Rubblization over Soft Soils: The Florida Experience

In 1998, two concrete pavement sections were rehabilitated using rubblization techniques on a major Interstate in Florida. The pavement in general performed well, except for certain regions that failed pre-maturely and showed severe rutting. The Florida Department of Transportation was aware of the potential problems associated with rubblization especially over soft subgrade and took what were considered adequate precautions before and during construction. Edge drains below the rubblized layer were installed and the breaker speed was modified when sufficient compaction was not achieved due to soft subgrade. A study was conducted to determine the cause of failure in these regions. The analysis of FWD data showed that the failure of these regions was due to the development of pore pressures in the subgrade during rubblization. The pore pressures mobilized water to flow into the sandy-clay base underneath the rubblized layer, leading to poor compaction after rubblization and severe rutting with localized potholes immediately after the first holiday traffic. This study appears to show that in case of subgrade with high water table, the current techniques used for rubblization may not be enough to prevent catastrophic failures, as observed in this case. Allowing sufficient time for pore water to dissipate and drain through the edge may help in reducing pore pressure. However, in such cases, techniques other than rubblization as a method of rehabilitation, like crack and seat with a multiple head breakers should be considered.