Following months of heavy rainfall the access road into Piethorne Reservoir slipped significantly. As a critical asset of United Utilities they had a requirement for a topographical survey of the site to be carried out and control established to monitor the ground for further movement.
Initially a topographical survey of the road and surrounds was carried out to accurately establish the current lay of the land and identify key features in the area affected by the slip.
Once complete a combination of permanent control monuments were installed including Feno (see below image) and Bernt’sen markers.
This control was established on stable ground outside the affected area that were used as reference points.A resection will be performed at the start and end of each setup, sighting to the Bernt’sen markers, to validate the position of the Feno marker, detect instrument setup errors and identify any instrument movement during setup.
Within the land affected by the slippage a combination of survey nails and more permanent pre-drilled monuments were established.
Once all the monuments were established 2 rounds of observations were performed to establish principal coordinates for each monument. Monitoring observa- tions consisted of an average 5 measurements to guarantee accuracy. Upon completion of the fieldwork a Measure Deformation Report was issued documenting the layout of the monitoring scheme, the monitoring identification numbers and listing the principal coordinates.
Repeat observations were initially carried out every week gradually reducing to once per month as the land stabilised. An updated report was issued following each observation with the latest 3D Coordinates.
After over a year of monitoring the decision was made to construct a new access road through to the reservoir.The consistency and accuracy of the monitoring results was critical in United Utilities being able to manage heavy traffic using the road and in helping them make this final decision.