Exjet were approached by Aecom Consultant engineers in order to carry out an Internal survey of two in No. culverted water courses as part of the Siston and Warmley Flood Defence scheme. The surveys were to be carried out by a combination of utilising CCTV drainage survey equipment and man entry works in order to assess current silt levels with a view to assessing the necessity to cleanse the structures, and the current structural condition of the tunnel.

All customer liaison, highways notices, and site notification to the environment agency and other interested parties was undertaken in house by Exjet.

Tunnel one at Norton Midsomer Norton is constructed of 2100mm bolted PCO sections over a distance of 1100M with one intermediary access point.  Exjet were tasked with collating a safe system of work that allowed a perspective view of the entire tunnel.

In order to achieve the required output, a mixture of man entry and utilisation of CCTV drainage survey equipment with 500M capability and lighting for a 2100mm culvert was required.

Relying on extensive previous experience in this field of operations, Exjet assessed and planned the works in order to negate as much of the man entry works as possible. By utilising steerable CCTV drainage survey systems with wheel arrangements specifically for tracking through heavy silt, it was possible to survey in excess of 450M from both the inlet and outfall leaving approximately 200M that would need to be assessed by means CCTV assisted by man entry to the tunnel due to the configuration of the intermediary manhole and excessive silt levels within the un-surveyed sections.

The intermediary manhole is connected to the main line via a major branch situated approximately 20M from the culvert. In order to complete the survey Exjet mobilised a 5 man confined space entry team alongside a 2 man rescue team to allow the CCTV drainage survey system to be guided through the heavy siltation ensuring that the survey could be completed in full.

Tunnel two situated at Siston is constructed of a 34000mmx2400mm Armco Steel arched culvert over a distance of approximately 200M. Again, the basis of the works was to carry out a structural and conditional survey utilising CCTV equipment, and if the survey could not be completed by theses means, to effect man entry to complete the works.

Both elements of the survey were carried out and completed over a 4 day period with the subsequent collated information passed through to Aecoms engineers for use within hydraulic models for flood risk assessment.


Original award value of Project and final outturn cost. Please provide reason(s) for variances (if any)

£12400 (no variance)

Planned and actual duration Please provide reason(s) for variances (if any)

Planned over a 5 day period to allow for weather variations. Completed in 4 days.

Extent of work carried out by in-house resources.

All works carried out in house.

Value that you added to the project (e.g. innovation, cost and time efficiencies)

A concise and realistic system of work was submitted to the client that considered all risks and differing scenarios which would ensure that the works would be completed as fully as possible. Comprehensive risk and site specific method statements were also compiled and submitted to the client.Completed information was provided in both hard copy and via Exjet’s online viewing platform allowing multiple users access to the information at the click of a button.

Form of contract

NEC3 Option A