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CONTENTS
Volume 14, Number 1, January20 2018
 

Abstract
This paper presents an investigation of the liquefaction characteristics and particle crushing of isotropically consolidated silica sand specimens at a wide range of confining pressures varying from 0.1 MPa to 5 MPa during undrained cyclic shearing. Different failure patterns of silica sand specimens subjected to undrained cyclic loading were seen at low and high pressures. The sudden change points with regard to the increasing double amplitude of axial strain with cycle number were identified, regardless of confining pressure. A higher cyclic stress ratio caused the specimen to liquefy at a relatively smaller cycle number, conversely producing a larger relative breakage Br. The rise in confining pressure also resulted in the increasing relative breakage. At a specific cyclic stress ratio, the relative breakage and plastic work increased with the rise in the cyclic loading. Less particle crushing and plastic work consumption was observed for tests terminated after one cyclic loading. Majority of the particle crushing was produced and majority of the plastic work was consumed after the specimen passed through the phase transformation point and until reaching the failure state. The large amount of particle crushing resulted from the high-level strain induced by particle transformation and rotation.

Key Words
undrained cyclic test; liquefaction; particle crushing; relative density; cyclic stress ratio

Address
Yang Wu: 1.) School of Civil Engineering, Guangzhou University, Guangzhou 510006, China

2.) Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Ube 755-8611, Japan

Masayuki Hyodo: Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Ube 755-8611, Japan

Noritaka Aramaki: Horonobe Research Institute for the Subsurface Environment, Northern Advancement Center for Science and Technology, Hokkaido 098-3221, Japan

Abstract
Brazilian splitting tests, uniaxial compression tests and triaxial compression tests are carried out on the coal samples cored from Shanxi group II1 coal seam of Jiaozuo coal mine, Henan province, China, to obtain their property parameters. Considering the bedding has notable effect on the property parameter of coal, the samples with different bedding angles are prepared. The effects of bedding on the anisotropic characteristics of the coal seam are investigated. A geological geomechanical model is built based on the geology characteristics of the Jiaozuo coal mine target reservoir to study the effects of bedding on the fracture propagations during hydraulic fracturing. The effects of injection pressure, well completion method, in-situ stress difference coefficient, and fracturing fluid displacement on the fracture propagations are investigated. Results show bedding has notable effects on the property parameters of coal, which is the key factor affecting the anisotropy of coal. The hydraulic cracks trends to bifurcate and swerve at the bedding due to its low strength. Induced fractures are produced easily at the locations around the bedding. The bedding is beneficial to form a complicated fracture network. Experimental and numerical simulations can help to understand the effects of bedding on hydraulic fracturing in coalbed methane reservoirs.

Key Words
coal seam; coalbed methane; hydraulic fracturing; mechanical test; geomechanical model

Address
Ting T. Jiang, Jian H. Zhang,Gang Huang, Shao X. Song and Hao Wu: Hubei Province Key Laboratory of Processing of Mineral Resources and Environment, School of Resource and Environmental Engineering, Wuhan University of Technology, Luoshi road No.122, Wuhan 430070, Hubei, People

Abstract
It follows from the basic principles of mechanics of deformable solids relating to the strength, stability and propagation of elastic waves that the Earth\'s inner core cannot exist in the form of a spherical structure in the assumed thermobaric conditions and calculation values of physico-mechanical parameters. Pressure level reaches a value that is significantly greater than the theoretical limit of medium strength in the model approximations at the surface of the sphere of the inner core. On the other hand, equilibrium state of the sphere is unstable on the geometric forming at much lower loads under the influence of the \"dead\" surface loads. In case of the action of \"follower\" loads, the assumed pressure value on the surface of the sphere is comparable with the value of the critical load of \"internal\" instability. In these cases, due to the instability of the equilibrium state, propagation of homogeneous deformations becomes uneven in the sphere. Moreover, the elastic waves with actual velocity cannot propagate in such conditions in solid medium. Violation of these fundamental conditions of mechanics required in determining the physical and mechanical properties of the medium should be taken into account in the integrated interpretations of seismic and laboratory (experimental) data. In this case, application of the linear theory of elasticity and elastic waves does not ensure the reliability of results on the structure and composition of the Earth\'s core despite compliance with the required integral conditions on the mass, moment of inertia and natural oscillations of the Earth.

Key Words
Earth\'s core; high pressure; instability; elastic waves with actual velocity

Address
Hatam H. Guliyev: Department of Tectonophysics and Geomechanics, Institute of Geology and Geophysics of Azerbaijan National Academy of Sciences (ANAS), Ave. H. Javid 119, Baku AZ 1143, Azerbaijan

Abstract
This paper presents the results of an empirical study in which square rock-like blocks containing two parallel pre-existing rough non-persistent joints were subjected to uniaxial compression load. The main purpose of this study was to investigate uniaxial compressive strength and deformation modulus of jointed specimens. Response Surface Method (RSM) was utilized to design experiments and investigate the effect of four joint parameters, namely joint roughness coefficient (JRC), bridge length (L), bridge angle (y) and joint inclination (theta). The interaction of these parameters on the uniaxial compressive strength (UCS) and deformation modulus of the blocks was investigated as well. The results indicated that an increase in joint roughness coefficient, bridge length and bridge angle increased compressive strength and deformation modulus. Moreover, increasing joint inclination decreased the two mechanical properties. The concept of \'interlocking cracks\' which are mixed mode (shear-tensile cracks) was introduced. This type of cracks can happen in higher level of JRC. Initiation and propagation of this type of cracks reduces mechanical properties of sample before reaching its peak strength. The results of the Response Surface Methodology showed that the mutual interaction of the joint parameters had a significant influence on the compressive strength and deformation modulus.

Key Words
physical model; non-persistent joint; mechanical behavior; joint roughness coefficient

Address
Mostafa Asadizadeh: 1.) Department of Mining Engineering, Hamedan University of Technology, Mardom Street, Hamedan, 65155-579, Iran

2.) School of Mining Engineering, College of Engineering, University of Tehran, 1439957131 Tehran, Iran

Mahdi Moosavi and Mohammad Farouq Hossaini: School of Mining Engineering, College of Engineering, University of Tehran, 1439957131 Tehran, Iran

Abstract
Applicability of constructing piled raft foundations on soft clay has been given attention in recent years. Lack of sufficient stiffness for soil and thus excessive settlements to allow higher contribution of piles is the major concern in this regard. This paper presents a numerical investigation of performance of piled-raft foundations on soft clay with focusing on a case study. A 3D FEM numerical model is developed using ABAQUS. The model was calibrated by comparing physical and numerical modeling results of other researchers. Then the possibility of using piled-raft system in construction of foundation for a water storage tank in Sarbandar, Iran is assessed. Soil strength parameters in the numerical model were calibrated using the instrumentation data of a heavily instrumented preloading project at the construction site. The results indicate that choosing the proper combination of length and spacing for piles can lead to acceptable differential and total settlements while a high percentage of total bearing capacity of piles can be mobilized, which is an efficient solution for the project. Overall, the construction of piled-rafts on soft clays is promising as long as the total settlement of the structure is not imposing restrictions such as the common 25 mm allowable settlement. But instead, if higher allowable settlements are adopted, for example in the case of rigid steel tanks, the method shall be applicable with considerable cost savings.

Key Words
piled-raft; soft clay; numerical modeling; case study

Address
Mohammadreza Khanmohammadi and Kazem Fakharian: Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran 15875-4413, Iran

Abstract
The foundations are classified into shallow and deep, which have important differences: in terms of geometry, the behavior of the soil, its structural functionality, and its constructive systems. The shallow foundations may be of various types according to their function; isolated footings, combined footings, strip footings, and slabs foundation. The isolated footings are of the type rectangular, square and circular. The combined footing may be rectangular, trapezoidal or T-shaped in plan. This paper presents a new model for T-shaped combined footings to obtain the most economical contact surface on the soil (optimal dimensioning) to support an axial load and moment in two directions to each column. The new model considers the soil real pressure, i.e., the pressure varies linearly. The classical model uses the technique of test and error, i.e., a dimension is proposed, and subsequently, the equation of the biaxial bending is used to obtain the stresses acting on each vertex of the T-shaped combined footing, which must meet the conditions following: The minimum stress should be equal or greater than zero, and maximum stress must be equal or less than the allowable capacity that can withstand the soil. To illustrate the validity of the new model, numerical examples are presented to obtain the minimum area of the contact surface on the soil for T-shaped combined footings subjected to an axial load and moments in two directions applied to each column.

Key Words
T-shaped combined footings; optimal dimensioning; contact surface; more economical dimension; minimum area

Address
Arnulfo Luévanos-Rojas, Sandra López-Chavarria and Manuel Medina-Elizondo: Universidad Autónoma de Coahuila, Blvd. Revolución No, 151 Ote, CP 27000, Torreón, Coahuila, Mexico

Abstract
The first part shows the optimal contact surface for T-shaped combined footings to obtain the most economical dimensioning on the soil (optimal area). This paper presents the second part of a new model for T-shaped combined footings, this part shows a the mathematical model for design of such foundations subject to axial load and moments in two directions to each column considering the soil real pressure acting on the contact surface of the footing with one or two property lines restricted, the pressure is presented in terms of an axial load, moment around the axis \"X\" and moment around the axis \"Y\" to each column, and the methodology is developed using the principle that the derived of the moment is the shear force. The classic model considers an axial load and a moment around the axis \"X\" (transverse axis) applied to each column, i.e., the resultant force from the applied loads is located on the axis axis \"Y\" (longitudinal axis), and its position must match with the geometric center of the footing, and when the axial load and moments in two directions are presented, the maximum pressure and uniform applied throughout the contact surface of the footing is considered the same. To illustrate the validity of the new model, a numerical example is presented to obtain the design for T-shaped combined footings subjected to an axial load and moments in two directions applied to each column. The mathematical approach suggested in this paper produces results that have a tangible accuracy for all problems.

Key Words
mathematical model for design; T-shaped combined footings; moments; bending shear; punching shear

Address
Arnulfo Luévanos-Rojas, Sandra López-Chavarria and Manuel Medina-Elizondo: Universidad Autónoma de Coahuila, Blvd. Revolución No, 151 Ote, CP 27000, Torreón, Coahuila, Mexico

Abstract
Soils are mostly nonhomogeneous and anisotropic in nature. In this study, nonhomogeneity and anisotropy of soil are taken into consideration by assuming that the cohesion increases with depth linearly and also varies with respect to direction at a particular point. A three-dimensional rotational failure mechanism is adopted, and then a three-dimensional stability analysis of slope is carried out with the failure surface in the shape of a curvilinear cone in virtue of the limit analysis method. A quasi-static approach is used to develop stability charts in nonhomogeneous and anisotropic soils. One can easily read the safety factors from the charts without the need for iterative procedures for safety factors calculation. The charts are of practical importance to prevent a plane failure in excavation slope whether it is physically constrained or not. Then the most suitable location of piles within the reinforced slope in nonhomogeneous and anisotropic soils is explored, as well as the interactions of nonhomogeneous and anisotropic coefficients on pile reinforcement effects. The results indicate that piles are more effective when they are located between the middle and the crest of the slope, and the nonhomogeneous coefficient as well as the anisotropic coefficient will not only influence the most suitable location for piles but also affect the calculated safety factor of existing reinforced slope. In addition, the two coefficients will interact with each other on the effect on slope reinforcement.

Key Words
soil nonhomogeneity and anisotropy; three-dimensional; upper bound; piles; safety factor of slope

Address
Jingshu Xu, Yongxin Li and Xiaoli Yang: School of Civil Engineering, Central South University, Changsha, 410075, China

Abstract
A series of pullout tests were carried out on waste tire treadmats of various weave arrangements, with confining stresses ranging from 9 to 59 kPa approximately, in order to investigate the pullout behavior and to apply the results to the design of treadmat reinforced soil structures. A treadmat reinforcement can be considered as belonging to the extensible type thus progressive failure would develop in every tread. The pullout capacity of a treadmat was found to be generally equal to the sum of capacities of the longitudinal treads, with minor enhancement realized due to the presence of transverse treads. Pullout failures occurred in treadmats under light surcharge and with treadmats with higher material presence per unit area, while breakage failures occurred in treadmats under heavier surcharge and with treadmats with higher ratio of opening. The pullout capacity of a treadmat increased with increasing surcharge height and treadmat stiffness. A pullout test on a commercially available geogrid was also carried out for comparison and the pullout capacity of a treadmat was found higher than that of the comparable geogrid under identical loading conditions, indicating the merit of using the treadmat as an alternative to the chosen geogrid.

Key Words
pullout test; waste tire treadmat; geogrid; pullout capacity; reinforced structures

Address
Keun-Soo Kim: Naru EMS, #206 KEPCO Venture Business Incubation Center 105 Munjiro, Yuseong-gu, Daejeon-si 34056, Republic of Korea

Yeo-Won Yoon: 1.) Naru EMS, #206 KEPCO Venture Business Incubation Center 105 Munjiro, Yuseong-gu, Daejeon-si 34056, Republic of Korea

2.) Department of Civil Engineering, Inha University, 100 Inha-ro, Nam-gu, Incheon 22212, Republic of Korea

Ki-Il Song: Department of Civil Engineering, Inha University, 100 Inha-ro, Nam-gu, Incheon 22212, Republic of Korea

Abstract
Length of a vehicle is an important variation to generate different variants of an automotive platform. This parameter is usually adjusted by embedding dimensional flexibility into different components of the Body in White (BIW) including the floor pan. Due to future uncertainties, it is not necessarily possible to define certain values of wheelbase for the future products of a platform. This work is performed to add flexibility into the design process of a length-variable floor pan. By means of this analysis, the cost and time consuming process of optimization is not necessary to be performed for designing the different variants of a product family. Stiffness and mass of the floor pan are two important functional requirements of this component which directly affect the occupant comfort, dynamic characteristics, fuel economy and environmental protection of the vehicle. A combination of Genetic algorithm, GMDH-type of artificial neural networks and TOPSIS methods is used to optimally design the floor pan associated with arbitrary length of the variant in the defined system range. The correlation between the optimal results shows that for a constant mass of the floor pan, the first natural frequency decreases by increasing the length of this component.

Key Words
platform; floor plan; design; FEM; genetic algorithm; artificial neural networks

Address
Abdolah Tavakoli Lahijani, M.H. Shojaeefard and Abolfazl Khalkhali: Automotive Simulation and Optimal Design Research Laboratory, School of Automotive Engineering,
Iran University of Science and Technology, Tehran, Iran


Abstract
Soils are generally classified as fine-grained or coarse-grained depending on the percentage content of the primary constituents. In reality, soils are actually made up of mixed and composite constituents. Soils primarily classified as fine-grained, still consists of a range of coarse particles as secondary constituents in between 0% to 50%. A laboratory scale model test was conducted to investigate the influence of coarse particles on the physical (e.g., density, water content, and void ratio) and mechanical (e.g., quick undrained shear strength) properties of primarily classified fine-grained cohesive soils. Pure kaolinite clay and sand-mixed kaolinite soil (e.g., sand content: 10%, 20%, and 30%) having various water contents (60%, 65%, and 70%) were preconsolidated at different stress levels (0, 13, 17.5, 22 kPa). The quick undrained shear strength properties were determined using the conventional Static Cone Penetration Test (SCPT) method and the new Fall Cone Test (FCT) method. The corresponding void ratios and densities with respect to the quick undrained shear strength were also observed. Correlations of the physical properties and quick undrained shear strengths derived from the SCPT and FCT were also established. Comparison of results showed a significant relationship between the two methods. From the results of FCT and SCPT, there is a decreasing trend of quick undrained shear strength, strength increase ratio (Su/Po), and void ratio (e) as the sand content is increased. The quick undrained shear strength generally decreases with increased water content. For the same water content, increasing the sand content resulted to a decrease in quick undrained shear strength due to reduced adhesion, and also, resulted to an increase in density. Similarly, it is observed that the change in density is distinctively noticeable at sand content greater than 20%. However, for sand content lower than 10%, there is minimal change in density with respect to water content. In general, the results showed a decrease in quick undrained shear strength for soils with higher amounts of sand content. Therefore, as the soil adhesion is reduced, the cone penetration resistances of the FCT and SCPT reflects internal friction and density of sand in the total shear strength.

Key Words
fall cone test; static cone penetration test; kinetic energy; physical properties; quick undrained shear strength; bearing capacity factor

Address
Tae-Woong Park, Hyeong-Joo Kim, Mohammad Taimur Tanvir, Jang-Baek Lee and Sung-Gil Moon: Department of Civil and Environmental Engineering, Kunsan National University, Gunsan 54150, Republic of Korea

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