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Strengthening the core

With much of the UK’s drinking water impounded by Victorian-era dams, maintenance is an important task. GE reports on construction of a grout curtain at Upper Rivington Reservoir in the Pennines.

Grouting

Grouting work was carried out from the road that runs on the crest of the dam

Covering an area of 10.5ha and impounding over 800M litres of water, the Upper Rivington Reservoir in the western hills of the Pennine moors is a key asset for water company United Utilities. The reservoir provides fresh water to a large number of households in the Lancashire and Liverpool region. Its ability to continue this important task has just been ensured thanks to some recent work on its dam.

Bam Ritchies is on the verge of finishing construction of a new grout curtain at the site to ensure the water-tightness of the two, clay core, earth embankment dams that separate the reservoir from its lower counterpart.

“Despite some initial high grout takes during the TAM installation, we are pleased with the way works progressed”

Rachel Long, Bam Ritchies

Built between 1852 and 1857 to a design by Thomas Hawksley, the Upper Rivington reservoir is impounded by two dams - the 267m Horrobin Embankment thatseparates it from the lower reservoir and carries a road into the village from the west; and the 332m long, 12.2m high Yarrow Embankment.

Ritchies’ initial works consisted of drilling 250 boreholes on the upstream and downstream sides of the clay core of the reservoir dam.

The aim of the works was to create a grout curtain at the base of the clay core to prevent groundwater eroding the clay at rock head. With the road closed to traffic during the work, Ritchies had to ensure the work could be completed as quickly as possible.

Tubes-à-manchette (TAMs) were used to allow multiple injections at discreet zones at depth. A Jean Lutz grouting system was used to accurately track the volume and pressure of grout being injected into the TAMs.

The 133mm diameter holes were drilled from the centre of the centres in order to treat both sides of the clay core dam. The holes were drilled using two Deltabase 100 rigs to depths varying between 7m and 24m below the road level.

“Despite some initial high grout takes during the TAM installation we are pleased with the way works progressed,” says Bam Ritchies site agent Rachel Long. The initial phase of works used a total of 191t of grout.

DSC00323

The original scope of work called for the drilling of rotary cores to prove the presence and depth to the mudstone bedrock.

According to Long, six cores were drilled to try and prove the boundary between the mudstone bedrock and sandstone, which was to be used to define the limit ofthe grouting work. But Long says that the cores failed to find the geological boundary that the client had expected.

United Utilities decided to extend the TAM grouting and instructed Ritchies to extend the work to the end of the embankment, so that the entire dam was grouted.

This second phase led to the need for a further 224 holes to be drilled using the same method as the original works. Ritchies was due to complete this final part of the scheme as GE went to press but work on site has gone well and the road is expected to be reopened shortly.

However, the grouting is not the end of the work for the Upper Rivington Reservoir - during the drilling operation for the initial phase of work, a void was identified which is likely to require further treatment to ensure the dam is in shape for another 150 years of service.

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