Remediation of Settlement in Shallow-to-Deep Utility Trenches using Low Mobility Compaction Grouting Techniques in Cohesive Backfill

Cohesive clay backfill in utility trenches might not always be uniformly compacted to project specifications and can experience excessive settlement over time. Utilities are usually installed beneath paved roadways. Settlement can affect the performance and drainage characteristics of the paved surface and in severe cases can be a safety issue. Patching and overlays can provide short-term solutions but do not address the long-term risk or ongoing maintenance costs. Mechanical removal, reworking or replacement of fill may not be efficient, practical, or economical, and may have risk of future movement if not properly reconstructed. Densification of in-place cohesive trench backfill using compaction grouting techniques with low mobility grout is a suitable, efficient, and less intrusive method of improving the long term performance of trench backfill and support for surface improvements. In most cases the technique can lift the existing pavement surface or other features to desired grades, potentially minimizing the need to replace infrastructure, patching, or overlays. This technique has been used for numerous projects along the Front Range corridor of Colorado, in particular the Denver Metropolitan Area, over the past 20 years. This paper describes three recently completed projects that demonstrate the viability of low mobility compaction grouting in cohesive soils. The technique was successfully performed in trenches ranging in depth from 1.5 to 9.1 m (5 to 30 ft). In these cases the pavement surface was left intact with very little overlay patching or replacement being needed after remediation.