Virginia Tech Rasche Hall
Rasche Hall, built in 1894, expanded in the 1950’s and home to the Cadets, is being torn down and rebuilt in the first phase of the redevelopment of the Upper Quad at VT. The new building will offer 21st-century housing concepts to meet the needs of students while intentionally maintain the heritage of the Upper Quad.
Soil conditions generally consist of up to 5 ft of clay fill underlain by soft to very stiff lean and fat residual clay extending to partially weathered pinnacled limestone bedrock. Groundwater was generally encountered near the top of rock which was as deep as 55 feet below the ground surface.
With three large mat footings 30 to 35-foot square with loads up to 3000 kips adjacent to 300 to 400 kip column footings and 15 to 40 kips per lineal foot strip footings the one big challenge was how to control settlement to less than an inch. The adjacent footing stresses could not be controlled using aggregate piers alone (the solution specified) even if the piers were all installed up to 55 feet deep to tag rock.
A combination of Geopier Rigid Inclusions and Geopier aggregate piers ended up being the optimal solution. Cement treated aggregate Geopier elements were used to isolate heavy footings and transfer their loads down to bedrock. In this way, the stress from adjacent footings was eliminated. Lightly loaded footings could be supported on variable length aggregate Geopier elements which resulted in a cost effective solution.
To be able to transfer the load from the CTA Geopier rigid inclusion elements a load transfer mechanism consisting of a 12 inch thick conventional Geopier aggregate pier element was placed on top of the CTA Geopier element. This provided the necessary load transfer to the footing and provided a shear break for seismic considerations. It also allowed the footing excavations for all the Geopier elements to be identical for the footing contractor.
CTA Geopier element with a 12 inch thick Aggregate Pier Load Transfer Cap
Virginia Polytechnic Institute and State University - Blacksburg, VA
Barton Malow - Blacksburg, VA
Architect / Structural Engineer
Clark-Nexsen Architecture & Engineering - Charlotte, NC
Froehling & Robertson, Inc - Roanoke, VA