Learnings

Outcomes

There were several outcomes/outputs from the project which included the following;

1. Reproducibility and Repeatability
2. Development and validation of RSV
3. Embedment depth
4. Defect location
5. User feedback and device improvement
6. Limitations of the device
7. Automatic upload and download capability to DNO systems/THOR portal.

Reproducibility and Repeatability

During the testing undertaken, reproducibility and repeatability of the THOR device were considered. To determine the repeatability of the results, 3 tests were carried out on the same pole by the same user and device on a total of 4507 poles. The equivalent diameter and foundation strength outputs from the device for the 3 tests of each pole were compared.
The repeatability of the device found during the project was 90.87% with a 95% confidence level.

The reproducibility of results obtained from the device, were assessed on 35 poles, using 7 different THOR devices and 6 different users. It should be noted that the number of poles/tests used to analyse the reproducibility of the device was significantly limited when compared to number of poles/tests used for the repeatability.
The reproducibility of results of the device found during the project was 85.4% with a 95% confidence level.

Development and Validation of RSV calculation

During the project, Groundline Engineering developed a proprietary residual strength value evaluation for wood poles. This calculation incorporates a range of factors including;

• Timber Pole Age
• Timber immaturity factor based on diameter
• THOR field diameter evaluation
• Characteristic fibre strength

The THOR field diameter evaluation gives a percentage equivalent diameter compared to the measured diameter at the base of the pole. The equivalent diameter is a function of the density of the timber pole, stress wave propagation velocity and cross-sectional area at ground level. More information on this can be requested from Groundline Engineering.

The RSV evaluation results from the THOR device were validated against actual breakage loads at a test site in Scotland. The breakage tests were completed by an independent third party. Poles that had be THOR tested were identified and subsequently removed from service.

A total of 82 poles were THOR tested with RSV results recorded and compared with the actual RSV results derived from the actual failure load force.

For the automated analysis, 90% of the poles had a predicted embedment depth within 3.5% of the measured value. This embedment depth measurement has now been included as an output from the THOR device.

Defect Location

An algorithm to automatically determine defect location has been developed and trialled on the field data collected. The work to validate the defect location during the destructive testing was limited during the project due to limited poles with above ground defects. There were two poles successfully identified as having above ground defects. However, there was also 1 pole which THOR predicted had an above ground defect, that failed at ground level.
At this stage, it is not possible to accurately predict location and severity of the defects.

User Feedback and Device Improvement

Throughout the project, the DNO users of the THOR device provided feedback from the testing regime. This included:

1. Difficulty in transporting device due to 3 separate parts connected via cables.
2. Keeping geophone receiver level and flush against the pole during testing, while striking with THOR hammer.
3. Inputting of pole information (pole height, timber species, pole diameter etc) into the THOR handheld unit during testing.
4. Viewing and interpretating results on site
5. Manual upload of THOR results onto THOR portal.

Several improvements were made to the device by Groundline Engineering as a result of this feedback resulting in a newer version of the device. This upgraded device also incorporates the RSV and Embedment depth calculations developed and validated during the project. The upgraded device addressed the above issues in the following ways:

1. Replacement of handheld unit and more robust cable connections resulting in an easier to use device.
2. Addition of audio warning if geophone is not level and flush, aiding user in ensuring geophone is located correctly without need for visual confirmation.
3. All pole information now input into device using separate tablet. Once pole information is recorded against pole ID, device will remember information based on GPS co-ordinates and Pole ID for future tests.
4. User interface on tablet is now easier to interpret with traffic light system shown against pole health, embedment depth and foundation strength.
5. Upload of THOR results to the THOR portal is now automatic.

Limitations of the Device

Throughout the testing regime during the project there were several limitations of use of the THOR device were identified. For approximately 5% of the total 6085 poles tested during the project, an excessive equivalent pole diameter of greater than 160% was found. Several reasons for these unrealistic results were identified during the project, highlighting potential limitations of the device when testing:

• Frozen Poles – With freezing conditions the equivalent diameter is increased due the effects on fibre strength
• Cobra Wraps – If a cobra wrap is present on the pole then this should be safely removed before THOR testing if possible otherwise the result will be affected.
• Brick Wall or Concrete foundations resting against pole or Tree trunk around pole. This has the same affect on the THOR results as is the case for frozen poles.

The THOR training material has been updated accordingly to factor in these potential issues.

Automatic Upload/Download of results

At the start of the project, the THOR results taken from site were downloaded manually from the THOR device on to a laptop/desktop. The results were subsequently uploaded to the THOR portal.

During the project, upgrades to the device and portal now mean that THOR results can be uploaded directly from site at the time of test straight to the THOR portal. The results can also now be easily interpretated on site with the health of the pole clearly indicated.

Lessons Learnt

1. Remote training and learning due to COVID-19 restrictions proved difficult due to some miscommunication at the start of the project. This was improved throughout the duration of the project as training was provided followed by further sessions to ensure accurate use of the device.
2. Effective destructive testing developed and undertaken. Lessons learnt on data recording methods throughout this time as some poles were not identified and marked correctly leading to loss of data validation not being possible.