Background/Objectives. In-situ capping is one of the commonly used remediation techniques for contaminated subaqueous sediments.
Sediments often encountered in capping projects are very soft, which makes collection of undisturbed samples for laboratory testing practically impossible. Because capping projects commonly cover a large area, spatial variation of subsurface conditions and geotechnical properties can be significant. Conducting a comprehensive geotechnical field investigation can be difficult, time-consuming, and expensive. The purpose of this presentation is to discuss an integrated approach using geophysical and in-situ geotechnical methods in order to analyze the slope stability of capping placement.
Approach/Activities. This presentation describes various in-situ geophysical and geotechnical site investigation techniques that are applicable to soft sediments, including the multi- and single-beam bathymetry, back-scatter sonar, sub-bottom profiler, and in-situ geotechnical methods (e.g., full flow penetrometer testing). Pros and cons of each technique are described. The practicality of these techniques to soft sediments will be discussed too. An example of an integrated site characterization using both geotechnical and geophysical methods for a large sediment dredging and capping project will be presented.
Results/Lessons Learned. Geophysical methods can delineate the areas where there is a stability concern and/or a higher variation in geotechnical properties is expected. For the example subsurface sediment investigation project, the data from geophysical methods compared well with the in-situ geotechnical data. The data from the integrated site investigation program assisted in developing a subsurface model and characterizing the subsurface condition and supported the sediment capping slope stability evaluation.