Precision Utility Mapping was commissioned to carry out a topographical survey at M5 Junction 21, focusing on St Georges Bridge. The survey was conducted at a 1:500 scale and was performed using a combination of static and mobile laser scanning techniques. The objective was to collect comprehensive spatial data to support infrastructure planning and maintenance.

Scope of Work

The scope of services included, but was not limited to:

• Conducting a detailed topographical survey in accordance with the Design Manual for Roads and Bridges (DMRB) GG 951 and GS 952.
• Establishing, locating, and surveying a framework of Permanent Ground Markers (PGMs) to ensure consistent geospatial referencing.
• Documenting underground apparatus within the survey extents, including survey type, depth, and position.
• Presenting results in AutoCAD 2018 and PDF formats.

 

 

Survey Methodology

The survey was executed through a multi-method approach to ensure accuracy and efficiency:

1. Control Establishment

• Permanent Ground Markers (PGMs) were installed using York Survey 600mm Pema-Mark ground markers.
• Traverse and levelling were conducted using a Trimble S9 HP 1” total station and a Leica LS15 digital level.
• Control points were observed multiple times from different setups using a Leica mini prism for increased precision.

 

 

2. Data Acquisition

• Laser Scanning: The bridge was scanned using a Trimble X12 laser scanner, and data was registered using cloud-to-cloud techniques.
• Mobile Mapping: A Trimble MX9 mobile laser scanner was deployed to capture extensive roadway data at high speed without the need for road closures.
• Traditional Surveying: Areas with limited visibility were surveyed using total stations and GNSS equipment.

 

 

3. Data Processing & Quality Control

• Data was tied to the OS National Grid using a local scale factor of 1.
• Control values were assessed, demonstrating millimeter-level accuracy.
• Ground control points were adjusted to match OSTN15 coordinate systems with OSGB15 geoid.
• Point clouds were georeferenced and delivered in AutoCAD DWG format.

 

 

Challenges & Solutions

• Vegetation Obstructions: Embankment surveys required vegetation clearance, which was initially incomplete. This was mitigated through daily communication with the contractor to address clearing gaps.
• Access Constraints: Survey teams navigated restrictions by conducting scans from multiple vantage points and supplementing data with targeted ground surveys.
• Weather Conditions: Laser scanning was scheduled around optimal weather conditions to minimize data inconsistencies.

 

 

Project Deliverables

• 2D/3D topographical drawings in DWG format.
• Registered laser point clouds in LAS 1.2 format.
• PGM diagrams with detailed coordinate information.
• Survey report including control values and methodology.

 

 

Client Impact & Outcome

The survey successfully provided a comprehensive topographical dataset that met the project specifications. The high-resolution data facilitated precise planning and infrastructure assessment for BAM Ritchies. The use of advanced laser scanning technology, combined with traditional survey methods, ensured a high level of detail and accuracy.

This project demonstrated the effectiveness of integrating cutting-edge geospatial technology with best practices in topographical surveying, setting a standard for future infrastructure surveys.

BAM Ritchies

Noel Greally

Noel.Greally@bam.com

Start Date: 16^th October 2023

End Date: 22^nd November 2023

Contract Value: £130,000