AES Total Energy, Guayama, Puerto Rico, a Case Study of Design Build Foundations
The construction of a new coal-fired power plant in Guayama, Puerto Rico required foundation support for the main powerhouse, exhaust stack, and coal conveyor system. In addition, the construction of a dock to be used for raw material handling adjacent to the plant was required.
Budget and schedule problems on the base bid options were recognized on both the power plant and dock.
Morris-Shea offered and was awarded a design-build option for both the power plant and the dock. Total savings over the base bid options were in excess of $2 million were realized, in addition to a schedule saving on the power plant piles in excess of 2 months.
The soil profile in the power plant area comprised a sequence of alluvial sands, sandy clays, and clayey sands, overlying weathered rock. Several feet of fill was placed over natural grade, resulting in down drag loads on the piles. The base bid foundation design was 12 inch and 14 inch precast concrete piles, with allowable loads of 60 tons and 90 tons respectively. Approximately 4,000 piles were included in the power plant facility and material handling structures.
The loading and unloading dock was required to supply coal and limestone to the plant, and remove fly ash waste. The shallow marine dock, which was severely over budget, was to be designed to accommodate 750-foot long Panamax class bulk cargo carriers. The soil profile in the dock area comprised loose silty sands grading to medium dense sands, overlying weathered bedrock at depths of up to 100 feet.
Morris-Shea offered an H-pile alternate for the power plant foundations. HP 10X42 piles were proposed for the 60 ton piles, and HP 12X53 piles for the 90 ton piles.
Prior to production pile installation, a load test program was performed comprising extensive Pile Driving Analyzer (PDA) testing and static load testing. A total of 14 PDA monitored probe plies were driven in addition to the static compression, tension, and lateral load testing.
PDA testing, which was calibrated to static test results by restiking the test piles upon completion of static tests, allowed comprehensive coverage of the project area. The relationship in end of initial drive blow counts and long term capacities was evaluated across the site by monitoring initial drive and restrike testing of probe piles. This enabled the setting of a drive criteria for initial drive, and restrike testing.
Production pile driving was performed using two Delmag D-19 diesel hammers, which achieved productions for the 45 foot long piles of up to 100 piles per day. A schedule acceleration of almost 2 months was achieved over the base bid schedule.
A total redesign of the dock was performed by Morris-Shea. This involved design of mooring and breasting dolphins, an access bridge, and substructure for the material handling system.
In designing the dock foundations, seismic loads were to be considered, in addition to hurricane wind loads, ship loads, and loads from the material handling and conveyor systems.
Construction of the dock was performed from barges in up to 25 feet of water. Kobelco CK1000 and CK1750 cranes were used for pile driving, dock and dolphin construction, in addition to the lifting and placing of conveyor units. All piling and concrete work was completed by Morris-Shea personnel.
Piles were coated over the upper section to provide corrosion protection. Cathodic protection in the form of sacrificial aluminum bars was also used as corrosion protection.
Pile Driving Analyzer (PDA) testing and CAPWAP analysis were used to verify capacity and establish driving criteria.
Piles with diameters up to 24 inches were driven with a Delmag D-19 hammer with a rated energy of 42,800 foot-lbs. Larger piles were driven with a Delmag D-62, which has a rated energy of 152,000 foot-lbs. Marine leads were use for both hammers.
On completion of driving foundation piles, concrete forms were set for the pile caps, dolphins, and material handling substructure beams. This involved the construction of extensive falsework to support the weight of the reinforcement and concrete.
All concrete work for the dolphins, access bridge, and material handling facility was performed by Morris-Shea. In addition, the setting of 60-ton conveyor trusses was by completed by Morris-Shea from barges.
The combination of Morris-Shea’s experience in design-build foundations, ability to price various options and to include constructability considerations in the design was key to the project’s success.