筋箍碎石桩复合地基承载机理及其设计计算方法研究

A new foundation treatment concerned with geosynthetic encased stone columns has been increasingly used in engineering practice. Due to the effective lateral confinement, the geosynthetic encasement plays a great role in increasing the stiffness of stone column, preventing the loss of stones into the surrounding soft soil, and reducing the lateral bulging of the column. Stone columns encasing/wrapping with high-strength geosynthetic reinforcements on the top portion of the columns demonstrate better bearing capacity than the conventional stone columns without encasements. Then, using the encased stone columns to reinforce the soft foundation soil can increase bearing capacity and decrease settlements to a great extent. Despite of the many successful field applications, the geosynthetic encased stone column is still not widely used at the same level as those conventional methods such as piling, due to the lack of design procedures. Not so many analytical solutions have been developed for the analysis of the encased stone column in the literature. Based on the research of several groups of indoor model tests, the encasing mechanism of the geosynthetic reinforcement on the stone column and working mechanism of the composite foundation is studied. Bearing and deformation behavior of geosynthetic encased stone column under vertical load is analyzed as well. Based on the load transfer method and deformation compatibility principle, nonlinear controlling equations for composite foundation reinforced with geosynthetic encased stone columns are set up by employing the nonlinear complementary method. The confinement effect of the geosynthetic reinforcement and the nonlinear large deformation characteristic of the composite foundation are also considered. The homotopy perturbation method is used to solve the above controlling equations. In addition, with consideration of the stress concentration effect, radial and vertical coupled consolidation by encased stone column, bulging deformation of the column, the consolidation problem of the composite foundation is studied. Then,time effect on the bearing and deformation behavior of the composite founation is disscussed on the presented consolidation solutions. On the base of the above solutions, the relationship between the bearing capacity and the deformaiton of the composite foundation is eastablished. Then, the relative design method design method for composite foundation reinforced with encased stone columns is developed in this reasearch.

在工程中应用极为广泛的碎石桩桩顶一定深度范围内设置土工加筋套筒构成一种新型的筋箍碎石桩复合地基技术，由于加筋套筒的环箍约束作用，可增加碎石桩的桩身刚度，有效控制桩体鼓胀变形，提高地基承载力和减少沉降，近年来备受工程界重视，但目前其相关的理论研究尚处于初级阶段，其承载机理及受力变形特性尚缺乏深入系统地研究。为此，本研究拟从几组室内模型试验入手，深入研究筋箍碎石桩的加筋机理及其复合地基的承载机理。针对其受力变形特性，结合荷载传递法及变形协调思想，考虑筋材的环箍作用及复合地基非线性大变形特性，引入非线性互补算法，建立筋箍碎石桩复合地基的非线性控制方程组并采用同伦摄动法进行求解。同时综合考虑应力集中效应、桩内径竖向组合渗透、桩体鼓胀变形等的影响，对筋箍碎石桩复合地基承载及变形的时间效应进行深入探讨，进而建立筋箍碎石桩复合地基变形与荷载之间的关系，提出相应的设计计算方法。

在工程中应用极为广泛的碎石桩桩顶一定深度范围内设置土工加筋套筒构成一种新型的筋箍碎石桩复合地基技术，由于加筋套筒的环箍约束作用，可增加碎石桩的桩身刚度，有效控制桩体鼓胀变形，提高地基承载力和减少沉降，近年来备受工程界重视，但目前其相关的理论研究尚处于初级阶段，其承载机理及受力变形特性尚缺乏深入系统地研究。为此，本研究基于已有研究成果，通过试验分析、理论研究、及工程应用分析等多种途径对筋箍碎石桩复合地基承载机理及其设计计算理论进行了较深入的研究。.首先基于相似理论，设计并完成了多组筋箍碎石桩复合地基模型试验，探讨分析筋箍碎石桩复合地基的荷载传递过程、变形发展模式、破坏模式以及桩顶荷载-沉降曲线特征等。其次，基于室内模型试验实测数据及承载机理分析，针对桩-筋材-土三者协调变形的特殊机制，结合荷载传递法及变形协调思想，探讨分析筋材的侧向环箍作用及复合地基非线性大变形特性。最后，本研究结合筋箍碎石桩复合地基非线性大变形特性以及室内试验资料，考虑桩-筋材-土三者协调变形，提出了筋箍碎石桩复合地基承载力及沉降等计算公式，进而建立筋箍碎石桩复合地基变形与荷载之间的关系，提出相应的设计计算方法。.归纳总结筋箍碎石桩复合地基的加固机理可得如下结论：(1) 与传统碎石桩相比，加箍碎石桩具有更大的极限承载力、更小的桩身竖向变形以及侧向臌胀变形；(2) 土工材料加箍套筒对桩体起着显著的约束作用，尤其以2倍桩径范围内格栅套筒对整个桩体承载力的提高效果最为明显； (3) 筋箍复合地基中桩体可分担更多的上部结构荷载，提高地基承载力，减少地基沉降。湖南省通平高速公路某路段现场静载试验结果标明：相比较于传统碎石桩，筋箍碎石桩的单桩承载力有明显提高，加筋长度2m单桩承载力可提高30%；相同处治面积下，采用筋箍碎石桩复合地基技术，置换率可减少30.7%，筋箍碎石桩复合地基技术较普通碎石桩复合地基技术更为经济。. 相关研究成果在核心期刊上发表(录用)期刊论文8篇（SCI论文4篇，其中1篇录用待刊），获发明专利1项。通过本项目的研究，能更深入地认识筋箍碎石桩复合地基承的载机理，可促进该处治技术及其设计理论的进一步完善，加速其推广应用，其成果具有一定的学术价值与广泛的社会经济效益。