Question Statement:
Flow through a layered soil system (soils M over N, each 1000 mm² cross-section, per the given elevation figure) has head loss in N equal to 20× the head loss in M. If permeability of M = 3×10⁻⁴ mm/s, the permeability of N, in mm/s, is:
*Figure (reconstructed): Layered soil column, uniform area 1000 mm², under vertical (series) flow — Soil M (upper layer, 250–400 mm elevation) over Soil N (lower layer, 0–250 mm elevation), total column 0–600/800 mm as marked on the source figure.*
For flow in series through layered soils, Darcy velocity v is identical through both layers: v = k_M·i_M = k_N·i_N. Since head loss (and hence gradient, for comparable thickness) in N is 20× that in M, continuity of v requires k_N to be smaller.
Options:
- (A) 4×10⁻⁴
- (B) 3×10⁻⁴
- (C) 2.5×10⁻⁵
- (D) 1.5×10⁻⁵