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CONTENTS
Volume 12, Number 6, June 2017
 

Abstract
Indirect measure of the tensile strength of laboratory samples is an important topic in rock engineering. One of the most important tests, the Brazilian strength test is performed to obtain the tensile strength of rock, concrete and other quasi brittle materials. Because the measurements are provided indirectly and the inspected rock materials may have heterogeneous properties, uncertainty quantification is required for a reliable test evaluation. In addition to the conventional measurement evaluation uncertainty methods recommended by the Guide to the Expression of Uncertainty in Measurement (GUM), such as Taylor.s and Monte Carlo Methods, a fuzzy set-based approach is also proposed and resulting uncertainties are discussed. The results showed that when a tensile strength measurement is measured by a laboratory test, its uncertainty can also be expressed by one of the methods presented.

Key Words
measurement uncertainty; Brazilian test; GUM; fuzzy set; Monte Carlo method

Address
Department of Mining Engineering, Inonu University, Malatya, Turkey.

Abstract
To eliminate the holding and gluing problems making the direct tensile strength test hard to be applied, a new method of testing specimens prepared using lathe machine to make the dog bone shape is assessed whether it could be applied to determine accurate direct tensile strength values of rock materials. A series of numerical modelling analyses was performed using finite element method to investigate the effect of different specimen and steel holder geometries. In addition to numerical modelling study, a series of direct tensile strength tests was performed on three different groups of rock materials and a rock-like cemented material to compare the results with those obtained from the finite element analyses. A proper physical property of the lathed specimens was suggested and ideal failure of the dog bone shaped specimens was determined according to the results obtained from this study.

Key Words
tensile strength; rock testing; direct tensile strength test for rock materials; static loading

Address
(1) Eren Komurlu, Ayhan Kesimal:
Department of Mining Engineering, Karadeniz Technical University, Trabzon, Turkey;
(2) Aysegul Durmus Demir:
Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey.

Abstract
Sixty four tests were performed in a steel tank to investigate the axial responses of piles driven into organic soil prepared at two different densities using a drop hammer. Four different pile materials were used: wood, steel, smooth concrete, and rough concrete, with different length to diameter ratios. The results of the load tests showed that the shaft load capacity of rough concrete piles continuously increased with pile settlement. In contrast, the others pile types reached the ultimate shaft resistance at a settlement equal to about 10% of the pile diameter. The ratios of base to shaft capacities of the piles were found to vary with the length to diameter ratio, surface roughness, and the density of the organic soil. The ultimate unit shaft resistance of the rough concrete pile was always greater than that of other piles irrespective of soil condition and pile length. However, the ultimate base resistance of all piles was approximately close to each other.

Key Words
organic soil; pile driving; pile roughness; pile load capacity

Address
(1) Hanifi Canakci:
Department of Civil Engineering, Gaziantep University, Gaziantep, Turkey;
(2) Majid Hamed:
Department of Civil Engineering, Kirkuk University, Kirkuk, Iraq.

Abstract
A series of Brazilian tests under diameter compression for disc specimens was carried out to investigate the strength and failure behavior by using acoustic emission (AE) and photography monitoring technique. On the basis of experimental results, load-displacement curves, AE counts, real-time crack evolution process, failure modes and strength property of granite specimens containing two pre-existing holes were analyzed in detail. Two typical types of load-displacement curves are identified, i.e., sudden instability (type I) and progressive failure (type II). In accordance with the two types of load-displacement curves, the AE events also have different responses. The present experiments on disc specimens containing two pre-existing holes under Brazilian test reveal four distinct failure modes, including diametrical splitting failure mode (mode I), one crack coalescence failure mode (mode II), two crack coalescences failure mode (mode III) and no crack coalescence failure mode (mode IV). Compared with intact granite specimen, the disc specimen containing two holes fails with lower strength, which is closely related to the bridge angle. The failure strength of pre-holed specimen first decreases and then increases with the bridge angle. Finally, a preliminary interpretation was proposed to explain the strength evolution law of granite specimen containing two holes based on the microscopic observation of fracture plane.

Key Words
granite; two pre-existing holes; disc specimen; tensile strength; crack coalescence

Address
(1) Yan-Hua Huang, Sheng-Qi Yang:
State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, P.R. China;
(2) Chun-Shun Zhang:
Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia.

Abstract
An experimental program was conducted to investigate the effects of the static compaction pressure, cement content, water/cement ratio, and curing time on unconfined compressive strength (UCS) of the cement treated sand. UCS were conducted on samples prepared with 4 different cement/sand ratios and were compacted under the lowest and highest static pressures (8 MPa and 40 MPa). Each sample was cured for 7 and 28 days to observe the impact of curing time on UCS of cement treated samples. Results of the study showed the unconfined compressive strength of sand increased as the cement content (5% to 10%) of the cement-sand mixture and compaction pressure (8 MPa to 40 MPa) increased. UCS of sand soil increased 30% to 800% when cement content was increased from 2.5% to 10%. Impact of compaction pressure on UCS decreased with a reduction in cement contents. On the other hand, it was observed that as the water content the cement-sand mixture increased, the unconfined compressive strength showed tendency to decrease regardless of compaction pressure and cement content. When the curing time was extended from 7 days to 28 days, the unconfined compressive strengths of almost all the samples increased approximately by 2 or 3 times.

Key Words
static compaction; sand; cement; curing period; unconfined compressive strength

Address
(1) Yuksel Yilmaz, Vahid Barzegari Kahnemouei:
Department of Civil Engineering, Gazi University, Maltepe (06570) Ankara, Turkey;
(2) Bora Cetin:
Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA, USA.

Abstract
The main purpose of the current study is to develop the new coefficients for consideration of soil-structure interaction effects to find the elevated tank natural period. Most of the recommended relations to find the natural period just assumed the fixed base condition of elevated tank systems and the soil effects on the natural period are neglected. Two different analytical systems considering soil-structure- fluid interaction effects are recommended in the current study. Achieved results of natural impulsive and convective period, concluded from mentioned models are compared with the results of a numerical model. Two different sets of new coefficients for impulsive and convective periods are developed. The values of the developed coefficients directly depend to soil stiffness values. Additional results show that the soil stiffness not only has significant effects on natural period but also it is effective on liquid sloshing wave height. Both frequency content and soil stiffness have significant effects on the values of liquid wave height.

Key Words
coefficient; impulsive; convective; elevated tanks; soil effect

Address
(1) Pouyan Abbasi Maedeh:
International Campus, Kharazmi University, No. 49 Mofatteh Ave. Tehran, I.R. Iran;
(2) Ali Ghanbari:
Faculty of Engineering, Kharazmi University, No. 49 Mofatteh Ave., Tehran, I.R. Iran;
(3) Wei Wu:
Faculty of Engineering, University of Bodenkultur, Wien, Austria.

Abstract
Stability of vertical escarpments has been the subject of discussion for long time. However, available literature provides scarce knowledge about the effect of the formation of undercut and surface cracks on the stability of a vertical escarpment. The present study deals with a systematic analysis of the effect of surface cracks and undercut on slope stability using finite element based lower bound limit analysis. In the present analysis, the nondimensional stability factor (γH/c) is used to inspect the degrading effect of undercut and cracks developed at different offset distances from the edge of the vertical escarpment. Failure patterns are also studied in detail to understand the extent and the type of failure zone which may generate during the state of collapse.

Key Words
undercut; crack; vertical escarpment; lower bound limit analysis; failure

Address
(1) Sounik K. Banerjee:School of Civil Engineering, Kalinga Institute of Industrial Technology, Bhubaneswar, India;
(2) Debarghya Chakraborty:
Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur, India.

Abstract
The extent by which economy and safety concerns can be addressed in earth retaining structure design depends on the accuracy of the assumed failure surface. Accordingly, this study attempts to investigate and quantify mechanical backfill properties that control failure surface geometry of cohesionless backfills at the active state for translational mode of wall movements. For this purpose, a small scale 1 g physical model study was conducted. The experimental setup simulated the conditions of a backfill behind a laterally translating vertical retaining wall in plane strain conditions. To monitor the influence of dilative behavior on failure surface geometry, model tests were conducted on backfills with different densities corresponding to different dilation angles. Failure surface geometries were identified using particle image velocimetry (PIV) method. Friction and dilation angles of the backfill are calculated as functions of failure stress state and relative density of the backfill using a well-known empirical equation, making it possible to quantify the influence of dilation angle on failure surface geometry. As a result, an empirical equation is proposed to predict active failure surface geometry for cohesionless backfills based on peak dilatancy angle. It is shown that the failure surface geometries calculated using the proposed equation are in good agreement with the identified failure surfaces.

Key Words
active state; particle image velocimetry (PIV); dilatancy; retaining wall; physical modelling

Address
(1) Adlen Altunbas:
Department of Civil Engineering, Beykent University, Istanbul 34398, Turkey;
(2) Behzad Soltanbeigi:
Institute for Infrastructure & Environment, School of Engineering, University of Edinburgh, UK;
(3) Ozer Cinicioglu:
Department of Civil Engineering, Bogazici University, Bebek, Istanbul 34342, Turkey.

Abstract
Estimation of groundwater inflow into underground opening is of critical importance for the design and construction of underground structures. Groundwater inflow into a pilot underground storage facility in China was estimated using analytical equations, numerical modeling and field measurement. The applicability of analytical and numerical methods was examined by comparing the estimated and measured results. Field geological investigation indicated that in local scale the high groundwater inflows are associated with the appearance of open joints, fractured zone or dykes induced by shear and/or tensile tectonic stresses. It was found that 8 groundwater inflow spots with high inflow rates account for about 82% of the total rate for the 9 caverns. On the prediction of the magnitude of groundwater inflow rate, it was found that could both (Finite Element Method) FEM and (Discrete Element Method) DEM perform better than analytical equations, due to the fact that in analytical equations simplified assumptions were adopted. However, on the prediction of the spatial distribution estimation of groundwater inflow, both analytical and numerical methods failed to predict at the present state. Nevertheless, numerical simulations would prevail over analytical methods to predict the distribution if more details in the simulations were taken into consideration.

Key Words
groundwater inflow; rock caverns; numerical modeling, analytical solution; field measurement; heterogeneity

Address
(1) Zhechao Wang, Liping Qiao:
Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang, Liaoning, 110004, China;
(2) Zhechao Wang, Liyuan Yu:
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou, Jiangshu, 221008, China;
(3) Sangki Kwon:
Department of Energy Resources Engineering, Inha University, Chung-Hak Dong, Yeun-Su Ku, Incheon, 402751, Korea;
(4) Liping Bi:
Geotechnical and Structural Engineering Research Center, Shandong University, Jinan, Shandong, 250061, China.

Abstract
The assessment of slope stability is an essential task in geotechnical engineering. In this paper, a threedimensional (3D) finite element analysis (FEA) was employed to investigate the performance of different shear pin arrangements to increase the stability of a soil block resting on an inclined plane with a low-interface friction plane. In the numerical models, the soil block was modeled by volume elements with linear elastic perfectly plastic material in a drained condition, while the shear pins were modeled by volume elements with linear elastic material. Interface elements were used along the bedding plane (bedding interface element) and around the shear pins (shear pin interface element) to simulate the soil-structure interaction. Bedding interface elements were used to capture the shear sliding of the soil on the low-interface friction plane while shear pin interface elements were used to model the shear bonding of the soil around the pins. A failure analysis was performed by means of the gravity loading method. The results of the 3D FEA with the numerical models were compared to those with the physical models for all cases. The effects of the number of shear pins, the shear pin locations, the different shear pin arrangements, the thickness and the width of the soil block and the associated failure mechanisms were discussed.

Key Words
slope stability; shear pin; numerical model; interface element

Address
(1) Rithy Ouch, Boonchai Ukritchon:
Geotechnical Research Unit, Department of Civil Engineering, Chulalongkorn University, Bangkok, Thailand;
(2) Thirapong Pipatpongsa:
Department of Urban Management, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto, 615-8540, Japan;
(3) Mohammad Hossein Khosravi:
School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran.


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