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CONTENTS
Volume 5, Number 5, October 2013
 

Abstract
In practice, analysis of laterally loaded piles is carried out using beams on non-linear Winkler springs model (often known as p-y method) due to its simplicity, low computational cost and the ability to model layered soils. In this approach, soil-pile interaction along the depth is characterized by a set of discrete non-linear springs represented by p-y curves where p is the pressure on the soil that causes a relative deformation of y. p-y curves are usually constructed based on semi-empirical correlations. In order to construct API/DNV proposed p-y curve for clay, one needs two values from the monotonic stress-strain test results i.e., undrained strength (su) and the strain at 50% yield stress (

Key Words
semi-analytical FE analysis; MSD; p-y curves; interface elements; laterally loaded single piles; strain energy

Address
1) Dj. Amar Bouzid: Department of Civil Engineering, Faculty of Sciences and Technology, University of Medea, Quartier Ain D\'hab, Medea 26000, Algeria;
2) S. Bhattachary: Department of Civil Engineering, University of Bristol, Room 237, Queens Building, Bristol BS8 1TR, UK;
3) S.R. Dash: Department of Civil Engineering, Indian Institute of Technology, Bhubaneswar, India.

Abstract
The results of an experimental program regarding the effects of gradation on shear strength and volume change behavior of silty sands are presented. Consolidated drained direct shear tests were performed on two clean base sands and twelve silty sands obtained by mixing those base sands with two different non-plastic silts at various fines contents (

Key Words
sand; silt; gradation; volume change; shear strength; void ratio

Address
1) Mehmet Murat Monkul: Department of Civil Engineering, Yeditepe University, Ístanbul, Turkey.

Abstract
This paper presents an experimental study on the influence of principal stress direction and magnitude of intermediate principal stress on the undrained stress-strain-strength behaviors of Bangkok Clay. The results of torsional shear hollow cylinder and advanced triaxial tests with various principal stress directions and magnitudes of intermediate principal stress on undisturbed Bangkok Clay specimens are presented. The analysis of testing results include: (i) stress-strain and pore pressure behaviors, (ii) stiffness characteristics, and (iii) strength characteristics. The results assert clear evidences of anisotropic characteristics of Bangkok Clay at pre-failure and failure conditions. The magnitude of intermediate principal stress for plane-strain condition is also investigated. Both failure surface and plastic potential in deviatoric plane of Bangkok Clay are demonstrated to be isotropic and of circular shape which implies an associated flow rule. It is also observed that the shape of failure surface in deviatoric plane changes its size, while retaining its circular shape, with the change in direction of major principal stress. Concerning the behavior of Bangkok Clay found from this study, the discussions on the effects of employed constitutive modeling approach on the resulting numerical analysis are made.

Key Words
torsional shear hollow cylinder; stress-strain characteristics; failure criteria; generalised stress; Bangkok Clay

Address
1) Siam Yimsiri, Wanwarang Ratananikom: Department of Civil Engineering, Faculty of Engineering, Burapha University, Chonburi, Thailand;
2) Fumihiko Fukuda: Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan;
3) Suched Likitlersuang: Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, Thailand.

Abstract
An analysis model for predicting the tip bearing capacity of drilled shafts in cohesionless soils is improved in this study. The evaluation is based on large amounts of drilled shaft load test data. Assessment on the analysis model reveals a greater variation in two coefficients, namely, the overburden bearing capacity factor (Nq) and the bearing capacity modifier for soil rigidity (

Key Words
drilled shafts; cohesionless soils; tip bearing capacity; friction angle; effective shaft depth

Address
1) Yit-Jin Chen, Hao-Wei Wu, Maria Cecilia M. Marcos and Shiu-Shin Lin: Department of Civil Engineering, Chung Yuan Christian University, Chung-Li, 32023, Taiwan;
2) Maria Cecilia M. Marcos: Department of Civil Engineering, Adamson University, Manila, Philippines.

Abstract
Considering the influences of fluid penetration, casing, excavation processes of wellbore and perforation tunnels, the seepage-deformation finite element model of oil and gas well coupled with perforating technique is established using the tensile strength failure criterion, in which the user-defined subroutine is developed to investigate the dynamic evolvement of the reservoir porosity and permeability. The results show that the increases of perforation angle and decreases of perforation density lead to a higher fracture initiation pressure, while the changes of the perforation diameter and length have no evident influences on the fracture initiation pressure. As for initiation location for the fracture in wellbore, it is on the wellbore face while considering the presence of the casing. By contrast, the fractures firstly initiate on the root of the tunnels without considering casing. Besides, the initial fracture position is also related with the perforation angle. The fracture initiation position is located in the point far away from the wellbore face, when the perforation angle is around 30

Key Words
perforation parameters; finite elements; initiation pressure; hydraulic fracturing

Address
1) Hai Yan Zhu, Jin Gen Deng and Zi Jian Chen: State Key Laboratory of Petroleum Resource and Prospecting (China University of Petroleum), Beijing 102249, China;
2) Hai Yan Zhu and Feng Chen An: School of petroleum engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China;
3) Shu Jie Liu, Cheng yong Peng and Min Wen: School of Engineering and Electronics, Edinburgh University, Edinburgh EH9 3JN, UK;
4) Guang Dong: CNOOC Research Institute, Beijing 100027, China.

Abstract
The factor of safety is the most common measure of the safety margin for slopes. When the traditionally defined factor is used in kinematic approach of limit analysis, calculations can become elaborate, and iterative methods have to be used. To avoid this inconvenience, the safety factor was defined in terms of the work rates that are part of the work balance equation used in limit analysis. It was demonstrated for two simple slopes that the safety factors calculated according to the new definition fall close to those calculated using the traditional definition. Statistical analysis was carried out to find out whether, given normal distribution of the strength parameters, the distribution of the safety factor can be approximated with a well-defined probability density function. Knowing this function would make it convenient to calculate the probability of failure. The results indicated that the normal distribution could be used for low internal friction angle (up to about 16

Key Words
slope stability analysis; factor of safety

Address
1) Antoni Florkiewicz and Albert Kubzdela: Department of Civil and Environmental Engineering, Poznan University of Technology, Piotrowo 5, 60-965 Poznan, Poland.


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