Study On Bearing Mechanism Of Rotary Digging And Sqeezing Pile Casted-in-place With Expanded Plates In Application Of Highway Bridge Engineering

As the Current leap-forward development of infrastruction, bearing capacity and settlement of the bridge pile foundation are raised very high demand. multi-section Piles (DX pile) has the characteristics of multi-layer distributed load, and the advantages of high bearing capacity and small settlement. in order to promote this new technology to be applied in the railway bridge pile foundation, this paper uses field test as the main research methods, with theoretical calculations and numerical simulation and other means, and does a series of studies on the DX pile design methods, bearing mechanisms, and bearing capacity and settlement of DX pile groups, the main research results are as follows:1. the analysis of several engineering case shows that it is more in line with the actual situation to caculate tip resistance and side resistancin accordance with the "foundation and basis for Railway Bridge Design Code" TB10002.5-2005's provisions and calculate plate resistance according to "Sancha way Piles Design Code" JGJ171-2009's provisions2. using measured test data to analyze, based on meter installed in the pile of steel to come to the axial force under different load levels, it come to the plates resistance, side friction of piles, the load transfer mechanism of pile side resistance and tip resistence. plates Resistance plays early, only with a small displacement. When Displacement reaches a certain value, part of the side resistance has reached the limit,and the total resistance began to decrease, while the plate resistance and the proportion of load shared rapidly increase. Tip resistance in the whole loading process shares a small proportion of load and need significant settlement to play. The bearing capacity of plates to play has an order effect on time, the plate above play first, the beneath to play next.3.using numerical simulation method to analyze upper and lower soil stress state of bearing plates, it come to the upper and lower soil stress distribution principle of bearing plates. When the load is large, side friction of bearing plate's upper soil decreases, and its range of influence was about 35 percent of the plate diameter, side friction of bearing plate's upper soil increase and its sphere of influence is as 30 percent of the diameters. with the increase of the settlement, tensile stress in the bearing plate's upper soil occurs, which may prove the existence of the free face. 4. By means of numerical simulation the DX pile group model is established, and qualitative analysis of the pile and soil settlement cloud, pile stress curve is made; a settlement rules and pile-soil stress transfer rule is reached, and with pile group and single pile QS curve quantitatively,comparison of different spacing DX pile group bearing capacity and settlement control, bearing capacity and settlement control of the straight and DX pile group, bearing capacity and settlement control of plate staggered arrangement and plate parallel arrangement. The optimum pile spacing and the best layout and the difference of bearing capacity and settlement between straight pile group and the DX pile group is determined,which prove the advantage of DX pile group on the bearing capacity and the settlement control.