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During Hurricane Katrina in 2005 and the events thereafter, failures of levees with I-walls caused extensive flooding and damage. The geological background in the New Orleans area and associated uncertainties contributed significantly to the failures. To increase the robustness of the I-walls and levee system and reduce the associated risk of failure, the uncertainties of the system must be incorporated into the design procedures, especially in a geological environment mainly composed of sand deposits. This paper presents a robust optimization procedure to identify optimal designs for the stability of an I-walls and levee system supported on sandy foundation soil in the face of flood hazards. The uncertainties associated with the I-walls and levee system, including the strength parameters of levee and foundation soils and the height of the floodwater behind the I-walls, were considered in a systematic manner. The wall embedded depth, levee crown width, and slope ratio of the levee in the landside were considered as the design parameters. For the robust optimization, the construction cost of the I-walls and levee system and the standard deviation of the failure probability were considered as the design objectives. Finally, the multi-objective optimization resulted in a set of acceptable designs that were presented in a graphical form called Pareto front, which is combined with the knee point concept to provide useful decision aids for selecting the most preferred design that meets both the economics and performance requirements. [ABSTRACT FROM AUTHOR]

A systematic robust design optimization methodology is presented in this study for cantilever retaining wall backfilled with shredded tire in the face of earthquake hazards. Regarding the merits of application of shredded tire backfill in seismically active areas, the uncertainties in properties of this material (e.g., friction angle and cohesion) as well as uncertainties in earthquake load (e.g., peak ground acceleration) necessitate examining the robustness of design along cost efficiency in geotechnical design procedures. The wall tip deflection was treated as the response of concern for which a response surface was developed based on the design and random (uncertain) variables. Coupling with Monte Carlo simulations, the optimization in terms of cost and standard deviation of response as a measure of robustness yielded a set of preferred designs, or Pareto front, and the final optimal design was determined via selection procedures based on knee point concept. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology for selecting hazard-consistent hurricane scenarios (with similar return periods) for estimating the regional losses due to combined hurricane wind and flood. An in-house stochastic hurricane simulation program was used to simulate 50,000 years of full-track synthetic hurricanes. A wind field model along with a boundary layer model was utilized to compute the surface wind speeds. As illustrative examples, the SLOSH (Sea, Lake, and Overland Surges from Hurricanes) model was employed to calculate the corresponding flood elevations for two loss estimation domains (Charleston Peninsula, South Carolina and Miami Beach, Florida) with each of them divided into census blocks. The peak wind speeds and maximum flood elevations at the centroids of respective census blocks were utilized to determine the joint mean recurrence intervals (MRIs) of individual hurricane events. For regional loss estimation purpose, the joint MRIs of hurricanes were weighted by the population of every census block. A hurricane selection procedure was developed to select hazard-consistent hurricane scenarios with a joint MRI of 100 years. Three hurricane ensembles, selected based on only wind speeds, only flood elevations, and joint wind speeds and flood elevations, were imported into the HAZUS-MH (Hazards US Multi-Hazards) program to perform combined wind and flood loss estimations. The results indicate that hurricane selection using either only wind speeds or only flood elevations can overestimate the combined losses. The different characteristics of the selected hurricane scenarios for the two loss estimation domains are also discussed. [ABSTRACT FROM AUTHOR]

Combined effects of hurricane wind and surge can pose significant threats to coastal cities. Although current design codes consider the joint occurrence of wind and surge, information on site-specific joint distributions of hurricane wind and surge along the US Coast is still sparse and limited. In this study, joint hazard maps for combined hurricane wind and surge for Charleston, South Carolina (SC), were developed. A stochastic Markov chain hurricane simulation program was utilized to generate 50,000 years of full-track hurricane events. The surface wind speeds and surge heights from individual hurricanes were computed using the Georgiou's wind field model and the Sea, Lake and Overland Surges from Hurricanes (SLOSH) model, respectively. To validate the accuracy of the SLOSH model, the simulated surge levels were compared to the surge levels calculated by another state-of-the-art storm surge model, ADCIRC (Advanced Circulation), and the actual observed water elevations from historical hurricane events. Good agreements were found between the simulated and observed water elevations. The model surface wind speeds were also compared with the design wind speeds in ASCE 7-10 and were found to agree well with the design values. Using the peak wind speeds and maximum surge heights, the joint hazard surfaces and the joint hazard maps for Charleston, SC, were developed. As part of this study, an interactive computer program, which can be used to obtain the joint wind speed and surge height distributions for any location in terms of latitude and longitude in Charleston area, was created. These joint hazard surfaces and hazard maps can be used in a multi-hazard design or risk assessment framework to consider the combined effects of hurricane wind and surge. [ABSTRACT FROM AUTHOR]