Pile P20 – A Case History

supported by 3D tomography and verified by coring

Erez I Amir. Piletest

 

Background

Pile P20 is part of a sensitive project so just a few details can be disclosed at this stage.

The pile is ACIP (augered-cast-in-place) 1m diameter and 14m long

The pile was pre-installed with 4 CSL access tubes and was tested more than 5 days after casting.

CSL Test Results

CSL (Cross-Hole Logging) was performed using CHUM (Cross Hole Ultrasonic Monitor) manufactured piletest.com

Testing revealed a significant relative energy (RE) decrease and a matching first arrival time (FAT) increase in profiles 13 and 23, and to a lesser degree also in profile 12 (Images 1, 2)

Image1
CSL results – showing an anomaly at all profiles at the same level

Image 2

A zoom into the anomaly zone, profile 23.

The bars on the left indicate that at 10m both FAT is increased by > 20% and RE decreased by > 12dB

 

Although the data was tested by 1D CSL and the pile was equipped with just 3 access tubes, a 3D tomography was attempted and reveals the location of the flaw (image 3)

Image 3

A 3D tomography view of the anomaly at 10m, showing velocities lower than 2750m/Sec, higher velocities are transparent

 

Coring

Following the CSL results, the inspector ordered coring of the pile which confirmed the CSL results (Image 4) – The concrete at 10m was totally washed-out leaving just aggregates.

Image 4

Cores showing the defect

 

Conclusions

1. CSL is a viable test method with few false-positives
2. Interpretation is usually straightforward
3. 3D tomography supports tough decisions regarding anomalies.

 

Thanks

As this project is undergoing litigations, we thank the anonymous testing lab for sharing this information with us.