710 freeway – proposed tunnels
and related earthquake issues
Ken Hudnut, Ph.D.
Geophysicist
MISCONCEPTION
Underground structures are ‘safe’ against earthquakes
Deep structures are ‘safer’ than shallow structures
Tunnels do not collapse or suffer other damage in earthquakes
Note: So much information is easily available to disprove these myths, it is hard to understand how such misinformation persists these days… even among practitioners
TRUTH
Underground structures are safer than above‐ground structures during a seismic event (because of lateral confinement), but…
Tunnels have collapsed and suffered damage in many earthquakes, so
seismic countermeasure designs are essential for these new tunnels
Summary of Occurrences
(Prior to Japan 2004 and China 2008)
From Lanzano et al., 2008 presentation Japan (1923, 1978, 1995 & 2004), Taiwan (1999), Turkey (1999) and China (2008)
Proximity to large
earthquakes with
severe ground motion
results in damage or
even collapse of tunnels What an
earthquake
tunnel
collapse
looks like
(Bolu, Turkey)
Damage and collapse of
tunnels has occurred even in newly built
and very strong tunnels in advanced nations with many extremely
well‐documented cases
Portal and internal collapses, Longxi Tunnel
Types of tunnel damage from earthquakes
Portals
and shallow
sections are
vulnerable
Examples of problematic designs
Design Countermeasures
With enough money, things that work well in theory may be tried to strengthen
tunnels at points of likely seismic vulnerability. For example, where faults and material
contrasts occur, a strong jacket or isolation layer can harden the tunnel in such places. 710 tunnel alternatives & faults
710 tunnel alternatives & faults
710 tunnel alternatives & faults
710 tunnel alternatives & faults
710 tunnel alternatives & faults
890 feet
Two fault crossings
680 feet
830 feet
410 feet