Footbridge, Guildford

Technics conducted a series of ground investigations and survey works in Park Barn, Guildford, to support a civil engineering project involving the removal and replacement of a footbridge and the surrounding infrastructure. This multi-phased project utilised a range of techniques to gather detailed geotechnical and structural data, which is essential for informed decision-making and the safe execution of the project.

This case study highlights the investigative and structural works conducted on a footbridge and an adjacent vehicle bridge, both crossing the railway. Our client for these works was Ringway Infrastructure Services Ltd. The project encompassed geotechnical investigations, structural assessments, topographical surveys, and ground movement monitoring to ensure the integrity and safety of both structures.

Footbridge Works

The removal and replacement of the footbridge necessitated extensive preparatory work. A 10-metre window sampling borehole was drilled to evaluate subsurface conditions and assist with the temporary works required for crane installation to remove the old footbridge. To monitor structural movement, extensometers were installed, and fixed-point movement surveys were conducted to track any displacement over time. Additionally, topographical surveys of the embankment and track were conducted, with track surveys undertaken under possession to ensure precise planning.

To support the deep foundation design of the new footbridge, a geotechnical investigation was performed, consisting of two rotary coring boreholes drilled to a depth of 20 metres. These boreholes aided in determining ground conditions and groundwater levels, ensuring stability for the future structure. A slope stability assessment was also carried out to mitigate the risk of collapse during construction. This involved two windowless sampling boreholes drilled to a depth of 5 metres to analyse soil properties. Due to access constraints, these works were executed using a modular window sampling rig, operating under a separate safe system of work.

Vehicle Bridge Works

A comprehensive structural assessment was conducted to evaluate the condition and integrity of the vehicle bridge deck. This involved four Ground Penetrating Radar (GPR) surveys to identify subsurface anomalies, assess the deck conditions, and ascertain the depth and diameter of the rebar as requested by the client. A concrete breakout was performed to verify the characteristics of the rebar and the structural composition. Moreover, fifteen Schmidt Hammer Tests were carried out across the bridge spans to evaluate concrete strength. These works were completed during track possession to ensure safety and minimise disruption.

To support forthcoming civil engineering works on the upper deck of the vehicle bridge, a detailed topographical survey was undertaken. This provided precise mapping of the structure and its surrounding area, ensuring informed engineering decisions.

The investigative work provided valuable insights into the condition of both structures. The geotechnical investigation for the footbridge revealed stable ground conditions, although access constraints necessitated the use of a modular window sampling rig. The structural assessment of the vehicle bridge identified critical data on rebar depth and diameter, ensuring well-informed engineering decisions. One of the main challenges was conducting work under track possession, which required meticulous planning to minimise disruption while upholding safety standards.

The investigative and assessment work on both the footbridge and vehicle bridge provided crucial data to inform future construction and maintenance efforts. These investigations ensured compliance with engineering and safety standards, contributing to the long-term stability and functionality of the transport infrastructure.

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