竖向受荷PCC桩宏细观工作性状研究

 采用可视化模型试验及离散元数值仿真方法，对竖向受荷现浇混凝土大直径薄壁管桩(简称PCC桩)桩土传力特性、位移场发展规律及破坏性状进行深入研究。研究结果表明：PCC桩荷载–沉降曲线呈缓变型，桩外侧摩阻力高于内侧摩阻力，内侧摩阻力发展滞后于外侧摩阻力，桩外侧摩阻力在桩身上段发挥较充分，内侧摩阻力在桩身下段发挥较充分，桩内侧摩阻力及端阻力控制PCC桩后期承载力；桩外侧土体以斜向下的剪切变形为主，其影响范围约为2D；内侧以竖向压缩变形为主，加载初期与桩同步变形，加载后期桩内侧下部土体与桩之间相对位移明显大于桩内侧上部土体；桩端土体可分为圆锥形竖向压缩区及侧向变形区，其在深度方向的影响范围达到4D，桩端土变形模式在平面上呈扇形；接触力链的分布与侧阻力沿桩长分布特征基本保持一致，而桩端土孔隙率的变化则从细观角度反映侧阻先于端阻发挥。研究成果对于进一步明确PCC桩与土相互作用的内在机制具有意义。

MACROSCOPIC AND MESOSCOPIC WORKING PERFORMANCE OF PCC PILE SUBJECTED TO VERTICAL LOAD

The visual model test and distinct element method are employed to study the pile-soil force transmission characteristics，soil progressive deformation around pile，and failure behavior of cast-in-place concrete pipe pile(PCC pile). The study results show that the load-settlement curve of PCC pile varies gradually，outside shaft resistance is higher than inside，inside shaft resistance development lags behind outside. Outside shaft resistance plays more fully on upper part of pile，inside shaft resistance plays more fully on lower part of pile，inside shaft resistance and tip resistance controls later bearing capacity of PCC pile. Soil outside the pile presents inclined downward shear deformation，influence scope is cylindrical with a radius of 2D. Soil inside pile is given with the vertical deformation，and kept the step with pile at the beginning of loading，the inside relative displacement of pile and soil at the bottom of pile is bigger than upper soil during the later stage of loading. Pile tip soil can be divided into conical vertical compression area and lateral deformation area，and the influence depth is 4D，deformation pattern presents fan-shaped in the plane. The distribution of pile contact force chain brings into correspondence with shaft resistance distribution characteristics along pile length，soil porosity changes under pile tip reveal the shaft resistance plays before tip resistance from mesoscopic angle. Research results are important for further understand the interaction between PCC pile and soil.