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CONTENTS
Volume 17, Number 3, February28 2019
 

Abstract
In practice, the natural slopes are frequently with soils of spatial properties and irregular features. The traditional limit analysis method meets an inherent difficulty to deal with the stability problem for such slopes due to the normal condition in the associated flow rule. To overcome the problem, a novel technique based on the upper bound limit analysis, which is called the discretization technique, is employed for the stability evaluation of complex slopes. In this paper, the discretization mechanism for complex slopes was presented, and the safety factors of several examples were calculated. The good agreement between the discretization-based and previous results shows the accuracy of the proposed mechanism, proving that it can be an alternative and reliable approach for complex slope stability analysis.

Key Words
stability analysis; upper bound limit analysis; complex slopes; safety factor; slip surface

Address
Chaoqun Hou, Tingting Zhang, Zhibin Sun and Jianfei Li: School of Automotive and Transportation Engineering, Hefei University of Technology, No. 193, Tunxi Road, China

Daniel Dias: 1.) School of Automotive and Transportation Engineering, Hefei University of Technology, No. 193, Tunxi Road, China
2.) Laboratory 3SR, Grenoble Alpes University, CNRS UMR5521, France


Abstract
In deep mixed rock strata, a double shield TBM (DS-TBM) is easy to be entrapped by a large force during tunneling. In order to reduce the probability of the entrapment, we need to investigate a favorable driving direction, either driving with or against dip, which mainly associates with the angle between the tunneling axis and strike, theta, as well as the dip angle of rock strata, a. We, therefore, establish a 3DEC model to show the changes of displacements and contact forces in mixed rock strata through LDP (longitudinal displacement profile) and LFP (longitudinal contact force profile) curves at four characteristic points on the surrounding rock. This is followed by a series of numerical models to investigate the favorable driving direction. The computational results indicate driving with dip is the favorable tunneling direction to reduce the probability of DS-TBM entrapment, irrespective of theta and a, which is not in full agreement with the guidelines proposed in RMR. From the favorable driving direction (i.e., driving with dip), the smallest contact force is found when theta is equal to 90o.The present study is therefore beneficial for route selection and construction design in TBM tunneling.

Key Words
tunnel engineering; mixed rock strata; double shield TBM; TBM entrapment; three-dimensional numerical simulation; driving direction

Address
Sen Wen and Ya Zhang: School of Civil Engineering and Architecture, Henan University, Kaifeng 475004, China

Chunshun Zhang:Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia

Abstract
Modulus of deformation of soil is an essential parameter used for design analysis of foundations, despite its importance; little attention is paid to developing empirical models for predicting the sensitivity of deformation moduli to other parameters that obtained from the pressuremeter tests. Various methods of analysis used to predict the horizontal at rest pressure from pressuremeter testing (Po) ,these values showed distinctive variations ,five methods used to evaluate the values of horizontal at rest pressure, these values been used to evaluate the modulus of elasticity using three methods of analysis. The values of modulus showed distinctive increase when the values of horizontal at rest pressure increase for the same pressuremeter test ,these increases may reach to 65%. This sensitivity of the moduli to values of horizontal lead the author to propose some reliable methods of analysis for both the horizontal at rest pressure and the modulus of deformation from pressuremeter testing.

Key Words
pressuremeter; modulus of elasticity; horizontal at rest pressure; sensitivity

Address
Radhi M. Alzubaidi: Civil Engineering Department, University of Sharjah, Sharjah, UAE

Abstract
Concrete-to-concrete bedding planes (CCBP) are observed from time to time due to the multistep hardening process of the concrete materials. In this paper, a series of direct/cyclic shear tests are performed on CCBP under static and dynamic normal load conditions to study the frictional behavior effect by the shear velocities, normal impact frequencies, horizontal shear frequencies, normal impact force amplitudes, horizontal shear displacement amplitudes and normal load levels. According to the experimental results, apparent friction coefficient k (k = FShear/FNormal) shows different patterns under static and dynamic load conditions at the stable shear stage. k is nearly constant in direct shear tests under constant normal load conditions (DCNL), while it is cyclically changing with nearly constant peak value and valley value for the direct shear tests under dynamic normal load conditions (DDNL), where k increases with decreasing normal force and decreases with increasing normal force. Shear velocity has little influence on peak values of k for the DCNL tests, but increasing shear velocity leads to increasing valley values of k for DDNL tests. It is also found that, the valley values of k ascend with decreasing impact normal force amplitude in DDNL tests. The changing pattern of k for the cyclic shear tests under constant and dynamic normal load conditions (CCNL and CDNL tests) are similar, but the peak value of k is smaller in CDNL tests than that in CCNL tests. Normal load levels, shear displacement amplitudes, vertical impact frequencies, horizontal shear frequencies and normal impact force amplitudes have little influence on the changing pattern of k for the cyclic shear tests. The tests of this study provide useful data in understanding the frictional behavior of the CCBP under distinct loadings, and these findings are very important for analyzing the stability of the jointed geotechnical structures under complicated in situ stress conditions.

Key Words
concrete-to-concrete; dynamic normal force; constant normal force; cyclic/direct shear

Address
Wengang Dang: School of Civil Engineering, Sun Yat-sen University, Gungzhou 520275, China

Heinz Konietzky: Geotechnical Institute, TU Bergakademie Freiberg, Gustav-Zeuner-Strabe 1, Freiberg 09599, Germany

Xiang Li: School of Resources and Safety Engineering, Central South University, Changsha 410083, Hunan, China

Abstract
Because the estimation of the tensile strength is very important in any geotechnical project, many attempts have been made to determine. But the immediate determination of the tensile strength is usually difficult owing to well-shaped specimens, time-consuming, expensive and sometimes unreliable. In this study, engineering properties of several ultramafic rock samples were measured to assess the correlations between the Brazilian Tensile Strength (BTS) and degree of serpentinization, physical, dynamic and mechanical characteristics. For this purpose, a comprehensive laboratory testing program was conducted after collecting thirty-two peridotite and fifty-one serpentinite rock samples, taken from central Greece, in accordance with ASTM and ISRM standards. In addition, a representative number of them were subjected to petrographic studies and the obtained results were statistically described and analysed. Simple and multiple regression analyses were used to investigate the relationships between the Brazilian Tensile Strength and the other measured properties. Thus, empirical equations were developed and they showed that all of the properties are well correlated with Brazilian Tensile Strength. The curves with the 45o line (y = x) were extracted for evaluating the validity degree of concluded empirical equations which approved approximately close relationships between Brazilian Tensile Strength and the measured properties.

Key Words
ultramafic rocks; rock mechanics; correlation; Brazilian tensile strength; serpentinization percentage; engineering properties

Address
Konstantinos Diamantis: Department of Natural Resources Management and Agricultural Engineering, Laboratory of Mineralogy-Geology, Agricultural University of Athens, 75 Iera Street 11855 Athens, Greece


Abstract
In recent years, the crack accidents of earth and rockfill dams occur frequently. It is urgent to study the tensile strength and tensile failure mechanism of the gravelly soil in the core for the anti-crack design of the actual high earth core rockfill dam. Based on the self-developed uniaxial tensile test device, a series of uniaxial tensile test was carried out on gravelly soil with different gravel content. The compaction test shows a good linear relationship between the optimum water content and gravel content, and the relation curve of optimum water content versus maximum dry density can be fitting by two times polynomial. For the gravelly soil under its optimum water content and maximum dry density, as the gravel content increased from 0% to 50%, the tensile strength of specimens decreased from 122.6 kPa to 49.8 kPa linearly. The peak tensile strain and ultimate tensile strain all decrease with the increase of the gravel content. From the analysis of fracture energy, it is proved that the tensile capacity of gravelly soil decreases slightly with the increasing gravel content. In the case that the sample under the maximum dry density and the water content higher than the optimum water content, the comprehensive tensile capacity of the sample is the strongest. The relevant test results can provide support for the anti-crack design of the high earth core rockfill dam.

Key Words
gravelly soil; gravel content; uniaxial tensile test; tensile strength; tensile strain; fracture energy

Address
Enyue Ji: 1.) Geotechnical Engineering Department, Nanjing Hydraulic Research Institute, Nanjing 210024, China
2.) Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,Hohai University, Nanjing 210098, China
3.) Key Laboratory of Failure Mechanism and Safety Control Techniques of Earth-Rock Dam of the Ministry of Water Resources, Nanjing Hydraulic Research Institute, Nanjing 210029, China

Shengshui Chen and Zhongzhi Fu: 1.) Geotechnical Engineering Department, Nanjing Hydraulic Research Institute, Nanjing 210024, China
2.) Key Laboratory of Failure Mechanism and Safety Control Techniques of Earth-Rock Dam of the Ministry of Water Resources, Nanjing Hydraulic Research Institute, Nanjing 210029, China

Jungao Zhu: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China


Abstract
The process of slope stability analysis is one of the most important stages in design of some civil and mining projects. Bimslopes are made from bimrocks (block-in-matrix rocks) where rocky blocks are distributed in a bonded matrix of finer texture. These kind of slopes are often seen in weathered and near-surface depths. Previous studies have shown that VBP (Volumetric Block Proportion) is one of the most significant factors affecting bimrocks strength and consequently the stability of bimslopes. In this paper, the influence of block inclinations on bimslope stability have been investigated. For this purpose, 180 theoretical models have been made with various VBPs, all of them have a specified block size distribution. These bimslopes contain blocks with differing dips relative the slope inclination. Also for each kind of block inclination, 10 different blocks arrangements have been modeled. The Finite Element Method (FEM) was used to analysis the stability of these bimslopes models. The results showed the inclination of blocks has a strong impact on the Safety Factor and stability of bimslopes. When the difference in angle of dip of blocks relative to the slope angle is maximum, the Safety Factor of bimslopes tends to be a maximum compared with the matrix-only state. Furthermore, with increasing VBP of bimslopes stability increases. The graphs obtained from this study could be used for preliminary guidance in the projects design with bimslopes.

Key Words
bimrocks; bimslopes; blocks inclination; numerical modeling; FEM

Address
Emad Khorasani and Mehdi Amini: School of Mining Engineering, University of Tehran, Tehran, Iran

Mohammad Farouq Hossaini: School of Minerals and Energy Resources Engineering, UNSW, Sydney, Australia

Edmund Medley: Principal Consultant, Terraphase Engineering, Oakland, CA 94612, U.S.A.

Abstract
The finite element method (FEM) is widely used to evaluate the seismic performance of pile-supported buildings. However, there are problems associated with modeling the pile end resistance using the FEM, such as the dependence on the mesh size. This paper proposes a new method of modeling around the pile tip to avoid the mesh size effect in two-dimensional (2D) analyses. Specifically, we consider the area of influence around the pile tip as an artificial constraint on the behavior of the soil. We explain the problems with existing methods of modeling the pile tip. We then conduct a three-dimensional (3D) analysis of a pile in various soil conditions to evaluate the area of influence of the soil around the pile tip. The analysis results show that the normalized area of influence extends approximately 2.5 times the diameter of the pile below the pile tip. Finally, we propose a new method for modeling pile foundations with artificial constraints on the nodal points within the area of influence. The proposed model is expected to be useful in the practical seismic design of pile-supported buildings via a 2D analysis.

Key Words
area of influence; 2D analysis; pile-supported building

Address
Junichi Hyodo: Civil Engineering Division, Tokyo Electric Power Services Co. Ltd, Japan, 7-12 Shinonome 1-chome Koto-ku, Tokyo 135-0062, Japan

Yoshio Shiozaki: Steel Research Laboratory, JFE Steel Corporation, Japan

Yukio Tamari: Business Incubation Unit, Tokyo Electric Power Services Co. Ltd, Japan

Osamu Ozutsumi: Meisosha Corporation, Japan

Koji Ichii: Faculty of Societal Safety Sciences, Kansai University, Japan

Abstract
The bedding plane has a significant influence on the effect of blasting fragmentation and the overall performance of underground mining. This paper explores the effects of fragmentation of the bedding plane and different angles by using the numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include a dynamic compressive and tensile failure which is applied to simulate the fractures generated by the explosion. Firstly, the cracks propagation with the non-bedding plane in the coal with two boreholes detonated simultaneously is calculated and the particle velocity and maximum principal stress at different points from the borehole are also discussed. Secondly, different delay times between the two boreholes are calculated to explore its effects on the propagation of the fractures. The results indicate that the coal around the right borehole is broken more fully and the range of the cracks propagation expanded with the delay time increases. The peak particle velocity decreases first and then increases with the distance from the right borehole increasing. Thirdly, different angles between the bedding plane and the centerline of the two boreholes and the transmission coefficient of stress wave at a bedding plane are considered. The results indicated that with the angles increase, the number of the fractures decreases while the transmission coefficient increases.

Key Words
underground mining; geological discontinuity; explosion-induced stress wave; fractures

Address
Jiachen Wang, Fei Liu and Jinwang Zhang: 1.) College of Resources & Safety Engineering, China University of Mining & Technology, Beijing 100083, China
2.) Top-coal Caving Mining Research of Coal Mining Industry, Beijing 100083, China


Abstract
Dam deformation should be strictly controlled for the construction of 300m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.

Key Words
rockfill materials; composite grout; porosity; compressibility; shear strength; permeability; suffusion susceptibility

Address
Tao Wang, Sihong Liu and Yang Lu: College of Water Conservancy and Hydropower, Hohai University, No.1, Xikang Road, Nanjing 210098, China

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