Geotechnical Design Reduces Construction Cost and Supports Sustainability

Photo Courtesy of WDG Architecture , PLLC

More than a bedrock for engineers, architects and contractors to build upon, subsurface exploration and geotechnical design can generate significant cost savings for new facilities through value engineering and seismic classification, and even support greater sustainability initiatives, as demonstrated at Prince Frederick Hall. The new six-story dormitory is the University of Maryland’s latest addition to its suite of on-campus student housing in College Park, Maryland.

Approximately 42 percent of the university’s nearly 40,000 students live on campus. The 186,000-square-foot residence hall offers traditional and suite-style dormitories for a capacity of 462 beds. Completed in 2014 by a design-build team led by Clark Construction Group and WDG Architecture, PLLC, Prince Frederick Hall recently earned LEED Gold certification.

Prince-Frederick-Post-Construction-Dormitory-credit-WDG-Architecture
Photo Courtesy of WDG Architecture, PLLC

KCI’s geotechnical engineers provided foundation design, constructability review and construction document review services for the building. Our team’s design recommendations helped move the project forward, accelerating the schedule and reducing construction costs.

Although the soils in the area typically require costly deep foundations, such as piles or drilled shafts, we felt there was a better alternative that was more economical and environmentally friendly.

Kwabena Ofori-Awuah, PE, ENV SPPractice Leader, Senior Geotechnical Engineer

Kwabena Ofori-Awuah, PE, ENV SP

The firm had also served previously as the geotechnical engineer working with the same design-build team on the recently completed Oakland Hall, a 700-student dormitory only a mile away. Both sites had the same subsurface challenges—deep deposits of expansive clayey soils with low bearing strength. Our team’s familiarity and understanding of the soil strata throughout the south campus helped create opportunities for sharing alternative design strategies.

Intermediate Foundations

“Ordinarily, a traditional geotechnical company would have recommended 70 or 80-foot deep foundations,” said KCI Practice Leader Kwabena Ofori-Awuah, PE, ENV SP. “Instead, we were able to use an innovative ground improvement technique—rammed aggregate piers—to create cost savings.” This historical knowledge from Oakland Hall, where a similar approach was used, allowed the team to develop designs without requiring a complete proof of concept. This intermediate foundation involved columns of compacted stone up to 30 feet deep and between three and four feet wide.

Sustainability

In addition to the cost savings associated with minimizing foundation depth, the geotechnical design also created opportunities for sustainability. More than 75 percent (nearly 6,000 tons) of the stone aggregate used in the GeoPiers consisted of 100 percent post-consumer recycled concrete. The rest came from local certified “clean” quarries that were less than 25 miles from the project site. Both types of stone were submitted for materials and resources credits to the U.S. Green Building Council as part of the facility’s LEED Gold application.

Seismic Classification

As part of the subsurface exploration, KCI was also responsible for classifying the site in terms of seismic risk. Based on the results of soil borings and standard penetration tests conducted, the soil in place had a low shear wave velocity, meaning that a building could experience significant shaking during an earthquake. Shear waves, also called secondary or S-waves, move through the earth during a seismic event. In the most basic terms, the higher the shear wave velocity, the stronger the material and the less effects on structures.

ReMi results
By utilizing the state of the art refraction microtremor technique, engineers were able to improve the seismic site classification from Class D to Class C, saving design and construction costs.

Following the borings and laboratory analysis, KCI recommended conducting an alternative geophysical testing technique known as Refraction Microtremor (ReMi). At Prince Frederick Hall, engineers collected twenty 30-second recordings of ambient noise (microtremors) using a field seismograph and an array of Geophones spaced approximately 20 feet apart.

Based on two tests, the average shear wave velocity fell into the range associated with Site Classification C (between 1,200 and 2,500 feet per second) according to the International Building Code, significantly reducing the structural detail required to withstand the expected level of seismicity.

Together, the foundation design and seismic classification saved hundreds of thousands of dollars in overall construction costs. Watch a time lapse of the complete construction project here.

Prince-Frederick-Post-Construction-credit-WDG-Architecture
Photo Courtesy of WDG Architecture, PLLC