A model of a time-dependent intrusion governed by
the swelling pressure Psw[ρ(t)] has been presented by
assuming a constant clay viscosity μ and Poisseuilletype
flow of the bentonite gel in a fracture (Grindrod et
al., 1999):
ds
dt
¼ d2
12A
Psw½qðtÞ
sðtÞ
ð11Þ
where ρ(t) is the time-dependent density of the compacted
bentonite block, s(t) is the time-dependent penetration
distance, and δ is the aperture width of the exposed
fracture.