Probabilistic Evaluation of Seismic Levee Performance using Field Performance Data
- Author(s): Kwak, Dong Youp
- Advisor(s): Stewart, Jonathan P
- et al.
I characterize the seismic fragility of levees along the Shinano River system in Japan using field performance data from two M 6.6 shallow crustal earthquakes. I quantify levee damage using crack depth, crack width, and crest subsidence for 3318 levee segments each 50 m long. Variables considered for possible correlation to damage include peak ground velocity (PGV), geomorphology, groundwater elevation, and levee geometry. For site conditions beneath levees without geophysical measurements, a model for shear wave velocity is proposed considering soil type, penetration resistance, vertical effective stress, geomorphology, and spatial variation of boring-to-boring residuals. Seismic levee fragility is expressed as the probability of exceeding a damage level conditioned on PGV alone and PGV in combination with other variables. The probability of damage (at any level) monotonically increases from effectively zero for PGV < 14 cm/s to approximately 0.5 for PGV ¡Ö 80 cm/s. Of the additional parameters considered, groundwater elevation relative to levee base most significantly affects fragility functions, increasing and decreasing failure probabilities (relative to the PGV-only function) for shallow and deep groundwater conditions, respectively.
I demonstrate applicability of the fragility models developed from data in the Shinano River region of Japan (SRJ) for geotechnical conditions along urban levees in the Central Valley region of California (CVC) by comparing penetration resistance data between regions for common soil types and geology. For Holocene flood plain deposits I find penetration resistance for coarse-grained soils in the SRJ and CVC study regions to be similar, whereas for fine-grained soils the CVC sediments are stiffer. For Holocene basin and Pleistocene deposits mostly appeared only in the CVC, both coarse- and fine-grained deposits are stiffer than Holocene floodplain deposits.
Spatial correlations of demand and damage are important to consider when evaluating the performance of a complete levee system. I develop a numerical methodology to evaluate the system fragility utilizing the spatial correlations of damage capacity and demands between segments. System level damage probabilities are found to decrease with the strength of these correlations. The damage demand exhibits positive correlation over larger distances than does the damage capacity.