b) Based on a DESA of 5.79E +06. a subgrade with a CBR of 3%, and the available
ID: 1712250 • Letter: B
Question
b) Based on a DESA of 5.79E +06. a subgrade with a CBR of 3%, and the available material as per table below a pavement engineer recommended the following design. Crushed Rock Quarry Rubble Waste CBR 90% 20% 10% Cost per m3 557 $41 $24 400 Material 500 600 700 800 900 t-(219-211(logCBR) 58ogCBR Design Traffic in ESA (DESA) 150mm Base 450mm Quarry Waste CBR 10% Due to the high costs, you are asked for a second opinion on the design. Please answer the following questions: (i) Is it a valid design for the given paramcters? ii) What would you recommend (no calculation needed)? (ii) What is the impact if your recommendation is adopted? (3.0 marks) (1.3 marks) (0.5 marks)Explanation / Answer
i) From the above design of 150 mm of the base and 450 mm of quarry waste, it is economical but at the same time, it should satisfy the minimum CBR of 10 or greater. so, it is economical and valid design.
ii) Otherwise, 300 mm of quarry waste, 150 mm of quarry rubble and 150 mm of crushed rock can be adopted which is higher cost than the previous one.
iii) The recommended one is more stronger than the given one, but it costs more.
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