The dragload

which caused by negative skin friction on pile side

may lead to many engineering disasters

such as pile failure

uneven settlement

etc.Although several methods have been established to study the negative skin friction of single pile

they have different occasions for application

and the deduced results from them may differ greatly.Firstly

the usual methods are summarized

such as limit analysis method

load transfer method

elastic or elastic-plastic theory method

shear displacement method and numerical analysis method.Secondly

two case studies are used to appraise the methods

which offer important reference to engineering design.