Article

Development of negative skin friction on driven piles in soft Bangkok clay

Canadian Geotechnical Journal (Impact Factor: 0.81). 01/2011; 29(3):393-404. DOI: 10.1139/t92-044

ABSTRACT This paper describes the results of short-term pullout tests and long-term full-scale measurements of negative skin friction on driven piles in Bangkok subsoils. Two instrumented cylindrical (hollow) prestressed concrete piles were fully equipped with two independent load-measurement systems, load cells, and telltale rods. Pore pressures and ground movements in the vicinity of the piles were monitored throughout the period of investigation. The effect of bitumen coating on negative skin friction was also studied. The long-term behaviour of driven piles was compared with the estimated values obtained from short-term pullout tests and soil strength data. It was found that the negative skin friction can be predicted well by the effective stress approach using values of β between 0.1 and 0.2. The load–settlement and load–transfer behaviour were numerically modelled to acquire a more comprehensive understanding of negative skin friction developed on driven piles. A settlement-controlled concept is also introduced for piles subjected to negative skin friction, on the basis of these findings. Key words : consolidation, downdrag, driven pile, embankment, finite elements, pore pressures, pullout, settlements, soft clay.

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    ABSTRACT: Negative skin friction is a long term, and nonlinear time dependent problem which cannot be investigated only through field measurements. Numerical analysis using finite element method provides a powerful tool that enables more detailed study of negative skin friction on piles in soft clay. In this paper, an axisymmetric finite element model was used to analyze the pile-soil interaction problem of negative skin friction. The soft clay was simulated by the double hardening model, and the pile was represented by a plate element. An extensive parametric study was carried out to investigate the effect of different factors on the behavior of a floating pile subjected to downdrag. The studied parameters are: surcharge value, surcharge radius, and clearance between pile toe and a stiff stratum. Also, a comparison between the effect of negative skin friction on both end bearing, and floating piles was carried out. The comparison incorporated the following points: shear stress distribution along pile, neutral plane location, dragload, and pile movement. Keywords: pile-soil interaction, negative skin friction, dragload, downdrag, neutral plane, floating pile
    5t International conference for young geotechnical Engineers, Paris, France; 09/2013
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    ABSTRACT: This paper presents finite element analyses of negative skin friction on a single pile under various conditions. Negative skin friction is a common problem if a pile is designed in a highly compressible soil. There are two most important parameters in estimating the load caused by negative skin friction: (1) the distribution and magnitude of skin friction and (2) the location of the neutral plane. The neutral plane is the location where the pile and soil settle the same amount or have no relative displacement. Negative skin friction is a very complex phenomenon influenced by many factors. In this paper, a two-dimensional axisymmetric model is built in the finite element program, ABAQUS. The model is first verified with a known case history. A systematic parametric analysis is performed to investigate the influence on both the neutral plane and the magnitude and distribution of negative skin friction along the pile length of various influencing factors, including the consolidation time, the properties of pile/soil interface, the lateral earth pressure coefficient, pile-soil limiting displacement, the intensity of surcharge, and soil stiffness. Based on the analyses, it is found that the location of the neutral plane is significantly influenced by the consolidation time and the stiffness of bearing layer. The distribution and magnitude of negative skin friction is influenced mainly by the pile/soil interface, soil compressibility, and the surcharge intensity. Based on the field measurements from literature and this investigation, a simple design procedure is proposed for estimating the pile load caused by negative skin friction.
    Acta Geotechnica 7(3). · 1.86 Impact Factor
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    ABSTRACT: Negative skin friction is considered one of the problems in the design of piled foundations in soft soil. The negative skin friction induces an additional compressive force on the pile called the dragload as well as, an additional pile movement called the downdrag. Ignoring the effect of negative skin friction in the design of piles leads to structural, and serviceability problems. The dragload depends on various factors such as, pile characteristics (method of installation, material, and surface treatment), soil properties (shear strength and compressibility), pile–soil relative movement, and degree of consolidation.In this paper, an axisymmetric finite element model was used to simulate, and analyze the pile–soil interaction problem of negative skin friction. The soft soil was simulated by the double hardening soil model, and the pile was described by a linear elastic model. A field case study for two instrumented end bearing driven pipe precast concrete piles in Bangkok soft clay was back analyzed. The various approaches to model the pile element, and load configurations were analyzed, and compared. An extensive parametric study was carried out to investigate the effect of different factors on the dragload value, neutral plane location, slip length, and pile movement.
    HBRC Journal. 04/2013; 9(1):68–76.

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Jun 11, 2014