5-8 Section 505
505-1 Description
Construct aggregate subgrades in accordance with the contract. Install geotextile for subgrade stabilization and place Class IV subgrade stabilization at locations shown i n the plans and as directed by the Engineer . Undercut natural soil materials if necessary to construct aggregate subgrades. Define “subsoil” as the portion of the roadbed below the Class IV subgrade stabilization. For Type 2 aggregate subgrades, undercut subsoil as needed. The types of aggregate subgrades with thickness and compaction requirements for each are as shown below. Type 1 – A 6 to 24 inch thick aggregate subgrade with Class IV subgrade stabilization compacted to 92% of AASHTO T 180 as modified by the Department or to the highest density that can be reasonably obtained. Type 2 – An 8 inch thick aggregate subgrade on a proof rolled subsoil with Class IV subgrade stabilization compacted to 97% of AASHTO T 180 as modified by the Department.
505-2 Mater Ials
Refer to Division 10. Item Section Geotextile for Subgrade Stabilization, Type 5a 1056 Select Material, Class IV 1016 Use Class IV select material for Class IV subgrade stabilization .
505-3 Construction Methods
When shallow undercut is required to construct aggregate subgrades, undercut 6 inches to 24 inches as shown on the plans or as directed by the Engineer . For Type 2 aggregate subgrades, proof roll subsoil in accordance with Section 260 before installing geotextile for subgrade stabilization. Perform undercut excavation in accordance with Section 225. Do not leave geotextiles exposed for more than 7 days before covering geotextiles with Class IV subgrade stabilization (standard size no. ABC). Install geotextile for subgrade stabilization on subsoil with the long dimension, i.e., machine direction (MD), of the roll parallel to the roadway centerline and completely cover subsoil with geotextiles. For fill sections, the minimum roll width is required under roadway edges and shoulders adjacent to fill slopes as shown in the plans. Overlap adjacent geotextiles at least 18 inches in the direction that AB C will be placed to prevent lifting the edge of the top geotextile. Pull geotextiles taut so they are in tension and free of kinks, folds, wrinkles or creases. Hold geotextiles in place as needed with wire staples or anchor pins. Do not operate heavy e quipment on geotextiles until geotextiles are covered with Class IV subgrade stabilization (standard size no. ABC) . Replace any damaged geotextiles to the satisfaction of the Engineer . Place Class IV subgrade stabilization (standard size no. ABC) by end dumping ABC on geotextile s. Compact ABC as required for the type of aggregate subgrade constructed. Maintain Class IV subgrade stabilization in an acceptable condition and minimize the use of heavy equipment on ABC in order to avoid damaging aggregate subgrades. Provide and maintain drainage ditches and drains as required to prevent entrapping water in aggregate subgrades.