Harahan Bridge - Construction

Construction

The first work was to build two miles of track from an existing line in the Arkansas flood plains to bring materials in place for construction. When this track was complete, 60 cars of timber waited for delivery. This material was used in building barges used for construction and moving materials into place. The first three months of construction were used to build 15 barges, and a total of 21 barges were needed to complete construction.

The next phase of the project involved building massive willow mats. These mats were constructed on the river. When completed, they measured 200 feet x 300 feet. They were floated to the location of the piers (held in place by barges) and sunk to the bottom of the river with rip-rap and stone. The purposed of the willow mats was to reduce scouring, keeping the river bed in place as the pneumatic caissons were dug into the river bed.

The Harahan Bridge was to be located 200 feet north of the Frisco Bridge. Use of pneumatic caissons had been used on the Frisco and other major bridges; this did not eliminate the dangers involved. The Harahan pneumatic caissons were constructed on shore out of wood. The walls were 3 feet thick, with heavy caulking and tar to make them airtight. The caisson was 40 feet wide x 90 feet long x 60 feet tall. In reality, it was a large wooden box, open at the bottom. The chamber at the bottom of the caisson had a 7 foot ceiling for the sandhogs to work.

Digging the river bottoms to sink the caissons into the river bed was difficult and dangerous work. All the material inside the walls of the caisson had to be removed to the surface. The caisson was built with excavation shafts for removing dirt and clay. The pressure was increased to match the water pressure, keeping the river water out of the work area. When the pressure was high enough, the excavation shafts were opened and air pressure would remove the light weight river bottom in a “blow off.” This eased the process greatly and saved a tremendous amount of time and effort for the sand hogs. It did, however, make a spectacular sight as a fountain of river bottom erupted from the caisson, it also left quite a mess on the top of it and any barges nearby.

As the caissons were being sunk into the riverbed, the piers were being built on top of them, adding weight and driving the caisson deeper into the river bottom. The piers were masonry blocks of granite backed with concrete. The piers of the Harahan were located directly upstream of the piers of the Frisco Bridge to keep the navigation channels open to river traffic. Pier IV was moved 17 feet toward the river relative to the Frisco Pier IV. This enabled the engineers to design two suspended spans and three cantilevered arms identically.

With the caissons sunk and the substructure complete, work began on the steel superstructure. The longest span between Pier I and Pier II was the first to be built. This span would be built without falsework, employing two cantilevered arms and a suspended arm. The next span to be complete was between Pier II and Pier III, using temporary falsework wood support timbers driven into the river bottom to hold the fixed span in place until it was complete. The span between Pier III and Pier IV was started concurrently. Span II to III was finished on December 22, 1915. On December 24, 1915, the river rose too quickly and washed away the false work. Span II to III was not damaged, although it moved 8 inches. Span III to IV was completely washed out, forcing a delay in the construction and a redesign on the span.

On July 14, 1916, the first train crossed the bridge. The celebration that had been planned was cancelled due to the war in Europe. The wagonways were not opened until September 17, 1917. The delay was due to construction problems with a wooden viaduct in Arkansas.