The 23rd Ralph B. Peck Lecture: Earthquake Cracking of Embankment Dams

It is well known within the dam engineering profession that the potential for earthquake-induced cracking is a key consideration in the design and construction of dams. Transverse cracking of embankment dams is a major concern of engineers involved in dam safety management and commonly represents a potential failure mode for such dams. If transverse cracking extends below the reservoir level, it may lead to leakage from the reservoir, internal erosion of the embankment soils, and dam failure. Considerable effort has been made in the engineering profession during the last few decades to study the nature and effects of dam earthquake cracking and to develop design measures to mitigate its potential occurrence. However, few studies exist on earthquake-induced cracking of embankment dams, and the profession's ability to accurately predict its characteristics is limited. Thus, it seems useful to review key aspects of earthquake cracking of embankment dams and some of the lessons learned about cracking from the past performance of dams during earthquakes. This paper aims to fulfill this objective by providing an overview of the observed effects of earthquakes on embankment dams, discussing the potential for embankment dam failure by cracking, reviewing basic concepts about the mechanics of cracking in soils, discussing the analysis of embankment dam cracking in practice, and presenting two case histories of cracking of embankment dams. The case histories describe (1) the performance of Matahina dam during construction, reservoir filling, and the 1987 Edgecumbe earthquake in New Zealand and (2) the performance of Lenihan dam during the 1989 Loma Prieta earthquake in California and an analysis of the dam for that earthquake.