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Fort Pike

3rd Qtr 2014

Location

New Orleans, LA

Description

Fort Pike was built by the U.S. Army following the War of 1812 during the period 1817-1821 when numerous forts were built all across the U. S. The fort was named for Brig. Gen. Zebulon Montgomery Pike who was killed in action during the War of 1812.

Fort Pike is located on the Pass Rigolets, one of two passes (straits) that connect the Gulf of Mexico to Lake Pontchartrain, which is on the north boundary of the City of New Orleans. The other Pass is Chef Menteur, which has a twin of Fort Pike guarding it: Fort Macomb. Both forts are located on Chef Menteur Highway (U.S. 90), and are within the city limits of New Orleans. These forts were defensive structures built to guard against invasive attacks of the city from the north in Lake Pontchartrain, accessed through the two passes draining the lake.

During the Seminole Wars in Florida during the 1820s, the U.S. held Seminole prisoners of war at Fort Pike. These prisoners were eventually relocated to the Seminole Reservation in Indian territory, now Oklahoma. Interestingly, P. G. T Beauregard, also an engineer, was stationed at Fort Pike in one of his earliest postings as a then Lieutenant. In 1861, the Louisiana Continental Guard took control of the fort weeks before Louisiana joined the Confederacy and the begin- ning of the American Civil War. When the Union Army captured the city in 1862. they also took over the fort. It was then used as a base for raids and training of the United States Colored Troops, which was established in 1864 of former slaves. The USCT were instrumental in Union success. The fort was abandoned by the U.S. Army in 1890 without a cannon ever having been fired in battle. It was listed on the National Register of Historic Places in 1972 and became a state park known as the Fort Pike State Historic Site, and has functioned as a very popular tourist attraction ever since.

The fort had been deteriorating for years for reasons that will be later explained, and was severely damaged by Hurricane Katrina in August 2005 when the 25' high storm surge overtopped the struc- ture, submerging it under about 10' of water. It was again damaged in Hurricanes Gustav in 2008 and Isaac in 2012.

E&A was selected by the State of Louisiana in 2009 to design repairs to the Museum located within Fort Pike in the Citadel, a building in the center, and to repair various masonry walls to the extent that funds are available from both FEMA and State Capital Outlay. To accomplish this, we have had to study the design and construction history, and perform assessments of the current conditions.

The original design of the fort was documented by obtaining the original design documents from the National Archives, and also having topographical and sounding surveys performed, and extensive soil borings and analyses of same. The foundation consisted of a mat of 3 layers of tidewater red cypress timbers, 1' x 1' in cross section, criss-crossed. This mat was laid after first excavating the top most organic soil from the footprint of the fort. The perimeter walls were founded upon corbeled brick spread footings (there was no concrete in usage in the early 19th century) supported on the timber mat, while the walls supporting the casemate vaults are supported upon upside down arched vaults, to distribute the load evenly on the timber mat. The bastions (the outside corner wall junctures) were filled with soil to the tops of the walls plus some, as was the space above the casemate vaults. Only the area in the center, where the Citadel Building is, was filled to the floor level of the casemate vaults. The various vaults functioned as cannon locations, ammunition bunkers, and Suttler store. On the top of the casemate vaults on the paved fill, were also cannon locations. The Citadel was a mess hall on the lower level and the upper level was sleeping quarters (now destroyed). The entire structure is surrounded by a moat and accessed by a bridge across. There was a dock, and a hospital structure also that has been destroyed, north of the highway.

In the early 19th century, the understanding of soil mechanics was very primitive and intuitive. Hence the foundation design was essentially faulty. The timber mat was not loaded equally in all areas - the bastions were the most heavily loaded, next the casemate vault areas, and next the center. These three loadings produced severe settlement and differential settlement. Based upon the historic drawings, we estimate that the fort has settled 30" to 36" (6” differentially), with the most settlement at the three bastion areas. The timber mat has served to soften and blend the differentials, by bending, but the differential is severe enough for the shoulder vaults next to the bastions to have opened up at the keystone at the tops of the shoulder vaults. These have been permanently shored to prevent collapse.

The overtopping storm surges by the hurricanes have caused severe erosion of the soil fill in the bastions, with large cracks at the corners, and caused the northeast section of the seaward wall to rotate such that the battered portion of the wall is now vertical. There may also be some unknown deterioration of the timber mat contributing to this wall rotation. We calculated that the factor of safety of these walls when originally designed and built was 1.2 to 1, and that this rotated portion of the wall now has a 1.05 to 1 factor of safety, essentially no factor of safety at all. If overtopped again by a storm surge, this wall may well collapse into the Rigolets.

In his later years, P.G.T. Beauregard monitored the construction and foundation settlement later of the U.S. Customhouse in New Orleans over about a 10 year period. He recorded settlements and differential settlements greater than we estimate / measure at Fort Pike. This is important because the foundations of the two structures are identical: a timber mat supporting both corbeled brick spread footings and upside down arched vaults. We suspected that Beauregard also recorded settlements at Fort Pike since he was stationed there earlier, but have not been able to locate any documents. One interesting bit of folklore: the public was under the erroneous impression that the foundation of the Customhouse was built upon cotton bales, because people witnessed numerous cotton bales being delivered and incorporated into the construction. The cotton was actually used to caulk between the boards of the vertical wooden sheet piling supporting the soil sides of the excavation below grade to prevent its leaking, as one also did in those days between the wood planking of a boat.

Unfortunately, funds do not permit the proper, complete rebuilding of Fort Pike. There are finds only to restore the museum, repair some very damaged walls, and to install stabilization measures consisting of some temporary tension rods at the tops of diagonally opposing columns attached on the outside of the bastion walls, where the walls balance each other to prevent futher rotation and collapse of either side of the bastions.

We had recommended that the soil be removed from the bastions and that geofoam replace half the soil fill to equalize the loading between the bastions and the casemates, and to repair / rebuild all of the cracks in the walls, installing permanent tie rods with pressure plates at the bastions. The estimates are such that FEMA can’t fund it since much of the damage preceded the storm.

Ladd P. Ehlinger, AIA

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