Significance of Primary Waves on the Seismic Stability of Underground Tunnels: A Numerical Perspective 

The influence of primary waves on the seismic stability of underground structures is often overlooked, assuming that these structures remain stable under increased vertical body forces. Only a limited number of studies have examined the combined action of shear and primary waves on tunnel response, while clear guidance on whether the inclusion of primary wave effects is necessary remains unavailable. Moreover, seismic design standards typically specify only the vertical acceleration coefficient, providing little insight into the conditions under which its inclusion is essential or negligible. The present study addresses this gap by evaluating the variation of dynamic support pressure in circular tunnels embedded in granular and cohesive-frictional soils over various frequencies and time instances. The results highlight conditions where considering primary waves is crucial for designing safe and efficient systems. The influence of primary waves on support pressure is found to be more significant in soils with higher shear strength (higher friction angle for granular soils and increased cohesion and/or friction angle for cohesive-frictional soils) and an increasing tunnel cover depth. For the parameters analyzed, neglecting vertical acceleration effects can lead to an underestimation of the maximum dynamic support pressure by up to 94%. Finally, design charts incorporating shear and primary wave effects are proposed to facilitate reliable and efficient tunnel design under seismic loading.

Keywords: Tunnel, Dynamic support pressure, Primary waves, Limit analysis, Earthquake, Stability 

Gowtham, G., and Sahoo, J.P. (xxxx). Significance of Primary Waves on the Seismic Stability of Underground Tunnels: A Numerical Perspective. International Journal for Numerical and Analytical Methods in Geomechanics. Accepted.