Sidewalk Undermining Studies: Phase III, Field and Model Studies

Report No: 79-R35

Published in 1979

About the report:

The results of the early studies of the undermining problems are summarized in the initial portion of this report. Additionally, the design and use of a model sidewalk for testing procedures for preventing undermining are described. Based upon tests with the various model setups the following conclusions are made: 1. Close to maximum compaction of the subgrade soil does not prevent sidewalk undermining. 2. A No. 21-A stone compacted as a sidewalk subbase prevents sidewalk undermining, but may transfer the undermining to another location. 3. Modification of the subgrade soil by the addition of 2% agricultural grade hydrated lime prevents sidewalk undermining, while the transfer phenomenon could be prevented by modifying the strip of soil 4" from the back of the sidewalk to the edge of pavement. Through the observation and evaluation of field test sites and sidewalk undermining sites the following conclusions are made: 1. Close to maximum compaction of the subgrade soil, either with or without use of cut-off walls, does not prevent sidewalk undermining. 2. A drainage system constructed under the sidewalk has been very effective in preventing sidewalk undermining. 3. The reuse of existing sidewalk slabs is feasible for sidewalk repair.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


  • Harold W. Plott

Last updated: January 26, 2024

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