Model Test Research of Cushion Thickness on the Long-short Piles Composite Foundation

In order to study the impact of cushion thickness on the long-short piles composite foundation,the relation between bearing capacity and settlement,distribution of the axial force and skin friction along pile,pile-soil stress ratio, load sharing ratio and the bearing mechanics of long-short-pile composite foundation with long and short piles were studied based on laboratory tests in three different conditions:zero-centimeter-thick cushion, two-centimeter-thick cushion and five-centimeter-thick cushion in this paper. Conclusions were as follows: The settlement of long-short piles composite foundation increased with the increasing of cushion thickness,Without cushion,the maximum axial force occurred in the pile top.After having paved cushion,it occurred in the neutral dot.The axial force of long and short piles decreased with the increasing of cushion thickness; Without cushion, only positive skin friction occurred. After having paved cushion,negative skin friction came into being existence.The value of long piles skin friction increased with the increasing of the cushion thickness,the value of short piles skin friction decreased with the increasing of the cushion thickness;The pile-soil stress ratio of long pile decreased with the increasing of the cushion thickness while the pile-soil stress ratio of short pile change little,The load sharing ratio of long piles were larger than that of short piles and soil.With the increasing of cushion thickness,the load sharing ratio of long and short piles became smaller while that of soil became larger.