Strengthening a New Mexico subgrade

Jan. 14, 2015

The New Mexico State Highway and Transportation Department’s reconstruction of 118 miles (190 km) of four-lane highway along a northwestern route was challenged with a construction timetable of just two years and a construction season limited by cold Rocky Mountain winter weather.

With time pressures, extremely soft subgrade conditions, relatively shallow underground utility lines running under the highway and a need to tie into the existing elevations of sidewalks and parking lots of businesses adjacent to the highway, design engineers were faced with a challenge. They were unable to proceed on a timely basis with any of the three conventional alternatives:
• Excavating deep deposits of saturated soils and replacing them with more stable materials,
• Thickening the base and sub-base structural section to a higher elevation in order to bridge the soft subgrade, or
• Strengthening the limited structural sections with conventional chemical stabilizers or other geotextile/geogrid type products.

The Geoweb geocell system was offered as a solution to meet project requirements. Geocells are three-dimensional geosynthetic structures that provide strength to soils through confinement. This confinement technology has a proven record of providing an easily deployed stiffened flexural beam for bridging extremely soft subgrade conditions.  Geocells can also typically reduce the cross-section depth by 50%.

The Geoweb system was integrated as a reinforced base layer under the asphalt pavement to solve the soft subgrade problem that threatened to stop paving operations with just a half-mile of highway to complete. Because the cellular system is functional with either clean sand or aggregate infill materials, designers selected a locally available low-cost source of free-draining sand for placement within the 6-in.-deep cell structure. The system was deployed over a geotextile to protect the sand infill from subgrade contamination.

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