考虑双重挤土效应的补桩承载力计算方法研究

研究目的：为满足实际工程中补桩设计的需要，需考虑已就位群桩的挤土效应和补桩自身的挤土效应对补桩承载力的双重影响。 研究方法和结果：先考虑群桩挤土效应，在引入“桩土面积比”这一概念的前提下，采用等效圆截面单桩模拟群桩，基于孔隙比协调的原则，运用圆柱形孔扩张理论、弹性理论、比奥固结理论，求出等效半径，进而得出等效半径处土体变化后的应力场和强度指标；并以这一应力场和强度指标作为补桩施工时土体的初始值，考虑补桩自身挤土效应，运用圆柱形孔扩张理论、弹性理论，以土力学原理为基础，推导出饱和砂土中考虑双重挤土效应的补桩承载力计算公式；本文同时推导出了群桩挤土效应对补桩承载力的影响是否明显的临界状态。 研究结论：计算结果与实测数据，比较接近，表明该计算方法具有实用价值。

Research on Computing Method of Supplementary Pile's Bearing Capacity with Consideration of Response of Dual Earth Squeezing

Research purposes: It was necessary to consider the dual influences on supplementary pile's bearing capacity by the response of earth squeezing from group pile in place and supplementary pile in order to meet the needs of designing supplementary pile in actual construction.Research methods and results: As to consideration of the response of earth squeezing from group pile,first it was required to introduce concept of pile-earth KK ratio and to seek equivalent radius by applying single pile of equivalent circular section to simulating group pile and adopting cylindrical cavity expansion theory,elastic theory and Bio consolidation theory on the basis of principle of void ratio coordination.Then it was required to seek the stress field and strength index after soil mass changed in the place of equivalent radius.As to consideration of response of earth squeezing from supplementary,taking the stress field and strength index as the start values of soil mass during construction of supplementary pile,the computing formula was derived for bearing capacity of supplementary pile in saturated sand and soil by adopting cylindrical cavity expansion theory and elastic theory on the basis of principle of soil mechanics and with consideration of response of dual earth squeezing.At the same time,the critical status was obtained for defining sharp influence on bearing capacity of supplementary pile by response of earth squeezing from group pile in this paper.Research conclusions: The computing result was close to the actually survey data through making comparison.