Liffey Siphons Rehabilitation Project, Dublin

The Liffey Siphons are twin DN900 foul sewers approximately 3.4km in length. The siphons commence at an inlet chamber in Phoenix Park and travel south, beneath the River Liffey and the Cammock River, and discharge into a Dublin City Council (DCC) gravity sewer network from a siphon outlet chamber. The outlet chamber is located on the northern bank of the Grand Canal at Devoy Road, Inchicore. The siphons were constructed in the mid-1980s as part of the 9C sewer system connecting the Blanchardstown area to the Grand Canal Sewer System and onward to Ringsend WwTP for treatment.

Many of the chambers on the siphon are deep, varying in depth from 3m to 23m. There are two sections, 70 metres and 200 metres long, where the siphon is laid within a 3.66m diameter tunnel. It is known that these tunnels are flooded with groundwater.

The Contract Works included rehabilitating the siphon inlet and outlet chambers, rehabilitating the two tunnels through which the siphons pass, rehabilitating the tunnel access shafts, and upgrade works to the hatch boxes, flow meter and inlet and outlet chambers on the siphon line. A CCTV survey of the cleaned siphons to confirm their condition was also carried out.

It was also a requirement of the contract that one of the Siphons remained operational during the rehabilitation Works.

We were appointed by Terra Pfeifer as the Contractors designer. Our role comprised the civil and structural design of the gate valves, inlet works, outlet chamber, pipe diversion layouts and associated Phoenix Park Traffic Management.