Rock masses may present
remarked geostatic stress anisotropy and anisotropic material properties; thus,
the tunnel alignment with the geostatic principal stress directions and with
the axes of material anisotropy is unlikely. Nevertheless, tunnel design often
neglects those misalignments and; yet, the misalignment effects were unknown.
In this doctoral research, tunnels under complex anisotropic conditions were
modelled analytically and numerically with 3D nonlinear Finite Element Method
(FEM). When the tunnel misaligns with the geostatic principal stress
directions, anti-symmetric axial displacements and shear stresses are induced
around the tunnel. Analytical solutions for misaligned shallow and deep tunnels
in isotropic elastic ground are provided. The analytical solutions were
validated with 3D FEM analyses. Near the face, the anti-symmetric axial
displacements are partially constrained by the tunnel face, producing
asymmetric radial displacements and stresses. The asymmetric radial
displacements at the face can be divided into a rigid body displacement of the
tunnel cross-section and anti-symmetric radial displacements. Those asymmetries
may affect the rock-support interaction and the plastic zone developed around
the tunnel. In anisotropic rock masses, the tunnel misalignment with the axes
of material anisotropy also produces anti-symmetric axial displacements and
stresses around the tunnel. It occurs because when the tunnel is not aligned
with the principal material directions, the in-plane stresses are coupled with
the axial displacements (i.e. the compliance matrix is fully populated). Thus,
tunnels in anisotropic rock mass not aligned with the geostatic principal
stresses and with the axes of material anisotropy are substantially more
complex than tunnels not aligned with the principal stress directions in
isotropic rock mass. An analytical solution for misaligned tunnels in
anisotropic rock mass is provided. It was observed that the relative
orientation of the geostatic principal stresses with respect to the axes of
material anisotropy plays an important role. The axial displacements produced
by far-field axial shear stresses and by the rock mass anisotropy may
compensate each other; thus, axial and radial displacements around the tunnel
are reduced. On the other hand, those anti-symmetric axial displacements may be
amplified; thus, the ground deformations are increased. Asymmetric radial and
axial deformations, and asymmetric spalling of the tunnel walls are commonly
observed on tunnels in anisotropic rock masses. The tunnel misalignment with
the geostatic principal stress directions and with the axes of material
anisotropy could be associated with those phenomena that, so far, are not well
comprehended
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12302600 |
| Date | 15 May 2020 |
| Creators | Osvaldo Paiva Maga Vitali (8842580) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/TUNNEL_BEHAVIOR_UNDER_COMPLEX_ANISOTROPIC_CONDITIONS/12302600 |
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