Date of Award
Doctor of Philosophy
For the design of underground structures in rocks, the initial stresses in the rock mass are a pre-requisite for any analysis. The hydraulic fracturing technique is the only practical method for determining these initial stresses at great depth. For vertical fractures, existing solutions for calculation of stresses are satisfactory. For horizontal or mixed-mode fractures, appropriate solutions are required.;Closed-form solutions for horizontal and mixed-mode fractures including strength anisotropy are developed and applied to several case histories. The reinterpreted horizontal stresses agreed with results derived from convergence measurements and they are also consistent with field observations of excavation performance, indicating that the stresses are correct and readily applicable to practice. Stress values obtained using the conventional method in these cases are too low and may lead to unsafe design.;With the initial stresses correctly determined, the stability of tunnels immediately after excavation may be evaluated. For this purpose, Closed-form solutions for the stresses and displacements around unlined circular tunnels in cross-anisotropic rocks such as shales are derived. For convenience of application, design charts are prepared for the determination of stresses and displacements for given values of initial stresses and the elastic parameters.;After the stability conditions during construction are satisfied, the long-term deformation and consequent stress built-up in the lining are important design considerations, so as to ensure that the structural integrity of the lining is not affected. An experimental study is carried out to investigate the characteristics of the time-dependent deformation of Queenston Shale. The study has shown that Queenston Shale exhibits long-term time-dependent deformation upon stress relief and that the deformation is non-linearly stress dependent. This deformation is represented by a model consisting of three Kelvin units connected in series. The predicted swelling deformations using this model are in good agreement with the measured values in laboratory tests.;Using the theory of viscoelasticity, closed-form solutions for the time-dependent stresses and displacements in the rock mass and the lining of tunnels driven in swelling rocks are derived. A semi-analytical approach is then developed to account for the increase of the values of the moduli of rock as the pressure built-up behind the lining increases with time. It is shown that this solution taking into account stress-dependency of swelling reduces significantly the final stresses and displacements in the lining and the final pressure built-up behind the lining. Therefore, use of the analytical method developed will lead to a more economical design.
Hefny, Ashraf Mohamed, "Analysis Of Initial Stresses, Long Term Deformation And Rock Lining Interaction In Tunnels" (1994). Digitized Theses. 2427.