IS 1893Cl. 7.6 (Part 1)

Liquefaction — simplified screening

Sites with saturated cohesionless soils within 20 m of GL must be screened for liquefaction. Cyclic stress ratio (CSR) compared with cyclic resistance ratio (CRR) — FoS_liq < 1.0 indicates liquefiable.

Formulas

CSR (NCEER)
CSR = 0.65 × (a_max / g) × (σ_v / σ'_v) × r_d

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Editorial paraphrase for fast lookup — the official IS 1893 text is authoritative. For exact wording, refer to the published code.