for Highway Construction Page 182 of 715 SECTION 300 – BASES for Highway Construction Page 183 of 715 SECTION 301 – GRANULAR SUBBASE
301.01 Description.
Provide, place, and c onstruct 1 or more courses of granular subbase on a prepared subgrade.
301.02 Materials.
Provide materials as specified i n 703. The Engineer will accept granular subbase for quality requirements at the point of delivery. Use the following standard methods for tests: Compaction Standard for Coarse Granular Materials by Use of the Vibratory Spring- load Compactor .............................................................................................. Idaho IT 74 In-Place Density and Moisture Content of Soil and Soil Aggregate by Nuclear Methods (Shallow Depth) ................................................. AASHTO T 310 Method B Prepare and submit an Idah o IT 74 density curve for the subbase material to be incorporated into the work, before placing granular subbase on the roadway. This testing is incidental and a separate payment will not be made. RAP may be used in granular subbase when appr oved. Do not exceed a RAP size of 3 inches. The Engineer will visually verify the RAP daily, in place, to confirm the size requirement has been met.
301.03 Construction Requirements.
A.General. Do not exceed a maximum compacted thickness of 0.8 foot for each layer. Construct the subbase in 2 or more layers of approximate equal thickness if the required compacted thickness of the granular subbase layer exceeds 0.8 foot. The compacted thickness of a single layer of the subbase may be increased to 1 foot when vibrating or other approved types of special compacting equipment are used. The minimum compacted thickness of any course is 1.5 times the maximum particle size. Mix the subbase as specified in 303.03.A. After each layer has been spread, compact the layer for its full width. Continue compaction until at least 95 percent of the maximum dry density is attained as specified in 301.02. Determine the in- place density of granular subbase in accordance with AASHTO T 310 Method B. Maintain the surface of each layer during the compaction operations so a uniform texture is produced and the subbase is firmly keyed. Apply enough water uniformly over the base materials during compaction to ensure proper compaction is achieved.
B.Granular Subbase Material in Stockpile. Provide granular subbase material in stockpiles at designated locations. Stockpile as specified in 303.03.B.
C.Granular Subbase Material, Load, Haul, and Place. Lo ad, haul, and place designated stockpiled granular subbase material on the roadbed.
Source: Idaho Standard Specifications for Highway Construction, 2023 Edition. Pages 218–218 of 768.