Maccaferri Ringnet Attenuator

The 'Road to Hana' is one of the most winding roads in the Nation. Yet each day thousands of locals and tourists drive this 65 mile stretch of highway that includes over 620 curves and 59 narrow, one-lane bridges. Very steep slopes, often saturated with tropical rain and lush jungle vegetation provide optimal conditions for rockfall. This beautiful and scenic road that threads between the ocean cliffs and hugs the steep mountainsides requires constant vigilance and more than routine maintenance to keep everyone safe. In 2024 when large rocks fell and damages the roadway and guardrails, the Hawaii DOT called on Maccaferri to support the rockfall mitigation design efforts and local Rousseau Services to install the rockfall infrastructure. .

The geology along the Hana Highway near mile marker 10 consists of primarily of basalt bedded between tuff or ash layers. The basalt layers resist weathering, but are often undercut when the weaker tuff erodes. There is no freeze/thaw cycle in Hawaii, but root jacking and frequent, heavy, tropical rain provides constant erosive forces to the slopes adjacent to the highway. The solution chosen by the Hawaii DOT is threefold; first, the predominant basalt layer near the highway was bolted and pinned in place with a stainless steel Maccaferri HEA Cable Net. This 1/2-inch diameter cable net will support and hold in place the thick basalt layer despite erosive undercutting of the tuff. For the rocks that were identified to have detached and fell from hundreds of feet above the highway, a ringnet attenuator was designed with 14-feet high posts for capturing the rolling and bouncing rocks. Heavy Maccaferri ringnets provide the catchment to reduce the velocity and energy of these falling rocks, and the 2,000 kJ post and cable will support the barrier infrastructure and withstand the climbing vines and mass of vegetation for years. The final design requirement was that the toe of the attenuator be pinned to the slope because there is no shoulder or catchment ditch. At best the Hana Highway is considered a two lane highway, but in many places it is realistically 1.5 lanes wide, and it is constantly reduced even further at the 1-lane bridges. A secondary layer of Maccaferri HEA cable nets is loosely secured with three sets of energy dissipation 'brakes' to retain any blocks that are caught by the attenuator system. Because of the strength of the HEA panels and 3/4-inch support cables, these blocks will remain safely suspended above the highway traffic until maintenance workers are able to close the road and remove the material.

Maccaferri has the experience, employees, and manufacturing to provide design assistance, nearly 100,000 sqft of powder coated ringnets, 30,000 sqft of HEA cable nets, and custom 22 posts to Hawaii DOT. With our distribution partner, Geotech Solutions, over 650 linear feet of this custom rockfall attenuator was installed by Rousseau Services. Another example of truly engineering a better solution for the people of Maui!