Question

Which of the following is not a cause for the hydrostatic pressure on the lining?

(a) Seeping of the rainwater in the backfill

(b) When the water table remains below the canal bed

(c) The backfill is of low drainage

(d) The backfill is of high permeability (i.e. > 3 cm/sec)

The question was posed to me during an interview for a job.

The doubt is from Canal Lining in chapter Lining of Irrigation Canals and its Economics of Irrigation Engineering

Answer 1

Correct answer is (d) The backfill is of high permeability (i.e. > 3 cm/sec)

Explanation: If the subgrade is made of clear gravel or sand of good permeability (> 3 cm/sec) and the water table is not likely to go above the canal bed no drainage arrangements may be necessary. There will be no appreciable time lag in the dissipation of drawdown pore pressures in the subgrade for such case.