A Numerical Study of Seismic Response of Shallow Square Tunnels in Two-Layered Ground
In this study, the seismic behavior of a shallow tunnel with square cross section is investigated in a two layered and elastic heterogeneous environment using numerical method. To do so, FLAC finite difference software was used. Behavioral model of the ground and tunnel structure was assumed linear elastic. Dynamic load was applied to the model for 0.2 seconds from the bottom in form of a square pulse with maximum acceleration of 1 m/s2. The interface between the two layers was considered at three different levels of crest, middle, and bottom of the tunnel. The stiffness of the two upper and lower layers was considered to be varied from 10 MPa to 1000 MPa. Deformation of cross section of the tunnel due to dynamic load propagation, as well as the values of axial force and bending moment created in the tunnel structure, were examined in the three states mentioned above. The results of analyses show that heterogeneity of the environment, its stratification, and positioning of the interface of the two layers with respect to tunnel height and the stiffness ratio of the two layers have significant effects on the value of bending moment, axial force, and distortion of tunnel cross-section.
 Amorosi, A. and D. Boldini, Numerical modelling of the transverse dynamic behaviour of circular tunnels in clayey soils. Soil Dynamics and Earthquake Engineering, 2009. 29(6): p. 1059-1072.
 Pakbaz, M.C. and A. Yareevand, 2-D analysis of circular tunnel against earthquake loading. Tunnelling and Underground Space Technology, 2005. 20(5): p. 411-417.
 Owen, G.N. and R.E. Scholl, Earthquake engineering of large underground structures. NASA STI/Recon Technical Report N, 1981. 82: p. 16291.
 Hashash, Y.M., et al., Seismic design and analysis of underground structures. Tunnelling and Underground Space Technology, 2001. 16(4): p. 247-293.
 Debiasi, E., A. Gajo, and D. Zonta, On the seismic response of shallow-buried rectangular structures. Tunnelling and underground space technology, 2013. 38: p. 99-113.
 Dowding, C.H. and A. Rozan, Damage to rock tunnels from earthquake shaking. Journal of the Soil Mechanics and Foundations Division, 1978. 104(2): p. 175-191.
 Gomes, R.C., Effect of stress disturbance induced by construction on the seismic response of shallow bored tunnels. Computers and Geotechnics, 2013. 49: p. 338-351.
 Gomes, R.C., et al., Seismic response of shallow circular tunnels in two-layered ground. Soil Dynamics and Earthquake Engineering, 2015. 75: p. 37-43.
 Owen GN, Scholl RE. Earthquake engineering of large underground structures. NASA STI/Recon Technical Report N. 1981 Jan;82.
 Hori M. Introduction to computational earthquake engineering. World Scientific; 2011.
 Sharma S, Judd WR. Underground opening damage from earthquakes. Engineering Geology. 1991 Jun 1;30(3-4):263-76.
 Kuhlemeyer, R.L. and J. Lysmer, Finite element method accuracy for wave propagation problems. Journal of Soil Mechanics & Foundations Div, 1973. 99(Tech Rpt).