Crosshole Sonic Logging

CSL is a method for determining the structural integrity of bored concrete piles.

CSL requires steel or PVC pipes to be embedded in the finished pile. The pipes are attached to the reinforcing mesh before the reinforcement is placed in the shaft and concrete is filled in. Steel pipes are often preferred over PVC pipes, as studies have shown that PPCV pipes have a tendency to escape from the concrete due to the heat created by the hydration process from the concrete. Depending on how big the pile is, the correct number of gauge tubes is cast in. The pipes are filled with water, which is used as a conducting medium. After the pile has hardened approx. 3-7 days, a sound source and receiver are led down two separate pipes at a constant speed, where the sound source and receiver follow each other.

A signal generator generates a sonic pulse from the sound source which is picked up by the receiver. Relative energy, waveform and differential time are recorded and stored. This procedure is repeated until the entire pile is mapped.

Areas with signal loss or wave speed reduction greater than 10% represent potential physical abnormalities and can be selected for further investigation. Measurements with relative energy or amplitude loss can indicate a poor curing process or concrete heterogeneity, including e.g. poor mix of concrete mix.

By comparing data from a number of combinations of boreholes, you can get an idea of ​​the structural health of the entire pile. When the measurement is done, the pipes are filled with concrete. A more advanced method is to create a graphical 3D model, better known as Crosshole Sonic Tomography.