As part of a Florida Department of Transportation (FDOT) Interstate I-75 Improvement project, an existing bridgernon Fowler Av. over the Hillsborough River was to be replaced. The Hillsborough River is an Outstanding FloridarnWaterway and a very sensitive environmental area. The City of Temple Terrace had an existing 12 inch force mainrn(FM) attached to the bridge that required replacement. Cardno TBE was retained to provide design, permitting andrnconstruction administration services for the City to relocate their utilities for the project. The utility relocation designrnincluded a subaqueous relocation of 1,000 feet of 12-inch sanitary sewer FM beneath the Hillsborough River byrnhorizontal directional drilling (HDD).rnThe geotechnical investigation revealed that the soils encountered were sandy soils underlain by weatheredrnlimestone/calcareous clay and chert. The chert material had a relative Moh's hardness of 7. The boring logs alsornnoted a loss of circulation.rnThe HDD operations presented its own unique challenges due to the chert and maintaining circulation. However,rnafter the FM was constructed and in order to construct the new bridge over the Hillsborough River, FDOT allowedrnthe contractor to construct temporary piles to enhance crane activities, adjacent to the FM. Due to the subsurfacernconditions and the close proximity to the FM special requirements were initiated to maintain the integrity of the FM.
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