CS12A - Concurrent Session 12A: Liquefaction Triggering Analysis of Construction and Long-Term Surcharge Loading on Earth Embankment Dams

Following the failure of the Edenville Dam, reconstruction design efforts included an updated Potential
Failure Modes Analysis (PFMA). New Potential Failure Modes (PFMs) were identified related to static
liquefaction triggered by a variety of load cases. These load cases included surcharge loads from
flooding, construction equipment crest surcharge loads, toe excavations and long-term maintenance
equipment crest surcharge loads. PFMs were related to static liquefaction of the embankment soils and
foundation soils. The PFMA team identified these loads as potential load cases that could lead to
failures but did not evaluate if the magnitude of those loads were sufficient to trigger static liquefaction.
Therefore, the reconstruction design team checked for a strain weakening response due to the change
in stress to determine if that load is sufficient to weaken the soils (e.g. trigger liquefaction). This
evaluation step is an important intermediate step necessary to rule out PFMs or address potential
failure concerns in existing and newly constructed earth embankment dams when foundation soils
and/or embankment soils are susceptible to static liquefaction.

Reconstruction design for Secord Dam, Smallwood Dam and Edenville Dam followed this process for
diligent consideration of these types of failure modes and to be critical of a load’s ability to trigger static
liquefaction. The geotechnical data (boring logs, cross sections, lab data, etc.) from those three dams
and a discussion on the analysis approach is presented.