Pile Integrity Survey

A communications infrastructure client in Alberta took over from an older telecommunications company and needed to assess the condition of the existing towers.

Situation

Communications towers are extremely important, especially in remote areas and, due to their location, they are very expensive to maintain or replace. With no construction records available, our client needed to have a good understanding of the condition of the concrete pile of the tower in order to estimate its lifespan.

A pile integrity survey would allow them to investigate if an immediate intervention would be needed on the communication towers, or if they were able to continue in service.

Solution

Pile integrity testing is based on sonic echo principles, where an impact is applied on the top of the pile and the reflected echoes are recorded after each individual impact. The wave propagation and reflection is generally based on the same principles as of GPR, but with a lot slower speed.

Pile integrity can provide information about: the continuity of the pile, defects, such as cracks, necking or bulging. It can evaluate unknown length of piles or shafts. Although it has important limitations to account for (e.g. can’t be used over pile caps, it doesn’t provide information about bearing capacity, not effective in evaluating sections of pile below cracks that crosses the entire cross section of the pile) it is an excellent methodology for a quick evaluation of a pile. The results usually indicating major defect or the depth of the toe of the pile.

The pile integrity test for the project was carried out as per ASTM D 5882 standard. It governs how the data collection should be carried out and what measures must be taken to get accurate results. The data analysis was done using a signal analysis software package.

Due to the short length of the pile and the limitations of the equipment, the results showed some uncertainty, but overall it seemed the pile is in good condition.

As an addition, a couple of circumferential GPR lines were collected to investigate the rebar pattern of the pile. The results indicated four vertical rebar at various depths.

Pile integrity test results. Orange line represents the toe of the pile.
Circumferential GPR line. Blue dots represent vertical rebar, blue line represents stirrup.

Xradar used a high frequency GPR survey to achieve the required accuracy and a mid-range frequency GPR to reveal information about the structural details underpinning the area. Several grids with evenly spaced lines were laid out resulting an approximately 350 sqm of total coverage.

The Xradar systems used were carefully calibrated onsite to ensure accurate depth measurements. Data was processed and compiled to produce contoured heatmap style results. Results were presented in a CAD workspace and digital reports delivered.

The Xradar survey was complimented with Vuit 3D laser scanning to achieve accurate, scaled georeferencing of our survey grids, and a convenient way to view and present the asphalt thickness results.

The survey revealed a distinct change in the asphalt thickness due to the structural change to the subsurface that was confirmed with the survey results from the mid-range frequency GPR. The data uncovered not only the asphalt thickness but also the nature and location of the subsurface features such as: beams, voids and structural slab changes.

3D Laser Scan, with Xradar results overlaid
Asphalt Thickness Map