Drilled Shaft Foundation Specs May Need Serious Attention
The use of drilled shaft foundations is growing nationwide, prompting many industry leaders to say state highway specifications are flawed, outdated and lead to claims and lawsuits. To develop a dialogue between industry and the public sector, the Northeast Chapter of the Association of Drilled Shaft Contractors has been meeting with state officials to help improve design criteria.
"We're not saying drilled shafts are the answer to all foundation needs," says John Roma, vice president of New England Foundation Co. Inc., Quincy, Mass. "But when shafts are used, we are finding outdated concrete specifications on slump, flow through rebar cage, obstructions, rebar spacing and load testing that are causing needless problems. It is in the public interest to establish good practices for drilled shafts." He notes, for example, that many specs typically call for 6-in. slump for concrete, but tremie-placed concrete needs 8 in. to 9 in. Similarly, aggregate is being specified too large to flow through tight, seismically designed rebar cages used in shafts.