Halifax sits on a drumlin field. Glacial till dominates the landscape, but the composition varies block by block. One street gives you dense, well-graded material. The next, a silty pocket that refuses to compact. The city's rapid growth in Bedford and Dartmouth Crossing pushes earthworks into these marginal soils. A lab curve from a generic soil manual won't help. The Proctor test must match the actual fill coming off the site. We run both Standard (ASTM D698) and Modified (ASTM D1557) procedures to establish the moisture-density relationship that the field crew will chase with the nuclear gauge. For deep structural fills over compressible marine clay, the compaction spec often ties directly to the slope stability analysis of adjacent cuts.
A Proctor test is not a soil classification. It's a compaction recipe for a specific fill material.
Local considerations
Compaction failure in Halifax follows a pattern. The south end, with its slate bedrock and thin till cover, rarely surprises. But the clay plain around Fairview Cove and the filled ravines in Clayton Park are different. Loose, undocumented fill from the 1970s sits over compressible marine clay. If the Proctor curve was developed on a blended sample that doesn't represent the actual fill, the field density test will pass while the fill settles later. Another risk is moisture control during wet weather. Halifax averages over 1,400 mm of precipitation annually. A stockpile can go from optimum to saturated in one rainstorm. The lab re-runs the Proctor when the source material changes. That's the spec. CSA A23.1 references ASTM D698 for structural backfill. The NBCC requires compaction to 95% or 98% of standard Proctor maximum dry density for foundation support, depending on the bearing stratum classification.
