Laboratory Model Test On Negative Friction Of Pile Foundation In Recent Fill

With the rapid development of urbanization in China,a large number of buildings are built on recent fill,whose consolidation has not yet been completed.The pile foundation in recent fill will be affected by negative friction,which reduces the bearing capacity of pile foundation and increases its settlement.Based on the pile foundations in an engineering project,11 groups of laboratory model tests were done.Silt sand,fine sand and coarse sand with different compactness were used as model fills respectively.Two different types of piles,friction pile and,were used in the test.The axial load and gravity load were applied on the pile in different order.A set of separated steel annular boxes were designed to produce the gravity stress in the fill.The settlement of pile and fill,the axial force(the side friction)were measured in the test.Following results have been achieved:(1)With the development of consolidation of the fill,the pile negative side friction increases gradually and reach to limit finally.The negative side friction in limit state distributes along the pile linearly,else,it distributes quadratically.(2)The range of negative side friction on friction pile is smaller than that on end bearing pile while the end bearing conditions have little effect on the limit value of negative side friction.(3)The range of the negative side friction is wider when the gravity load is applied first.However,the loading sequence has little effect on the limit value of the negative side friction.(4)The denser the sands are,the smaller the distribution range and the limit value of the side negative friction.