Question

5. How can you reduce the quantity of granular materials for construction of pavements to be constructed on marine clay deposits in coastal areas of Australia?

6. You may notice some distresses in bituminous pavements in your local suburb. Include the site photographs of at least 2 types of distress, and explain their possible causes.

Answer 1

5.the Marine Clay deposits in the coastal areas are fine grained which have capability to retain water. Coming in contact with the high stream of coastal water, it may liquify and cause reduction in strengh & stiffness.so excessive settlement may take place due to low bearing capacity. Various techniques are available based on cement and lime to improve the compaction properties and CBR value. On the other hand, marine clay has high moisture content with high liquid limit. Lime and cement treated marine clay result in good behaviour of strength of soil. Chemical Stabilizer are also available like Polyurethene in optimum percentage to marine clay sample to achieve the maximum value of strength.

To reduce the thinkness of Base and Subbase granular material. Here cementitious material like OPC and some percentage of fly ash. Resulting mix will have higher compressive strength. This will provide a firm subgrade. Hence it will reduce the thickness of granular layer.

6. Type of distress and its causes:-

Aligator or Fatigue distress- This type of cracks generally appear due to repetitive traffic loadings on bituminous surface. Excessive settlement and interconnected cracks leads to aligator crackings. However, week base and subgrade due to water also effects the top layers.

Block Cracking- It is generated due to HMA (asphalt concrete) shrinkage and daily temperature cycling results in to stress strain cycling and leading to block failure. The longitudinal and transverse cracks are interconnected lead to formation of failed block. The image is shown below:-