Objective

While the mechanisms for munitions burial in non-cohesive sediments are well established, be it through scour-burial processes (see the Office of Naval Research's mine burial studies) or granular sorting (Calantoni, MR-2320), the resistive nature of cohesive sediment to granular erosion reduces the likelihood of granular sorting as a primary mechanism for burial, inhibits scour (Inman and Jenkins, 2002), and may result in other mechanisms for burial not characteristic of non-cohesive sediments (Baeye et al., 2012; Sheremet et al., 2005). This study expands the research on the Munitions and Explosives of Concern (MEC) mobility and burial in cohesive sediments by investigating the geotechnical properties of cohesive sediments that contribute to MEC mobility and burial as observed in detailed field experiments in MR-2730.  

University of Delaware R/V Joanne Daiber equipped with Edgetech 6205 Phase-measuring Echo Sounder.

Technical Approach

Leveraging existing resources and knowledge gained from previous and ongoing SERDP Munitions Response studies, this study couples periodic site-wide geophysical surveying with contemporaneous in-field geotechnical sediment characterization through repetitive sampling and application of a SERDP supported penetrometer (Dr. Nina Stark, MR18-1233) at an munitions mobility and burial study site (MR-2730).

Geotechnical site characterization was provided by Dr. Nina Stark and her team. Data was collected with a portable freefall penetrometer (A), and ground-truthed with sediment samples and gravity cores (B).

Results

Sediment bearing capacity is shown to be an important predictor for surrogate burial in mixed-cohesive or cohesive sediments. A Hertzian contact model introduced here provides a simple method to predict munitions burial due to bearing capacity. This study additionally demonstrates methods to link sediment geotechnical properties such as bearing capacity to sonar classification/surficial sediment distributions maps.  

Benefits

Results from this combined effort include better characterization of munitions mobility as influenced by cohesive sediment geotechnical properties, as well as providing an in-field demonstration of the penetrometer technology and methods being refined by  MR18-1233. Data from this study contributed significantly to the munitions mobility and burial analysis presented in  MR-2730 and assists in the continued development of existing expert system modeling of unexploded ordnance burial and mobility (e.g. Underwater Munitions Expert System, Rennie MR-2645). The methods and results presented in this study provide additional information pertinent to formerly-used defense site (FUDS) management. Extrapolating subsurface properties based on surficial sediment distributions will reduce the amount of geotechnical sampling required at FUDS sites and allow for modeling of surrogate burial across a wide spatial domain.

  • Munitions Mobility and Burial ,

  • Cohesive Sediment Properties ,

  • Instrumented Munition Surrogates ,

  • Penetrometer Sediment Measurements