Effective geotechnical site characterization is essential for the planning, design, and long-term performance of transportation infrastructure. Unanticipated subsurface conditions (such as buried voids, weak soils, or highly variable stratigraphy) can lead to costly construction delays, change orders, and, in severe cases, structural distress or failure. For State DOTs responsible for delivering safe and resilient infrastructure, obtaining reliable information on subsurface conditions and their spatial variability is therefore critical during the early stages of project development.

Current practice relies heavily on invasive point-based methods such as Standard Penetration Test (SPT), Cone Penetration Test (CPT), and rock coring. While these methods provide high-quality measurements, they sample only a very small volume of material within individual boreholes. As a result, large portions of the subsurface remain uncharacterized, and critical features (such as voids, soft zones, or irregular bedrock surfaces) remain undetected between boreholes. Surface-based geophysical methods can provide broader spatial coverage; however, their resolution typically decreases rapidly with depth due to signal attenuation, limiting their effectiveness for deeper subsurface imaging.

Recent advancements in seismic testing have led to the development of the 3D SPT-seismic method, an innovative approach that integrates seismic wave analysis with conventional SPT operations to enable volumetric imaging around boreholes. The method records seismic waves generated by routine SPT hammer blows at depth using a 2D geophone array deployed at the ground surface. These waveforms are then analyzed using advanced 3D full-waveform inversion techniques to reconstruct a high-resolution three-dimensional shear-wave velocity (Vs) model surrounding the borehole. Field demonstrations at sites in Florida, Kansas, and Minnesota show that the method can produce subsurface images with approximately 2-ft spatial resolution across a large 3D domain extending up to 60 ft from the borehole at any tested depth (see additional document), with Vs profiles showing strong agreement with SPT-N values.

Despite its demonstrated potential, the current implementation still requires substantial manual data processing, limiting its routine use in practice. This project aims to advance the 3D SPT-seismic method by developing automated processing workflows and practical implementation guidelines that will enable state DOTs to efficiently generate high-resolution 3D subsurface images with routine SPT site investigations. The resulting capability will help reduce subsurface uncertainty, improve risk management, and support more informed design and construction decisions for transportation projects.

The primary objectives of this research are: (1) to automate the 3D SPT-seismic method and (2) to validate its applicability across a range of geological conditions commonly encountered by State DOTs to support widespread implementation. The project will focus on developing an integrated workflow that streamlines both data acquisition and analysis, enabling the method to be deployed efficiently alongside routine geotechnical investigations without disrupting standard SPT operations.

For automation, seismic signals generated by SPT hammer blows will be continuously recorded using a surface geophone array for all blows without interfering with the drilling crew. Advanced machine-learning algorithms will be implemented to automate key data-processing tasks, including signal conditioning, noise suppression, event detection, and removal of low-quality records. The processed data will be then analyzed via advanced 3D full-waveform inversion (FWI) to reconstruct a high-resolution 3D shear-wave velocity (Vs) image around the borehole, extending up to approximately 60 ft into the surrounding subsurface.

For validation, the methodology will be demonstrated through field testing at State DOT sites, with two test locations for each participating agency, representing a variety of soil and geological conditions. The results will be compared with SPT-N values to assess accuracy and practical benefits. By automating the analysis procedures and validating the method under real field conditions, this project will help transform the SPT-seismic approach into a practical and cost-effective tool for high-resolution geotechnical site characterization.

The scope of work consists of four main tasks: (1) automation of 3D SPT-seismic method, (2) development of a practical software tool, (3) validation of the method at participating State DOT sites, and 4) technology transfer and training

Task 1: Automation of 3D SPT-seismic method (year 1)

• Implement machine-learning algorithms to automatically process SPT-seismic data, including signal conditioning, noise suppression, event detection, and removal of low-quality records.
• Implement and accelerate a 3D full-waveform inversion (3D-FWI) framework to analyze the processed SPT-seismic data to obtain high-resolution shear-wave velocity (Vs) images around boreholes
• Apply adaptive meshing and fast-convergence optimization strategies within the 3D-FWI framework to enable practical turnaround times for engineering applications.

Task 2: Implementation of automated 3D SPT-seismic software (year 2)

• Develop a user-friendly software package with a graphical interface that allows engineers to import field data, run automated processing, and visualize 3D subsurface images.
• Include tools for data quality assessment, visualization of seismic waveforms, and interactive interpretation of Vs profiles and volumetric models.
• Prepare user manuals, implementation guidelines, and example datasets to facilitate adoption by transportation agencies.

Task 3: Validation of 3D SPT-seismic method at State DOT sites (years 3 and 4)

• Conduct field demonstrations at two test sites for each participating State DOT, selected to represent a range of common geological environments such as karst limestone, clayey deposits, and sandy soils.
• Collect seismic data generated by SPT hammer blows, analyze the data by the SPT-seismic software developed in Tasks 1 and 2, and compare the resulting 3D Vs images with SPT-N values to evaluate accuracy, resolution, and efficiency.
• Document the field procedures, performance, and lessons learned to develop practical recommendations for routine implementation by DOTs.

Task 4: Technology Transfer and Training (year 4)

• Transfer the SPT-seismic software package and associated documentation to participating State DOTs.
• Provide training and technical support to ensure successful implementation of the 3D SPT-seismic technology.

The estimated total project cost is $500,000, and the estimated duration is 4 years. Funding requested: $100,000 from each participating state/agency ($25,000/year for 4 years).