Abstract
An increasing attention has been given to clarifying the mechanism of negative friction on piles and to developing a method of reducing it. In spite of many related studies, however, several unknown points still appear to remain as to the group action of downdrag forces on vertical piles and the flexural behaviour of batter piles subjected to surrounding ground settlement. In this paper, a program of model tests has been performed to investigate the characteristics of negative friction on both vertical and batter pile groups, and to assess the efficiency of bitumen coatings in reducing these frictions. The main results obtained can be summarized as follows : Firstly, a method of estimating the group action of negative friction has been derived for vertical pile groups, and the validity of proposed method has been confirmed based on available data of laboratory and field tests. Secondly, it was shown that the theoretical model advocated by Broms and Fredriksson (1976) can give good insight into the overall flexural behaviour of batter piles when subjected to the surrounding ground settlement. Lastly, the model tests have demonstrated that the negative friction on vertical piles can be reduced to an acceptably low level if the piles are provided with a slip layer of bitumen.
