WorldWide Drilling Resource

40 JUNE 2019 WorldWide Drilling Resource ® A Foundation Support Home Run Adapted from Information by Helical Drilling The need for a new ballpark for the hometown fans of the Hartford Yard Goats, the Double-A affiliate of Major League Baseball’s Colorado Rockies, meant overcoming construction challenges. The site selected for Dunkin’ Donuts Park was a corner lot in a highly developed downtown area of North Hartford, Connecticut. The ballpark design consisted of a multilevel steel- framed structure with several large retaining walls. Subsurface soil conditions consisted of up to 20 feet of granular urban fill, 2 feet of alluvial sand, up to 35 feet of soft to very soft varved silt and clay, overlying relatively dense glacial till and bedrock. The varved silt and clay layer is regionally known as “Connecticut Valley Varved Clay”, which has a reddish color, but also high sensitivity and compressibility. The primary geotechnical challenge was the compressible urban fill and relatively soft varved clay layers. Excessive post-construction settlements exceeding the specified maximum allowable settlement of one-inch would have been caused by supporting footings on the unimproved fill and varved clay layers. The owner required an economically viable foundation support solution which would not disrupt surrounding businesses with excessive noise or vibrations. The design team considered several foundation support alternatives, including driven piles combined with pile caps and grade beams, but Geopier GeoConcrete ® Column (GCC) elements and shallow footings were selected as the most economical foundation support approach to address the project’s highly populated urban setting, chal- lenging subsurface conditions, and schedule demands. Geopier GCCs consist of high-capacity rigid inclusions, and allowed for shallow foundation support of the structure, instead of the more costly pile caps and grade beams. The GCCs were designed to limit total and differential post-construction footing settlement to less than one-inch and ¾- inch respectively, with a maximum allowable footing bearing pressure of four kips per square foot (ksf). Some late project design changes were needed to eliminate lightweight backfilling in the left field section of the structure. Design adjustments were made to the Geopier GCC system in these areas to increase the allowable bearing pressure to six ksf. This localized adjustment provided further cost savings on the project. Helical Drilling installed more than 1400 GCCs with one Geopier rig and crew. They were installed using a patented dis- placement mandrel which did not require dewatering or generate excess spoils. Helical’s designer engineered a structural fill pad (footing pad) beneath the footings to help transfer footing stresses to the GCCs and surrounding matrix soil. The footing pads also provided a stable subgrade for footing construction. C&G