River Gorge Drive at Black Creek

Roller-Compacted Concrete Utilized for a Two-Mile Public Extension Mountain Road

River Gorge Drive, a two-mile public road extension, was the first public road in Chattanooga, TN, to utilize roller-compacted concrete for a roadway surface. LaBella served as the prime consultant for the design and permitting of this boulevard-style mountain road, which extends from the intersection of River Gorge Drive and Alston Drive to the top of Aetna Mountain.

The boulevard-style approach was the most cost-effective method to facilitate access in the event that one lane is blocked as well as to provide access for emergency vehicles. The road has two 17-foot-wide travel ways to support dedicated bidirectional traffic and bike lanes. To traverse the mountain side and achieve the 1000-foot rise in elevation, the road was constructed at a 14-percent grade with sections of 4-percent roadway every 1000 feet to provide relief.

Due to the terrain, LaBella’s geotechnical team was integral in designing and permitting several earth-retaining systems that were cost effective and environmentally sensitive to the mountainous terrain. Reinforced soil slopes were designed and installed to prevent erosion and stabilize the upland slope. Design modifications were made quickly during construction as stability issues and groundwater seeps were encountered. Upwards of 300,000 cubic yards of material has been moved for this roadway project. About 200,000 cubic yards were transported to another project within the Black Creek community called The Garrison. The remaining material was used at the top of the mountain in Phase 13 and exchanged with the neighboring quarry for material used to form rock slopes for additional stabilization.

The roadway was completed in October 2021, allowing access to develop 1,200 future residential lots.

Utility Expansion

Public Roadway Allowed for the Extension of Public Utilities

The creation of the public roadway allowed for the extension of public utilities, including water, wastewater, gas, power, and communication. LaBella was responsible for the permitting of the public sewer extension with Hamilton County. This sewer extension is noteworthy due to the elevation and energy change from top to bottom. At one point, harnessing the elevation change as a mechanism for power output was considered. However, after careful consideration, the authorities having jurisdiction opted not to move forward with this approach. The installed sewer extension is comprised of redundant dual-force, low-pressure, welded high-density polyethylene sewer mains running underneath the roadway.

LaBella also worked with Tennessee American Water to design a welded steel watermain at 650 psi to boost pressure from the bottom of the mountain to the water tank at the top.