06/11/2015
Steven Gledhill
Yeoman Hey
Case Study
Copyright © United Utilities Water Limited 2015
Copyright © United Utilities Water Limited 2015
Description of Reservoir
Constructed in 1880
Earth embankment with central puddle clay core and concrete cut-off trench.
20m high, 250m long, 934Ml Capacity.
Copyright © United Utilities Water Limited 2015
06/11/2015
Details of Conduit
120m long, brick lined discharge culvert.
Founded on natural ground.
Surrounded by concrete at intersect with cut-off trench.
Contains two 61cm CI mains.
Copyright © United Utilities Water Limited 2015
Background to the
Problem
•
Considerable leakage into the culvert began shortly after completion.
•
Main leakage through soffit and walls with small spouts observed in
the invert.
•
Large deposits of ochre deposited on invert.
•
Drawings exist dated 1885 indicating the pattern of cracking at the
point where the culvert crosses the cut-off.
•
Pattern and rate of leakage remained unchanged for 130 years.
•
Continual pumping required at downstream portal to prevent
inundation.
Copyright © United Utilities Water Limited 2015
06/11/2015
Copyright © United Utilities Water Limited 2015
Copyright © United Utilities Water Limited 2015
06/11/2015
Investigations and
Potential Failure Mode
Investigations into the cause of the leakage included:
• Visual survey of the upstream face using an ROV
• Sonar scan
• Temperature probe survey.
• Installation of piezometers.
• Detailed structural condition assessment and survey of culvert.
• Willowstick survey.
Flow shown to be passing vertically into culvert from upstream shoulder via
cracks upstream of core.
Sampling and analysis of leakage water indicated the presence of clay particles.
Inspecting Engineer recommendation to prevent leakage into culvert as loss of
material could lead to collapse of culvert, breaching the clay core.
Copyright © United Utilities Water Limited 2015
Copyright © United Utilities Water Limited 2015
06/11/2015
50mm
Copyright © United Utilities Water Limited 2015
Remedial Works
Remedial works were carried out in 2008 and consisted of injecting a hydrophilic
epoxy grout into the leakage flow.
Grouting was carried out without lowering the reservoir level.
The voids behind the brickwork were filled and leakage stopped almost entirely.
Project cost was approximately £500,000
Leakage into culvert measured at the downstream portal has reduced from 120
l/min to below 20 l/min (which includes some ingress from downstream
shoulder).
Leakage is still continually monitored by SupE and site staff.
The method proved successful and has been used on other leaks
Copyright © United Utilities Water Limited 2015
06/11/2015
Copyright © United Utilities Water Limited 2015
Lessons Learnt
Settlement of a brick culvert across a rock outcrop or concrete cut-off
trench could lead to cracking.
It is possible for high leakage flows to continue for considerable time
periods, depositing ocherous material into the culvert without causing
the culvert to fail.
Modern grouts can effectively be used to seal high levels of leakage in
a brick, masonry or concrete culvert without having to lower the
reservoir water level.
Copyright © United Utilities Water Limited 2015
06/11/2015
Thank You
Do you need to print this?
Really? Think of the trees!
Copyright © United Utilities Water Limited 2015
Copyright © United Utilities Water Limited 2015