SlipSurface IQ Liquefaction

Foundations

Liquefaction from the SPT and CPT

Susceptibility, triggering by Idriss & Boulanger (2014), NCEER, Cetin and TBDY 2018, post-liquefaction settlement, lateral spreading, LPI and LSN; cyclic softening and reliability studies.

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English, Turkish

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A borehole — soil layers with their fines content and Atterberg limits, and the SPT blow counts or a CPT sounding beside it — is assessed for the design earthquake, depth by depth:

1. Susceptibility — can the soil liquefy at all? Coarse-grained and non-plastic soils are sand-like; fine-grained soils are judged from their liquid limit, plasticity index, water content and clay fraction by Bray & Sancio (2006), Boulanger & Idriss (2006), Seed et al. (2003), Andrews & Martin (2000) or the Chinese criteria.
2. SPT corrections — N₆₀ from the hammer energy, borehole diameter, rod length and sampler, reduced in gravelly layers (JRA 1996); (N₁)₆₀ with the overburden correction; the clean-sand equivalent (N₁)_60cs from the fines content. CPT — q_t, the soil behaviour type index I_c, the fines content from I_c, q_c1N and q_c1Ncs; soundings are pasted or imported from CSV.
3. Triggering — the cyclic stress ratio of the earthquake against the cyclic resistance ratio of the soil, and the factor of safety with depth, by Idriss & Boulanger (2014), Youd et al. (2001, NCEER), Cetin et al. (2004) or TBDY 2018 from the SPT; by Idriss & Boulanger (2014) or Robertson & Wride (1998) from the CPT. The procedures not chosen are run too, for a comparison; clay-like soils are checked for cyclic softening (Boulanger & Idriss 2007).
4. Consequences — post-liquefaction volumetric strain and settlement, the seismic compression of dry sand above the water table, lateral spreading of a gentle slope or towards a free face, and the indices LPI and LSN.
5. Checks — the lowest factor of safety against the required one (1.1 in TBDY 2018) and the settlement against the allowable.

On top of it, a parametric or reliability study sweeps any input — the acceleration, the magnitude, the water table, a layer's fines content, a single blow count — and reports sensitivities and the probability of liquefaction or of exceeding the allowable settlement, with the reliability index β.

Screenshots

Results summary and borehole log

Factor of safety against liquefaction with depth

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SlipSurface IQ Liquefaction runs in the browser as part of the online SlipSurface IQ suite. It is on the Plus plan.

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Next steps

• Reference — inputs, methods, figures and reports.
• Theory — the formulas, their limits and the full references.