Keystone Black developed a bespoke remote survey methodology to overcome these constraints and deliver reliable, repeatable data.

Figure 2 Survey methodology: the remote Phase 1 approach and the controlled Phase 2 upgrade.

3.1 Remote Access Innovation

A custom-designed floating pontoon system enabled safe deployment of survey equipment from the culvert outfall, allowing access without man entry.

3.2 SLAM Scanning Technology

We deployed SLAM (Simultaneous Localisation and Mapping) scanning, enabling:

• Rapid capture of high-density 3D point cloud data
• Accurate mapping of internal geometry over extended distances
• Operation in GPS-denied and hazardous environments

SLAM technology allows fast and comprehensive data capture, with modern systems capable of achieving millimetre-level accuracy when integrated with survey control.

3.3 Integrated Video Inspection

The system also incorporated high-definition video capture, providing:

• Visual condition assessment
• Correlation with geometric data
• Enhanced assurance for both contractor and asset owner

3.4 Data Processing & Analysis (Phase 1 – Remote Survey)

Due to the uncoordinated nature of the 2020 baseline survey, Keystone Black implemented a geometry-based comparison methodology, focusing on internal shape rather than absolute positioning.

This included:

• Sectional analysis at regular intervals
• Direct comparison between survey epochs
• Identification of key deformation characteristics:
  • Crown settlement
  • Springline movement
  • Ovalisation

This ensured results were:

• Technically robust
• Independent of survey control limitations
• Suitable for engineering and asset management decisions

4.  Enhanced Survey Control (Phase 2 – Controlled Monitoring Upgrade)

As site conditions evolved, Keystone Black was able to safely access the culvert internally, enabling a significant enhancement to the monitoring strategy.

4.1 Introduction of Survey Control Network

A fixed control network was established within the culvert, creating a framework of precisely known reference points used to anchor all subsequent survey data.

This development provided several key advantages:

• Alignment of all datasets to a common coordinate framework
• Significant reduction in positional uncertainty and drift
• Ability to directly compare survey epochs with high confidence.

 

Survey control networks are fundamental to achieving high-precision results, providing definitive reference points that ensure consistency, accuracy, and alignment across all survey data.

 

Figure 3 [Caption to confirm: left, instrument set up inside the culvert on the control network; right, equipment at the culvert outfall]

4.2 Improved Data Integrity

By tying SLAM data to fixed control:

• Point cloud accuracy was significantly improved.
• Deformation could be quantified with greater precision.
• Data became fully repeatable and defensible.

 

Establishing control also enables accurate merging and comparison of multiple datasets, reducing errors and supporting reliable decision-making across project phases.

5.  Key Findings

The analysis identified:

• A localised deformation zone within the culvert
• Peak deformation characterised by:
  • Approximately 50 mm vertical compression at the crown (soffit)
  • Corresponding lateral expansion at the Springline

The deformation pattern is consistent with:

• Historic settlement behaviour
• A localised structural response, rather than systemic failure

The culvert was assessed as:

• Structurally serviceable
• Exhibiting moderate Ovalisation (~5%)
• Suitable for continued monitoring rather than immediate intervention

Figure 4 Deformation at the peak zone: crown compression with corresponding Springline expansion (schematic).

6.  Outcome & Client Value

Keystone Black’s approach delivered clear value to both the contractor and Network Rail:

6.1 Programme Confidence

• Enabled works to proceed without delay.
• Provided confidence that the asset was being actively monitored.

6.2 Risk Reduction

• Early identification of deformation zones
• Improved understanding of structural behaviour

6.3 Asset Assurance (Network Rail)

• Delivered reliable, defensible condition data.
• Supported evidence-based asset management decisions.

6.4 Innovation in Delivery

• Overcame severe access and safety constraints.
• Progressed from remote-only survey to fully controlled monitoring environment.

Why Keystone Black?

This project demonstrates our ability to:

• Deliver innovative survey solutions in constrained and hazardous environments.
• Combine advanced technology with practical engineering insight.
• Continuously evolve methodology to improve accuracy, reliability, and client confidence
• Provide clear, defensible outputs for critical infrastructure assets such as those owned by Network Rail

8.  Services Delivered

• SLAM-based 3D culvert surveys.
• Remote access inspection solutions
• High-definition video inspection
• Establishment of internal survey control networks
• Deformation and condition analysis
• Dilapidation reporting and monitoring strategy

9.  Looking Ahead

The enhanced monitoring regime—now supported by fixed internal survey control—provides a robust, repeatable framework for future surveys, enabling both John Sisk & Son and Network Rail to track any ongoing movement with a high degree of confidence.