What corrections are applied to raw SPT N-values?

The normalized value is (N1)60 = N × CN × CE × CB × CR × CS, where CN is the overburden correction (Liao & Whitman, 1986: CN = min(2.0, (Pa/σ'v)^0.5)), CE is energy ratio correction (typically CE = ER/60), CB is borehole diameter correction, CR is rod length correction, and CS is sampler type correction. Values are per ASTM D1586 and Youd et al. (2001).

Why is SPT N-value correction important?

Raw N-values depend on equipment, procedure, and overburden stress. Normalising to (N1)60 allows comparison between sites and is required as input for liquefaction potential assessment (Seed & Idriss, 1971), bearing capacity correlations, and relative density estimates per ASCE 7.

SPT N-Value Correction (Liao-Whitman)

Correct field SPT blow counts to normalized (N1)60 values for effective overburden pressure, hammer energy, borehole diameter, rod length, and sampler type per Liao & Whitman (1986).

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How to Use

Enter the values for the patient or scenario you are assessing. Correct field SPT blow counts to normalized (N1)60 values for effective overburden pressure, hammer energy, borehole diameter, rod length, and sampler type per Liao & Whitman (1986). Use the spt n correction result to inform your clinical assessment.

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SPT N-Value Correction (Liao-Whitman)

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Frequently Asked Questions

What corrections are applied to raw SPT N-values?

Why is SPT N-value correction important?