Low Strain Testing

- Jun 05, 2019-

The main function of the low-strain reflected wave method is to verify the integrity of the pile structure, such as the position judgment of the pile body defect, the proof of the construction pile length and the qualitative estimation of the concrete strength grade.

The hammer wave or the force hammer and the force bar hit the top of the pile, and the resulting stress wave propagates down the pile body at the wave speed C. When the stress wave changes the interface through the pile impedance z(Z:AC) (such as the diameter reduction, the clamp) Foreign matter, concrete separation or expansion), a part of the stress wave produces a reflection upward, and another part of the stress wave propagates downward to the pile end, and a reflection occurs at the pile end. The acceleration time history curve is obtained by receiving an reflected wave signal from an acceleration or speed sensor installed at the top of the pile, and performing signal amplification and the like by the pile measuring instrument. From the curve shape characteristics, it is possible to judge the position of the impedance change or the length of the pile, and estimate the strength level of the concrete from the average wave speed.