Author/Authors :
Fahimifar، Ahmad نويسنده He is currently Professor and Head of the Civil Engineering Department at Amirkabir University of Technology , , Ghadami، Hamed نويسنده Currently he is geotechnical expert in the Alborz Regional Water Company, in Karaj, ,
Abstract :
In this paper, an elastoplastic model is proposed to analyze the circular tunnels
below a groundwater table under axial-symmetric conditions, considering the e ects of
seepage and gravitational loads. In the proposed method, the strain-softening behavior
model and Hoek-Brown failure criterion are used. To evaluate the e ect of gravitational
loads and variations of pore pressure, the equations concerning di erent directions around
the tunnel (crown, wall and
oor) are derived. Since the derived di erential equations do
not have a closed-form solution in the plastic zone, the numerical nite di erence method
is applied. Considering the strain-softening behavior of the rock mass, the problem in the
plastic zone is solved through a stepwise method, where the strength parameters of the
rock mass vary, step-by-step, from their maximum values to the constant values. Besides,
the stresses, strains, and deformations of the rock mass also vary step-by-step from the
elastoplastic boundary to tunnel boundary values. Furthermore, the closed-form analytical
solutions are obtained for the elastic zone. The accuracy and application of the proposed
method are demonstrated by a number of examples. The results well exhibit the e ects
of dilatancy angle and increment of elastic strain in the plastic zone. Based on the results
obtained, ignoring the e ects of gravitational loads and seepage will de nitely produce
computational errors.
