Towson University Liberal Arts Building – Phase II
153,000 sf Liberal Arts Complex which includes impressive galleries, a writing center, additional labs, student areas and lounges.
LEED Gold Certified
Building loads ranged from 100 to 840 kips. Phase I of the complex incorporated a drilled shaft foundation system; however, due to scheduling concerns, an alternative was needed for phase II.
The building was sited such that footings for the western section of the building could bear on decomposed rock with an allowable bearing pressure of 7.5 ksf, but fill soils and loose residual silty sands required a deep foundation system in the eastern section. The soil conditions for the eastern section consisted of approximately 10 feet of loose silty sand fill, overlying 25 feet of natural, loose to dense residual silty sands, which were underlain by decomposed rock and highly weathered to weathered gneiss bedrock.
Geopier elements were used to replace a drilled shaft foundation system. The original geotechnical report recommended that all shafts be a minimum of 36 inches in diameter so that the bottom could be inspected to verify shafts were bearing on suitable material. Due to the variability of the weathering in the bedrock profile, drilled shafts needed to be socketed into rock with an RQD (Rock Quality Designation) of at least 50%. The shafts were designed for an allowable bearing pressure of 40 ksf.
The general contractor, who was familiar with Geopier RAP elements, proposed an alternate of 30-inch diameter RAP elements. The RAP elements supported spread footings designed for 6 ksf bearing and controlled settlement to less than 1 inch. Having a designed system that was consistent with the spread footings used on the western section of the building simplified the design and construction sequencing for the GC and the owner.
The Geopier alternative proved to be faster and eliminated the risk of potential overruns associated with variable drilled shaft lengths, rock socket depths, and rock testing to find rock with an RQD > 50%.
Using ground improvement versus drilled shafts provided the owner the assurance that the foundation would be completed on schedule with no cost overruns and also contributed to the LEED goals for this project by using recycled concrete for pier installation. Specific benefits included:
- Ability to use spread footings for all the foundations
- Eliminating the requirement to socket piers into rock or case holes for inspection and testing
- Eliminating the risk of overruns due to encountering poor quality rock
- Generating fewer spoils saving time and haul-off costs
Towson University - Towson, MD
The Whiting-Turner Contracting Company - Baltimore, MD
Burt Hill Architects - Washington, DC
ReStl Designers, Inc - Washington, DC
EBA Engineering, Inc - Baltimore, MD