Question

highway engineering

Q2: Truck A has two single axles. One axle weighs 12,000 lb and the other weighs 23,000 lb. Truck B has an 8000-1b single axle and a 43,000-1b tandem axle. On a flexible pavement with 3-inch hot-mix asphalt (HMA) wearing surface (a1 +0.44), 6-inch granular base (a2 = 0.2), and 8-inch crushed stone subbase (a3 = 0.11), which truck will cause more pavement damage? (Assume drainage coefficients are 1.0.)

Answer 1

Given data: Di= 3 in wearing surface gramular base crushed stone subbase D2 = 6 in Dz= 8 in 0.44, A2= a, 0.2, az = 0.11 for single We know that ; structural number (SN) = a, D + O₂ D M H M ₂ D3 M3 MI = M2 = M3=1.0 So, SN= (0.44x 3) + (0.286) + (0.1188) SN- Now, equivalenty foctors for flexible pavements axles: For Fruck: Equivaleney factor for 12 kips Axle lood 4 SN 3 0.229 [from table] Equivaleny factor fon 12 kips axle lood and SN 4 0.213 [ from table Now equivalency factor for 12 kips and 3.4 SN : 0.229+ (0.229-0-213) (3.4-3) (4-3) O. 2226 similarly for za Kips axle Load - Equivalency factor from table For 3 SN 4 SN 2.17 2.09

Now, for SN 3.4 the equivalency factor for 29.Kips 2.17 - (2.17 -2.09) x (3.4-3) 4-9 2.138. For 24 Kips axle load; 3 SN 4SN For SN 3.4 3.09 - 3.09 2.89 (3.09-2.89) (3.4-3) 4-3 SN 3.4 X 23-22 3.01 Now We have; 22 kips - EF - 2.138 24 kips SN 3.60 E.F=3.01 For 23 kips : 2.138 + (3.01 - 2.138) 24-22 2.574 Total ESALA 0.2226 +2.574 2.766. for Truck B: Equivalency factor for 8 kips! → SNB I 0.051 SN4 - 0.041 SN3.4 = 0.051- (0.061-0.041 x (5.4-3) 2-3 » 0.047 Equivalency factor for 42 kips ! SNA For SN 3.4 2.49 - (2.49-2:43 x (3.4-3) 4-3 2.466 2.49 ; SNY 2.43

SNB For SN3.4 For Axle load 44 kips: - 2.99 SN 4 2.88 2.99- (2.99-2.88) x (3.4-3) 4-3 2.946 Now for 43 kips: 42 2.466 2.946 43 = 2.466+ (2.946--2.466) x (43-42) 44-42 - 44 2.706 Total ESALBE 0.047 +2.706 2.7530 so, from above calculation; ESAREA > ESALB Hence, Truck A will causes more damage.