塑料类材料与砂土接触界面直剪试验研究

在桩身中性点以上增加一个预制塑料套筒是一种减小桩身负摩阻力的方法。为了研究该方法优化负摩阻力的效果,考虑塑料种类和砂土颗粒粒径变化两个因素,通过直剪仪进行了砂土与四种塑料类材料(PVC,ABS,PC,PP)及混凝土的剪切试验。试验结果显示:塑料类材料与砂土接触界面特性与塑料类材料种类及砂土粒径密切相关。塑料类材料与砂土接触界面剪应力随着相对剪切位移的增大而增大,最大剪应力随着法向应力的增大而增大。砂土粒径越大,接触界面抗剪强度越高。塑料类材料与砂土接触界面的抗剪强度都明显低于混凝土与砂土接触界面的抗剪强度。四种塑料材料与砂土接触界面的抗剪强度,PCPVCABSPP,选用PP塑料套筒减少桩身的负摩阻力效果最佳。

Study on Contact Interface between Plastic Materials and Sand by Direct Shear Test

Adding a prefabricated plastic sleeve on pile above its neutral point is a way to reduce the negative skin friction thereon. In order to study the optimization effect of this method on negative skin friction, this paper took plastic kinds and sand particle size into consideration to conduct shear tests on sand, 4 kinds of plastic (PVC, ABS, PC and PP) and concrete with direct shear apparatus.The results of test show that the plastic-sand contact interface has the characteristics closely related to the kinds of plastic and the sand particle size. The shear stress on this interface increases with the relative shear displacement and the maximum shear stress with the normal stress. The larger the particle size, the higher the shear strength of the contact interface. The shear strength of PVC-sand contact interface is lower than that of concrete-sand interface obviously. Shear strength of 4 kinds of plastic and plastic-sand contact interface is PC PVC ABS PP, thus PP sleeve has optimal effect on reduction of negative skin friction on pile.