5837-8 - 2 = m 3 = 0.9 Procedure for determining...

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Flexible Pavement Design Example The reliability level to be used is based on the functional classification of the pavement Solution using nomograph Nomograph Solution (continued) Selection of Layer Thicknesses Minimum Recommended Thicknesses for Surface and Base Layers
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Chart for estimation of a 1 for asphalt concrete Chart for estimation of base layer coefficient (a 2 ) based on strength parameters Chart for estimation of subbase layer coefficient (a 3 ) based on strength parameters Recommended m i values for modifying layer coefficients of untreated base and subbase materials Assume that the following pavement materials are to be used: • Asphalt concrete: E AC = 400,000 psi, a 1 = 0.42 • Granular base: E BS = 30,000 psi, a 2 =0.14 • Granular subbase: E SB = 11,000 psi, a 3 = 0.08 • Assume drainage coefficients, m
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Unformatted text preview: 2 = m 3 = 0.9 Procedure for determining thicknesses of layers using a layered analysis approach Determine the required SN1 and SN2 (using the elastic modulus of the base and subbase as subgrade modulus) Computation of layer thicknesses SN 1 = 2.7 D* 1 = SN 1 /a 1 = 2.7 / 0.42 = 6.4 inches Use D* 1 = 7 inches SN* 1 = 0.42 X 7 = 2.94 SN 2 = 3.8 D* 2 = (SN 2 – SN* 1 ) / m 2 a 2 = (3.8 – 2.94) / (0.9 X 0.14) = 6.8 inches Use D* 2 = 7 inches SN* 2 = 0.14 X 7 X 0.9 = 0.88 Computation of required subbase thickness: SN 3 =5 D* 3 = (SN 3 – SN* 1- SN* 2 )/ (m 3 a 3 ) = (5 – 2.94 –0.88) / ( 0.9 X 0.08) = 16.4 inches Use D* 3 = 17 inches Summary of Design Asphalt Concrete 7 inches Granular Base 7 inches Granular Subbase 17 inches...
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5837-8 - 2 = m 3 = 0.9 Procedure for determining...

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