Non-Destructive Evaluation of Installed Soil Nails
Recent forensic studies that investigated failure of several Texas Department of Transportation (TxDOT) soil nailed retaining walls revealed that incomplete grouting of soil nails was a very common problem. This finding has raised serious questions about the adequacy of QC/QA procedures currently used by TxDOT for verifying the integrity of installed soil nails. The research study described in this report attempted to address these concerns by: (a) developing of a non destructive test method to check the integrity of soil nails, (b) identifying the construction variables that have the most dominant influence on grout integrity and developing guidelines to control them. Sonic Echo method was selected, further refined and "customized" for non-destructive evaluation of soil nail grout columns. Optimum test parameter combination to be used with Sonic Echo testing was determined through several cycles of NDT testing that were conducted at an experimental soil wall that was specially built for this research. Among the various construction variables examined, grout rheology (or flowability) and tremie insertion length were found to be the most important parameters that influence integrity of soil nail grout columns. A new grout consistency requirement is proposed based on the findings from the research.