FPrimeC Solutions Inc. was engaged by the client to perform non-destructive evaluation (NDE) for estimating the unknown depth of hollow tube steel piles for an existing 130 year old rail bridge at Bio Bio River in Concepcion, Chile. No drawing or construction document was available. The construction of a new bridge in the vicinity of existing bridge had resulted in minor tilting of several pile groups. The client was interested to assess the length and integrity of piles across different pile groups.
A multi-technology approach was used for the assessment of the existing foundations:
1- Visual Inspection
Visual inspection of piles was conducted by divers. The approximate length of the piles at several locations was assessed.
2- Guided Waves for Pipe Length Estimates
A Guided Wave Based Method (GWBM) was used to evaluate the unknown length of piles in this project. To do so, a project specified setup was designed and executed. Accelerometers were installed on the sides of the piles just above the ground level. Accelerometers were attached to the pipes using bonding agent. A set of nylon hammers (of different size) were used to strike the pipe. The hammer strikes generate required stress-waves running all the way down, then reflected from the pile toe and other intermediate events (e.g., joints and significant defects). The reflections are collected by the accelerometer sensors.
2- Downhole Seismic (sCPT)
Downhole seismic test was conducted to assess the length of existing foundations. sCPT probe was used to collect seismic waves generated as a result of stress wave created by instrumented hammer impact were collected. The data were cross-examined against data collected from the visual inspection and Guided Waves method.
The combined methodology helped FPrimeC estimate the length of one select pile at each of the 60 pile groups. The results were promising, and did not require any major intrustive assessment.