Brayman Construction Corporation offers innovative specialty geotechnical design and build foundation solutions to a variety of applications. The selection of the applicable foundation support is dependent upon criteria such as: economy of selection, type of ground conditions, required load capacity, ground water level, proximity of existing structures, and installation constraints. Brayman’s Caisson Group has extensive experience in the innovative and successful application of caissons in multiple applications and site conditions.

What is a Caisson?

Caissons are a deep foundation support that is constructed by placing fresh concrete and reinforcing steel into a drilled shaft. These reinforced concrete piles are cast in holes of predetermined diameters and depths drilled through soil and rock to the desired bearing stratum. The Large Diameter Drilling Group of Brayman has the capability and experience of drilling shafts from 18 inches to 96 inches (and larger) in diameter, and to depths of 150 feet.

Caissons, which are capable of supporting high, concentrated loads, are typically used to set piers for bridges, underpasses, structural supports, as well as in slide prevention applications. Caissons are  viewed as a reliable, versatile, and economical foundation support solution.

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Susquehanna River Bridge Replacement

Installation of 176 total shafts ranging from 42 - 72 inches in dia. and depths of 23 - 55 feet for the foundation of the 40 span pre-cast concrete segmental box girder bridge.

Mellon Bank Client Service Center

Installation of 180 caissons with dia. between 30 - 60 inches and an average depth of 35 feet. Project required that the caissons be socketed into rock up to depths of 20 feet.

SR-51 Emergency Slide Repair

Emergency slide repair project that involved the installation of 103 - 48” diameter caissons averaging 50’ depths and 21 adjacent - 30” diameter caissons averaging a depth of 25’ in a low overhead clearance area with live electrical power lines active during the work.

Advantages

In addition to the cost advantage of a drilled foundation, there is minimal soil displacement or vibration that could damage adjacent structures, noise of installation is reduced, and lengths can be adjusted readily to fit soil conditions. In addition, there is no damage to piles due to handling, minimal handling equipment is required for placement of reinforcing cage, and placement is sometimes possible in types of soil that a driven pile could not penetrate (bedrock, boulders, hard layers, etc.).

Construction of Caissons:

Construction of the drilled shaft is accomplished by rotary methods using portable drill rigs. The drills are self propelled with either track or truck mounted rigs. Brayman has experience in each of these applications. The drilling auger is the most commonly used piece of equipment for drilling shafts.

There are a variety of different types of augers that may be used in different situations. Soil augers are equipped with a cutting edge that cuts into the soil during rotation. Rock augers are equipped with high-strength steel cutting teeth that cut through rock. The drill cuttings are carried on the flights as the auger is removed from the drilled shaft and are the “spun off”. Likewise, drilling and/or cleanout buckets are used when augers are unable to extract residual material from the drilled hole.

Likewise, the ground formation in which the shafts for the caissons are to be drilled must be of such a nature that the drilled shafts will retain their shape and will not cave in when concrete is placed. Steel casings are used to support drilled holes when unstable conditions are encountered. Various methods can be used to advance the steel casing. Such methods may include spinning the casing while applying a vertical force, driving the casing with whatever means are available as the hole is drilled, or using a vibratory hammer. Steel casings are generally removed from the hole in the manner specified in the contract specifications as concrete is being placed.

Prior to placing concrete, the bottom of the drilled shaft must be cleaned of loose materials or small amounts of water. This can be easily accomplished a cleanout bucket. Failure to do so may compromise the integrity of the caisson by having the caisson resting on soft material.

Caisson Project Examples:

Mon Fayette Expressway, Section 51B Location: Fayette County, PA Owner: Pennsylvania Turnpike Commission Client/GC: Swank Construction Allegheny County Sanitation Authority Location: Pittsburgh, PA Owner: Alcosan Client/GC: Walsh Construction Westinghouse Location: Cranberry, PA Owner: Westinghouse Corp. Client/GC: Turner Construction

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