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CONTENTS
Volume 10, Number 5, May 2016
 

Abstract
Geosynthetics reinforced soil (GRS) walls constructed on weak grounds may change in both the horizontal earth pressure and deformation on wall facing. However, only few studies were done in the literature to measure and analyze the horizontal external deformation behavior of GRS walls constructed on soft grounds for a long period of time. The present study describes the external deformation behavior of GRS walls observed for 12-year long-term performance. The horizontal deformation of the geosynthetics-wrapped-facing GRS walls shows a passive behavior along one third of the wall height, from top going downwards, and active behavior for the rest of the wall height. Even if the geogrid and nonwoven geotextiles are exposed directly to sunlight and rainfalls in a span of 12 years, they have functioned well as wall facing. Therefore, the geosynthetic reinforcement material is strong enough to resist ultraviolet rays.

Key Words
GRS walls; long-term deformation behavior; geogrid; nonwoven geotextile; wall facing

Address
(1) Myoung-Soo Won:
Department of Civil Engineering, Kunsan National University, 558 Deahagro, Gunsan, Jeollabuk-do 54150, Republic of Korea;
(2) O-Hyeon Lee:
Department of Civil and Environmental Engineering, Kunsan National University, 558 Deahagro, Gunsan, Jeollabuk-do 54150, Republic of Korea;
(3) You-Seong Kim, Se-Kyung Choi:
Department of Civil Engineering, Chongbuk National University, 567 Baekje-daero, deokjin-gu, Jeonju, Jeollabuk-do 54896 Republic of Korea.

Abstract
This paper presents a numerical study of pile force distribution in a pile group foundation subjected to vertical load and large moment. The physical modeling of a pile foundation for a wind turbine is analyzed using 3D finite element software, PLAXIS 3D. The soil profile consists of several clay layers, which are modeled as Mohr-Coulomb material in an undrained condition. The piles in the pile group foundation are modeled as special elements called embedded pile elements. To model the problem of a pile group foundation, a small gap is created between the pile cap and underlying soil. The pile cap is modeled as a rigid plate element connected to each pile by a hinge. As a result, applied vertical load and large moment are transferred only to piles without any load sharing to underlying soil. Results of the study focus on pile load distribution for the square shape of a pile group foundation. Mathematical expression is proposed to describe pile force distribution for the cases of vertical load and large moment and purely vertical load.

Key Words
numerical analysis; finite element; pile group foundation; pile load distribution; biquartic interpolation

Address
Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, Thailand.


Abstract
The present research presents experimental and finite element studies to investigate the behavior of piled raft-tunnel system in a sandy soil. In the experimental work, a small scale model was tested in a sand box with load applied vertically to the raft through a hydraulic jack. Five configurations of piles were tested in the laboratory. The effects of pile length (L), number of piles in the group and the clearance distance between pile tip and top of tunnel surface (H) on the load carrying capacity of the piled raft-tunnel system are investigated. The load sharing percent between piles and rafts are included in the load-settlement presentation. The experimental work on piled raft-tunnel system yielded that all piles in the group carry the same fraction of load. The load carrying capacity of the piled rafttunnel model was increased with increasing (L) for variable (H) distances and decreased with increasing (H) for constant pile lengths. The total load carrying capacity of the piled raft-tunnel model decreases with decreasing number of piles in the group. The total load carrying capacity of the piles relative to the total applied load (piles share) increases with increasing (L) and the number of piles in the group. The increase in (L/H) ratio for variable (H) distance and number of piles leads to an increase in piles share. ANSYS finite element program is used to model and analyze the piled raft-tunnel system. A three dimensional analysis with elastoplastic soil model is carried out. The obtained results revealed that the finite element method and the experimental modeling are rationally agreed.

Key Words
piled raft; tunnel; load test; piles share; finite element

Address
(1) Raid R. Al-Omari, Adel A. Al-Azzawi:
Civil Engineering Department, Nahrain University, Baghdad, Iraq;
(2) Kadhim A. AlAbbas:
Civil Engineering Department, Al-Qadisia University, Al-Qadisia, Iraq.

Abstract
A numerical study has been conducted to examine the improvement achieved in the ultimate pullout capacity of horizontal circular anchor plates embedded in undrained clay, by constructing granular columns of varying diameter over the anchor plates. The analysis has been carried out by using lower bound theorem of limit analysis and finite elements in combination with linear programming. The improvement in uplifting capacity of anchor plate is expressed in terms of an efficiency factor (ξ). The efficiency factor (ξ) has been defined as the ratio of ultimate vertical pullout capacity of anchor plate having diameter D embedded in soft clay reinforced by granular column to the vertical pullout capacity of the anchor plate with same diameter D embedded in soft clay only. The variation of efficiency factor (ζ) for different embedment ratios and different diameter of granular column has been studied considering a wide range of softness of clay and different value of soil internal friction angle (φ) of the granular material. It is observed that ξ increases with an increase in diameter of the granular column (Dt) and increase in friction angle of granular material. Also, the effectiveness of the usage of granular column increases with decrease in cohesion of the clay.

Key Words
circular anchor plate; granular column; limit analysis; efficiency; anchor in clay; uplift resistance

Address
Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur- 721302, India.


Abstract
The effects of reinforcement on the horizontal and vertical deformations of geosynthetic reinforced retaining walls are investigated under a well-known seismic load (San Jose earthquake, 1955). Retaining walls are designed with internal and external stability (with appropriate factor of safety) and deformation is chosen as the main parameter for describing the wall behavior under seismic load. Retaining walls with various heights (6, 8, 10, 12 and 14 meter) are optimized for geosynthetics arrangement, and modeled with a finite element method. The stress-strain behavior of the walls under a well-known loading type, which has been used by many previous researchers, is investigated. A comparison is made between the reinforced and non-reinforced systems to evaluate the effect of reinforcement on decreasing the deformation of the retaining walls. The results show that the reinforcement system significantly controls the deformation of the top and middle of the retaining walls, which are the critical points under dynamic loading. It is shown that the optimized reinforcement system in retaining walls under the studied seismic loading could decrease horizontal and vertical deformation up to 90% and 40% respectively.

Key Words
reinforced soils; retaining walls; geosynthetic; seismic load; numerical method

Address
(1) Mehrab Jesmani:
Department of Civil Engineering, Imam Khomeini International University, Ghazvin, Iran;
(2) Mehrad Kamalzare:
Department of Civil and Environmental Engineering, Rutgers University, Piscataway, NJ, USA;
(3) Babak Bahrami Sarbandi:
3Department of Civil Engineering, Islamic Azad University, Arak, Iran.

Abstract
In this paper, the active lateral earth pressure is evaluated using the stress characteristics or slip line method. The lateral earth pressure is expressed as the lateral earth pressure coefficients due to the surcharge, the unit weight and cohesion of the backfill soil. Seismic horizontal and vertical pseudo-static coefficients are used to consider the seismic effects. The equilibrium equations along the characteristics lines are solved by the finite difference method. The slope of the ground surface, the wall angle and the adhesion and friction angle of the soil-wall interface are also considered in the analysis. A computer code is provided for the analysis. The code is capable of solving the characteristics network, determining active lateral earth pressure distribution and calculating active lateral earth pressure coefficients. Closed-form solutions are provided for the lateral earth pressure coefficients due to the surcharge and cohesion. The results of this study have a good agreement with other reported results. The effects of the geometry of the retaining wall, the soil and soil-wall interface parameters are evaluated. Non-dimensional graphs are presented for the active lateral earth pressure coefficients.

Key Words
lateral earth pressure coefficients; seismic; active; stress characteristics; slip line

Address
School of Engineering, Persian Gulf University, Bushehr, Iran.


Abstract
Industrialization and urbanization are the two phenomena that are going relentless all over the world. The consequence of this economic success has been a massive increase in waste on one hand and increasing demand for suitable sites for construction on the other. Owing to the surplus raw materials and energy requirement needed for manufacturing synthetic fibers, applications of waste fibers for reinforcing soils evidenced to offer economic and environmental benefits. The main objective of the proposed work is to explore the possibilities of improving the strength of soil using fly ash waste as an admixture and Human Hair Fiber (HHF) as reinforcement such that they can be used for construction of embankments and land reclamation projects. The effect of fiber content on soil — fly ash mixture was observed through a series of laboratory tests such as compaction tests, CBR and unconfined compression tests. From the stress - strain curves, it was observed that the UCC strength for the optimised soil — flyash mixture reinforced with 0.75% human hair fibers is nearly 2.85 times higher than that of the untreated soil. Further, it has been noticed that there is about 7.73 times increase in CBR for the reinforced soil compared to untreated soil. This drastic increase in strength may be due to the fact that HHF offer more pull-out resistance which makes the fibers act like a bridge to prevent further cracking and thereby it improves the toughness which in turn prevent the brittle failure of soil-flyash specimen. Hence, the test results reveal that the inclusion of randomly distributed HHF in soil significantly improves the engineering properties of soil and can be effectively utilized in pavements. SEM analysis explained the change of microstructures and the formation of hydration products that offered increase in strength and it was found to be in accordance with strength tests.

Key Words
clay; ground improvement; fly ash; randomly distributed fiber; soil reinforcement

Address
School of Civil Engineering, SASTRA University, Thanjavur, Tamil Nadu 613401, India.


Abstract
Soil stabilization is one of the useful method of ground improvement for soil with low bearing capacity and high settlement and unrequired swelling potential. Generally, the stabilization is carried out by adding some solid materials. The main objective of this research was to investigate the feasibility of stabilization of organic soils and sewage sludge to obtain low cost alternative embankment material by the addition of two different slags. Slags were used as a replacement for weak soil at ratios of 0%, 25%, 50%, 75% and 100%, where sewage sludge and organic soil were blended with slags separately. The maximum dry unit weights and the optimum water contents for all soil mixtures were determined. In order to investigate the influence of the slags on the strength of sewage sludge and organic soil, and to obtain the optimal mix design; compaction tests, the California bearing ratio (CBR) test, unconfined compressive strength (UCS) test, hydraulic conductivity test (HCT) and pH tests were carried out on slag-soil specimens. Unconfined compressive tests were performed on non-cured samples and those cured at 7 days. The test results obtained from untreated specimens were compared to tests results obtained from soil samples treated with slag. Laboratory tests results indicated that blending slags with organic soil or sewage sludge improved the engineering properties of organic or sewage sludge. Therefore, it is concluded that slag can be potentially used as a stabilizer to improve the properties of organic soils and sewage sludge.

Key Words
organic soil; sewage sludge; slag; CBR; UCS; hydraulic conductivity; pH

Address
Erciyes University, Engineering Faculty, Department of Civil Engineering, 38039, Kayseri, Turkey.



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