Centrifuge Tests On Bearing Character Of Bored Pile

Behavior of bored pile installed in soft soil was studied by means of geotechnical centrifuge tests in Hydraulic Research Institute of Nanjing. In these tests, the model piles were considered with mud-cake and without mud-cake, besides, on the basis of placing strain gauge on the pile body, the stress-strain properties of bored pile(single pile and pile group) were observed when piles were supported vertical force. Furthermore, the effect of raft had been researched by 4 kind of pile groups which the place among piles were different.The test results indicate that bored pile is penetrated when bearing course is loose. But when bearing course is dense, the pile will break slowly. The capacity of single pile will enhance when the length and diameter of pile increases, but effect of pile diameter is more obvious. While pile diameter increases 20,40 and 60 percents, the capacity of pile will enhance 20.4,53.7 and 78.1 percents. And with the effect of mud-cake, the capacity of single bored pile will fall down nearly 20 percents, and pile-side resistance will also reduce 15 — 35 percents. In the centrifuge tests, when the relative displacement between pile and soil was 45 —85mm, which is much more than the criterion's, the pile-side resistance will become most. Meanwhile the intenerated value of utmost resistance is close to the resistance in situ. In the pile group tests, the capacity of pile group , which the space among piles increases from 2D to 3D, 4D and 5D , will enhance 6.1,9.6,18 percents . Besides, the efficient of pile group effect is close to or greater than 1, and it increases with augmentation of the space among piles. Furthermore the distribution of pile-side resistance of pile group is different to the single pile's.Finally, the capacity properties of bored pile were analyzed using FEA, and it found that the effect of pile-side mud-cake is more important to affecting the settlement of the soil surround pile than the length and diameter of pile. And meanwhile the effect of pile-side mud-cake, length of pile, diameter of pile to affecting the capacity mechanism of the bored pile is similar to the centrifuge results, but the distribution of the pile-side resistance is different to it.