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5.3.1. Select fill shall consist of well-graded native soils consisting of silty sands and gravels obtained from borrow or from the excavations. Select fills shall be free of topsoil, organic material, debris, and other deleterious material. Occasional gravels and cobbles no larger than three inches (3") in size and no greater than twenty percent (20%) for cobble sizes larger than two inches (2") by weight will be allowed. Select fill shall have a minimum of 25 percent by weight passing the #100 sieve. 5.3.2. Select fill materials shall be selected from the borrow and trench excavations for certain charac- teristics such as high density, high strength and low compressibility. If sufficient quantities of select fill are not found locally as native soils, Engineer may require that the Contractor use processed material or Aggregate Base Course material. 5.4. CULVERT MATERIAL 5.4.1. All culverts and associated assemblies shall be fabricated in accordance with AASHTO M218 specification and ASTM A 444. 5.4.2. All culverts shall have a minimum wall thickness of 14 gage 5.4.3. All couplings shall include "O"-ring style gaskets. 5.4.4. All culverts larger than 18-inch diameter shall be arched sections with equivalent diameters shown on the Drawings. 5.5. RIPRAP BEDDING 5.5.1. Riprap Bedding shall have a minimum size of No. 200 sieve, and shall generally conform to the gradation limits listed in the following table. The Engineer may approve deviation from these gradation limits when an on-site material is close to these limits and otherwise proves to be suitable for bedding. Percent Passing Sieve Size by Weight 3-inch 90-100 3/4-inch 20- 90 No. 4 0- 20 No. 100 0- 10 5.6. RIPRAP 5.6.1. Riprap shall be used to provide erosion protection at culvert discharge aprons, designated slopes, and in storm water channels as shown on the Drawings or to replace existing riprap that is disturbed by construction. 5.6.2. Riprap shall be obtained from Area D. 5.6.3. Riprap shall consist of reasonably well graded, hard and durable, angular rock. Excessively flat, slabby, or overly elongated pieces will not be acceptable. 5.6.4. The medium riprap size (D50) shall be 6-inch unless otherwise designated on the Drawings. The minimum rock fragment size shall be 1-inch, and the maximum size shall be approximately 1.75 times the D50 size. The following table lists the approximate riprap gradation limits. Riprap - D50 Size Percent Smaller by Weight Rock Size 9-inch 6-inch 15-inch 70-100 100 12-inch 50-70 70-100 9-inch 35-50 50-70 SPECIFICATION A EARTHWORK PAGE3