Research Of Ram-compaction Multiple Expansion Pedestal Pile's Single Pile Settlement Mechanism And Features

Ram-compaction multiple expansion pedestal pile is a successfully developed new type of compaction piles based on ordinary driven cast-in-place pile.By improving the equipment and process of pile,it sets expanding "ball" at different positions of the pile body which greatly improve the bearing capacity of piles,and overcome the exsiting problem of common driven cast-in-place pile,such as necking,broken pile driving pile,honeycomb and reinforcing cage deformation distortion and so on.Engineering practice shows that ram-compaction multiple expansion pedestal pile has the advantages of high bearing capacity,small settlement,and pile efficiency higher.As a result of the existence of pile body expanding head makes the settlement of the pile type model complex.In this thesis,the author conducts situ test,indoor model test,numerical simulation and theoretical analysis methods to give an research of the ram-compaction multiple expansion pedestal pile's settlement characteristics,exploring the discipline of expanding head's role in the process of settlement of single pile,all these statistics provides basis to the calculation of the settlement of single pile for the ram-compaction multiple expansion pedestal pile and the calculation formula is acquired through theoretical derivation.The following conclusions are obtained through this study:1)With the same pile length and pile diameter,ram-compaction multiple expansion pedestal pile has improved its ultimate bearing capacity for almost 2 times compared with ordinary straight pile.Accordingly,under the same settlement of pile top loads,its sedimentation is less than half the straight hole pile.2)Due to the extensions in different parts of the pile body,ram-compaction multiple expansion pedestal pile's P~S curve has obvious “footing” leaps.It can adjust the adjacent “footing” leap space by changing different extensions spacing between.Pile body's extension's "footing" leap range is greater than below extension of the pile.3)With the change of the number of expanding head of ram-compaction multiple expansion pedestal pile,it can significantly change the bearing capacity and reduce settlement value.Under the experimental conditions of this thesis,supposing the bearing capacity is at the same,the more the expanding head,the lower subsidence value.When the pile top is under 4000 kn,the settlement of ordinary straight pile is expanded for 4 times of the pile head,single expanded pile head settlement is 2 times of the expanded pile head.4)The existence of pile body expanding head has changed the distribution rule and range of the pile side friction.The stress effect of the soil located in the first part of the expanding head is bigger than the stress value produced by the pile side friction.Besides,the influencing scope of surrounding soil produced by expanding head is about 4 times the diameter of the pile body.5)There are many factors that can influence the settlement of pile,such as expansion diameter,diameter of pile,expand spacing,pile-soil stiffness ratio,slenderness ratio of the Ram type extrusion expansion long piles.Therefore,selecting appropriate parameters to reduce the settlement of piles is worthy considering in the pile foundation design.6)On the basis of Mindlin solution,this thesis offers calculation for the settlement of single pile for ram-compaction multiple expansion pedestal pile,combining with layered summation method.Though the comparison of the indoor model test and theoretical calculation values,we can get the conclusion that the calculated value and experimental value error is in a reasonable range,which can be used as reference of future design work.