October 2017 Vol. 72 No. 10
Features
Hydraulic Excavation Brace Saves Contractor Time and Money
A Central Florida contractor was performing one portion of a water expansion project that would require a bore beneath existing rail tracks. The contractor estimated the excavation would need to be about 40-ft long, 16-ft wide and about 19-ft deep to provide the necessary room to operate the boring machine and complete the work. The contractor’s competent person had classified the clay and brown sand mixture as a Type C-60 soil.
The contractor had identified several requirements that an eventual shoring system would need to address. The excavation site would feature two fiber optic lines that would traverse the excavation at different depths. The bore pit would be located within 25-ft of the railroad tracks, while the receiving pit would be within 10-ft of an active roadway and within 50-ft of a retention pond. The contractor and rail authority would be monitoring the tracks to ensure that there was no sinking of the tracks as a result of the project work.
The contractor called NTS to discuss shoring options for the project. In this area of Florida, this type of excavation would typically feature slide rail shoring or sheeting to provide positive soil support throughout the excavation process given the proximity to a roadway and the rail tracks. The fiber optic lines presented an issue that would require flexible placement along the site to ensure that the fiber optic lines weren’t damaged during excavation. The contractor elected to use steel sheeting with hydraulic bracing to shore the project, as the sheeting could be installed around the fiber optic lines, while wood lagging could be used to fill the associated gaps. Hydraulic bracing was chosen due to its strength and efficient installation process. If the contractor had elected to use welded in place beam walers, the contractor had estimated that process would have taken about a week to weld the beams. Using the hydraulic bracing, the contractor was able to install the sheeting and set the hydraulic bracing quickly to advance the project schedule.
The combination of sheeting and hydraulic bracing provided positive soil support throughout the excavation and helped to prevent any soil raveling that could have led to the road or train tracks being undermined.
The system was site specific engineered to ensure compliance and was presented to the rail authority as well as department of transportation beforehand for review and approval.
The contractor was extremely satisfied with the system’s performance and the time and cost savings its use generated.
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