Negative Skin Friction for Abutment Pile

[1967pradyot]

Generally for a calculation of pile capacity which may be affected by negative drag down, we do not consider the positive skin friction of those soft layer which will undergo settlement.
But there is a case which is explained below, I am little bit confused how to account the negative skin friction:
In this case around 5.0 - 6.0 m thick compressible soft clay is present below which stiff to hard clay. The abutment piles as well as the abutment and structure will be constructed first. Then the approach embankment will be built besides abutment. So, initially there is no negative skin friction and full positive skin friction will be generated.In this case whether -ve skin friction will be dedcted from full positive skin friction or the +ve skin friction for the top layer will not be consider at all.

please advise me.
Thank you

 

[GTeng]

I suggest you consider the "Unified Method" as proposed by Bengt Fellenius. The Unisoft website (unisoftltd.com) includes several technical papers that can be downloaded and which explain a proposed relationship between drag loads and settlement. These can help you get a better understanding of how to treat the problem you described.