This project used fusible PVC (FPVC) pipe – supplied by Underground Solutions (UGSI) – and set a world record for installation of this type of pipe product at a diameter of 24 inches or larger.

The new FPVC water line replaced an existing cast iron line that connects MWC’s northern water distribution system near the city of Perth Amboy to their South River Basin supply system south of the Raritan River near Sayreville, and included crossing the Raritan River as it merged with Raritan Bay.

A large section of the existing water main was located within marshland and wetlands, with portions having less than 2 ft of cover. Due to the age, corrositivity and instability of the surrounding environment, the existing main had experienced several breaks that required costly emergency repairs on an increasingly frequent basis. These outages caused major operational disruptions, with costly repairs due to access impediments associated with the river, soft sediments and regulatory considerations associated with the adjacent wetlands and river navigation.

MWC determined that the existing 24 inch water main had to be replaced to continue providing a reliable source of drinking water to its customers. CDM conducted the planning, design and construction phases of the project. Various construction methods were evaluated by CDM, including pipejacking, open-cut, microtunnelling, conventional tunnelling and horizontal directional drilling (HDD). After an extensive evaluation phase, HDD was selected based on project conditions and cost-effectiveness.

A geotechnical investigation of the site revealed various zones of stiff, silty clay, sand, gravel and extremely soft material, underlain by a bedrock shelf on the north side of the crossing. Due to these conditions, the final drill path selected was at a depth of 65 ft in order to remain above the bedrock layer.

For installation, Mears used two drilling rigs on the river crossing – a 140,000 lb rig and an 880,000 lb rig. The 140,000 lb drill unit performed drilling of the pilot hole with the use of a Drillguide GST (gyro) system for the first portion of the hole. The 880,000 lb rig was used for the reaming and pullback of the pipeline.

A 42 inch steel casing pipe was installed, due to the entry’s proximity to the river edge and shallow depth of cover on the proposed line. Mears installed the casing pipe through rubble and concrete debris at the entry site. Once complete, the casing was cleared and centralisers were installed to initiate pilot hole drilling.

When the pilot hole reached approximately 700 ft, Mears switched from the GST system to its Para-Track II system, combined with a pressure probe. Switching steering tools allowed the team to monitor the annular pressures and avoid exceeding overburden pressures to minimise inadvertent returns of drilling fluid escaping into the river. The final exit location of the pilot hole was within 5 ft of the target hole.

Mears Superintendent Bert Chapman and CDM Senior Project Manager David Tanzi dealt with numerous other challenges on the project. Drilling quality during the reaming and swab pass and the carefully designed and managed buoyancy control ensured that the 23 hour pullback process maintained the pullback forces well below the established maximum pull loads.

An additional project challenge was that the pipe staging area was only long enough to allow pipe strings to be fabricated up to a maximum of 1,500 ft. Four pipe strings were required, necessitating three tie-in fusion welds to be completed by UGSI during pullback operations. Moving the pipeline from its fabrication site to the HDD exit point – where it entered the HDD bore – involved suspending the pipeline over a major roadway and supporting it over a steep hillside with numerous elevation changes. Remsco proficiently handled the pipeline using cranes and track hoes to overcome this challenging area.

Teamwork and professionalism between MWC, CDM, Remsco, Mears and UGSI were prominent throughout the project. The complexity of design and ingenuity of all parties involved made this record-breaking installation a success.