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Abstract
Numerical study of seepage flow around drainage-type tunnel was
conducted using Z-Soil Program based on the Finite Element Method. The
groundwater flows under steady-state flow conditions and seepage force acts on
the tunnel lining. It acts as a volume force and thus increases the pressure on the
lining. Circular tunnels in homogeneous isotropic and anisotropic soils with
anisotropy ratio, KxlKy= 2, 3, 4 and 5, were studied. The effect of relative
groundwater level, Hlr, relative depth of the impermeable layer, D/r, relative
depth of tunnel under ground surface, Clr, and soil anisotropy ratio, KxlKy, on
hydraulic head distribution and seepage characteristics were presented excluding
the effect of earth pressure. Also the effect of relative impermeable layer depth,
D/r, was studied for two and three adjacent circular tunnels in homogeneous
isotropic soil. A comparison was made between the average seepage pressure,
Pay, in case of one, two and three adjacent circular tunnels in homogeneous
isotropic soil. The results were presented in dimensionless curves. These curves
could be a simple estimation for the seepage pressure acting on the tunnel in
homogeneous isotropic and anisotropic soils. It was found that, in designing the
drainage-type tunnels, it could be dangerous to neglect the seepage force acting
on the tunnel lining. The change in the relative impermeable layer depth, D/r,
had a significant effect on hydraulic head distribution. But the change in the
relative ground surface height, Clr, had a very slight effect on hydraulic head
distribution. The seepage pressure acting on the tunnel is proportional to the
relative groundwater level, Hlr. The increase of the relative impermeable layer
depth, D/r, or anisotropy ratio, KJKy, caused an increase in average seepage
pressure, Pay, and seepage pressure ratio, Pavlpc. But the increase of the adjacent
tunnels number caused a decrease in average seepage pressure, Pay, and seepage
pressure ratio, Pavlpc.