Single circular tunnels in soils with homogeneous wave velocities
Single circular tunnels in soils with homogeneous wave velocities
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Circular tunnels in cohesive-frictional soils
Circular tunnels in cohesive-frictional soils
The peripheral stability of tunnels is maintained by installing support systems in the form of linings. The required resistance of the linings depends on the stresses exerted by the surrounding medium. This study evaluated the support pressure of the lining for circular tunnels in cohesive-frictional soil under earthquake loading by applying the modified pseudo-dynamic approach in the finite element lower bound limit analysis framework. The normal stresses exerted by the surrounding soil vary along the tunnel’s periphery, and the tunnel’s stability is ensured when the minimum support pressure offered by the tunnel lining is equal to or greater than the maximum normal stress exerted by the soil at the ultimate failure condition. The horizontal and vertical earthquake accelerations, amplitude, and phase of the accelerations were varied with depth by satisfying the stress boundary conditions. The shear strength parameters of soil (cohesion and friction angle), tunnel cover and its diameter, and the parameters owing to an event of an earthquake (acceleration, frequency of primary and shear waves, and the time of shaking) influence the magnitude and location of maximum normal stress along the tunnel’s periphery.
Sahoo, J. P., and Gowtham, G. (2023). Stability evaluation of circular tunnels in cohesive frictional soil under earthquake loading using the modified pseudo-dynamic approach. Soil Dynamics and Earthquake Engineering, 166. https://doi.org/10.1016/j.soildyn.2022.107740
Comparison of normal stress distribution from uniform (red) and non-uniform (black) stress distributions.© Gowtham G. All rights reserved by authors.
Horizontal and vertical stress contours for different anisotropy ratios under ground surcharge. This figure indicates soil arching.© Gowtham G. All rights reserved by authors.
Gowtham, G., and Sahoo, J.P. (2024). Seismic stability of circular tunnels in anisotropic granular soil with surcharge loading based on the modified pseudo-dynamic approach. International Journal of Geomechanics, ASCE, 24(5). https://doi.org/10.1061/IJGNAI.GMENG-9293
Circular tunnels in anisotropic granular soils with ground surcharge
Circular tunnels in anisotropic granular soils with ground surcharge
This study evaluated the stability of circular tunnels constructed in anisotropic granular soil in the presence of surcharges on the ground surface and seismic loads. The stability problem was solved using the lower bound limit analysis method in conjunction with the finite element technique. In addition, the modified pseudo-dynamic technique was employed, which permits seismic accelerations to vary with depth and time, including the impact of amplitude and phase differences between shear and primary waves. The forces exerted by the soil on the tunnel lining vary over the perimeter. Therefore, the ultimate support pressure should at least be equal to the maximum normal stress from the earth surrounding the tunnel. It was discovered that parameters such as the tunnel cover depth, tunnel diameter, magnitude of surcharge, soil friction angle and its degree of anisotropy, seismic acceleration coefficients, period, and frequency of seismic waves determine the support pressure’s magnitude and location. The influence of surcharge diminished beyond a certain cover depth and diameter ratio for given soil and seismic wave parameter magnitudes. This study showed that the maximum normal stress was 8.5 times greater than the uniform stress distribution. Furthermore, the support pressure was found to be a maximum of about 45.5% higher for a tunnel cover depth-to-diameter ratio of 3 than for 1%, 34% higher for anisotropy than for isotropic case, 25% higher in the presence of ground surcharge than its absence, and 60% higher for the horizontal acceleration coefficient of 0.3 compared to the static case.
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