Clear Route Limited was engaged to carry out a full tunnel survey of two existing Electricity cable tun­nels to enable the development of various key environmental and planning statements for future develop­ments.

The tunnels are maintained by UK Power Networks Limited (UKPN) and as such, all entry was undertaken with respect to the UKPN Distribution Safety Rules for access and safe working in confined spaces.

Method

The scope of the tunnel survey included:

• Condition Surveys to assess the structures themselves
• 3D scanning of all shaft entries
• Topographic Surveys, linked to the above ground surface, of the line and level of the cable tunnels

Survey Control was placed around the entry shafts, and a control point at the base of each shaft was transferred down through the use of Laser Scanner and Laser Plummet.

Using the known position of the control at the bottom of each shaft, extra survey stations were then positioned along the length of the tunnel, and were traversed between, allowing accurate known 3D co-ordinates to be produced for all points within the tunnels. These identified the complete extent of the tunnels both in vertical and horizontal positions.