A new surface water sewer is to be installed crossing the railway at Woodside Park London Underground Station.
An auger bore is to be 7m below the depth of the railway tracks, driven from a temporary shaft at the base of the embankment to the west side of the London Underground Limited (LUL) tracks.
The reception pit will be situated in the car park to the east of the LUL tracks.
The project requires an appropriate scheme to monitor embankment, building, cable rack and ground movement.

Solution

Survey Control was established to set out the launch and reception pits and provide direction for the auger drive.
The monitoring control was geometrically linked to the main survey control in line and level.
The extent of the monitoring was 14m to the west and east of the centre of the proposed bore. A further row of prisms was installed 20m to the west and 20m to the east.
Prisms were attached to the cable rack at the top of the embankment, with the permission of LUL, and to pegs at the top, middle and bottom of the embankment.
Prisms were attached in the webbing of the eastbound and westbound running rails at 2m intervals.
A grid of nails were installed in the car park to the east of the tracks.
The prisms were monitored from a fixed station location outside the zone of influence.
The orientation of the measuring instrument was controlled by a free station (least squared adjustment) from a minimum of 4 No. prisms located on accessible stable structures out of the zone of influence.