Compacting or Filling With Concrete

(1)  The soil in trenches beneath footings for sewers and watermains shall be compacted by tamping up to the level of the footing base, or shall be filled with concrete having a strength not less than 10 MPa to support the footing.

Article 9.12.4.1 Ontario Regulation 332/12 Building Code,   Information published by oncodes.ca for educational purposes only.