Liquefaction Triggering Screening (Seed-Idriss CSR)
Seed-Idriss screen: rd = 1 - 0.00233172 z (z <= 30.02 ft; per-meter 0.00765/0.0267 scaled by 0.3048).
Example
You enter
- Peak ground acceleration (g) 0.3
- Total vertical stress (psf) 2000
- Effective vertical stress (psf) 1200
- Depth (ft) 16.4042
- Cyclic resistance ratio CRR 0.2
- Magnitude scaling factor (Mw 7.5 = 1.0) 1
You get
- Stress reduction factor rd 0.962
- Cyclic stress ratio CSR 0.313 (rd 0.962)
- Factor of safety FS 0.64 -- LIQUEFIABLE (FS < 1)
Checked against published worked examples from: Caltrans.
Details, formula, and sources
ScopeCSR = 0.65 amax (sv/s'v) rd, FS = (CRR/CSR) MSF, liquefiable if FS < 1. amax 0.30g, sv 2000, s'v 1200 psf, z 16.4 ft, CRR 0.20 -> CSR 0.313, FS 0.64, liquefiable; denser sand (CRR 0.40) -> FS 1.28. A level-ground screen; the geotechnical engineer of record governs.
Formula or tablerd = 1 - 0.00233172 z (z <= 30.02 ft), 1.174 - 0.00813816 z (to 75.46 ft), 0.744 - 0.0024384 z (to 98.43 ft), else 0.5; CSR = 0.65 amax (sigma_v/sigma'_v) rd; FS = (CRR/CSR) MSF; liquefiable if FS < 1.
Source and editionThe Seed-Idriss simplified liquefaction-triggering procedure (NCEER/NSF workshop consensus), by name.
Free accessThe Seed-Idriss simplified CSR/CRR procedure and the rd relation are standard published earthquake-geotechnical results.
What governsEstimate. AHJ and licensed professional govern.
API field namesamax_g, sigma_v_psf, sigma_vp_psf, depth_ft, crr, msf, rd, csr, fs
- Cyclic stress ratio CSR = 0.65 amax (sigma_v/sigma'_v) rdSeed-Idriss
- Factor of safety FS = (CRR/CSR) x MSF; liquefiable if FS < 1Seed-Idriss / NCEER
- Screening only level ground; fines/overburden corrections and settlement are separatescope of this tile