Mining Engineering > GATE 2025 > Tunnel Design
A ground reaction curve (GRC) of a 3 m radius unlined circular tunnel is shown in the figure. The tunnel is supported by 300 mm thick shotcrete lining. The uniaxial compressive strength (σc), modulus of elasticity (Ec) and Poisson's ratio (ν) of shotcrete material are 20 MPa, 15 GPa and 0.25 respectively. The maximum capacity (pmax) of the lining and its stiffness (k) are given as
pmax = (1/2)σc(1 - (a-t)2/a2)
k = Ec(a2-(a-t)2)/((1+ν)[(1-2ν)a2+(a-t)2])
where a= radius of the unlined tunnel and t= thickness of the lining.
If the lining is constructed after 5 mm radial deformation, the support reaction is best represented by the line
pmax = (1/2)σc(1 - (a-t)2/a2)
k = Ec(a2-(a-t)2)/((1+ν)[(1-2ν)a2+(a-t)2])
where a= radius of the unlined tunnel and t= thickness of the lining.
If the lining is constructed after 5 mm radial deformation, the support reaction is best represented by the line
Correct : b
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