Tunneling

Tunneling Construction Is Underway 

While most of the South Hillsborough Pipeline is being built by open-trench construction, about two of the project’s 26 miles are being built by tunneling construction, which allows crews to install pipe underneath roadways and waterways to minimize impact to traffic and the environment.   

Tunneling is occurring at 17 locations along South Hillsborough Pipeline route (see map): 

  1. On site at the Tampa Regional Water Treatment Plant 
  2. Falkenburg Road near Woodberry Road 
  3. Lakewood Drive at Woodberry and Limona roads 
  4. CSX railroad crossing at Limona Road 
  5. Brandon Boulevard at Moon Avenue 
  6. Lumsden Road at South Parsons Avenue and John Moore Road 
  7. Bloomingdale Avenue at South Kings Avenue  
  8. Alafia River (4142 Alafia Boulevard to 7202 Alafia Ridge Road) 
  9. McMullen Road near Boyette Road 
  10. Bell Creek and Bell Shoals Road 
  11. Fishhawk Creek (next to Fishhawk Boulevard) 
  12. Little Fishhawk Creek 
  13. Fishhawk Boulevard near the Fishhawk Sports Complex 
  14. Boyette Road near Hammock Crest 
  15. Boyette Road between Karlson Oak Lane and Forest Fern Drive 
  16. Boyette Road at Trails End Lane 
  17. Balm Boyette Road 
 
Two different trenchless construction techniques are being used for the South Hillsborough Pipeline: microtunneling and horizontal directional drilling. 

Microtunneling 

Microtunneling involves using a remote-controlled microtunnel boring machine to excavate a tunnel while simultaneously installing segments of  steel-casing pipe that are welded together.  

Two vertical shafts are excavated: the launch shaft at the entry point where the microtunnel boring machine and pipe are lowered, and the reception shaft where the microtunnel boring machine is retrieved after boring through the ground to create the tunnel. The machine is lowered into the entry shaft and bores a tunnel using a pressurized slurry system to remove excavated materials, or spoils, and maintain the integrity of the tunnel. As the machine advances, it simultaneously excavates and pushes pipe segments from the launch shaft. At the end of each pipe push, a new pipe segment is connected and the process repeats until the pipe string is completely installed. 

This construction technique is frequently used in congested corridors, under railroads or near buildings. 

Horizontal Directional Drilling (HDD) 

Horizontal directional drilling HDD is a steerable trenchless method that installs pipe along a controlled curved path between two surface points. It involves excavating a pit on either side of the tunnel location and drilling from entry point to exit point. The machine drills a pilot hole from the entry pit to the exit pit and then reams the tunnel to the desired diameter using increasingly larger drill bits before finally pulling the pipe back through the enlarged hole.  

During this process, the entire length of pipe must be laid out along the ground, fused together, and then pulled continuously through the tunnel until it is fully installed.