Question

The installation of sand drains in clayey soil causes the soil adjacent to the sand drains to undergo which one of the following?

• A. Increase in porosity
• B. Increase in compressibility
• C. Decrease in horizontal permeability
• D. Decrease in shear strength

Answer 1

The correct option is C Decrease in horizontal permeability

The installation of sand drains causes peripheral smear (i.e., wiping action caused by casing or hollow mandrel used to form the well as it is driven down into the soil and then pulled out after it has been filled with sand). For a soil originally having a greater permeability in the horizontal than that in the vertical direction, the smeared zone forms a barrier to the horizontal flow of water, thereby slowing down the process of consolidation considerably.