(A) Pavement structure. The design of pavement structures shall conform to the Guide for Design of Pavement Structures. The pavement design report shall be prepared and signed by, or shall be under the supervision of, a professional engineer.
(B) Length of service life. Pavement shall be designed for a 20-year service life.
(C) Serviceability. The “serviceability” of a pavement is defined as the pavement’s ride quality and its ability to serve the type of traffic (e.g., automobiles and trucks) that uses the facility. The initial serviceability index (p0) for flexible pavements shall be 4.2; for rigid pavements, it shall be 4.5. The minimum terminal serviceability index (Pt) for local streets shall be 2.0; for collectors and arterials, it shall be 2.5. A standard deviation (S0) for flexible pavement shall be 0.45; for rigid pavement, it shall be 0.35.
(D) Roadbed soil.
(1) A soil investigation must be performed for the design of pavement structures. The number of borings and locations shall be sufficient to accurately determine the stratum along the route. Any existing soil information that is available either from the city or from private sources will be evaluated and, if determined to be applicable and valid, will be allowed in place of new soil tests.
(2) Roadbed soil having a plasticity index (PI) greater than 20 shall be treated with lime to reduce the PI below 20. Application rate of lime shall be determined based on laboratory testing. In no case shall the lime be less than 15 pounds per square yard for six inches of lime-treated subgrade. Lime-treated subgrade will be included as a “structural layer” within the pavement design calculations. Proposals for stabilization alternatives in place of the use of lime will be considered upon submittal of an engineering report verifying adequate stabilization of the highly plastic soil.
(3) Where the roadbed is in a rock excavation, a “structural layer” within the pavement design calculations can be used that is equivalent to a structural layer for lime-stabilized subgrade. If a roadbed structural layer is used in the pavement calculation for rock subgrade, an engineering report will be provided to public works addressing the consistency of the subgrade prior to base placement.
(E) Pavement layer material. The combination of the following materials are permitted for the pavement structure:
(1) Lime treatment for subgrade;
(2) Flexible base;
(3) Prime coat;
(4) Tack coat;
(5) Hot-mix asphaltic concrete pavement;
(6) Asphalt-treated base;
(7) Reinforced concrete; and
(8) Base reinforcement (Geogrids).
(F) Minimum layer thickness (compacted). If the following components are utilized in proposed pavement sections, the minimum thickness for the components shall be the following:
(1) Hot-mix asphaltic concrete pavement shall not be less than one and one-half inches thick for surface course;
(2) Hot-mix asphaltic concrete pavement shall not be less than two and one-half inches thick for a leveling-up course;
(3) Asphalt-treated base shall not be less than four inches thick;
(4) Flexible base shall not be less than six inches thick; and
(5) Lime treatment for subgrade shall not be less than six inches thick.
(Ord. 3020, passed 9-10-2013, § 5.23.10)