Quick lab-floor trivia: SPT corrections target 60% energy — so with a 63.5 kg hammer dropping 760 mm, do you still convert N to N60 before correlating to bearing capacity and settlement for shallow footings, or have you moved to CPT and oedometer-based parameters? I’m curious what people are doing in routine foundation design.
I still convert to N60; our auto-hammer ER rarely sits at 60%, so we verify ER once per rig with an instrumented rod and scale via N60 = N*(60/ER) before footing correlations (FHWA NHI-16–009: https://www.fhwa.dot.gov/engineering/geotech/pubs/nhi16009.pdf). For clean sands I’ll cross-check with CPT if qc is available — are you seeing ER stay consistent across crews?
For routine footings I normalize to N60 and then to (N1)60 with overburden (C_N), and I only use the SPT correlations if sampler/rod/borehole corrections per NCEER ’97 and an ASTM D4633 energy check are on record. If CPT is in the hole, I’ll use qc1Ncs for settlement and keep SPT as a check — “apples to apples” beats heroic assumptions; curious how often you’re re-checking ER on your rigs, @jackson4243.
I convert N to N60 using the measured ER for the actual rod string on the 63.5 kg rig — short rods make the raw N useless, — and keep SPT‑N60 for bearing while leaning on CPT/oedometer for settlement. One concrete step: pull the hammer’s calibration sheet and back‑calc ER for that day before any other corrections. @jackson4243 do you fix ER at a nominal 70% or update it after tool changes?