A Case Study of the Application of Lightweight Fill for the Restoration of an Interchange Ramp

A highway embankment and a sanitary sewer were constructed in the City of London, Ontario, Canada. During construction, a manhole settled approximately 1.5m. There were signs of rotational movement and slope instability in the interchange ramp embankment itself. These movements were attributed to insufficient removal of a deep deposit of peat beneath the ramp embankment identified in the original site investigation. As part of remedial work, additional peat was removed and replaced with compacted sand. Despite these measures, the manhole continued to settle. Monitoring over a period of 30 months showed that the manhole settled by an additional 260mm. Four alternatives were considered to correct the problem. 1. Repair the sanitary sewer at its present location using the same methods as previously employed (excavate and replace). 2. Relocate the sanitary sewer outside the area of influence of the ramp fill and support it on piles and restore the upper part of the embankment with lightweight fill. 3. Reinforce and support the sewer in its present location with pile foundations. 4. Re-route the sanitary sewer. The final remedial strategy consisted of Alternative No. 2 to reduce the amount of further settlements and instabilities. The case history of this project and application of lightweight fill under the conditions described above are discussed in this paper