桩基低应变完整性测试的双速度分析

Double wave speeds analyse for low-strain foundation pile integrity test

传统的低应变测试是将一个加速度传感器安装在桩的自由表面 ,从信号的反射特性来判读桩中变截面及桩端。这种情况下 ,要正确判读速度信号 ,需考虑两个因素 :首先 ,混凝土的应力波波速是未知的 ,这是一个非常重要的量 ,它直接影响桩长的确定。其次 ,桩基测试时 ,由于桩与上部结构物相连或桩不均匀 ,桩中的应力波不仅只有下行波还有由于上部结构反射的上行波。这些二次反射必须区分出来 ,以免与桩阻抗变化和桩端反射混淆起来。因此 ,沿着桩身同时测量两个加速度信号可得到精确的应力波波速。本文给出了由理论模型导出的相应分析过程。

The traditional low-strain surface-impact pile shaft testing is to mount acceleration sensor on the free surface of the pile and to conclude shifting sections and the bottom of the pile by receiving reflected signal.At this occasion, two facts must be considered:first,the importan strain wave speed by which to conclude the length of the pile is unknown; the second,the vaves in the pile body include the down direction wave,the waves reflected by structures above and waves reflected by the asymmetry body of the pile.these second reflected waves must be read out so that to conclude right result.So,right result can be concluded by measuring the two acceleration signals moving along body of pile at the same time. This paper is to discuss how to conclude the analytical process by theory model.