混凝土表面粗糙度对桩土接触面剪切特性影响试验研究

Experiment study on the effect of concrete roughness on shear behavior of pile-soil interface

桩侧表面粗糙程度是决定桩土接触面力学特性的主要因素之一,其对桩侧摩阻力的发挥具有重要影响。为研究桩侧表面粗糙度对桩土接触面剪切特性的影响,制作不同粗糙度的混凝土板模拟桩侧表面,并给出了混凝土表面粗糙程度计算方法。采用大型室内剪切系统,依次在不同法向应力下进行剪切试验,从剪应力-剪切位移关系、剪胀性和接触面抗剪强度三方面对接触面力学特性进行分析。结果表明:接触面剪应力-剪切位移曲线大体呈折线型,存在较为明显的应变软化现象。表面粗糙度越大,剪应力峰值越高,不同粗糙度界面达到剪应力峰值强度所对应的剪切位移变化不大。在法向应力较低时接触面有剪胀现象发生,随着粗糙度的增大,剪胀现象越明显;法向应力较高时则出现剪缩。接触面抗剪强度及残余剪切强度均随着表面粗糙度的增大而增大。根据试验结果建立的接触面力学参数与混凝土表面粗糙度关系式,可为进一步研究预制抗拔桩承载力发挥机理提供参考。

The roughness of the pile surface is one of the main factors to determine the behavior of the pile-soil interface, and besides, it shows significant affection on the pile friction resistance. In order to study the effect of roughness of pile surface on shear behavior of the interface, concrete slabs of different roughness are designed to simulate the pile surface, and the calculation method of the concrete surface roughness is put forward at the same time. Then, a series of large-scale shear tests are carried out with different normal press. Test results are presented in aspect of shear stress-shear strain curves, dilatancy and shear strength of interface. The results show that the shape of shear stress-shear strain curves generally appears to fold line. Relatively obvious strain-softening phenomenon is observed in the curves. The larger roughness offers higher shear stress peak value. Furthermore, the peak value of shear stress of different rough interface corresponding to shear displacement has little distinction. In addition, the shear dilatation occurs in the case of smaller normal stress but shrinkage under higher normal stress, and the rougher interface offers more obvious shear dilatancy. Moreover, the higher shear strength and residual strength of the interface are received form larger roughness. According to the results, the theoretical formula between mechanical parameters of pile-soil interface and concrete surface roughness is put forward. The results can be applied for the further study of the mechanism of the bearing capacity of precast uplift pile.