Overhead line (OHL) foundation condition is difficult to assess without costly and disruptive excavation. Based on existing knowledge or previous data, non-intrusive techniques can be used and have been available for many years but are inadequately researched/developed for use in OHL foundations to base refurbishment and replacement decisions upon. The proposed solution will carry out the development, testing, and trial of a new method with an aim to achieve a reliable non-intrusive foundation assessment.
Benefits
This project has the potential to provide benefits for all Transmission network overhead line foundations and is likely to also be entirely relevant to distribution networks. The benefits are expected to be:
• Reduction of foundation intrusive exploration expenditure.
• Reduction of foundation upgrade works, with cost and time savings, and safety improvements through reducing construction works. This reduction will be justified through a better, more evidence-based understanding of residual risks, allowing policy adjustments to be made.
• Better ability to predict higher-risk foundations reducing the chance of future foundation-related incidents.
• Improve health and safety by removing damage to OHL/towers during foundation upgrades, hence, reducing the probability of risk events.
• Environmental impact – Reduction in materials and concrete required during foundation upgrades and reduction in access works.
An existing 132kV OHL with 193 towers of which 72 initial proposed foundation upgrades was examined to assess potential benefits for a single case.
Cost Benefit Analysis
The CBA Model is based on some assumptions below:
• The CBA model incorporates the project cost as part of the development cost.
• Due to the uncertainty and low level of TRL, an assumption that this project has a 40% probability of success has been made to estimate the low-level benefits.
• The capitalisation rate is 90% which is based on the current versus non-current cost.
• The number of foundation upgrades required will reduce by 40% when intrusive and non-intrusive testing method are employed.
• In the current approach, the percentage of foundations tested intrusively is 5% to 10% per line, and this rate is factored into the base case for this analysis.
• 50% of total foundations are tested non-intrusively, and 2% of total foundations are tested intrusively to validate non-intrusive findings. This approach is considered as a preferable option.
Summary of Benefits
Preferable option: Combining both non-intrusive and intrusive foundation testing.
• For a single case, the estimated saving is £1.4m discounted in 2018 real price. The benefit of this project will realise in 2029.
• For scaled benefits, it is estimated £2.3m discounted in 2018 real price. For £1 spending in this project, it can return £1 in cost saving by T3 or £5.9 through the lifetime of all eligible projects. (Annualised ROI: 15.2%).
• Due to uncertainty of this technology, the probability of success for this project is assumed to be 40%, which leads to the low benefits estimated at £915k in 2018 real price for the scaled benefits.
• In addition to a potential saving in CAPEX, there are also social impacts and other savings due to risk reduction. The total risk benefit saving is estimated at £132k.
Breakeven point analysis:
• For a single case, this innovation will need to achieve at least an 8% reduction in the number of foundation upgrades or 6 towers to break even and be considered a feasible investment.
• If not accounting for the development cost, this innovation project will reach break-even point if it can reduce 1 foundation upgrade compared to the initial number of foundation upgrade proposed in a single case.
Learnings
Outcomes
7.1 Principal Technical Outcomes
The principal outcomes of the project are summarised below.
Echo Testing Methodology: A validated, enhanced echo testing methodology has been developed that combines standardised field measurement procedures with physics-based signal interpretation. The methodology incorporates ultrasonic concrete velocity measurement to determine site-specific wave speed, a defined test protocol for sensor and hammer positioning, and a multi-technique analytical framework implemented in the echo simulator software. When applied to the project’s full-scale test foundations, this methodology reduced depth estimation error from the industry-typical range of 10–15% to approximately 2–4%.
Echo Simulator Software: The echo simulator software provides four complementary analytical techniques for echo waveform interpretation: ray tracing, time-amplitude analysis (displacement, velocity, and acceleration), Fast Fourier Transform (FFT) analysis, and cepstrum analysis. The platform compares measured and modelled waveforms to assist the analyst in identifying the correct toe reflection and determining foundation depth.
Prototype Hardware: A portable, field-capable data acquisition system has been developed based on a high-speed accelerometer and data acquisition card. This hardware enables the capture of echo waveforms at the data quality required for the enhanced analysis methodology. The system has been used for comparative testing alongside proprietary third-party equipment at the Blackhillock site.
7.2 Comparative Testing Results
Comparative testing was carried out at the Blackhillock Substation test site on the D-type (L8-D) foundation, which has a known toe depth of 3.07 m. Twelve hardware configurations were tested, covering two sensor positions, three sensor types (PET accelerometer, PICOPAD, and PICOPIN), and two hammer types (metal and plastic). The PICOPAD and PICOPIN are Xytecs’ custom-developed data acquisition systems using a 20 mm padded contact sensor and a 1 mm needle-type sensor respectively. Of the twelve configurations, eleven produced a valid depth estimate. Ten of these were within 10 cm of the actual toe depth, with a mean absolute error of 8 cm across all valid configurations. The best single result, using the PICOPAD sensor with a plastic-tipped hammer at Position 2, achieved a pick of 3.06 m, an error of 1 cm against the known depth. The use of multi-method analysis within the echo simulator (combining the time-domain pick with independent cepstrum confirmation) was found to be essential: in two configurations the cepstrum corrected a time-domain error of 20 cm or more. Analysis of the D30-type (PL16-D30) foundation comparative testing results is ongoing and will be completed as a post-project activity. During the D30 analysis, additional work was identified relating to impact pulse size modelling and FFT interpretation for this foundation type; this work will be resolved before the D30 results are finalised. The full comparative results table covering both foundation types will be submitted to SSEN as part of the post-project learning supplement.
7.3 Technology Readiness Level
At the commencement of this project, the echo testing technique as applied to OHL foundations was operating at approximately Technology Readiness Level (TRL) 3–4, analytical and experimental proof of concept. The outcomes of this project, in particular the development of the echo simulator software and prototype hardware and their validation against full-scale test foundations, are assessed to have advanced the technique to TRL 6, representing technology demonstrated in a relevant environment. The completion of network field trials will provide the evidence base required to advance to TRL 7 (system prototype demonstrated in an operational environment).
Lessons Learnt
The following lessons have been identified from the project for the benefit of future innovation programmes:
- Value of Physics-Based Modelling: The development of a physics-based echo simulator, rather than relying solely on empirical data interpretation, proved to be the single most significant technical decision of the project. The ability to predict expected waveform characteristics for a given foundation geometry and directly compare these with measured signals substantially improved the reliability of depth estimation and provided a principled basis for interpreting complex multi-reflection waveforms. Future projects in this field are strongly encouraged to invest in analogous modelling approaches.
- Standardisation of Test Procedure is Critical: Echo test results were shown to be highly sensitive to sensor and impact positioning. The absence of a standardised procedure in conventional practice is a significant contributor to the variability observed in industry results. A clear, formalised test methodology, including defined sensor and hammer positions relative to the foundation centreline, is essential for achieving repeatable results and should be established at the outset of any future programme.
- Equipment Selection and Support: The LPR equipment used during Stage 3 proved to be obsolete and without manufacturer support. Lessons from this experience highlight the importance of verifying equipment status, availability of calibration services, and manufacturer support before committing to a test technique for a multi-year project. Where possible, non-proprietary or open-platform hardware should be preferred to avoid dependency on a single supplier.
- Controlled Test Foundations as a Lasting Asset: The two full-scale test foundations installed at the Blackhillock Substation training site represent a valuable long-term resource for SSEN. These foundations provide a known-geometry reference asset for continued validation, method development, and training purposes beyond the life of this project.
- Iterative Development Approach: The project benefited from an iterative approach in which findings from each stage directly informed the design and scope of subsequent activities. This was particularly evident in the progression from laboratory-scale modelling to full-scale testing to prototype development. Innovation projects of this nature are well-suited to this adaptive approach, provided that scope changes are documented and agreed within the project team.
