Leaders at Roanoke College in Salem, Virginia, have a simple but ambitious vision for their school: to educate mind, body and soul. That vision became sharply focused with their commitment to build a new campus flagship facility, the Cregger Center.
The Cregger Center will be a setting for what Roanoke does best—education of mind, body and soul. he new center will include a performance gym with a 2,500-seat capacity and a field house with a 200-meter indoor track. The athletic portion of the complex also will include a fitness center to be used by the entire community, and an athletic training room. New event seating space for 3,500, along with several other social spaces, including dining areas, will allow the College to host outside speakers and events and bring our entire community together in ways that are not currently possible. A literal and metaphorical campus crossroads, the Cregger Center will be a hallmark of best educational practices today—intentionally designed to enhance engagement between and among students and faculty. The center will also serve the larger Roanoke Valley community, hosting academic, cultural and athletic events, and become a flagship for the Roanoke experience.
But just as a stiff keel is crucial to any flagship, a solid foundation is crucial to any flagship facility. The Cregger Center provided us not only with technical challenges but also with an unusual opportunity.
With design in hand for a facility using a traditional shallow foundation, the College Board must have been disappointed when subsurface investigation found the soil to be so poor that a shallow foundation was inadequate. They were faced with a dilemma – either redesign the building for a deep foundation system, or find a way to make a shallow foundation work. After further consideration, they settled on the latter of the two. Then they called Rembco. (Good move!)
A shallow foundation is dependent on adequate and uniform bearing of the underlying soils. It is not designed to withstand point loading that is inherent to deep foundation piles. Making a shallow foundation work in this poor soil condition would require a unique ground modification system. This system would have to provide sufficient bearing capacity and lateral strength without imposing point load on the footing.
Rembco proposed a hybrid system designed to achieve both. As is commonly done, compaction piles were to be constructed extending from competent rock up to the desired elevation. The hybrid twist is that the piles were not to be anchored to the footing, but would instead terminate 18 inches below each section of the stepped footing. A trench would be excavated from grade level down to the pile caps and then would be filled with two feet of compacted stone. The building’s shallow foundation system would rest on this stone filled trench – taking advantage of an improved subgrade and structural elements without experiencing point load from the piles.
A concern on this job that is not usually associated with compaction piles was that ground heave could compromise the bearing capacity of the soil near the shallow footing, so surface conditions had to be monitored closely during compaction grouting. If any lifting was noted, the volume of grout injected in each subsequent lift was reduced. If the injection volume had to be decreased below a minimum threshold (affecting the column’s diameter), supplemental piles were installed to ensure adequate performance.
And, finally, an unusual opportunity arose when our client required that two piles be excavated and inspected. Although testing the load capacity of our piles is common, we very seldom dig-out a pile to look at it. We were very pleased to see that the theoretically uniform piles were indeed cylindrical.
The Roanoke community can rest assured that their campus flagship will set sail with a stiff keel. (You can watch current construction of the Cregger Center online at this webcam.
No cookie cutter solutions here. When you have a geotechnical problem, no matter the size, it pays to make Rembco your first call. Mike Bivens, our Chief Engineer, can be reached at (865) 363-4708.