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SPT-Based Liquefaction Triggering — Boulanger & Idriss (2014)

Factor of safety against liquefaction triggering for an SPT profile: cyclic stress ratio with r_d, overburden-corrected (N₁)_60cs with the fines adjustment, CRR for M 7.5 and 1 atm, the 2014 soil-dependent magnitude scaling factor and K_σ.

Earthquake and site

a_max (geometric mean PGA) g

Moment magnitude M

Water table depth ft

MSF

SPT readings — one per line: depth (ft), N₆₀, fines content FC (%), total unit weight (pcf); add “C” to mark a clay-like (plastic) layer

Results

Minimum FS · layers with FS < 1—

z (ft)	σ′_v (psf)	r_d	CSR	(N₁)_60cs	CRR_7.5	MSF	K_σ	FS

MethodBoulanger & Idriss (2014), CPT and SPT Based Liquefaction Triggering Procedures, Report UCD/CGM-14/01: Eqs. 2.2, 2.14 (r_d), 2.15 (C_N), 2.16 (K_σ), 2.19–2.21 (MSF), 2.23 (fines), 2.25 (CRR). The 2014 update changed the MSF; the SPT CRR curve and fines adjustment are unchanged from Idriss & Boulanger (2008).

Verifiedr_d, CSR and the MSF and K_σ functional forms reproduced for case histories in the authors' Table 3.1; SPT coefficients checked against the values stated in the report.

Preliminary calculation tool. Final design requires the full text of the referenced standard (see the sources on this page) and review by a licensed PE.