Powerful Solutions: A Trashy Story

10.2.17

When one thinks of Merrill Field Airport (MRI), images of small planes taking off against a picturesque backdrop of mountains and endless sun come to mind. What likely doesn’t come to mind? Trash…tons of it. Forty-two percent of MRI is built over an old Municipality of Anchorage landfill, closed in 1987. The trash is causing problems for aircraft safety. CRW’s team solved the issues posed by the trash when they designed upgrades to Taxiway Q.

 


Trash from an old landfill under Taxiway Q. 


Phases 5 and 6 of the Taxiway Q Reconstruction project improved the transportation corridor used by private small planes, the associated parking apron, and the medevac route with direct access to Alaska Regional Hospital. The trash beneath the airport is settling at different rates, causing the taxiways and parking aprons to look like a roller-coaster, with up to three-foot swells, making it impossible to traverse comfortably at high speeds, particularly an issue for flights headed towards the hospital. The uneven pavement also led to intense ponding, which attracted birds. As one may imagine, birds and planes do not mix well, so eliminating features that attract birds was high in the project’s priorities.


Bumps, dips, and significant ponding on Taxiway Q before reconstruction. 

CRW solved the differential settlement of the trash problem by using dynamic compaction. This technique drops a large amount of weight over and over on undesirable soil. In this case, that meant dropping 16 tons 12 times on every inch of soil in the Taxiway area in a systematic, grid-manner. The dynamic compaction creates 4 to 5 feet of visual settlement, with compaction results up to 25 feet below the surface. Upon completion, the soil is a stable base for the pavement that is not likely to develop bumps or ponds in the coming years. As the Phase 5 construction (completed in 2016) demonstrated, the smooth, flat result is appreciated by all users. The trash is still there, but it is no longer a source of problems. 

 

CRW Project Engineer Erica Jensen, PE overseeing dynamic compaction.