Area: Marine Facilities
Marine-Based Construction Schedule and Equipment Profile
With marine-based construction, the basic sequence for installation of the pile foundations and the trestle superstructure is similar to the Cantilever Method. For the most part the actual installation techniques will be the same except the equipment is based on floating platforms instead of a fixed platform. Although mobilization and demobilization will be quicker with marine-based methods, the possible need for erecting false work and temporary templates for installing the pile bent foundations may reduce overall productivity. For those piles that need to be socketed into the rock, the critical activity will be the drilling operation which may take slightly longer with floating equipment than it would with the Cantilever Method. Also for those pile foundations that are not socketed, the productivity of the marine-based crane operations may be reduced due to weather and sea state delays. However, unlike the Cantilever Method, overall productivity can be easily improved by just adding additional crews and equipment. Multiple crews and equipment can advance on multiple work fronts. The productivity rate will be directly proportional to the number of additional crews and equipment deployed.
The overall estimated schedule duration for the construction of the trestle and berth structures is 14 months and 18 months respectively. Since neither of these structures is on the critical path, it is possible to construct them either simultaneously or sequentially. As a possible mitigation measure, constructing the two components sequentially may help minimize construction equipment requirements and reduce possible cumulative noise effects from multiple work sites.
For the LNG Jetty Berth Structures it is expected that there will be one or two marine derricks and one or two flat deck scows mobilized to conduct the work. For the Trestle it is expected that one marine derrick and one flat deck scow would be mobilized. Since these construction sites are in open water, there is space for additional crews and equipment to be mobilized as required to improve productivity. Although the construction vessels are not subject to tidal restrictions in the deep waters of the LNG Berth Structures and the outer Trestle, it is unlikely the EPC contractor will allow the equipment to stay in open water overnight. Thus the marine derricks and scows will likely be moved between the construction site and a safe anchorage or staging area daily. The anchorage or staging area could be located in Port Edward.
However to mitigate possible marine traffic congestion in Porpoise Channel, the working vessels could transit to a location within the inner harbour of Prince Rupert.
Since the marine derricks and scows would be transferred to and from a staging area every day, they could be used to resupply the work front without the need for additional supply barges. Alternatively one or more supply barges could also be used for transporting materials from the mainland to the work front depending on construction requirements.
In general the construction of the Trestle and Berth Structures via marine-based methods should not be an impediment to marine traffic. The work faces will occur in relatively small areas in open waters away from or adjacent to approach channels. A safety zone would be enforced around the work site which may prohibit vessels from approaching closer than 50 m.
Work site restrictions would be promulgated through a variety of channels, such as Notices to Mariners, in accordance with the Marine Communication Plan.