One of the greatest challenges to Owners and Contractors in the renovation of existing buildings, is the need to keep the facility operational during the construction period. Keeping a site open was the challenge facing Robinson-May Department store in Laurel Plaza during a recent seismic upgrade. The original plan required forty-four 24"diameter piles up to 50' deep inside the basement level of the store at eleven column locations. To install, extensive demolition was required; the removal of the main electric panels and portions of the internal stairwells. That was an undesirable prospect for the owners, who had as a minimum requirement an open store during the construction.

It was clear that an alternate plan had to be conceived and implemented. Just days before bid date, the owner suggested they would be open to micropiles (even though the engineered plan was complete and submitted for a permit). To address the owners needs for a practical construction solution, Bob Morrison of Morley Construction worked closely with August Construction, a specialty drilling contractor, to substitute large diameter piles, (24" plus) with Micropiles (7" in diameter) to clinch the winning bid.

August Construction called upon the services of Ulf Werner & Associates to modify the existing plan and Groundtech to provide construction and testing procedures. The new design employed two to six Micropiles per column to reflect the actual forces required. In order to determine the length / capacity of the Micropiles, August worked with Law/Crandall, the soils engineers. Three Micropiles were installed in the parking lot prior to final design. When tested, the 7" diameter Micropiles (1 3/8" diameter, Grade 150ksi from Williams Form Engineering) were "post-grouted" with neat cement and produced greater capacity than that assigned to the 24" diameter piles. Because the greatest loads required were all in tension (not compression). The Micropiles were tested in tension as follows: Group action of 2 @ 25 foot micro piles (tiedowns) at 504 kips. Test of 1 @ 35 foot micro pile (tiedown) at 320 kips and 1 @ 25 foot micro pile (tiedown) at 324 kips. None of the micro piles failed. However after careful analysis, a design load of 7.6 kips/ foot was chosen by the engineers for the final design values.

The primary advantage of Micro or mini piles in this application was that the holes could be drilled inside an "active store" site. Due to the size and mobility of August’s drill rigs, the rigs could be maneuvered inside the store to drill the holes without extensive demolition (as would have been required with traditional piles). Some of August’s custom drill units successfully drilled 50 foot holes (in sandy matrix and river bed boulders) and yet were small enough to be able to fit between steel column and concrete walls – a mere 2 foot distance. This type of equipment adaptability saved the power panels and stairwells – a major economic savings. Additionally, August’s equipment was remotely powered (in the parking lot) which totally eliminated the noise and pollution from the engine, a key benefit when working inside an active store.

"If the owner’s construction department had not expressed an openness to an alternate design just a few days before bid-date, the original design would have been implemented – to disastrous effects I’m sure", Agust Agustsson, the project manager for August Construction noted. "It’s really to their credit that they recognized that a more elegant solution could be implemented; and the plan was modified and refined and approved without delaying the project."