As the Skyline rail transit project continues its eastward expansion toward Honolulu’s urban core, contractors are working to relocate above-ground electrical utility lines along Kapalama Canal underground via a process known as microtunneling.

The utility lines are being moved to make way for future guideway construction.

Microtunneling is a trenchless construction method is typically used to build utility tunnels across physical barriers like waterways.

According to the Honolulu Authority for Rapid Transportation, a crew excavated a 30x30-foot entrance pit (called a jacking pit) on Kokea Street and is pushing pipes through the tunnels under and across the canal to the other side on Kohou Street and into a receiving pit. 

To push the pipes from the jacking pit to the receiving pit, a tunnel boring machine and steering can are placed at the front of the tunnel’s entrance point, pipes are positioned behind the boring machine, and then a hydraulic press pushes the machinery and pipes through. 

The tunnel boring machine is equipped with a slurry machine and cutting head to excavate the soil, which is then passed through a cutting chamber and transported to a separation plant, where liquid and solid components are divided. The liquid is then recycled back into the TBM’s closed-circuit system. 

To date, two out of three planned tunnels have been excavated. The operation is expected to be completed next month, according to HART.

Michael Tsai covers local and state politics for Spectrum News Hawaii. He can be reached at michael.tsai@charter.com.