Alphatec Engineering reports successful completion of repairs to the foundations of a Mitsubishi–MAN diesel engine, type 18V52/55B, at a CUC (Commonwealth Utility Corporation) power plant on the island of Saipan, the largest of the islands that comprise the Commonwealth of the Northern Mariana Islands, located in the middle of the Pacific Ocean.

The engine in question drives a brushless alternator of 13 MW capacity. It was originally installed in 1989. Even though it is not oldest of the units at the site, this one, unit 5, developed vibration problems, forcing a reduction in engine speed to avoid major damage, and resulting in decreased efficiency.

Eventually the vibration problem became so acute that the engine was shut down, giving the opportunity to Alphatec to do what they have been doing for almost 40 years, fix foundations.

The project involved mobilisation of a highly experienced team, including specialists in diamond core drilling and diamond wire cutting.

Because of the remote location, all materials required to complete the repair work, with the exception of reinforcing steel, and ready-mixed concrete, had to be shipped to the island.

The first step was cutting out, by diamond wire, of concrete on both sides of the engine foundation, in the form of twelve blocks (total volume 32 m3), allowing the existing 2.31 m long anchor bolts to be chipped out and removed. Next, new 3.2 m long anchor bolts were set in place (21 on each side).

Formwork was installed to contain the first pour of epoxy grout, Alphatec 800, which embedded the lower 650 mm of the anchor bolts. After 24 hours of curing, the first batch of replacement concrete, up to 

one meter below floor level, was poured. Prior to that a layer of Alphatec 440 epoxy bonding agent was applied to all surfaces to ensure adherence between the existing and new concrete. Then a further grout of Alphatec 800 was poured into the anchor bolt cavities to a level 15 cm below the base frame of the engine.

After curing, Alphapad hydraulic jack units were set in place to take the weight of the engine and the engine frame was aligned. A second pour of replacement concrete was then done, bringing the level up to 280 mm below floor level. Finally, Alphatec 800 epoxy grout was poured to floor level.

A series of injection holes was drilled alongside the engine and alternator foundation, to a depth of 3.6 m, and Alphatec 342 epoxy resin pressure injected, repairing the “cold joint” that became apparent just above the 45° sloping part of the foundation, as well other separations and stress cracks, raising the effective damping inertia of the foundation.

Finally, the engine crankshaft was aligned using a digital web deflection tool, the anchor bolt nuts being replaced with Supernuts to eliminate any movement of the crankcase after alignment.