Discussion On Calculation Model Of Double-Row Piles

In recent years, with the development and utilization of the underground space in China’s major cities, the surrounding environment of urban excavation becomes more and more complicated, especially subway lines and underground pipelines will form a dense network underground, which means that the control requirement of pit deformation is more strict, at the same time, the protection of underground space outside the red line has become increasingly strict. For some large underground support, when support within the span is too long, and supporting anchor outside is severely restricted, double-row piles supporting structure is the best choice. This situation appears more and more in the project. However, the internal force and deformation calculation theory of double-row piles structure has not been fully mature yet, and the specification method is a convenient and effective method, but in the actual application it found that the general calculation of displacement is large which is not reasonable. Therefore, some work has been done for improving the calculation model of the double-row pile, the main contents are as follows:(1) Firstly, through simple examples, discusses the applicability problem of geotechnical constitutive model when using the finite element method for calculating the problem of pit support which is needed to consider the interaction between structure and soil. It finds that the model can consider loading and unloading is more reasonable, at the same time, the tangential modulus the contact unit has greater influence on calculation.(2) For the double-row piles in soft soil foundation, the calculation results of the back row pile by the current specification way is too large, to improve the results, the calculation method of soil pressure and soil spring stiffness between piles have been improved, and the effect is better.(3) In comparison with the results of finite element method, the displacement of double-row pile by currently calculation model is too large. This is because not fully take into account the role of soil column between the piles. To this end, an equivalent stiffness method is proposed, which makes the results more reasonable.(4) According to the two double-row pile engineering examples, one is “rectangular lattice” pile layout type, one is “front pile dense and back pile sparse” layout type, respectively use the new method, the stratum structure method and the standard method to calculate the deformation of the double-row piles stucture, and compare the results with the monitoring data to verify the rationality of the new calculation model of the double-row piles structure.