Keeping Material Moving on the Connaught Crossing
Tunnelling contractor Gallagher’s contacted Euroflo to supply a dredging pump system for a major rail-tunnelling project in east London – The Connaught Crossing.
The Cofferdams were positioned at the Royal Albert and Royal Victoria docks, some 50metres apart. This left water between the two Cofferdams, which was then pumped out to leave a residue of heavy silt and slurry, situated 15 metres below.
The civil engineering work involved in the project comprised of accessing the tunnels through the base of the excavation, which allowed for the already existing tunnels to be enlarged. Initially, they used standard diesel driven Hydraulic Drainer Pumps when attempting to pump heavy silt and slurry from the bottom of the excavation. However, these pumps were completely unsuitable for this dredging pump application as they were constantly blocking, causing lengthy delays.
Euroflo proposed a temporary dredging pump system that could cope with the heavy slurry, and supplied the entire packaged solution including generators, control equipment, cabling, pumps and pipework. The aim was to move the heavy slurry with a specific gravity of around 1.3. It was proposed that a Euroflo Dredging Pump be installed along with a jetting ring attachment, which would help to create a consistent 70/30 percent ratio of water to soil mix for pumping.
The technical challenge presented was fairly straightforward. The key to success in managing high specific gravity applications is to keep the material moving. Critical to this, is selecting the right pump. This is to ensure that the correct velocities are maintained so that material blockage in the pipework is avoided. Using our expert knowledge, derived from many years of experience in the field, Euroflo recommend a Heavy-Duty Hard Iron Pump for the dredging pump application – which is capable of withstanding often abrasive and sometimes corrosive environments.
Euroflo were also commissioned to automate the operation of the Dragflow Heavy-Duty Slurry Pump System so that it could run unmanned. Therefore, we proposed that once the slurry removal process was complete, an 8” Grindex Maxi Drainage Pump be installed to manage the water levels for the remainder of the project.
Also, because of the variable densities of slurry and compacted materials that the project presented, Euroflo recommended jetting the material at high pressure in order to help break it down.
PLAN OF ACTION
Firstly, the Euroflo Dredging Pump was positioned at the deepest part of the excavation so that the material would gravitate towards the dredging pump. In order to help break up the heavy material and move it towards the main dredging pump, water was high pressure jetted using a Grindex Master H Pump. This was suspended in the main dock and it delivered water at 3 bar pressure over the 15 metre Cofferdam to a tee piece, with one spur used on the jetting ring to create agitation, and the other spur used to provide cooling water to the dredging pump.
The slurry removal process was aided by smaller excavators, along with the use of lightweight dredging pumps that could be more easily moved around. This was to aid in the transferring of slurry from the dock floor to the heavy duty dredging pump. The material collected was then discharged over the Cofferdam 100metres away by the Dredging Pump.
A submersible pump is normally cooled by the media it’s submerged in, but in this case, it was only possible to semi-submerge the dredging pump. The pump therefore needed to be kept cool in order to avoid the motor overheating or the possibility of breakdown, and so the Grindex Master pump facilitated this by producing a cooling water spray.
A Euroflo Hard Iron Dredging Pump with a 44 Kilowatt motor was then installed with an 8-inch discharge and pumped 100 metres through a wire armoured hose.
A total of approximately 6000 Qm3 of slurry was moved over 10 weeks with intermittent breaks and 12000-18000 Qm3 of water was used to mix with slurry. Towards the end of the project, a 37 Kilowatt Grindex Maxi Pump was installed and level controls were introduced to manage intermittent residual slurries and Cofferdam leakage.