Kevin W. Franke

Procedure for the Empirical Evaluation of Lateral Spread Displacement Hazard Curves

AbstractLiquefaction-induced lateral spread has caused substantial damage to buildings, bridges, embankments, buried utilities, and other critical components of infrastructure in numerous past earthquakes. Although many practitioners use analytical Newmark-based seismic slope displacement models to estimate liquefaction-induced lateral spread displacements, empirical regression models remain popular among most practicing professionals today. However, all lateral spread estimates have a significant level of uncertainty. This paper introduces a procedure to develop performance-based estimates of liquefaction-induced lateral spread displacement by incorporating a widely used empirical model into a probabilistic framework. Utilizing the same principles used in probabilistic seismic hazard analysis, the empirical lateral spread equation is modified and inserted into a performance-based framework modeled after the framework introduced by the Pacific Earthquake Engineering Research Center. Lateral spread hazard ...

Simplified Hybrid p-y Spring Model for Liquefied Soils

AbstractThe beam-on-Winkler foundation (BWF) method is a popular analysis approach for computing the lateral pile response resulting from both inertial and kinematic loading. However, there is significant uncertainty regarding how to properly represent the load-resistance (i.e., p-y) behavior of liquefied soils. This confusion stems from the significant variability observed with the phenomenon and the large number of p-y spring models for liquefied soils that have attempted to account for that variability. In an attempt to develop a practical but broadly applicable approach, a simplified hybrid p-y spring model is presented. This hybrid model incorporates aspects of existing p-y spring models for liquefied soil and is applicable to a wide range of soil types, relative densities, pile/shaft diameters, and loading conditions. Comparisons with a variety of published case histories involving single piles indicate that the hybrid p-y spring model provides reasonable estimates of response for both kinematic and...

Simplified Uniform Hazard Liquefaction Analysis for Bridges

Many bridge designers currently rely on the design specifications provided by AASHTO to evaluate liquefaction hazards for foundations and embankments. These guide specifications recommend a pseudo-probabilistic approach (i.e., an approach in which probabilistic estimates of seismic loading are incorporated into a deterministic liquefaction hazard analysis) for most conventional projects. A more consistent approach for the assessment of liquefaction hazards would involve a performance-based or uniform hazard evaluation of liquefaction potential. However, a performance-based liquefaction analysis is complex and difficult to implement in practice. This paper describes a simplified procedure for uniform hazard liquefaction analysis that uses the standard penetration test to closely approximate the results of a performance-based liquefaction analysis at a desired uniform hazard level. The simplified procedure is compatible with current AASHTO load and resistance factor bridge design specifications and is intended for use on bridges and other transportation-related structures. The procedure is summarized and shown to produce more consistent results for liquefaction hazards across different seismic environments than the existing AASHTO pseudo-probabilistic procedure. An example application of the simplified procedure is presented and discussed, and limitations for the procedures proper use are provided.

Comparative Study between Two Performance-Based Liquefaction Triggering Models for the Standard Penetration Test

AbstractSimplified empirical liquefaction triggering models are commonly used throughout the world to assess the liquefaction initiation hazard. Significant differences between two popular liquefaction triggering models have precipitated a substantial amount of confusion in modern engineering practice. Past research to study these differences has generally focused on deterministic or scenario-based applications of the liquefaction models without directly accounting for uncertainties from the models or seismic loading. This paper investigates how accounting for these uncertainties through a performance-based liquefaction triggering assessment affects the differences between these two probabilistic liquefaction models. A comparative parametric study is performed in which a wide range of soil parameters, seismicity levels, and return periods is considered in assessing the disparity between the two models. This disparity is shown to vary significantly with variations in the parameters that were evaluated. Add...

Reconnaissance of Two Liquefaction Sites Using Small Unmanned Aerial Vehicles and Structure from Motion Computer Vision Following the April 1, 2014 Chile Earthquake

AbstractSmall unmanned aerial vehicles (sUAVs) were used to reconnoiter, image, and model the effects of soil liquefaction at two separate sites following the M8.2 and M7.6 earthquakes near Iquique...

Simplified Procedure for the Performance-Based Prediction of Lateral Spread Displacements

AbstractPast researchers have introduced performance-based methods to simultaneously account for the various sources of uncertainty in the prediction of lateral spread displacements through the incorporation of a probabilistic analytical framework. Although these methods can effectively handle the various sources of uncertainty associated with empirical lateral spread displacement prediction, they are difficult for engineers to perform without the use of specialized numerical tools. This paper introduces a simplified procedure that approximates the results of the performance-based method through the use of lateral spread reference parameter maps. Equations are provided to correct mapped reference parameter displacements for site-specific geotechnical and topographical information to produce hazard-targeted estimates of lateral spread displacement. The simplified performance-based procedure is validated through a comparative study using several soil profiles across several cities in the United States. Resu...

Application and Accuracy of Structure from Motion Computer Vision Models with Full- Scale Geotechnical Field Tests

Structure from motion (SfM) computer vision is a relatively new technology that allows engineers to reconstruct a three-dimensional (3D) model of a given scene using two- dimensional digital photographs captured from a single, moving camera. SfM computer vision provides an economic and user-friendly alternative to other 3D scene-capture and modeling tools such as light distance and ranging (LiDAR). Although the resolution and accuracy of laser-based modeling methods are generally superior to vision-based modeling methods, the economic advantages associated with the latter may make it a useful and practical alternative for many geotechnical engineering applications. Although other engineering disciplines have investigated the potential usefulness of SfM computer vision for years, its application to geotechnical engineering generally remains unexplored. Researchers are currently investigating the application of this technology to select full-scale geotechnical field experiments and assessing its potential usefulness as a high-resolution instrumentation/monitoring tool. This paper presents preliminary computer vision results and findings from these studies. The field experiments, as well as the hardware and software details used to develop 3D SfM computer models of the experiments are summarized. The developed 3D models are presented, and displacements measured in the models are compared against ground truth to evaluate accuracy. Observed advantages and limitations of SfM computer vision are discussed, and several potentially useful applications of the technology in geotechnical engineering are listed.

Lateral Spread Displacement and Bridge Foundation Case Histories from the 1991 Magnitude 7.6 Earthquake near Limón, Costa Rica

AbstractThis paper presents four liquefaction and pile response case histories associated with highway bridges from the April 22, 1991 7.6 magnitude (M) earthquake near Limon, Costa Rica that were ...

Modified Performance-Based Liquefaction Triggering Procedure Using Liquefaction Loading Parameter Maps

AbstractSimplified performance-based liquefaction triggering procedures have sought to address observed inconsistencies in predicted liquefaction triggering hazards across the United States resulting from conventional, pseudoprobabilistic analysis procedures. Unfortunately, current simplified performance-based procedures are limited to use with a single liquefaction triggering curve. This paper introduces a modified performance-based procedure and applies it to a different liquefaction triggering curve that is currently used by many engineering practitioners. The modified procedure is derived, and the concept of liquefaction loading parameter maps is introduced. Validation of the modified procedure against the full performance-based procedure is performed for multiple U.S. cities and soil profiles at three different return periods. The results of the validation demonstrate that the modified performance-based procedure reasonably approximates the full performance-based procedure across multiple return peri...

Seismic Hazard Curves for the Probability of Liquefaction

Seismically-induced soil liquefaction is a significant seismic hazard that has caused substantial damage to foundations and other aspects of infrastructure in past earthquakes. The risk of soil liquefaction and subsequent unsatisfactory foundation performance often leads to the installation of remedial ground improvement, usually at significant cost to the project. While the majority of engineering practitioners use empirical triggering models to evaluate liquefaction initiation hazard, there is typically substantial uncertainty associated with these types of approaches. Performance-based earthquake engineering (PBEE) design methods have recently been introduced that will allow engineers to directly account for this uncertainty and express liquefaction triggering potential in seismic hazard curves for factor of safety against liquefaction. However, many engineering practitioners are choosing to move away from subjective factor of safety metrics. Although PBEE liquefaction assessment methods already incorporate the probability of liquefaction into the development of factor of safety hazard curves, these engineers would prefer the development of probability of liquefaction hazard curves. This paper derives a simplified approach for obtaining such hazard curves directly from factor of safety or req N hazard curves for two popular probabilistic liquefaction triggering models. Such an approach allows engineers to easily switch between factor of safety and/or probability of liquefaction metrics. An example case study is demonstrated with the two probabilistic liquefaction approaches. The potential for probability of liquefaction to be incorporated into the performance-based assessment of certain liquefaction effects is briefly discussed.