Seismic Design of Tunnels - Parsons Brinckerhoff

- Formation of plastic hinges at the top and bottom of walls
The conclusions made by Owen and Scholl, based on their study, echoed the findings
by Dowding and Rozen discussed above. In addition, they suggested the following:
• Damage to cut-and-cover structures appeared to be caused mainly by the large
increase in the lateral forces from the surrounding soil backfill.
• Duration of strong seismic motion appeared to be an important factor contributing to
the severity of damage to underground structures. Damage initially inflicted by earth
movements, such as faulting and landslides, may be greatly increased by continued
reversal of stresses on already damaged sections.
Wang (1985)
In describing the performance of underground facilities during the magnitude 7.8
Tang-Shan earthquake of 1976, the author reported the following:
• An inclined tunnel passing through 13 feet of soil into limestone was found to have
cracks up to 2 cm wide on the side wall. The plain concrete floor heaved up 5 to 30 cm.
• Damage to underground facilities decreased exponentially with depth to 500 m.
Schmidt and Richardson (1989) attributed this phenomenon to two factors:
- The increasing competence of the soil/rock with depth
- The attenuation of ground shaking intensity with depth
Sharma and Judd (1991)
The authors extended Owen and Scholl’s work and collected qualitative data for 192
reported observations from 85 worldwide earthquake events. They correlated the
vulnerability of underground facilities with six factors: overburden cover, rock type
(including soil), peak ground acceleration, earthquake magnitude, epicentral distance,
and type of support. It must be pointed out that most of the data reported are for
earthquakes of magnitude equal to 7 or greater. Therefore, the damage percentage of the
reported data may appear to be astonishingly higher than one can normally conceive.
The results are summarized in the following paragraphs. Readers should be aware
that these statistical data are of a very qualitative nature. In many cases, the damage
statistics, when correlated with a certain parameter, may show a trend that violates an
engineer’s intuition. This may be attributable to the statistical dependency on other
parameters which may be more influential.
10