软岩地层灌注桩抗压与抗拔承载性分析

Analysis on uplift and compression resistance of cast-in-situ piles in soft rock area

纳米比亚油码头软岩地层无经验参数可取。根据1根抗压桩和1根压拔桩现场静载试验和应力测试结果,分析软岩地层中抗压桩和抗拔桩的侧阻和端阻,得出抗拔桩的上部砂土及粉土层中抗拔系数以及Q-s曲线呈缓变形的抗拔桩极限承载力取值。结果表明:上部砂土及粉土层中抗压桩的桩侧摩阻力充分发挥所需桩土相对位移为9~15 mm,单位侧摩阻力极限值可取30.1~48.1 k Pa;下部软岩侧摩阻力充分发挥所需的桩土相对位移大于40 mm;对2根桩的抗压过程,在最大加载条件下,实测桩端阻力分别为桩顶荷载的22.3%、27.3%,表现为摩擦型桩。采用双曲线模型预测抗拔桩极限承载力为4 896.7 k N。

There are no empirical parameters for soft rock geologic strata in Namibia oil tanker jetty.According to the in-site static tests and stress measurement results of one compression cast-in-situ pile and one compression-uplift pile, we analyze the mobilizations of skin friction and tip resistance in soft rock , and obtainthe uplift coefficients of sand and silt at upper layers and the uplift ultimate bearing capacity of Q-s curves ,which is characterized by slow variation.The test results show that the relative displacement of pile and soil atupper layers is from 9 to 15 mm when the skin friction resistance of compressive pile gives fully play , and theultimate value of unit skin friction resistance is from 30.1 to 48.1 kPa.The relative displacement of pile andsoil is more than 40 mm when the skin friction resistance gives fully play in soft rock geologic strata. For thecompressive process of two piles , under the maximum test load the pile toe resistances are separately 22. 3%and 27. 3% of the pile head load.They act as friction piles because of small toe resistance.The ultimate bearing capacity of the uplift pile is 4 896.7 kN by using a hyperbolic model.