Liquefaction Analysis (Seed–Idriss) — Ebora

💧 Liquefaction Analysis

SPT-based Seed–Idriss simplified liquefaction triggering at a depth — the cyclic stress ratio CSR, the corrected (N₁)₆₀ and fines-corrected (N₁)₆₀cs, the cyclic resistance ratio CRR₇.₅ (Youd et al. / NCEER), the magnitude scaling factor MSF and overburden K_σ → the factor of safety against liquefaction, with a soil-column diagram, worked steps and a PDF report.

💧 Free for Ebora students · analyse any depth · Balance … EP

Earthquake

a_max (g)

Moment magnitude M_w

K_σ (overburden)

Soil & depth

Depth z (m)

Water table depth (m)

γ moist (kN/m³)

γ_sat (kN/m³)

SPT N (field)

Hammer energy ER (%)

Fines content FC (%)

N₆₀ = N·(ER/60) (fold rod/borehole/sampler corrections into ER if you apply them). C_N = √(Pₐ/σ′ᵥ) ≤ 1.7 with Pₐ = 101.3 kPa. The depth must be at or below the water table for liquefaction to apply.

📘 Results

CSR

—

cyclic stress ratio

CRR₇.₅

—

(N₁)₆₀cs = —

FS against liquefaction

—

CRR·MSF·Kσ / CSR

Worked solution

⚠️ Teaching tool — Seed–Idriss simplified (SPT) with Youd et al. (2001) CRR and Idriss MSF. r_d, C_N, the fines correction and MSF are empirical; confirm against your course method / NCEER and the governing code before any real assessment. FS ≥ ~1.2–1.3 is commonly required for design.