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CONTENTS
Volume 5, Number 6, December 2013
 

Abstract
In order to investigate shear behavior of granular materials due to excavation and associated unloading actions, load-controlled plane strain compression tests under decreasing confining pressure were performed under drained conditions and the results were compared with the conventional plane strain compression tests. Four types of granular material consisting of two quartz sands and two glass beads were used to investigate particle shape effects. It is clarified that macro stress-strain behavior is more easily influenced by stress level and stress path in sands than in glass beads. Development of localized deformation was analyzed using photogrammetry method. It was found that shear bands are generated before peak strength and shear band patterns vary during the whole shearing process. Under the same test condition, shear band thickness in the two sands was smaller than that in one type of glass beads even if the materials have almost the same mean particle size. Shear band thickness also decreased with increase of confining pressure regardless of particle shape or size. Local maximum shear strain inside shear band grew approximately linearly with global axial strain from onset of shear band to the end of softening. The growth rate is found related to shear band thickness. The wider shear band, the relatively lower the growth rate. Finally, observed shear band inclination angles were compared with classical Coulomb and Roscoe solutions and different results were found for sands and glass beads.

Key Words
plane strain compression; unloading; stress path; particle shape; shear band; DIC analysis

Address
(1) Li Zhuang and In-Mo Lee: Civil, Environmental and Architectural Engineering, Korea University, Seoul 136-713, Korea;
(2) Yukio Nakata: Civil and Environmental Engineering, Yamaguchi University, Ube 755-0097, Japan.

Abstract
This paper presents an optimal design method for determining pile lengths of piled raft foundations. The foundation settlement is evaluated by taking into account the raft-pile-soil interaction. The analysis of settlement is simplified by using Steinbrenner's equation. Then the total pile length is minimized under the settlement constraint. An extended sequential linear programming technique combined with an adaptive step-length algorithm of pile lengths is used to solve the optimal design problem. The accuracy of the simplified settlement analysis method and the validity of the obtained optimal solution are investigated through the comparison with the actual measurement result in existing piled raft foundations.

Key Words
piled raft foundation; vertical load; optimum design; pile arrangement; settlement analysis; observed data; large-step numerical sensitivity

Address
(1) Keiji Nakanishi: Institute of Technology, Shimizu Corporation, Koto-ku, Tokyo 135-8530, Japan;
(2) Izuru Takewaki: Department of Architecture and Architectural Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan.

Abstract
In this study, artificial neural networks (ANNs) were used to predict the settlement of pad footings on cohesionless soils based on standard penetration test. To achieve this, a computer programme was developed to calculate the settlement of pad footings from five traditional methods. The footing geometry (length and width), the footing embedment depth, Df, the bulk unit weight, γ, of the cohesionless soil, the footing applied pressure, Q, and corrected standard penetration test, Ncor, varied during the settlement analyses and the settlement value of each footing was calculated for each method. Then, an ANN model was developed for each traditional method to predict the settlement by using the results of the analyses. The settlement values predicted from the ANN model were compared with the settlement values calculated from the traditional method for each method. The predicted values were found to be quite close to the calculated values. It has been demonstrated that the ANN models developed can be used as an accurate and quick tool at the preliminary designing stage of pad footings on cohesionless soils without a need to perform any manual work such as using tables or charts. Sensitivity analyses were also performed to examine the relative importance of the factors affecting settlement prediction. According to the analyses, for each traditional method, Ncor is found to be the most important parameter while γ is found to be the least important parameter.

Key Words
neural networks; cohesionless soils; pad footing; settlement; standard penetration test

Address
(1) Yusuf ErzÍn and T. Oktay Gul: Celal Bayar University, Faculty of Engineering, Department of Civil Engineering, 45140 Manisa, Turkey.

Abstract
Extensive study was carried out on Clay expansive soil. This soil was silty clay and can be classified as CH. The degree of expansion was found to range from low to medium depending on the free swell and swell pressure tests. The research investigated the effect of using cement dust on swelling potential, Atterberg Limit, linear shrinkage, and mineralogical composition of expansive soil. The results showed that the swelling potential, plasticity index, linear shrinkage, and clay minerals decrease with increasing cement dust percentage. The cement dust accumulates in huge amounts as a side product in cement factories, and the disposal of this fine dust is very difficult and poses an environmental threat.

Key Words
expansive soils; cement dust; swelling pressure; swelling

Address
(1) Raddi M. AlZubaidi: Department of Civil and Environmental Engineering, Sharjah University, UAE;
(2) Kawkab H. AlRawi and Ahmed J. AlFalahi: Department of Building Engineering, University of Technology, Baghdad, Iraq.

Abstract
Organic soils exhibit problematic properties such as high compressibility and low shear strength; these properties may cause differential settlement or failure in structures built on such soils. Organic soil removal or stabilization are the most important methods to overcome geotechnical problems related to peat soils' engineering characteristics. This paper presents soil mechanical intervention for stabilization of peat with sand columns and focuses on a comparison between the mechanical characteristics of undisturbed peat and peat stabilized with 20%, 30% and 40% of sand on the laboratory scale. Cylindrical columns were extruded in different diameters through a nearly undisturbed peat sample in the laboratory and filled with sand. By adding sand columns to peat, higher permeability, higher shear strength and a faster consolidation was achieved. The sample with 70% peat and 30% sand displayed the most reliable compressibility properties. This can be attributed to proper drainage provided by sand columns for peat in this specific percentage. It was observed that the granular texture of sand also increased the friction angle of peat. The addition of 30% sand led to the highest shear strength among all mixtures considered. The peat samples with 40% sand were sampled with two and three sand columns and tested in direct shear and consolidation tests to evaluate the influence of the number and geometry of sand columns. Samples with three sand columns showed higher compressibility and shear strength. Following the results of this laboratory study it appears that the introduction of sand columns could be suitable for geotechnical peat stabilization in the field scale.

Key Words
peat; sand; geotechnical stabilization; mechanical characteristics

Address
(1) M. Ehsan Jorat, Stefan Kreiter and Tobias Mörz: MARUM - Center for Marine and Environmental Sciences, University of Bremen, Klagenfurter Strasse, DE-28359 Bremen, Germany;
(2) Vicki Moon, and Willem de Lange: Department of Earth and Ocean Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand.

Abstract
This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

Key Words
breakwater; seabed response; wave-seabed-structure interactions; Biot's poro-elastic "quasi-static" and "fully-dynamic" model; Navier-Stokes equations

Address
(1) H.Y. Zhao and D.-S. Jeng: Griffith School of Engineering, Griffith University Gold Coast Campus, Queensland, QLD 4222, Australia;
(2) D.-S. Jeng and Y. Zhang: Center for Marine Geotechnical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;
(3) D.-S. Jeng, J.-S. Zhang and C. Zhang: State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, 210098, China;
(4) H.J. Zhang: Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, Jiangsu, China.


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