Assessing the Effectiveness of Compaction Grouting Using Seismic Methods

Grouting has been successfully used for decades as a ground improvement technique to stabilize and retrofit historic structures. Over the years, new technology, equipment, and chemicals have improved the feasibility of grouting over a wide range of applications. However, near real-time, in situ control methods to assess the effectiveness of ground improvement following subsurface grouting are lacking. Currently, the most commonly used quality assurance method is to obtain Standard or Cone Penetration Test (SET or CPT) measurements before and after ground treatment at pre-defined locations, typically between column/impact/injection locations to observe changes in relative density of in-place materials. All these methods are based on point measurements at specific locations and do not represent the overall treated ground mass. A volumetric, non-destructive, surface seismic evaluation method, that uses a state-of-the-art algorithm, was recently developed to collect and analyze seismic data describing the subsurface conditions. This relatively rapid and inexpensive seismic method was utilized in Rocky Mountain National Park, Colorado, during rehabilitation of a historic placed-rock armored slope structure located below roadway grade along the outboard lane. Compaction grouting was selected to stabilize roadway settlement caused by piping of a failed culvert within the fill while preserving the historic and aesthetic character of the structure. The seismic method proved effective in producing accurate pre- and post-grouting volumetric difference images that depicts the effect of grouting, including the resultant grout columns and ground densification characteristics.