The detection, classification, and remediation of military munitions found at underwater sites of varying environmental conditions ranging from shallow waters to water depths of up to 35 meters need innovative ideas and techniques for rapid site characterization. Rapid characterization is important for mapping targets, as well as the development of efficient solutions for management, removal, or disposal of the munitions. The characterization of the seabed soil is particularly important due to its direct interaction with the munitions and response actions. Additionally, the effects of benthic biogenic processes on seabed soils, potentially altering geotechnical soil properties on various spatiotemporal scales, need to be considered. For the application of soil characterization to unexploded ordnances (UXO), risk assessment and site management, it is crucial to deepen the fundamental knowledge of the impacts of different soil behavior classes on acoustic UXO detection and classification methods, soil erodibility and mobility, and the susceptibility of soils to liquefaction processes under wave action. Finally, it is important to integrate soil properties into a broader UXO risk assessment scheme such as Underwater Munitions Expert System (UnMES). In response to these needs, the objectives of this project are to: i) develop a soil behavior classification scheme based on portable free fall penetrometer measurements; ii) identify effects of benthic biogenic processes on geotechnical soil properties and integrate these effects in the soil classification scheme; iii) identify and quantify the impacts of the different soil classes on acoustic UXO detection and classification methods, on erodibility estimates, and on susceptibility to soil liquefaction processes; and iv) develop strategies to implement the effects of soil classes into UXO risk assessment with UnMES.

In line with the project objectives, four main tasks are identified: i) A soil classification scheme will be developed based on portable free fall penetrometer measurements (PFFP). In SERDP project MR18-1233 it has been demonstrated that rapid soil classification from PFFP is possible. Here, a classification scheme following examples from traditional Cone Penetration Testing (CPT) will be developed. Based on this soil behavior classification, a Bayesian framework will be explored for probabilistic soil behavior classification as also recently demonstrated for CPT. ii) The effects of benthic biogenic processes on soil behavior have been successfully detected by PFFP in the past. Here, this issue will be revisited more strategically through the development of a conceptual model relating geotechnical properties and benthic biogenic process groups, targeted field investigations, and quantification of impacts of benthic biogenic processes on geotechnical properties. The newly gained relationships will be integrated in the developed soil behavior classification. iii) A key challenge is to integrate information from the advanced soil classification into UXO detection and classification methods. For this reason, new field data will be collected and existing data sets assembled to advance the correlation of geotechnical and geoacoustic methods, and to enhance the understanding of the impacts of geotechnical properties on soil erosion and liquefaction processes. iv) Finally, this project aims to provide a soil classification scheme that enables the integration into UnMES. The project team will reach out to the UnMES developers and develop a pathway to a direct integration of the probabilistic soil classification framework into UnMES.

The main benefit to Department of Defense is the integration of rapid and cost-effective seabed site characterization into the broader context of UXO detection, classification, risk assessment, and management. This will lower uncertainty in UXO risk assessment and site management. Benefits to the scientific community include the increased understanding of correlations between biogenic seabed processes and geotechnical seabed properties, as well as correlations among geotechnical and geoacoustic properties, erodibility, and liquefaction under ocean wave action in shallow water (< 35 m) environments.