10%, 20%, 25% and 30% proportions. Test specimens were compacted in the laboratory and cured for 7, 28 and 84 days, after which they were tested for unconfined compression tests. In addition to this, they were subjected to 12 closed system freeze-thaw cycles after curing for 28 days. The results show that the addition of perlite as a pozzolanic additive to lime stabilized soil improves the strength and durability. Unconfined compressive strength increases with increased perlite content. The findings indicate that using natural pozzolan which is cheaper than lime, has positive effect in strength and durability of soils and can result cost reduction of stabilization.

Key Words
soil improvement; lime; perlite; freeze-thaw cycling; natural pozzolan

Address
Fatih Yilmaz and Duygu Fidan: Department of Civil Engineering, Bayburt University, 69000 Bayburt, Turkey


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