Simple Ideas Solve Problems
As Published in "Structure" Vol.2 No.3

By Stan Agee
The Stan Agee Company
Manufacturer's Representative for PIERESEARCH

Sometimes recurring problems, long plaguing an industry, can be solved with a simple and mundane solution. Such is the case with the problem of aligning rebar cages in drilled shafts, e.g., drilled piers, caissons, cast-in-drilled-hole piling, cast-in-place pile, etc.

Without proper alignment, the rebar cage cannot perform the function for which it was designed. Proper positioning helps protect against long-term corrosion of the rebar. Faulty alignment may cause foundation failure, which often leads to issues of contingent liability. Because the rebar cage cannot be inspected or tested after the concrete is placed in the drilled shaft, the cage must be aligned properly the first time.

Often spacers, such as rocks, bricks, or sticks, are used in an attempt to properly space the cage within the shaft. Usually these devices fail to stay attached to the cage. Also, they tend to gouge the side of the shaft, causing debris to clutter the shaft's floor. In instances where casing must be removed, these spacing devices typically hang the cage on the casing, causing the cage to pull out of the shaft with the casing. Several manufacturers produce products, such as plastic wheels and bolsters, to achieve proper positioning (see figures 1 & 2). Unfortunately, these products usually detach from the cage or get crushed. Also, the wheel products tend to intrude into the interior of the cage and interfere with the tremie. Because of these problems, many contractors fail to use any device to properly align the cage.

PIERESEARCH, Arlington, TX, developed a solution to these cage-positioning problems consisting of two 8,500 psi high-strength grout devices, a pier sled and a pier bolster. The half-moon shaped pier sled contains a notch for the spiral or circle tie and has four sets of integral, 16 gauge tie wires embedded therein for ease of installation (see figure 3). The pier bolster is disk-like in shape and contains two 9 gauge looped tie wires for installation (see figure 4). The high strength grout supports the weight of the concrete cage and will not shatter should the cage strike the casing or some other object. Because the sled and the bolster are tied to the cage, the possibility of them becoming detached is eliminated. The sled's shape prevents the cage from hanging on the casing. Furthermore, the sled does not protrude into the interior of the cage, so interference with the tremie is not a concern.

Figure 3

Figure 4

These products have been well received by the structural engineering and construction communities. They achieve a result that has been long sought by structural engineers. For a free specification kit, contact:

Stan Agee at PIERESEARCH (800-656-0417)