Aashto method, Civil Engineering

Question 1: A stationary 40 kN single axle load (applied on a circular contact area of radius = 152 mm = 6") is applied to each of the flexible pavement structures indicated below. Assuming linear elastic behaviour and no edge effects, use KENLAYER to determine for the two pavement systems given below:

a.  total maximum surface deflection of the pavement system;

b.  horizontal strain at the bottom of the HMA layer; and,

c.  vertical stress on the top of the subgrade.

Pavement systems:

i)  150 mm of HMA with 3,500 MPa modulus; placed directly on a sandy subgrade with 75 MPa modulus.

ii)  75 mm of HMA with 3,900 MPa; 200 mm of granular base with 150 MPa modulus; and clay subgrade with 40 MPa modulus.

2.) Assuming the HMA is the Asphalt Institute "standard mix", use both the Asphalt Institute and Shell methods (at 95% reliability) to predict the failure mode by either fatigue or rutting, and estimate the limiting number of load repetitions to achieve this failure mode for the two pavement systems described in Problem 1.

3.) Using the AASHTO method, design a flexible pavement system consisting of HMA and granular base placed on the subgrade described in Table 3.1 below, for the following conditions:

5-year predicted design traffic = W18 = 1.5(106) ESAL pt=1.8;R=95%;S0=0.35 Granular base modulus, E2 = K1-K2, where K1 = 7000 and K2 = 0.6 Base is expected to be exposed to moisture levels approaching saturation for 2% of the time.

Question 2:

Design a flexible pavement overlay using the AASHTO method for a 5-year old pavement structure consisting of 5.75 inches of HMA and 23 inches of granular base, placed on a silty clayey sand subgrade. The future traffic to be sustained over the next five years will be 2.1(106) ESAL.     Deflection testing conducted in October at a temperature of 68°F, using a load of 18 kips, provided a mean surface deflection of 0.191349 inches centred under the 5.9-inch radius loading plate and 0.022955 inches at a distance of 48 inches from the centre of the loading plate. Assume m2 = 1.10 due to contamination of the granular base with fines. Use p1 = 4.2, pt= 1.5, R=95% reliability and assume a standard deviation of 0.49.

Question 3: 

a)Using the PCA method, design the minimum slab thickness (to the nearest 1⁄2 inch) required for a 4-lane divided major highway (2 lanes in each direction separated by a grass median). Design a rigid concrete pavement with doweled joints and with concrete shoulders to be placed on a 9-inch thick untreated granular subbase which overlays a clay subgrade having a k-value of 100 pci. Modulus of rupture for the concrete is 650 psi. Design period = 20 years; current ADT is 13,500; annual growth rate is 3.5%; and ADTT = 20%.

b)Design the welded wire mesh reinforcement, tie bars, dowels and joints, and shoulders required if this pavement is to be a jointed reinforced concrete pavement with a lane width of 12 ft. Use a maximum allowable joint opening of 0.25 inches for a doweled joint.

Posted Date: 2/21/2013 5:22:06 AM | Location : United States

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