Mechanisms for Damage and Failure from the Great East Japan Tsunami - Tohoku, Japan Earthquake and Tsunami of 2011 - page 44

Chapter3
MechanismsforDamageandFailure
from the Great East Japan Tsunami
Despite the several hundred kilometers of coastal damage, some structures performed
remarkably well. The COPRI structures team sought to ascertain why some structures
remained viable while others failed, many catastrophically. The field investigation of
coastal structures extended from the Momoishi fishing port, located approximately 12
kilometers southeast of the Misawa Airport in the Aomori Prefecture, southward
along the coastline to Natori Beach, immediately adjacent to the Sendai Airport in the
Miyagi Prefecture.
Mechanisms for damage and failure discussed in Section 3.0 include the following:
 3.1 Tsunami Overtopping without Structural Failure
 3.2 Tsunami Overtopping with Structural Damage or Failure
 3.3 Tsunami Uplift Forces
 3.4 Movement of Structure from its Foundation due to Sliding, Rotation, and
Overtopping
 3.5 Impact Loads
 3.6 Hydrostatic Pressures
 3.7 Supercritical Flows
 3.8 Scour
 3.9 Erosion
 3.10 Subsidence: Regional and Local
Figures within the sub-sections of Section 3.0 provide representative photographs and
diagrams of tsunami-related damages at a variety of locations (referenced in Figure
18). Table 10 presents a general description of the mechanisms of failure shown in
these photographs.
Many structural failures occurred due to multiple mechanisms. For example, some of
the coastal dike failures most likely started when overtopping and uplift forces
removed some of the concrete panels from the inland side of the earthen berm.
Continued overtopping then scoured the earthen fill, reducing or removing the lateral
support for the seaward portion of the wall. Complete collapse would occur either
when tsunami forces removed critical lateral supports or when an impact load
exceeded resisting forces. Such failures resulted from overtopping, uplift forces,
scour, and impact loads rather than from a single cause. While this section discusses
each failure mechanism separately, in most real-world situations, failures result from
many concurrent weaknesses.
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