Effects of Temporal Changes in Site Conditions on Ground Motion Characteristics in Alaska
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Earthquake ground motions are strongly influenced by local subsurface conditions as seismic waves travel from bedrock to the ground surface. Current seismic design practices typically assume that site conditions remain constant over time; however, many regions of Alaska experience significant seasonal and long-term changes in subsurface conditions due to seasonal frost, groundwater fluctuations, and permafrost degradation. These changes can alter soil stiffness, site period, and ground motion amplification characteristics, potentially affecting the seismic demand on bridges and other critical transportation infrastructure.
This project investigates how temporal changes in geologic conditions influence earthquake ground motions and site response throughout Alaska. Particular emphasis is placed on understanding the effects of seasonal frost, thawing permafrost, groundwater variability, and associated changes in shear-wave velocity (Vs) profiles. The research combines geophysical field investigations, ground motion characterization, and advanced site response analyses to quantify how changing subsurface conditions affect seismic hazard and bridge performance.
Field studies will be conducted in Alaska using surface wave testing and microtremor measurements to develop new site-specific Vs profiles and site period estimates. These measurements will expand existing subsurface datasets and provide critical information for evaluating spatial and temporal variations in site conditions. The project will also investigate locations where permafrost degradation and seasonal freezing may significantly alter subsurface stiffness and ground motion amplification behavior over time.
The resulting framework will provide Alaska DOT&PF engineers with practical guidance for incorporating temporal changes in site conditions into seismic hazard evaluations and bridge design. By improving the understanding of how frozen and thawed ground conditions influence earthquake response, the research will support more resilient transportation infrastructure and enhance long-term planning for critical facilities throughout Alaska.
Geoengineered Materials Solutions: Task 5 Advanced Subsurface Condition Assessment
Accurate characterization of subsurface conditions is critical for the planning, design, construction, and maintenance of transportation and defense infrastructure. Traditional geotechnical investigations such as drilling and cone penetration testing provide valuable information but are often limited by cost, access constraints, and sparse spatial coverage. As a result, important subsurface features such as voids, weak zones, buried infrastructure, pavement defects, and variations in soil and rock conditions may remain undetected between investigation points.
The Geoengineered Materials Solutions (GEMS) Advanced Subsurface Condition Assessment task is developing and evaluating next-generation geophysical technologies capable of rapidly imaging subsurface conditions over large areas with greater efficiency than conventional investigation methods. A primary focus of the project is the development of an integrated Seismo-Electric Land-Streamer (SEL) system that combines seismic and electrical measurements within a single mobile platform. By simultaneously collecting seismic and electrical data, the SEL system has the potential to improve subsurface imaging efficiency while reducing field deployment time and personnel requirements. Conventional seismic methods and electrical resistivity tomography (ERT) approaches are being incorporated to evaluate system performance and establish benchmark comparisons.
A comprehensive literature review was conducted to assess the current state of practice in near-surface geophysics, emerging sensing technologies, and advanced data processing techniques. The review examined seismic, electrical, electromagnetic, and ground-penetrating radar methods while identifying opportunities to improve portability, data density, and operational efficiency. Particular attention was given to technologies capable of detecting subsurface features of engineering interest, including voids, soft zones, buried infrastructure, pavement defects, and variations in soil and rock properties. Advanced processing techniques incorporating machine learning and artificial intelligence were also evaluated to improve interpretation and automation of geophysical datasets.
Building upon the findings of the literature review, the project developed a comprehensive field testing program to evaluate advanced subsurface sensing technologies across a range of geological environments and infrastructure applications. Test sites include transportation corridors, levees, research facilities, and locations containing known subsurface anomalies. Multiple sensing approaches will be compared using standardized acquisition and processing procedures to evaluate their ability to characterize subsurface conditions from shallow investigations to larger-scale geotechnical assessments. Particular emphasis is being placed on evaluating the performance of the Seismo-Electric Land-Streamer system for detecting and characterizing subsurface hazards while maintaining rapid deployment capabilities.
The anticipated outcome of the project is a prototype advanced subsurface condition assessment methodology that integrates seismic, electrical, and advanced processing technologies into a portable and efficient field investigation platform. The resulting framework will support Department of Defense and civil infrastructure stakeholders by improving the ability to detect hidden subsurface hazards, evaluate existing infrastructure, reduce uncertainty in site characterization, and support more informed engineering decisions. By combining rapid field deployment with high-resolution imaging capabilities, the technology has the potential to significantly enhance subsurface investigations for future transportation, military, and civil engineering applications.
Enhancing Site Response Analysis for Bridge Infrastructure in the Southern Plains Region: Issues, Pitfalls, and Pathways to Improvement
Bridges throughout the Southern Plains Region are frequently constructed on complex subsurface conditions that can significantly influence earthquake ground motions. While current seismic bridge design procedures provide generalized methods for estimating site amplification, these approaches may not adequately capture the effects of deep sedimentary basins, soft soils, variable bedrock conditions, and nonlinear soil behavior that are common throughout the region. As a result, seismic demands may be overestimated or underestimated, leading to increased construction costs or uncertainty in structural performance.
This project investigates key challenges associated with site response analysis for bridge infrastructure, including differences between the AASHTO general procedure and site-specific analyses, the influence of bedrock shear-wave velocity assumptions, the effects of input motion depth, and the performance of equivalent-linear versus nonlinear modeling approaches. Using geotechnical and geophysical datasets from transportation agencies and previous research efforts, representative bridge sites throughout the Southern Plains Region will be evaluated to identify conditions where current practices may not accurately represent site behavior.
The research will produce practical modeling guidelines, decision-support tools, and region-specific recommendations that improve the reliability of seismic hazard assessments and bridge design. The resulting framework will help transportation agencies make more informed decisions regarding site characterization, site response analysis, and seismic design while supporting resilient and cost-effective infrastructure throughout the region.
Enhancing Seismic Design Strategies for Bridges: Leveraging Data-Driven Decision-Making through Shear Wave Velocity Testing and Site-Specific Ground Motion Response Analysis
Recent updates to the 2023 AASHTO seismic bridge design specifications have changed how seismic hazards and site conditions influence bridge design throughout the United States. These changes may significantly impact construction costs and design requirements, particularly in regions with moderate-to-high seismic hazard.
This project evaluates how shear wave velocity (Vs) testing and Site-Specific Ground Motion Response Analysis (SSGMRA) can improve seismic design decisions compared to traditional approaches based on Standard Penetration Test (SPT) data. Using seismic hazard maps and representative transportation sites across the Southern Plains and central United States, the research will identify where advanced site characterization can reduce uncertainty, refine seismic site classifications, and improve design ground motion estimates.
The resulting tools and guidance will help transportation agencies determine when additional testing and analysis are likely to provide meaningful benefits, supporting more resilient and cost-effective bridge designs through data-driven decision making.
Fault Displacement Mapping of the 2023 Türkiye Earthquake Ruptures for Seismic Risk Reduction in the U.S.
The 300-km-long magnitude (M) 7.8 earthquake rupture along the East Anatolian Fault in Türkiye is one of the largest strike-slip ruptures instrumented globally. At the same time, the 150-km-long M7.5 rupture of the largest aftershock on the Sürgü fault, produced surface displacements on the order of 8 m, exceeding, on average, the displacement-length relations used for the 2023 National Seismic Hazard Model (NSHM) update by more than fifty percent. These ruptures share a similar tectonic setting with the San Andreas Fault System (SAFS) in California, so evaluating the NSHM by comparison with the Türkiye fault ruptures is important in the context of risk reduction in the U.S. A similar rupture on the SAFS, often referred to as The Big One in California, will threaten the population and economy of major urban centers, national defense installations, and other critical infrastructures. Observing and documenting displacements along these exceedingly long and rare ruptures is therefore critical to understanding and reproducing earthquake rupture processes, empirically and numerically; to reducing uncertainty in regional hazard models; and reducing the risk of distributed infrastructure systems that are vital to the health and prosperity of communities, and vulnerable to ground deformation, such as water and gas pipelines. Findings and open-source datasets from our fieldwork will guide public policy and engineering design codes through future improvements of the NSHM, as well as decision makers for a greater extent of societal well-being and national defense. To complete our work, we have established partnerships between academia and government agencies in both the U.S. and Türkiye; our team is diverse and includes a balance of early-career scientists and senior scientists, geotechnical earthquake engineers and earthquake geologists, U.S.-based and in-country collaborators, and scientists from underrepresented backgrounds.
The intellectual merit of this work lies in setting a new paradigm in fault rupture field mapping for engineering applications. While there is field, laboratory and numerical evidence that shallow geological conditions affect fault displacements, the evidence is at best qualitative, and thus the documented data cannot be integrated in engineering models for risk reduction. If we want to capture these effects in predictive empirical models for engineering applications, we need a new kind of dataset that associates each fault displacement measurement site with geotechnical site characterization measurements. Our primary field objectives include characterization of the 2023 ruptures by means of: (1) mapping the main fault rupture with high-resolution (cm-scale) GNSS surveys, photographs, ground-based lidar, and UAV-based terrain models, (2) documenting discrete and perishable offsets of cultural and geomorphic features, (3) characterizing the width and style of the deformation zone, (4) accompanying the measurements of the transient deformation zones with dynamic site characterization measurements on a sub-km scale using active source and ambient wavefield surface wave methods, along with horizontal to vertical spectral ratio (HVSR) measurements, (5) providing geological context (e.g., dominant geological processes and depositional units) for site characterization efforts, and (6) identifying secondary effects such as gravitational failures and liquefaction. Insights and scaling behaviors stemming directly from our field data will provide the first of what we envision will constitute the next-generation fault displacement datasets that will allow future PFDHA models to capture repeatable effects associated with local geologic conditions and fault geometry among other parameters.
The intellectual merit of this work lies in setting a new paradigm in fault rupture field mapping for engineering applications. While there is field, laboratory and numerical evidence that shallow geological conditions affect fault displacements, the evidence is at best qualitative, and thus the documented data cannot be integrated in engineering models for risk reduction. If we want to capture these effects in predictive empirical models for engineering applications, we need a new kind of dataset that associates each fault displacement measurement site with geotechnical site characterization measurements. Our primary field objectives include characterization of the 2023 ruptures by means of: (1) mapping the main fault rupture with high-resolution (cm-scale) GNSS surveys, photographs, ground-based lidar, and UAV-based terrain models, (2) documenting discrete and perishable offsets of cultural and geomorphic features, (3) characterizing the width and style of the deformation zone, (4) accompanying the measurements of the transient deformation zones with dynamic site characterization measurements on a sub-km scale using active source and ambient wavefield surface wave methods, along with horizontal to vertical spectral ratio (HVSR) measurements, (5) providing geological context (e.g., dominant geological processes and depositional units) for site characterization efforts, and (6) identifying secondary effects such as gravitational failures and liquefaction. Insights and scaling behaviors stemming directly from our field data will provide the first of what we envision will constitute the next-generation fault displacement datasets that will allow future PFDHA models to capture repeatable effects associated with local geologic conditions and fault geometry among other parameters.
Seepage Investigation of Hindsville and Elmdale Lake Dams
Seepage has been observed along the toe and abutment of the Hindsville and Elmdale Lake dams and wet spots/flowing water have been observed along the face/abutment of the dam. This seepage may be coming from the lakes and traveling through the dam and foundation. The geophysical testing (electrical resistivity tomography) was conducted to understand the possible seepage paths through the dam/foundation to aid in the repair of the dam.
Updating ARDOT Liquefaction Evaluation Procedures
There currently exists a significant amount of uncertainty when designing piles for bridge foundations in liquefiable soil. Currently ARDOT engineers use a Standard Penetration Test (SPT) based liquefaction spreadsheet developed 10 years ago to evaluate liquefaction triggering. Since this spreadsheet was developed, updates to the liquefaction triggering procedures have been published making the spreadsheet out-of-date. In addition, recommendations regarding skin friction and end bearing of piles in liquefiable soils have been published providing additional guidance regarding the design of these piles. Moreover, additional methods of liquefaction evaluation using cone penetration test (CPT) and shear wave velocity (Vs) provide additional means of evaluating liquefaction potential. This project plans to update ARDOT's liquefaction triggering evaluation methodology with the newest procedures and incorporate additional empirical liquefaction hazard estimates such as the liquefaction potential index (LPI). This will provide ARDOT with the tools necessary to design pile foundations in liquefiable soils using the most up-to-date guidance and methods.
Advancing the Development of Realistic and Probabilistic Shear Wave Velocity Profiles Using Advanced Inversion Strategies
This grant will advance our ability to image the subsurface by utilizing surface wave methods to develop more realistic and probabilistic shear wave velocity profiles. As advanced as the tools of daily society have become, the world of in-situ site characterization still remains mired in the past and continues to rely heavily on empirical approaches developed over 100 years ago, while the medical industry has made leaps forward in the field of non-invasive imaging. As the profession moves forward, the advancement of non-invasive methods is critical to meeting the challenges of tomorrow in a cost-effective manner. As a step toward this goal, this project plans to advance our ability to develop realistic and probabilistic subsurface models through advanced inversion schemes. These schemes will harness artificial intelligence and additional wavefield information to replace a level of user skill now required to develop these subsurface models. These realistic subsurface models are critical to utilizing parameters, such as shear wave velocity, in applications including liquefaction triggering, site response analysis, bedrock rippability, and settlement analyses. In addition, the boarder impacts of the project center on promoting the use of non-invasive methods by educating students through an international student exchange program, and providing training to practicing engineers through a speaker’s bureau.
The intellectual merit of this research lies in the development of state-of-the-art surface wave inversion algorithms. These algorithms will incorporate a Bayesian statistical framework into high-level inversion algorithms using machine learning and trans-dimensional Monte Carlo methodologies. The algorithms will incorporate expert knowledge into the inverse problem and characterize the uncertainty of the developed Vs profiles based on the experimental data. The use of Bayesian and machine learning methods will allow uncertainty in the solution to be considered and presented in a more robust way than current approaches. In addition, further understanding of the petrophysical link between multiple data types advances our knowledge of how different data types work together within joint inversion frameworks to constrain the inversion problem. Advances in the inversion framework will produce broader impacts for multiple applications including site response, liquefaction analysis, and infrastructure evaluation. Moreover, the development of more accurate, realistic, and probabilistic Vs profiles allows for the inclusion of resulting shear wave velocity profiles into performance-based designs. Lastly, advancements in inversion algorithms and knowledge of petrophysical links are transferable to other non-invasive geophysical methods, which all suffer from non-uniqueness issues.
The intellectual merit of this research lies in the development of state-of-the-art surface wave inversion algorithms. These algorithms will incorporate a Bayesian statistical framework into high-level inversion algorithms using machine learning and trans-dimensional Monte Carlo methodologies. The algorithms will incorporate expert knowledge into the inverse problem and characterize the uncertainty of the developed Vs profiles based on the experimental data. The use of Bayesian and machine learning methods will allow uncertainty in the solution to be considered and presented in a more robust way than current approaches. In addition, further understanding of the petrophysical link between multiple data types advances our knowledge of how different data types work together within joint inversion frameworks to constrain the inversion problem. Advances in the inversion framework will produce broader impacts for multiple applications including site response, liquefaction analysis, and infrastructure evaluation. Moreover, the development of more accurate, realistic, and probabilistic Vs profiles allows for the inclusion of resulting shear wave velocity profiles into performance-based designs. Lastly, advancements in inversion algorithms and knowledge of petrophysical links are transferable to other non-invasive geophysical methods, which all suffer from non-uniqueness issues.
Rapid Assessment of Internal Erosion Damage and Erodibility in Levees
Recent flooding events in Oklahoma, Missouri, Illinois, and Arkansas have tested our nation's levee systems and highlighted the vulnerability of our transportation system to disruptions and delays caused by natural disasters. Levee failures not only disrupt navigable waterways, they can also impact rail and truck transportation. The majority of levee failures occur because of instabilities caused from internal and overtopping erosion. Sand boils are the most common signs of distress for levees experiencing underseepage or internal erosion. These surficial defects indicate that a path has developed through or below the levee in which water is able to freely move. In some cases, sand boils are low-risk and are left without repair, but in other cases sand boils can indicate that a much larger problem exists below the surface. Sand boils are often remediated using relief wells, seepage berms, or cutoff walls; however, determining the extent of the damage within the levee is difficult and estimating future performance of the levee without this information can be dangerous. Traditional drilling and sampling techniques only provide discrete data points which can lead to ineffective repairs and wasted funds. Alternatively, seismic and electrical geophysical techniques can be used to assess large sections of levees in a timely manner to locate weak and saturated zones which often indicate locations where internal erosion damage may be present. The ability of geophysical methods to enable quick measurements of material properties over large areas was demonstrated in a previous project, MarTREC 5006, however, there is currently no widely accepted correlation between geophysical properties and many vital engineering properties such as erodibility. This means the data gathered from geophysical methods may be used to compare different sections of the same levee qualitatively, but they cannot be used to make a quantitative assessment of the levee for engineering purposes. This hampers efforts to identify which levee segments are in the greatest need for repair. The main goal of this study is to develop a rapid technique for mapping and assessing erodibility and internal erosion damage by developing relationships between soil erodibility and geophysical data. The research objectives include: (1) identify levees where sand boils, seepage damage, or erosion damage are present, (2) conduct laboratory tests on benchmark samples and samples retrieved from levees to define relationships between soil type, erodibility, shear wave velocity, and resistivity, (3) measure resistivity and shear wave velocity in the field and map internal damage using the relationships defined, (4) evaluate erosion predictions by comparing mapped damage with visible distress signs and collect samples to confirm these predictions (when possible). A series of geophysical field trials will be conducted to determine the most accurate and efficient methods and the best procedures for imaging internal erosion zones. Field retrieved and benchmark samples will be used to link soil erodibility with the geophysical measures so that a more robust inspection system can be developed. These efforts will be conducted in collaboration with USACE and other levee owner entities to ensure that the findings align with current risk assessment developments. By linking soil type and internal erosion potential to the field geophysical data, a more rapid and proactive approach can be taken to estimate risk associated with a particular levee system and determine a mitigation strategy. In addition, the geophysical techniques allow for the eroded or damaged subsurface zones to be mapped to ensure efficient repairs are made with the limited funds available.
Applying UAS LiDAR for Developing Small Project Terrain Models
Providing digital terrain models and survey data for small area projects such as bridge replacements requires obtaining ground elevations in vegetated areas, which is time consuming using conventional total station surveying techniques. Other typical surveying methods, such airborne photogrammetry, have challenges obtaining ground elevations in the typically wooded areas surrounding the project sites. One of the strengths of LiDAR is the ability to penetrate vegetated areas by obtaining multiple returns to the sensor for a given horizontal position. Unmanned aerial systems (UAS) with a LiDAR sensor can reduce the time and effort required to develop these terrain models without sacrificing the accuracy of the data. UAS LiDAR has advanced significantly in the last 5 years providing easier to use systems with more standardized workflows for developing elevation models from the raw LiDAR data. The project would utilize an aerial LiDAR unit mounted on a UAS. The UAS LiDAR system utilized for the research shall be capable of achieving 0.3’ absolute vertical accuracy. The use of UAS is a FHWA Every Day Counts Innovation indicating the technology’s ability to make meaningful impacts on transportation projects today.
The overarching objective of this research effort is to assess the accuracy and benefits of using UAS LiDAR to collect high quality survey data for small area projects such as bridge replacements. This study will adhere to federal regulations 14 CFR Part 107, the FAA’s regulations for small unmanned aerial systems.
The overarching objective of this research effort is to assess the accuracy and benefits of using UAS LiDAR to collect high quality survey data for small area projects such as bridge replacements. This study will adhere to federal regulations 14 CFR Part 107, the FAA’s regulations for small unmanned aerial systems.
Ohio River Valley Supply Chain Scenario Analysis
This project is to develop an approach to monitor and characterize truck traffic along intermodal connectors serving inland waterway ports using a novel traffic sensor system composed of LiDAR and video sensing technologies. The system is novel because it allows for non-intrusive installation and operation (no pavement cuts or traffic stops required) and is capable of predicting the body type of a truck, providing unique insights into commodity flows along a roadway and/or in and out of port terminals. The classification algorithm uses data collected by a LiDAR sensor and is able to distinguish among tank, van, container, platform, livestock, dump, and other types of trailer configurations. An interdisciplinary team from the University of Arkansas (UA) will carry out this project under the direction of Dr. Sarah Hernandez, Assistant Professor of Civil Engineering. This project integrates within a larger project sponsored by Inter-Modal Holding, LLC. The overarching goal is to develop a network of interconnected data collection systems to monitor and manage inland waterway activity including port and terminal operations, vessel movements, and vehicle activity. The objectives of this SOW are to (1) develop a robust and environmentally hardened roadside sensor system to monitor trucks traversing intermodal connectors serving the inland waterway system, (2) develop classification models to predict truck body type, which are indicative of the commodity carried by the truck, based on data from the sensor system, and (3) integrate data from the sensor and classification models into field communications equipment and databases under development by Inter-Modal Holding, LLC (IMH) and its research partners.
RAPID/Collaborative: Dynamic site characterization following the Mw 7.1 Puebla Earthquake for the development of a refined 3D shallow crust velocity model of the Mexico City Basin
The 2017 Mw 7.1 Puebla-Mexico City Earthquake caused numerous building collapses, ground failures, and over 300 casualties. Documented field evidence revealed damage distribution patterns that have been recognized in published studies of previous earthquakes in the region, specifically that the complex regional and local geology, hydrology and geotechnical conditions play a decisive role in shaping the ground shaking characteristics of the clay sediments in Mexico City. While ground motion recordings showed clear evidence of one-dimensional (1D) site amplification in the lake zone of the basin, the uneven damage distribution and ground motion variability in areas of reportedly similar deposit depths and structural characteristics in the transition zone suggest that three-dimensional (3D) site effects played a significant role in the observed damage. The documented evidence of the role of site effects in Mexico City combined with the high density instrumentation and decades of site characterization research provide an excellent opportunity for engineers and earth scientists to study in real scale the coupling of 3D basin effects and 1D local (shallow) site response, and the interaction between hydrological conditions and seismic amplification. Advances in our understanding of these phenomena can be used to develop better prediction models for seismically active regions, including U.S. metropolitan areas such as Los Angeles, San Francisco and Seattle. The overarching goal of this project is to combine instrumentation and monitoring, data collection and analysis, and numerical modeling to better characterize regional basin and local site effects during earthquakes. The rapid response framework maximizes the project resources by aligning its goal with ongoing and upcoming activities of Mexican researchers and engineers to refine the geological and geotechnical site characterization of the basin, and map the evolution of dynamic geotechnical properties with time to the rapidly changing hydrologic conditions in the area.At a technical level, this project focuses on conducting dynamic site characterization of strong motion stations and other key places in Mexico City using active source and ambient wavefield surface wave methods along with horizontal-to-vertical spectral ratios. The goal of conducting these measurements is to develop seismic shear wave velocity profiles and estimate site periods that can lead to improved microzonation maps for the city and regional hazard assessment. Combining field measurements with the spatial variability of shallow deposits and geological information of the deeper sediments from Mexican research databases, we will develop a 3D shallow crust velocity model of Mexico City. This model is essential for physics based ground motion simulations, given the known influence that small-scale lateral heterogeneities in very soft materials have on ground motions, especially in cases of complex resonance interaction between the deeper geologic formations, the shallow sediments, and the structural vibration characteristics of buildings. A better understanding of these phenomena contributes by extension to improved seismic hazard estimates not only for Mexico City, but also for U.S. cities that lie on similar sedimentary basins.
Mapping Subsurface Conditions for Transportation Applications
Each year ARDOT spends millions of dollars to deal with problematic soil and rock conditions, which cause slope stability issues along roadways or require removal of rock layers. The remediation of slopes and the removal of bedrock can be both time consuming and expensive. While slope stability and shallow bedrock issues may be unavoidable or even expected on certain projects, encountering unexpected subsurface conditions during construction can lead to significant cost overruns, change orders, and construction delays. Currently, subsurface conditions are assessed on transportation projects using drilling and sampling along the project alignment. While this provides an acceptable level of accuracy for projects where soil and rock layers are consistent in depth and thickness, significant errors can occur when conditions are variable both inline and crossline to the alignment. If a more accurate/complete 3D understanding of the subsurface conditions were available during the design phase, some problems could be avoided or at least scheduled and budgeted for in advance. Obtaining this understanding of the subsurface using conventional drilling and sampling methods is extremely time and cost prohibitive; however, geophysical methods may offer a more practical solution for sites where the subsurface conditions are quite variable.Both 2D and 3D subsurface maps can be developed rapidly and cost-effectively using geophysical methods such as Capacitively Coupled Resistivity (CCR), Ground Penetrating Radar (GPR), Seismic Refraction, surface wave testing, horizontal to vertical spectral ratio (HVSR), etc. The overarching objective of this research effort is to examine the applicability of using various geophysical methods to map problematic soil and rock conditions along highway alignments. Then determine the effectiveness of these methods of providing information for rock cut estimation and for slope stability analysis for designing or repairing slopes.
Development of Deep Shear Wave Velocity Profiles at Seismic Stations in the Mississippi Embayment
The goal of this project is to develop deep site specific shear wave velocity profiles at five broadband seismic stations and the Central United States Seismic Observatory (CUSSO) all located in the Mississippi Embayment. Based on comparisons of the available site specific Vs profiles (Rosenblad et al. 2010, Cramer et al. 2004, Woolery et al. 2016), reference Vs profiles (Romero and Rix 2005), and profiles from the Central United States Seismic Velocity Model (CUSVM) (Ramirez-Guzman et al. 2012), there is significant uncertainty regarding the deep Vs structure of the Mississippi Embayment. This uncertainty results in differences of over 50% between different commonly referenced Vs sources with the greatest differences occurring at depths greater than 100 meters. These difference in the estimated Vs structure lead to uncertainties regarding the amplification frequencies and potential site effects within the embayment. Given the significant number of recent research studies focusing on potential amplification of seismic waves in the Mississippi Embayment (Malekmohammadi and Pezashk 2015, Hashash et al. 2014, Ramirez-Guzman et al. 2012, 2015, Cramer 2006) and the fact that numerous site response studies have demonstrated the significant influence of input Vs profiles on the site response estimates, the need for high quality and accurate Vs profiles which characterize the Vs of deep sediments within the Mississippi Embayment is great. Without additional Vs information in the embayment, site response studies and hazard models will continue to reference Vs profiles with significant uncertainty (typically without properly considering this uncertainty) leading to less reliable estimates of seismic hazard. The project plan focuses on dynamic site characterization of five broadband seismic stations and at the CUSSO. The seismic stations are distributed across the Mississippi Embayment and currently lack site specific or have only shallow Vs information available. Providing site specific Vs profiles at these sites will increase the usefulness of current and future recorded ground motions at the stations and represent a significant contribution to understanding of the deep Vs structure of sediments within the embayment. Testing at each station will include a combination of active and passive wavefield surface wave methods (SWM) along with horizontal to vertical spectral ratio. The combination of methods will allow the characterization of the Vs of sediments down to Paleozoic bedrock, which is the major contributor to potential site effects across the region. Data collected at the CUSSO and in Memphis, TN will be used as validation sites for SWM. Borehole P-S suspension logger information and shear wave travel time information at these two sites will be used as comparison tools for validation and establishment of a successful analysis methodology for other sites. Complex mode propagation, extremely low frequencies/long wavelengths, and non-uniqueness make development of Vs profiles from SWM at extreme depths more challenging requiring specialized equipment, methods, and significantly more time to develop these profiles than traditional shallow Vs profiles. Because of these challenges, there have been no studies which focus on validation of SWM in deep sedimentary basins at depths greater than 100 meters, making this a one of kind dataset. Vs information developed at CUSSO will also increase the usefulness of the borehole array. Borehole arrays such as CUSSO are often used as site response validation tools and the addition of SWM will allow future studies to include uncertainty associated with the use of multiple methods (Zalachoris and Rathje 2015, Kaklamanos et al. 2015). The Vs profiles developed at each location along with other available Vs profiles will also be used to validate and refine the CUSVM by establishing more accurate reference Vs profiles for each geologic unit in the Mississippi Embayment. The models will be a function of confining stress and therefore can be used along with geologic layering in the CUSVM to develop a more refined velocity model than is currently available. This updated velocity model can be used by researchers and consultants for site response estimates across the embayment.
Rapid and Continuous Assessment of Soil Condition Along Highway Alignments
For new highway alignments in the southern plains region and around the nation, shallow subsurface investigations are typically conducted using drilling and sampling methods. Drilling and sampling is conducted at discrete locations usually 1,000s of feet apart with the objective of determine the properties (resistant modulus and AASHTO soil classification) and subsurface stratigraphy for design of the new highway. Although this method is effective at determining design values, it is often slow to conduct and expensive. Moreover, it only provides information at discrete locations and can likely only detect major changes in stratigraphy. To improve upon this method of characterization, geophysical methods, particularly capacitively coupled resistivity (CCR), can be used to provide a rapid and continuous evaluation of the subsurface soil conditions along a new highway alignment. With this evaluation, localized changes in stratigraphy (expansive clay thickness) and localized anomalies (krast sinkholes, unknown landfills, etc) can be detected along the alignment with less chance of missing the localized features.The CCR method works by injecting an alternating current into the ground and measuring the potential of the subsurface capacitively without galvanic coupling.This method and other resistivity methods are particularly effective at differentiating between fine grained soils (clays) and course grained soils (sands and gravels) due to the difference in retained water between the soil types. This makes the method useful for evaluating the thickness of clay or sand layers in the near surface along highway alignments. When compared to traditional direct current (DC) resistivity, CCR is significantly faster because no probes are installed in the ground surface allowing data to be collected at walking speed (1-4 linear km per hour) rather than having to constantly install electrodes. However, the measured resistivity values are often very similar between the two techniques.The objectives of the study are to determine the applicability of CCR for conducting a preliminary survey along a new highway alignment with the purpose of developing a less extensive, but more detailed characterization of the alignment using drilling and sampling, where samples are taken from locations where stratigraphy changes occur rather than uniformly along the alignment. This has the purpose of reducing the number of drilling and sampling location, but providing a more comprehensive subsurface investigation with less uncertainty in the location of stratigraphy changes. In addition, the applicability of correlating resistivity results to index properties/soil classification from the drilling and sampling program will be tested with the goal of providing a continuous profile of engineering properties for design. Ultimately, the project hopes to develop a new testing methodology, which can be used to evaluate subsurface soil conditions for new highway alignments in order to reduce the cost of the investigation and provide more comprehensive results for design.
Rapid and non-destructive assessment of levees for strength and liquefaction resistance
In 2013, the American Society of Civil Engineers (ASCE) gave the levee system in the United States an overall rating of D-. This rating is based in part on information from the National Levee Database (NLD) which is comprised of approximately 14,700 miles of levees operated by the U.S. Army Corps of Engineers (USACE). These levees are more than 55 years old on average and were originally designed to protect farmland from flooding; however, due to urban sprawl and changes in land use, over 14 million people now live or work behind these structures. Unfortunately, only 8% of these levees are found to be in acceptable condition, while about 69% are minimally acceptable, and 22% are rated as unacceptable. In the coming decades, continued deterioration, urban development, and an increase in extreme weather events will test these structures to and beyond their capacity, leading to a significant increase in risk.To prevent failures in these structures, ASCE estimates more than $100 billion is needed to repair and rehabilitate the levee system. However, only a small portion of that money is currently allocated by the federal government. Therefore, the available money must to be used to repair the most critical levees first. Typically, levees are evaluated based on a simple visual inspection program to identify critical or weak spots in the levee system. This method can detect surface distress or erosion failures (post failure), but it cannot identify defects that exist within the inner core or foundation soil. Thus, local defects may be missed that could lead to a failure during an extreme event. To detect these local defects before failures occur, the visual inspections need to be combined with rapid, non-destructive geophysical testing that can detect these local defects so the limited repair funds can be used in the most effective manner.The goal of this research is to develop a rapid, non-destructive geophysical testing program and probabilistic framework that can be used to proactively evaluate levees. A series of geophysical field trials will be conducted to determine the most accurate and efficient methods and the best parameters for detecting various features or defects within levees. The results from the most effective methods along with traditional visual and geotechnical data will be used to build a probabilistic framework used to rapidly and cost effectively evaluate the condition of levee systems and identify the most critical areas of the levee system in need of repair. This will allow levee owners to use the limited funds available to repair the most critical parts of the levee first.
Deep Shear Wave Velocity Profiling in North-Eastern Arkansas
North-Eastern Arkansas is located in the heart of the New Madrid Seismic Zone, an area of the US that has some of the highest design ground motions in the nation. NE Arkansas is also located inside the Mississippi Embayment, a geologic unit characterized by very deep sedimentary deposits. These two characteristics significantly increase the seismic design costs of bridges, abutments and deep foundations in NE Arkansas. Currently the Arkansas State Highway Department (AHTD) uses the generic design method in the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) manual to estimate the seismic demand for these structures. Although this methodology typically provides a conservative design, the AASHTO LRFD manual clearly warns that short-period structures may be over-designed at a significant cost and long-period structures may be under-designed at a significant risk. To further understand the design ground motions at sites and insure safe and cost effect designs, the AASHTO LRFD manual recommends conducting a site-specific ground motion response analysis (SSGMRA) to better estimate the seismic demand being placed on highway structures.Recent research (MBTC-3032) has demonstrated the potential cost saving of doing a more in-depth SSGMRA, which could allow the seismic design demand to be lowered by up to the 33% permitted by the AASHTO LRFD manual. One of the primary inputs into the SSGMRA are shear wave velocity (Vs) profiles of the site down to bedrock. Although this can be relatively straight forward for some sites, the Mississippi embayment consists of very deep sediments to a great depth (>1000 m in some locations) before bedrock is encountered. These Vs profiles to bedrock have been shown to be critical to properly estimate the ground motions for a site (Cramer et al. 2004; Hashash and Park 2001). Many researchers, particularly Rix et al. (2001) and Rosenblad and Li (2009), have attempted to profile soils in the Mississippi embayment. However, they were only successful at developing Vs profiles to less than 300 m in depth, which would not reach bedrock in much of NE Arkansas. To insure accurate estimates of the ground motion demand using SSGMRA, a methodology to measure Vs to bedrock in the Mississippi Embayment needs to be established and a set of Vs profiles in the Mississippi Embayment need to be collected to further understand the subsurface condition in the embayment.The objective of this research effort is to develop a procedure to measure shear velocity profiles down to bedrock within the Mississippi Embayment. As part of this effort, shear wave velocity profiles will be developed at 15 sites in NE Arkansas to understand the dynamic and geologic properties of soils in that part of Arkansas. These 15 sites, along with additional information from well logs, Horizontal to Vertical Spectral Ratio (HVSR) and general geologic information, will be used to develop a geo-statistical 3D velocity model of NE Arkansas. Finally, the potential cost savings of doing a Site-Specific Ground Motion Response Analysis (SSGMRA) will be demonstrated using one of the 15 sites in the study. Potential cost savings for the project is estimated to be $2.5-$3.0 million per year based on work by Ketchum et al (2004) and past bridge construction rate and practices by AHTD.
Development of the MASW Method for Pavement Evaluation
Infrastructure deterioration is a major issue for transportation infrastructure in the southern plains region and around the nation. Delamination, cracking, and many other failure modes in bridge decks and pavement systems are a daily issue in the constant maintenance of transportation systems. The extreme weather across the nation further exasperates the problem of failing infrastructure by increasing the wear and tear on transportation systems through more frequent freeze-thaw cycles and larger temperature swings. To combat these problems in an economic way, highway departments need non-destructive testing (NDT) methods to determine the condition of infrastructure and the rate of decay to better plan for future repairs and replacement of transportation systems. The Multi-Channel Analysis of Surface Waves (MASW) is a NDT method developed as an improvement to the Spectral Analysis of Surface Waves (SASW) method for dynamic characterization of soil for geophysical and geotechnical engineering problems. Improvements on the SASW method include: (1) faster data collection in the field, (2) simpler and faster data processing, (3) a more robust technique of developing the experimental dispersion curve in which multiple modes of propagation can be resolved, and (4) the ability to utilize both Rayleigh and Love wave dispersion in the inversion analysis. The MASW method is gaining widespread use in the geophysical and geotechnical communities and is one of the fastest growing methods for dynamic site characterization around the world. This is primarily because MASW provides the same benefits as SASW, but in a faster and more robust way. However, the method has yet to gain widespread use in the transportation sector. This research aims to develop the MASW method into a tool for characterization of concrete and asphalt pavements, bases, and subgrades for transportation projects. In addition, the method can be utilized for detecting damage to infrastructure such as bridge decks. Early detection of delimitations, cracks, and concrete deterioration can be critical for planning future repairs or replacement of the existing infrastructure. To develop the MASW method as a transportation tool, the following three tasks are proposed: (1) Determine the optimal field data collection parameters for both concrete and asphalt pavements including source type, source location, number of receivers, receiver spacing, and receiver coupling. (2) Determine the practical vertical and horizontal resolution with depth of MASW given the optimal arrangement provided from the first task. This will provide a baseline for the methods ability to resolve problem areas in the pavement, base, and subgrade system. (3) MASW will be used on real bridge decks and pavement surfaces that show signs of deterioration to determine if the method is able to detect the damage when the damage is already apparent by visual inspection. The results will be compared to results from more proven methods such as SASW and Impact Echo to insure the accuracy of MASW.
Evaluating the Condition of Asbestos-Cement Pipe within the Bella Vista Village Water Distribution System
Asbestos Cement (AC) is a mixture of asbestos fibers, which act as a reinforcing element, and cement paste, which acts as a binding agent. The mixture can be used to create AC pipe. AC pipe was installed in North America from 1920 to the early 1980s and its use became widespread during the 1950’s and 1960’s, particularly in the smaller diameter distribution sizes (Mordak and Wheeler 1988). Williams and Aspern (2010) estimated that AC pipe makes up 12 to 15% of water mains in the United States. Asbestos cement water pipes are generally non-friable (i.e., cannot be crushed by hand pressure once the cement is set (HU et al. 2009)) therefore exposure to AC pipe isn’t generally a health risk. Asbestos cement pipes however, are known to deteriorate in certain environments, but the parameters controlling the rate of degradation, and their effect on pipe performance are not fully understood (Mordak and Wheeler 1988). Deterioration of AC is generally caused by either soft water leaching of the cementitious matrix, or by acid or sulphate attack.The Bella Vista Village Property Owners Association operates a municipal water distribution system that serves a population of over 26,000 residents and contains 300 miles of AC pipe. This pipe is nearing is design life and has shown some sign of deterioration. To proactively evaluate the current condition of the AC pipe and provide life expectancy figures, the project proposes a testing plan to evaluate the condition of different part of the distribution system by evaluating the condition of discrete sections of pipe. ASTM recommended values for new sections of pipe will be compared to values determined using hydrostatic pressure tests, crushing load compression tests, Phenolphthalein staining on pipe samples taken from the distribution system. These tests will determine the current condition of the pipe. Rates of degradation and future life expectance will be evaluated using accelerated acid degradation where pipes will be exposed to high concentration acids to accelerate the degradation process to determine at what point the pipe performance would be considered unacceptable.
Dynamic site characterisation of Canterbury strong motion stations using surface wave testing to resolve shallow and deep stratigraphy
The objective of this research is to characterise the shallow and deep shear wave velocity profiles at strong motion stations (SMSs) in the wider Canterbury region. This project has three main objectives: (1) Shallow dynamic characterisation of SMSs on alluvial soils in the wider Canterbury region, (2) Shallow dynamic characterisation of SMSs nominally on rock in the Port Hills, (3) Deep dynamic characterisation of SMSs in the wider Canterbury region.SMSs in the Canterbury region captured an extensive and unique set of ground motions (GM) during the Canterbury earthquake sequence. These GM can be used for back-analyses aimed at understanding the spatial variability of the ground shaking (particularly site and basin effects) during each event, followed by accurate forward-estimates aimed at quantifying the amplitude and frequency content of future design GMs. However, detailed GM analyses cannot presently be conducted because no information exists on the shear wave velocity (Vs) structure of the deep deposits at these locations that underlie Canterbury.This research will fill a gap in the current knowledge, as presently there is minimal geotechnical site investigation data at the strong motion stations in the Canterbury region outside Christchurch and Kaiapoi. This project builds on previous research by the proposal investigators at SMSs in urban Christchurch and Kaiapoi, where a range of surface and subsurface investigation techniques were used due to the complex nature of the near coast soil stratigraphy. Prior to this research, only generalised soil profile characteristics were available at each SMS location, based only on regional geological characteristics and historic boreholes (Cousins & McVerry 2010). No dynamic site characterisation has been carried out at any of the wider Canterbury SMS locations.This project falls under the Hazard source characterisation theme, as it makes use of techniques for the analysis of ground conditions that influence the local intensity and effect on geological hazards. Profile information will be collated and incorporated into SMS summaries in GeoNet (GNS Science 2013), and when combined with data from the 2012 Biennial Grant (12/629), will provide shear wave velocity profiles at all SMS in the wider Canterbury region that experienced appreciable levels of shaking during the Canterbury earthquake sequence. The use of the GeoNet system as an outlet for this information will enable efficient data dissemination to researchers in the seismological, geotechnical and structural fields.This project is the next step in the wider research plan of characterising the soil profiles at all strong motion stations in New Zealand, as a continued collaboration between the University of Auckland, University of Canterbury, and recognised international leaders in geotechnical testing.
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