A major silicon wafer production plant in Silicon Valley, California managed to carry on full 24 hour production whilst having seismic protection fitted to it's production plant, which presented an enormous challenge to the contractors.

It was decided to protect the building from seismic activity by strengthening the structure with external steel columns and shielding the building by excavating underneath the foundations and installing base isolators. Converting the existing footings into columns resting on the isolators required filling the gap between the footings and the concrete slabs and anchoring the rebar to the existing columns.

The problem seemed impossible due to the difficulties of locating the rebar, however, the problem was eventually solved by using the Borehole Probe attachment to accurately locate the rebar so as not to cause any damage. 21mm holes were drilled and the Borehole probe used to 'map' the rebar locations in all directions from the bore hole. Once the rebar had been found, holes could then be safely drilled to install epoxy dowels to bond the rebar to the columns.

Chuck Queen - Project Manager for Nielsen Dillingham Builders Inc said:

"We tried everything we could think of, but nothing on the market could meet our specifications - the most important of which was not to damage any rebar. I read a technical paper from Elcometer on the borehole probe attachment for their P120 Rebar Plus rebar locator. I spoke with the company and they sent me the prototype. It worked beautifully. Drilling just two holes per column side sufficed to locate the rebars in most cases.

Out of 3,500 drill holes, the Elcometer P120 Rebar Plus with the borehole probe only missed three times. That’s a remarkable record. When the product was launched, we bought two. They’re easy to use - we can put one into the hands of a carpenter with minimum training and he can come up with the layouts without a problem. It’s an excellent instrument"

Nielsen Dillingham Builders Inc Web-site