# Geosynthetic Reinforced Steep Slopes: Current Technology in the United States
## Appendix A  
**Case Study #1: Yeager Airport Runway Location:**: Charleston, West Virginia  
**Owner:**: Yeager Airport  
**Engineer: Triad Engineering  
**Contractor:**: Cast & Baker  
**Purpose:**: Support Structure for Airport Runway  
**Geosynthetic Material:**:  
* Reinforcement: Polyester Geogrid (12.9 kN/m & 18.6 kN/m)
* Facing: Polypropylene Mesh
* Drainage: Polypropylene Geotextile  
**Foundation & Embankment Soil:**: The onsite geomorphology consisted of weathered sandstone underlain by sandstone and some shale. Testing of the weathered sandstone soil showed it to have a maximum dry density of 2034 kg/m\({}^{3}\) and a peak friction angle of 39\({}^{\circ}\). The compressive strength of the rock foundation varied from 30 MPa to 95 MPa. **Slope Height:**: 73.8 m  
**Slope Angle:**: 1H:1V  
**Design Method:**: Limit Equilibrium Analysis  
**Construction Sequence:**:  
* The existing ground was excavated to the required level to provide a stable platform for the reinforced slope. * The geogrids were installed as horizontal reinforcing elements into the slope in conjunction with the backfill material. * Embedment lengths of the geogrid were on the order of 59.4 m in length. * A drainage composite was installed along the back of the excavation to intercept and drain seepage water from the existing mountain side away from the reinforced mass. * Mesh was installed on the face of the slope at 0.6 m vertical intervals, with 0.9 m embedded into the slope face and 0.76 m down the face for facial stability and erosion protection. **Performance:**: The reinforced slope was successfully completed and is performing as expected. Geogrids provided the high strengths required for a structure of this size, and the mesh allowed for facing stability and quick germination of surficial vegetation for improved stability. **Cost Effectiveness:**: Construction options for extending the runway past the existing hillside included evaluation of bridge structures, retaining walls, and reinforced slopes. Engineering evaluation indicated the reinforced slope provided the most cost effective and easiest constructed option of the structures considered. **Case Study #2: Reinforced Slope Failure & Reconstruction**  
**Location:**: Hondo Valley, New Mexico  
**Owner:**: New Mexico Department of Transportation  
**Engineer:**: [PERSON]  
**Contractor:**: Sierra Blanca Constructors  
**Purpose:**: Support Structure for Roadway  
**Geosynthetic Material:**  
* Reinforcement: Geogrid  
**Slope Height:**: 7.6 m  
**Slope Angle:**: 1H:2V  
**Construction Specifications:**: New Mexico DOT  
**Construction Sequence:**  
* The geotechnical investigation consisted of drilling two soil borings adjacent to the deepest parts of the roadway fill. The investigation indicated that the geology in the area was terrace deposits and alluvium overlying Yeso formation mudstone. * Groundwater was not encountered in the borings drilled at the site, and no signs of slope instability were noted during the site reconnaissance. * A major geotechnical slope failure occurred a year after construction due to movement associated with severe rain storms. The project team excavated a test trench through the roadway to evaluate the conditions at the cracked area, and noted vertical cracks observed at the surface were about 5.1 cm deep and were located directly behind the top layer of geogrid. * Additional field exploration activities began as the team drilled seven additional borings below the roadway. The borings were used to establish a detailed stratigraphic log of the subsurface conditions at the GRSS and to collect soil samples for laboratory testing. * The maximum cumulative displacement measured at the top of the inclinometers was approximately 8.9 cm, and a clear failure surface was apparent just beneath the bottom geogrid. * The analysis concluded that the distress was the result of peak flows and saturation during heavy and prolonged rainfall that developed excess water pressure at the rear of the slope.