Correct option is (d) Drainage of soil, Stabilisation of soil and Compaction of soil

The explanation: The major factors which governs the thickness of the pavement are ‘Traffic’ and ‘subgrade soil STRENGTH’ apart from climatic conditions ( frost action etc.), MATERIAL characteristics etc.

However, there were no OPTIONS related to the above discussed.

Option (Drainage of soil) affects the thickness because the subgrade soil strength (measured in CBR (%)) changes with the density of the soil.

Option (Stabilisation of soil) also affects the thickness because the stabilized soils do possess higher soil strength/desired properties than the unstabilized.

Option (Compaction of soil) deals with the drainage of the soils. Drainage affects the performance of the pavement. If the pavement results in a poor performance under drainage condition, an additional “drainage layer” should be provided (IRC 37:2012) and also while strengthening the roads, it is expected to get more characteristic deflection results in providing more thickness than the properly drained pavement.