13th Street Bridge Project Case Studies
Project Description: As part of a renovation project by the City of Gainesville Community Redevelopment
Agency (CRA), an old rail bridge was being converted into a pedestrian
bridge. A local commercial contractor was adding several retaining walls,
stair cases and gathering areas. During tropical storm Debbie, the foundation
of one of the newly constructed landing/gathering areas was undermined.
The heavy rains eroded a large area of bearing soil from beneath the foundation
of the structure. The loss of bearing soil caused the structure to settle
in the order of 1 to 4 inches. The construction of the structure consisted
of 1-foot thick concrete walls that were 12-feet tall bearing on a spread
footing foundation. Because of the settlement, the walls became misaligned
and several large stress fractures developed. The City of Gainesville
needed a quick and permanent solution before the entire structure was
lost so they contacted the experts at Ram Jack.
Solution: The immediate concern was to prevent the collapse of the structure. The
contractor formed around the perimeter of the footing where it was undermined.
Several yards of grout were pumped into the void space to reestablish
a temporary bearing surface. The site consisted of saturated clay soil
which made for a difficult work environment. Dry fill landings had to
be constructed for installing the piles and all-around workability. The
landing was designed to support a courtyard and a permanent train car.
Based on the construction weight, occupancy and surcharge loads, the wall
loads were calculated to be in the order of 9 kips per linear foot. Ram
Jack’s 4021 side load bracket was used on 2 7/8” diameter
helical piles to raise and stabilize the structure. The grout that was
placed in the void space had to be partially removed at the pile placement
locations in order to place the underpinning brackets and piles. As can
be seen from the photographs to the left, some of the piles had unbraced
lengths up to 5-feet above grade. Ram Jack’s patented internal threaded
connection, which is included in Ram Jack’s ICC-Evaluation Service
Report (ESR-1854), allows the exterior surface of the pile to be smooth
and homogeneous. This allows an exterior sleeve of infinite length to
be placed over the upper portion of the pile. The length of the exterior
sleeve is custom designed for projects like these to increase the stiffness
and bending stress resistance of the pile at its critical section. This
allows the pile to support higher design loads and longer unbraced lengths
than other systems while still using a smaller, more economical pile.
Conclusion: The piles were designed for a working load of 30 kips and spaced at approximately
40-inches on center around the settled portion on the structure. After
all the piles were installed, a synchronized hydraulic lift system was
used to raise the structure. During the lifting operation, the walls were
realigned and closure of the stress cracks were gained. Ram Jack was able
to accurately and safely restore the structure to its original position
and stabilize it to prevent its eminent collapse.
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