PHC Super-Long Pile Bearing Performance And Suitability Research

The prestressed high-intensity concrete pile(PHC pipe pile) is a new pile type in recent years, which has the advantages of high capacity, good seismic performance, short construction period, high quality of pile forming and no influence for the environment PHC pipe pile appeared earlier in the developed countries, such as Japan and American. In the domestic, it began to apply in the 80’s. Then as a national key project ,the state started to promote it. PHC pipe pile not only got rapid development, but also the research of it is increasing.The use of PHC pipe pile in Changzhi area started from 2005, which has been rapid development in recent years. The scope of application is gradually increasing, but a lot of problems encountered in the design and construction of Engineering. The use of PHC pipe pile has certain regional, for instance, the shortage of application in cohesive soil area and lack of study in-depth. As a result, further research is needed in this area of PHC super-long pile suitability, bearing capacity, the influencing factors and so on. This paper collects some engineering cases in the region, and carry on the discussion to the pipe pile encountered problems of application in Changzhi area.Firstly, this paper carries on the brief introduction to the engineering geology in Changzhi area, and analyzes the feasibility, applicability through collecting this area several engineering cases. For example, this article states the superiority of pipe pile of Yi Longwan project; secondly, the experimental study of 4 schemes carries on for the 11 test piles of spring city waterfront and Yi Longwan projects:(1) Analysis of the bearing mechanism and ultimate bearing capacity of PHC pipe pile through the segmentation method and Usher curve model;(2) Analysis of the effect of pile length on bearing capacity based on the similar geological conditions;(3) Analysis of the effect of the geological conditions (the depth of pile into the bearing stratum different) on bearing capacity based on the same-length pile;(4) Analysis of impact on the bearing capacity of pile length based on the same-design ultimate bearing capacity and different pile length (under the same bearing layer condition).Finally, compared with the measured data of projects, numerical simulation is conducted by FLAC3D software. The brief conclusions are as follows:(1) By collecting the materials of pipe pile project, it is found that the established engineering pile mostly used in Ⅱ1 and Ⅱ3 District where the surface soil possessed collapsibility, or the geological conditions in the presence of soft soil. The bearing layer is nearly silty clay layer with higher bearing capacity. In the complex geological conditions, the foundation scheme of PHC pipe pile has better economy.(2) Through the engineering example and numerical simulation analysis, found that the pipe pile and soil can be divided into elastic stage, elastoplastic stage and plastic stage. Pile soil pile interaction under normal state for the first two stages.(3) Research on the ultimate bearing capacity through construction project instances, it draws the following conclusion: (?) The ratio α coefficient of the measured ultimate bearing capacity and the ultimate bearing capacity design is between 1.15 and 1.25.(4) Through the analysis of construction project instances, in the similar geological conditions, same-length pile and same-load, the more depth pile tip into the bearing stratum, the smaller it subsided, and the Q-s curve is more smooth.Instead, the more depth pile tip into the bearing stratum and lager in designing ultimate load, under the action of the design ultimate load, the settlement slightly larger.(5) Through the analysis of construction project instances, under the similar geological condition and the design of the ultimate bearing capacity, settlement and pile length has positive correlation. The whole loading process, the growth rate of settlement and the pile length also has positive correlation.(6) Through the analysis of construction project instances, in similar geological conditions, the longer the pile length, the smaller the settlement, the Q-s curve is flat, the effect of the pile length is more significant; under the same load, the settlement and pile length is approximately linear relationship; the same displacement, the load and the pile length is nonlinear relationship.(7) Through analysis of the settlement on construction project instances, it is found that the mainly construction site in Changzhi area, compared with the specification limit value, the final settlement of super long pile under the design load has a larger degree of conservatism. The design of PHC pipe pile should take the load and settlement into considerations. Under the similar geological conditions, it recommended to use corresponding load value for calculating settlement of 45 mm as the characteristic value of design load.(8) The ratio of the measured value and the calculated value of the bearing capacity was 1.09 by FLAC3D numerical simulation. Compared with the measured correlation curve, the influence of the pile length on the bearing performance has a good and consistent trend. It shows that the simulation result of pipe pile by software of FLAC3D is very reliable.