LARIMER COUNTY RURAL AREA ROAD STANDARDS

Chapter 5 – Geotechnical Standards and Pavement DesignSection 5.4 Pavement Design Standards3. Mitigation Plans and Approval. All special problems found in soils investigation(e.g. expansion, frost, soluble sulfates, shallow bedrock, heave, groundwater,etc.) shall be addressed and mitigation procedure plans must be approved by theEngineer prior to use.5.4 PAVEMENT DESIGN STANDARDSPavement design procedures in this section provide for a 20 year service life of pavement whennormal maintenance is provided to keep roadway surface in an acceptable condition.5.4.1 General Design Factors5.4.1.1 Minimum ThicknessesTable 5-2 provides the minimum acceptable thicknesses for each component of thepavement section for each roadway classification. The pavement design shall bebased on actual subgrade support values and traffic projections for all newlyconstructed roads and maintenance overlays. However, in no case shall anycomponent of the designed pavement section be less than the minimum acceptablethickness outlined in Table 5-2.5.4.2 Special Considerations5.4.2.1 Staged ConstructionMinimum asphalt and aggregate base course thicknesses are given in Table 5-2.The staged construction design must include asphalt thickness for each proposedstage. Calculations, traffic numbers, and construction truck traffic numberssupporting the staged design must also be submitted and approved.5.4.2.2 Full Depth SectionsFull depth asphalt pavement sections will not typically be allowed but may beconsidered where depth of bedrock, drainage, and soil conditions are compatiblewith full-depth asphalt. They will only be allowed when approved by the Engineer.Full depth asphalt pavement sections will not be allowed on chemically treatedsubgrades with compressive strengths exceeding 160 psi.5.4.2.3 Rehabilitating Existing Asphalt RoadsPrior to overlaying existing asphalt, the Engineer may require testing to determinethe amount of overlay necessary to bring the road to current standards. All "potholes",cracking, and any other imperfections shall be repaired to the Engineer’ssatisfaction prior to overlaying.5.4.2.4 Auxiliary LanesAuxiliary lanes will be designed according to the classification of the adjacentroadway. The pavement design shall be based on actual subgrade support valuesand traffic projections for the through lane.Larimer County Rural Area Road Standards Page 5-4October 22, 2007