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Introduction
Development of the Maple Ridge Wind Farm required stability improvement to the subgrade of 26 miles of access roads to the locations of the farm’s wind turbines. A successful road design solution resulted following the installation of 463,000yds2 of geogrid.
Project site
The Maple Ridge Wind Farm near Lowville in upstate New York is the largest wind farm east of the Mississippi River. With more than 120 wind turbines, the Maple Ridge Wind Farm can produce approximately 240 megawatts (MW) online that provide electricity for about 60,000 residents. The wind turbines are 260ft tall with rotor blades that are 130ft long.
The American Wind Energy Association estimates that 1 MW of wind generation capacity is the equivalent of 1 mile2 of new forest in terms of offsetting or displacing carbon dioxide from conventional generating sources.
Challenges
Development of the Maple Ridge Wind Farm required the subgrade improvement of 26 miles of access roads leading to the wind turbine locations. The access roads needed to withstand constant and heavy traffic from concrete-mixer delivery trucks weighing approximately 50,000lbs., and also trucks hauling 800-ton cranes.
Design & Installation
First, a design analysis was completed by geotechnical specialist Martin Derby. This analysis contained 2 major components:
- calculating the California Bearing Ratio (CBR) or bearing capacity for each access road.
- determining the amount of aggregate material needed for a successful road design.
The CBR calculations required using soil boring information and estimating the numbers and weights of traffic loads. A 1.4 CBR was determined for an “average” road condition and 0.8 for a “worst case” condition. Once CBRs were calculated, Derby was able to determine the amount of aggregate material needed for both of those road conditions.
Derby’s analysis and design solution was conducted and presented within 24 hours of his site evaluation. The design solution also included installing geogrid, which required 14in. of NYSDOT Type 2 aggregate for “average” conditions and 22in. of aggregate for “worst case” conditions with extremely soft soils.
Construction
After a successful test run, the Maple Ridge Wind Farm implemented approximately 463,000yds2 of geogrid for the 26 miles of access roads. The project also included widening some roads from 16ft to 32ft and installing geogrid under crane platforms. The installation was a successful solution that allowed the site to improve the bearing capacity of the soils, reduce the amount of aggregate needed to stabilize the soils underlying the tower access roads, and provide ease of construction.
Similar plans are typically used for roadways, haul roads, rail yards, runways, construction platforms, and parking lots to increase structural capacity, extend pavement life, and improve pavement durability. This system combines geogrid with crushed aggregate or granular fill to improve subgrade and base course performance, all with less undercutting and lower material costs. The result is more durable and cost-efficient pavement.