Load transfer of super-long piles considering influences of non-Darcy flow
摘要
In order to establish the load transfer method for the super-long piles in loess areas, based on the non-Darcy flow law and the central difference method, the formula for calculating pore water pressure under the action of non-Darcy flow is deduced, and the method for soil settlement is derived. Then, based on the traditional load transfer method, the model for the relative displacement of pile-soil is obtained, and the theoretical method for the pull-down loads on the super-long piles in thick loess areas is deduced. Finally, by combining with a pile foundation test, the calculated results are compared with those derived from the traditional Darcy's law and the test. The results show that: (1) The soil settlement at the pile side, side friction and axial force distribution of the pile calculated by the proposed theoretical method are in good agreement with the test results, and can well reflect the load transfer law of the super-long piles; (2) The velocity calculated by the traditional Darcy flow is large, which leads to that the dissipation speed of pore water pressure at a certain time point of unconsolidated flow is faster than that calculated by the non-Darcy flow, and this is why the calculated results by the Darcy flow are deviated. (3) Compared with that by the non-Darcy flow, the value of the normal friction at the pile side calculated according to the traditional Darcy law is small, which can not give full play to the positive frictional resistance of the pile side and the bearing capacity of the pile foundation, resulting in a great waste. Therefore, it is very necessary to consider the influences of non-Darcy flow when calculating the side resistance of the pile and analyzing the deformation law of soils around the pile.