4. (10 points) Your firm has been contracted to design a road that will provide occasional access to a vehicle with a maximum single axle load of 22,600 lbf (11,300 Ibf per wheel) with 100 psi tire pressure. Site investigations indicate the existing subgrade is a clayey soil that will have a modulus as low as 3000 psi during the wet part of the year. Under these conditions, laboratory tests have determined that the subgrade cannot tolerate vertical stresses greater than 10 psi without incurring high permanent deformation (rutting). Using two layer theory, you are to consider one of two possible designs: · Crushed rock (Ex= 40,000 psi) with a thin bituminous seal coat surface to make the pavement impermeable. The cost of the crushed rock is $10.00 per ton (unit weight = 120 lb/ft) and the cost of the seal coat may be considered negligible for your analysis. Asphalt concrete (Exc-200,000 psi) at a cost of $50.00 per ton (unit weight = 145 lb ft) · Deermine whiceh of te wo ops wou he mosteconomical.
First option is more economical. Crushed rock is an inexpensive material. Cheaply available. An asphalt driveway will require more regular maintenance. It requires re- sealing every 3 years or so. Low end sealants cost around $5 for a five gallon bucket and cover around 40o square feet of asphalt. High end sealants can cost upwards of $20 per bucket. But a crack on a crushed rock pavement will cost less for the repair. More material and equipments and more manpower is required for asphalt pavement. Asphalt roads cannot last for long. Asphalt driveways need solid foundations prepared by experts. Asphalt will shrinks and expands with temperature changes and leads to high maintenance cost. Initial cost $2 to $5 per square foot of driveway. Overall we came to know crushed rock is more economical
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