This is a two phase project to replace an existing bridge on US-17 over the Brunswick River. A busy highway had to remain open raising the challenges of working in between the existing spans and working from a combination of trestles and barges. A. H. Beck used a crane attached drill rig to drill and install the 40 – 84” diameter shafts to depths of 111 ft. to 130 ft. The project was value engineered to shorten the shafts from a design depth of 180 feet by the use of shaft base post grouting. The shafts were installed through sands, clays and limestone and were constructed with a permanent steel casing at the top and were stabilized with bentonite slurry during the excavation.
The project consists of 33 drilled shafts 84” in diameter with depths between 92 and 126 feet. Twelve of the shafts on the project are located in the Intercoastal Waterway. The extremely sandy subsurface conditions combined with the presence of many organics make it a challenging slurry displaced drilling project. By using a “stretch” drilling attachment, the American 9299 mounted attachment is able to reach drilled shaft locations up to 47’ away from the machine’s center pin. This allowed the contractor more flexibility in designing and building trestle access to the bent locations in the waterway.
This unique project was to install multiple 72” drilled shafts for two large bent at the river crossing. The drilled shafts were installed within the confines of a coffer cell with the requirement that they were installed without permanent casing, even though they were installed through 80 feet of water. This challenge was met by the use of a double temporary casing sequence with a sand backfill placed within the annular space of the two casings. The shafts were drilled to a depth of 145 feet below the working trestle, the shaft was poured up to an elevation just above the mud line and the inner casing was extracted leaving the sand backfill to shaft and form the drilled shaft until the concrete set and the outer casing could be removed. The shafts were stabilized with bentonite slurry below the temporary casings. There were two Osterberg Load Tests performed to verify the strengths of the sandy subsurface soils.
This project consisted of constructing the bridge approaches of a new alignment for US-82 across the Mississippi River. The Mississippi approach consisted of 458 drilled shafts, ranging in diameter from 1200mm to 1650mm, and depths from 22.50 meters to 38.75 meters. The Arkansas approach consisted of 266 1200mm shafts, ranging in depth from 25.75 meters to 38.30 meters. Using temporary and permanent casings and the slurry displaced method, A. H. Beck completed both projects in under 23 months. Each bridge column was cast on a footing supported by a cluster of drilled shafts. A sequence was developed and implemented by A. H. Beck to install and extract temporary casing on multiple drilled shafts without imparting vibrations to the concrete that was curing in the shafts within the same cluster.
A. H. Beck Foundation Company worked with Cape Romain Contractors to construct two bridges on SC-171. The two bridges included a 825 ft. bridge spanning Folly Creek and another bridge 1,050 ft. over the Folly River. Each span was supported by two 72 inch drilled shafts x 80 to 100 feet deep. The shaft installation method specified permanent steel casings set approximately 70 feet deep, keying into the Cooper Marl. The drilled shaft was drilled into this Cooper Marl formation an additional 15 to 40 feet deeper than the casings. All work was performed using an A. H. Beck Crane Attached drill unit mounted to an American 9299 crawler crane. The majority of the drilled shafts were reached by barges.
All 136 lake bridge drill shafts were constructed on A. H. Beck barges using a A. H. Beck manufactured custom hydraulic drill attached to 135 ton Lieberr. A 50’ x 60’ barge was used to provide 3,560 cyds. of specially designed mix using A. H. Beck Volumetric mixers. A total of 3200 tons of rock, 2700 tons of sand and 1500 tons of cement had to be ferried out onto lake to produce the concrete. Permanent Casing was used on all lake piers. Water depths ranged from 4’ along the banks to 24’ at deepest points.
This project consisted of 97 drilled shaft foundations 60 inches in diameter, between 90 and 120 feet in depth. Phase I of the project had to be constructed in between the two existing IH 10 bridges, leaving a working width of only eighty feet (80’). The scope of work also included an Osterberg cell load test for design verification. Due to the footing for the new bridge foundations (consisting of clusters of 12-60” diameter shafts) and the narrow working width between the bridges, A. H. Beck used long reach drill attachments they had fabricated to be able to reach across the footings and construct each one from only one side.
The $46 million reconstruction of State Highway 332 over the Brazos River required 4 - 96” drilled shafts 130’ deep on each end of the long river span. All 8 of these shafts were constructed with permanent surface casing to bring them up out of the river. A. H. Beck manufactured a custom hydraulic drill that attached to 110-ton Link Belt crane in order to excavate the shafts. Concreting the shafts took 260 CY of a specially designed mix developed and supplied by Dorsett Brothers Concrete Supply, Inc., and was completed in less than a 5 hour period.