Seismic Design of Tunnels - Parsons Brinckerhoff

3.0 RUNNING LINE TUNNEL DESIGN
3.1 Overview
Discussions of the earthquake shaking effect on underground tunnels, specifically the
“EQ” term in Equations 2-1 through 2-4, are presented in a quantitative manner in this
chapter and in Chapters 4 and 5.
The response of tunnels to seismic shaking motions may be demonstrated in terms of
three principal types of deformations (Owen and Scholl, 1981):
• Axial
• Curvature
• Ovaling (for circular tunnels) or racking (for rectangular tunnels such as cut-and-cover
tunnels)
The first two types — axial and curvature — are considered in this chapter. Analytical
work developed in previous studies for tunnel lining design is presented. The work is
applicable to both circular mined tunnels and rectangular cut-and-cover tunnels.
Discussions of the third type — the ovaling effect on circular tunnels and the racking
effect on rectangular tunnels — are presented in detail in Chapters 4 and 5, respectively.
3.2 Types of Deformations
Axial and Curvature Deformations
Axial and curvature deformations develop in a horizontal or nearly horizontal linear
tunnel (such as most tunnels) when seismic waves propagate either parallel or obliquely to
the tunnel. The tunnel lining design considerations for these types of deformations are
basically in the longitudinal direction along the tunnel axis.
Figure 3 shows the idealized representations of axial and curvature deformations. The
general behavior of the linear tunnel is similar to that of an elastic beam subject to
deformations or strains imposed by the surrounding ground.
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