Selecting A Trenchless Construction Method for Crossing Florida SR 674 and I-75

摘要

The Hillsborough County Florida State Road 674 (SR 674) Force Main, Phase II project is part of a multi-phasernproject which will extend a new force main from central Hillsborough County to the South County WastewaterrnTreatment Plant. In April, 2010 Cardno TBE was retained to provide final route selection, design, permitting, bidrnassistance and construction phase services. The project includes approximately 11,000 linear feet of 30-inchrndiameter force main and the crossings of SR 674 and Interstate 75 (I-75).rnTrenchless construction methods considered and evaluated for the two major Florida Department of Transportationrn(FDOT) crossings included horizontal auger boring and pipe jacking, horizontal directional drilling andrnmicrotunneling. In general, the geotechnical investigation conducted at these crossings indicated fine to mediumrnsandy soils and the presence of a relatively shallow groundwater table. In addition, there was evidence of arnsignificant downward gradient between the surficial water table and the deeper piezometric level within the upperrnFloridan aquifer.rnMicrotunnel was ultimately selected as the preferred method for constructing the FDOT crossings. A number ofrnprecautions were implemented to insure a successful project. The project presents several intriguing challenges,rnmost notably the selection of the trenchless construction method and the logistics of the proposed tunnelingrnoperations.rnThis paper discusses several issues in selecting an appropriate trenchless method unique to a successful microtunnelrnoperation under heavily traveled roadways. Specific issues addressed during the planning, design, bidding andrnconstruction phases of this project will also be discussed.