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CONTENTS
Volume 10, Number 1, January 2016
 

Abstract
This paper presents the results of an intensive experimental investigation on cyclic behavior of various sands and structural materials interface. Comprehensive measurements of the horizontal displacement and shear stresses developed during testing were performed using an automated constant normal load (CNL) cyclic direct shear test apparatus. Two different particle sizes (0.5 mm-0.25 mm and, 2.0 mm-1.0 mm) of sands having distinct shapes (rounded and angular) were tested in a cyclic direct shear testing apparatus at two vertical stress levels (σ = 50 kPa, and 100 kPa) and two rates of displacement (RD = 2.0 mm/min, and 0.025 mm/min) against various structural materials (i.e., steel, concrete, and wood). The cyclic direct shear tests performed during this investigation indicate that (i) the shear stresses developed during shearing highly depend on both the shape and size of sand grains; (ii) characteristics of the structural materials are closely related to interface response; and (iii) the rate of displacement is slightly effective on the results.

Key Words
interface; sand; structural materials; cyclic direct shear test

Address
Department of Civil Engineering, University of Gaziantep, 27310, Gaziantep, Turkey.

Abstract
Employing non-associated flow rule and Power-Law failure criterion, the failure mechanisms of tunnel roof in homogeneous and layered soils are studied in present analysis. From the viewpoint of energy, limit analysis upper bound theorem and variation principle are introduced to study the influence of dilatancy on the collapse mechanism of rectangular tunnel considering effects of supporting force and seepage force. Through calculation, the collapsing curve expressions of rectangular tunnel which are excavated in homogeneous soil and layered soils respectively are derived. The accuracy of this work is verified by comparing with the existing research results. The collapsing surface shapes with different dilatancy coefficients are draw out and the influence of dilatancy coefficient on possible collapsing range is analyzed. The results show that, in homogeneous soil, the potential collapsing range decreases with the decrease of the dilatancy coefficient. In layered soils, the total height and the width on the layered position of possible collapsing block increase and the width of the falling block on tunnel roof decrease when only the upper soil's dilatancy coefficient decrease. When only the lower soil's dilatancy coefficient decrease or both layers' dilatancy coefficients decrease, the range of the potential collapsing block reduces.

Key Words
collapse; non-associated flow rule; Power-Law criterion; tunnel roof; upper bound

Address
School of Civil Engineering, Central South University, Hunan 410075, China.

Abstract
The hyperbolic stress-strain model has been shown to be valid for modeling nonlinear stress-strain behavior for rockfill materials. The Duncan-Chang nonlinear constitutive model was adopted to characterize the behavior of the modeled rockfill materials in this study. Accurately estimating the model parameters of rockfill materials is a key problem for simulating dam deformations during both the dam construction period and the dam operation period. In order to estimate model parameters, triaxial compression experiments of rockfill materials were performed. Based on a genetic algorithm, the constitutive model parameters of the rockfill material were determined from the triaxial compression experimental data. The investigation results show that the predicted strains provide satisfactory precision when compared with the observed strains and the strains forecasted by a gradient-based optimization algorithm. The effectiveness of the proposed inversion procedure of model parameters was verified by experimental investigation in a laboratory.

Key Words
parameter estimation; rockfill materials; genetic algorithm; strain measurement; triaxial compression experiment; Duncan-Chang model

Address
(1) Shouju Li, Shen Yu:
State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China;
(2) Zichang Shangguan, Zhiyun Wang:
Institute of Civil Engineering, Dalian Ocean University, Dalian 116023, China.

Abstract
The high permeability-high strength concrete belongs to the typical of porous materials. It is mainly used in underground engineering for cold area, it can act the role of heat preservation, also to be the bailing and buffer layer. In order to establish a suitable model to predict the thermal conductivity and directly applied for engineering, according to the structure characteristics, the thermal conductivity predicting model was built by resistance network model of parallel three-phase medium. For the selected geometric and physical cell model, the thermal conductivity forecast model can be set up with aggregate particle size and mixture ratio directly. Comparing with the experimental data and classic model, the prediction model could reflect the mixture ratio intuitively. When the experimental and calculating data are contrasted, the value of experiment is slightly higher than predicting, and the average relative error is about 6.6%. If the material can be used in underground engineering instead by the commonly insulation material, it can achieve the basic requirements to be the heat insulation material as well.

Key Words
high permeability; high strength concrete; porous materials; thermal resistance; heat conductivity; cold high altitudes

Address
(1) Yi-Zhong Tan, Yuan-Xue Liu, Pei-Yong Wang, Yu Zhang:
Chongqing Key Laboratory of Geomechanics & Geoenvironmental Protection in Department of Civil Engineering, Logistical Engineering University, Chongqing 401311, China;
(2) Yi-Zhong Tan:
PLA Engineering College, Xuzhou 221004, China.

Abstract
The non-linear Hoek-Brown failure criterion has been widely accepted and applied to evaluate the stability of rock slopes under plane-strain conditions. This paper presents a kinematic approach of limit analysis to assessing the static and seismic stability of three-dimensional (3D) rock slopes using the generalized Hoek.Brown failure criterion. A tangential technique is employed to obtain the equivalent Mohr-Coulomb strength parameters of rock material from the generalized Hoek-Brown criterion. The least upper bounds to the stability number are obtained in an optimization procedure and presented in the form of graphs and tables for a wide range of parameters. The calculated results demonstrate the influences of 3D geometrical constraint, non-linear strength parameters and seismic acceleration on the stability number and equivalent strength parameters. The presented upper-bound solutions can be used for preliminary assessment on the 3D rock slope stability in design and assessing other solutions from the developing methods in the stability analysis of 3D rock slopes.

Key Words
limit analysis; rock slope; three-dimensional; stability; failure criterion

Address
(1) Yufeng Gao, Di Wu, Fei Zhang, G.H. Lei, Yue Qiu:
Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing, 210098, China;
(2) Hongyu Qin:
School of Computer Science, Engineering and Mathematics, Flinders University, Adelaide, SA 5001, Australia.

Abstract
Cyclic triaxial and resonant column tests were conducted to understand the beneficial effects of various grouted sands on liquefaction resistance and dynamic properties. The test procedures were performed on a variety of grouted sands, such as silicate-grouted sand, silicate-cement grouted sand and cement-grouted sand. For each type of grout, sand specimen was mixed with a 3.5% and 5% grout by volume. The specimens were tested at a curing age of 3, 7, 28 and 91 days, and the results of the cyclic stress ratio, the maximum shear modulus and the damping ratio were obtained during the testing program. The influence of important parameters, including the type of grout, grout content, shear strain, confining pressure, and curing age, were investigated. Results indicated that sodium silicate grout does not improve the liquefaction resistance and shear modulus; however, silicate-cement and cement grout remarkably increased the liquefaction resistance and shear modulus. Shear modulus decreased and damping ratio increased with an increase in the amplitude of shear strain. The effect of confining pressure on clean sand and sodium silicate grouted sand was found to be insignificant. Furthermore, a nonlinear regression analysis was used to prove the agreement of the shear modulus-shear strain relation presented by the hyperbolic law for different grouted sands, and the coefficients of determination, R2, were nearly greater than 0.984.

Key Words
silicate-grouted sand; cement-grouted; silicate-cement grouted sand; dynamic properties

Address
(1) Darn-Horng Hsiao, Chi-Chang Huang:
Department of Civil Engineering, National Kaohsiung University of Applied Sciences, No. 415 Chien Kung Road, Kaohsiung 80778, Taiwan R.O.C.;
(2) Vu To-Anh Phan:
Faculty of Civil Engineering, Ton Duc Thang Univeristy, No. 19 Nguyen Huu Tho, Ho Chi Minh City, Vietnam.

Abstract
Deep soil mixing with cement and cement-lime mixtures has been widely used for decades to improve the strength of soils. In this study, small-scale laboratory model tests of polymer columns in soft clayey soil were conducted to evaluate the feasibility of using various polymeric compounds as binders in deep soil mixing. Floating and end bearing polymer columns were used to examine the load-settlement relationship of improved soft clayey soils for various area replacement ratios. The results indicate that polymer columns show good promise for use in deep mixing applications.

Key Words
clayey soil; deep soil mixing; polyester; polymer column; floating column; end bearing column

Address
(1) Seracettin Arasan, Majid Bagherinia, Ahmet Sahin Zaimoglu:
Ataturk University, Department of Civil Engineering, 25240 Erzurum, Turkey;
(2) Rahim Kagan Akbulut, Fatih Isik:
Ataturk University, Technical Vocational School of Higher Education, 25240 Erzurum, Turkey.

Abstract
this paper, process of dynamic powder compaction is investigated experimentally using impact of drop hammer and die tube. A series of test is performed using aluminum powder with different grain size. The energy of compaction of powder is determined by measuring height of hammer and the results presented in term of compact density and rupture stress. This paper also presents a mathematical modeling using experimental data and neural network. The purpose of this modeling is to display how the variations of the significant parameters changes with the compact density and rupture stress. The closed-form obtained model shows very good agreement with experimental results and it provides a way of studying and understanding the mechanics of dynamic powder compaction process. In the considered energy level (from 733 to 3580 J), the relative density is varied from 63.89% to 87.41%, 63.93% to 91.52%, 64.15% to 95.11% for powder A, B and C respectively. Also, the maximum rupture stress are obtained for different types of powder and the results shown that the rupture stress increases with increasing energy level and grain size.

Key Words
aluminum powder; compaction; drop hammer machine; impact loading; powder metallurgy

Address
(1) Hashem Babaei, Tohid Mirzababaie Mostofi, Majid Alitavoli, Nasir Namazi:
Department of Mechanical Engineering, Engineering Faculty, University of Guilan, Rasht 3756-41635, Iran;
(2) Ali Rahmanpoor:
Department of Mechanical Engineering, Roudbar Branch, Islamic Azad University, Roudbar, Iran.


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