长短桩组合支护在深厚软土基坑中的应用研究

Application of long and short pile combined support to deep soft soil foundation pit

基坑的支护桩通常采用等桩长布置,而在深厚软土地区的基坑工程中,围护桩需要嵌入软土以下的好土,所以桩长较长,等桩长布置的情况下经济性较差。为了研究部分围护桩嵌入好土的长短桩组合支护在深厚软土基坑中的作用及表现,采用现行设计方法计算全长桩支护和全短桩支护情况下围护桩的结构内力和变形,由此估计采用长短桩组合支护情况下围护桩的变形应介于全长桩支护和全短桩支护之间;进一步通过三维数值模拟对不同长度的长短桩组合支护进行对比分析,确定了合适的短桩桩长,然后将分析结果用于指导实际项目设计并对项目展开监测。研究表明:(1)长短桩组合支护的短桩桩长可截取至全长桩支护条件下围护桩弯矩计算的第二个反弯点,实现短桩与长桩共同受力、协调变形;(2)论文中给出的基于现行设计计算软件的长短桩组合支护设计计算方法是可行的;(3)长短桩组合支护设计方法可有效节约工程造价。研究成果可为深厚软土基坑工程提供参考。

The retaining piles for foundation pits are usually arranged with equal pile lengths.However,in foundation pit projects in deep and soft soil areas,the retaining piles need to be embedded in good soil below the soft soil,so the pile lengths are longer.The economy is poor when the pile lengths are arranged with equal pile lengths.In order to examine the effect and performance of long and short pile combined support with partial retaining piles embedded in good soil in deep soft soil foundation pits,current design methods are used to calculate the structural internal force and deformation of retaining piles under the conditions of full length pile support and full short pile support.Therefore,it is estimated that the deformation of retaining piles under the condition of using long and short pile combined support should be between full length pile support and full short pile support.Through 3D numerical simulation,a comparative analysis is conducted on the combined support of long and short piles with different lengths to determine the appropriate length of short piles,and the analysis results are used to guide the actual project design and monitor the project.The research results show:(1)The length of the short pile supported by the combination of long and short piles can be taken as the second inflection point for calculating the bending moment of the retaining pile under the condition of full length pile support,achieving joint stress and coordinated deformation of the short pile and long pile.(2)The design and calculation method for long short pile combined support based on current design and calculation software presented in the paper is feasible.(3)The design method of long and short pile combination support can effectively save project costs.The monitoring data show that the application of long and short pile composite support in the project is successful,and the research results can provide references for deep soft soil foundation pit engineering.