The project, for client London Underground, involved installing reinforced concrete slab foundations under the second arch of a four-arch brick-built bridge which carries the Metropolitan Line over the fast-flowing river.
Over the years the River has scoured the foundations which has resulted in the need to strengthen the structure. Dyer & Butler’s task was to isolate the affected area within a sheet-piled coffer dam, divert the river through the third arch and strengthen the bridge foundations with a 20m long reinforced concrete slab.
“The whole area is a flood plain and we were working 1.5m below the water table”says Dyer & Butler project manager Tom Bennison.
“Obviously, the coffer-dam was pretty well-sealed, but the water was gushing in and we needed to pump it out continuously” explains Mr Bennison.
To keep the cofferdam sufficiently dry during the concreting operation, the area had to be de-watered at a rate of 500 litres/sec.
When its original pumping set-up proved unable to cope with the flow, Dyer & Butler turned to Shorflo Specialist Pumps.
Shorflo’s solution was three of its 6” Super-silent diesel pumps and one 8” model. Both models are high output, solids handling pumps capable of handling clean or dirty water, also sewage and silt.
The 6” model will deliver a flow rate of 100 litres/sec at 5m head and is extremely quiet, with noise levels at 53db(A) at 7m. The 8” pump is the largest in the Shorflo range and is capable of pumping at 235 litre/sec at a similar head. Despite its size and capacity, it is almost as quiet at the 6” model at only 60db(A).
Besides their high output and low noise levels, the Shorflo Super Silent pumps offer unrivalled fuel consumption which gives extending running times between refuelling.
The 6” pump’s 180 litre fuel tank allows three days’ continuous running between refills, while the 8” model’s 420 litre tank holds enough fuel for four and a half days’ continuous pumping.
With the Shorflo pumps in place, Dyer & Butler was able to press on and complete the new bridge foundations in just six weeks, with the pumps finishing their work in mid-November.
“The Shorflo guys were always on hand if we needed any help or advice” says Mr Bennison.