# Numerical analysis of negative skin friction on piles

 Author: Lo, Ho-yin Jeffrey Title: Numerical analysis of negative skin friction on piles Degree: M.Sc. Year: 2002 Subject: Piling (Civil engineering)Skin friction (Aerodynamics)FrictionHong Kong Polytechnic University -- Dissertations Department: Multi-disciplinary StudiesDept. of Civil and Structural Engineering Pages: 56, [61] leaves : ill. (some col.) ; 30 cm Language: English InnoPac Record: http://library.polyu.edu.hk/record=b1641603 URI: http://theses.lib.polyu.edu.hk/handle/200/2861 Abstract: In Hong Kong, many developments are extended to the reclaimed land and originally farm land/ pond. In these areas, most piles are installed through old or newly reclaimed soil (soft materials) such as sand fill, marine clay deposits, alluvium clay or silt and rest on a hard bearing stratum, mostly on bedrock. These soft materials may experience compression namely settlement or downward movement after pile installation due to ground water draw down, additional imposed loading or uncompleted consolidation. Downward movement of the soils surrounding piles can impose a large downward drag force on the piles in the same direction as the vertical building load. The downward drag friction on the pile is called Negative Skin Friction (NSF). It is commonly applied in Hong Kong that the peak NSF value is determined similar to those methods as for positive skin friction and the peak value is further applied to the design of pile without consideration of the actual site condition (such as amount of settlement achieved, degree of consolidation). In order to take the additional load due to NSF, the pile diameters and/or the number of piles must be increased or special coating must be applied to the pile side surface. This will increase the cost of the foundation and is a great concern of the community. In this dissertation, a 2-D finite difference program FLAC is used to establish numerical model for the pile in soils. The soils arc modeled as elastic-plastic materials. Special interface elements are applied between the soils and piles. In the model, NSF will be mobilized by the downward movement of adjacent soil induced by drawdown of ground water table. This aims at the analysis of the development of negative skin friction. The analysis includes the study of the effect of varied adjacent soil properties, founding material properties and pile/soil interface properties. A case study is also carried out to compare the computed results with the field-measured data.

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