LARIMER COUNTY RURAL AREA ROAD STANDARDS

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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 <strong>STANDARDS</strong>Pavement 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
Chapter 5 – Geotechnical Standards and Pavement DesignSection 5.5 Flexible Pavement Design<strong>ROAD</strong>CLASSIFICATIONTable 5-2Flexible Pavement Design StandardsServiceabilityIndex (psi)MinimumDesignESAL (S i = 4.5)ESAL 2S tFinalD(psi)Reliability(%)AggregateBaseThickness –(Class 5 or 6) HMA 1(Minimumthickness)Layer, inches(Minimumthickness)Layer,inchesLOCAL- Residential two lane 36,500 2.0 2.5 70 6 3COLLECTOR- Minor 182,500 2.3 2.2 75 6 3.5- Major 365,000 2.3 2.2 85 6 4ARTERIAL- Two Lane 730,000 2.5 2.0 90 7 5- Four Lane 1,460,000 2.5 2.0 90 8 61 Wearing surface course shall be Grading S or SX for residential roadway classification and Grading S for collectorsand arterials.Full depth pavements without a base course layer are not typically allowed and may only be used with writtenapproval from the Engineer.CDOT Grading SG can be incorporated into the pavement design but not as a wearing course.Min/Max lift thicknesses: Grade SX – 1 ½”/2 ½”, Grade S – 2”/3 ½”, Grade SG – 3”/5”2 ESAL shall be calculated based on projected traffic uses. Minimum ESAL values are as given. The Engineer mayrequire greater ESAL values if warranted.5.5 FLEXIBLE PAVEMENT DESIGN5.5.1 DefinitionFlexible pavements are those pavements which have sufficiently low bending resistanceto maintain continuous contact with the underlying structure, yet have sufficient stabilityto support a given traffic loading condition.5.5.2 AASHTO Design ApproachAll pavement designs shall be prepared in accordance with AASHTO and CDOTPavement Design Procedures. Computer generated printouts and/or other designcalculations must be included with the design submittal.The following procedure should be used in determining the structural number andthickness of the pavement being designed:Larimer County Rural Area Road Standards Page 5-5October 22, 2007
Page 1 and 2: LARIMER COUNTYRURAL AREA ROAD STAND
Page 3 and 4: Table of Contents3.3.11 Typical Str
Page 5 and 6: Table of ContentsCHAPTER 8 - ENVIRO
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Page 9 and 10: Table of ContentsG.7.12 Other Permi
Page 11 and 12: Chapter 1 - General InformationSect
Page 17 and 18: Chapter 2 - Submittal ProceduresSec
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Page 21 and 22: Chapter 3 - Submittal Requirements
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Page 49 and 50: Chapter 6 - STORMWATER MANAGEMENTSe
Page 51 and 52: Chapter 7 - Bridges and Major Drain
Page 53 and 54: Chapter 8 - Environmental and Agric
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Appendix A - Definitions and Abbrev
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Appendix A - Definitions and Abbrev
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APPENDIX B - REFERENCES AND RESOURC
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APPENDIX D - CONSTRUCTION STANDARDS
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Appendix D - Construction Standards
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APPENDIX E - CONSTRUCTION TESTING F
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Appendix F - Guidelines for Traffic
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APPENDIX G - DESIGN AND CONSTRUCTIO
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Appendix G - Design and Constructio
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Appendix H - General NotesSection H
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APPENDIX I - VARIANCE REQUEST SUBMI
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LARIMER COUNTY RURAL AREA ROAD STANDARDS

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