Estimating CRR in laboratory

 

Panel Discussion at Geo-Congress, ASCE (2014). Idriss, Boulanger, Robertson, Cetin, Finn, Green, Stokoe, Mayne: “No laboratory tests are suitable for liquefaction estimation“. Only suitable field tests must be used.

 

 

Estimating CRR by CPT

 

Robertson & Wride (1998). CRR by CPT are adequate for low-risk projects. For high-risk : estimate CRR by more than one method.

Youd & Idriss (2001) (NCEER Workshops). Use 2 or more tests for a more reliable evaluation of CRR.

Idriss & Boulanger (2004). The allure of relying on a single approach (e.g. CPT-only) should be avoided.

Jamiolkowski et al. (1985). Use of Qc for evaluating CRR of natural sand subjected to a complex stress-strain history might appear questionable … Reliable predictions of sand liquefiability…require…some new in situ device [other than CPT or SPT] much more sensitive to the effects of past stress and -strain histories”.

Salgado et al. Jnl Asce (1997). OCR increases liquefaction resistance CRR, but changes negligibly Qcn.

Pyke (2003). Overconsolidation and aging are likely to have a much greater effect on increasing liquefaction resistance than they do on penetration resistance. Thus soils even lightly OC may have a greater resistance to liquefaction than indicated by the current SPT and CPT correlations, which are heavily weighted by data from hydraulic fills and very recent streambed deposits.

Lewis (1999). Using CPT current correlations in old/ aged sands will, at best, result in very conservative and uneconomical design, at worst in very costly remedial measures or cancellation of a project.

Schmertmann (1984). The cone appears to destroy a large part of the modification of soil structure caused by the overconsolidation and it therefore measures very little of the related increase in modulus. In contrast the lower strain penetration of the DMT preserves more of the effect of overconsolidation.

 

 

Estimating CRR by DMT

 

Williamson (2013). Thesis (Univ. of South Carolina). The SPT, CPT, and Vs tests are all well-developed methods of estimating liquefaction potential. However the DMT is believed by many researchers to be a superior alternative. Due to the DMT’s minimal disturbance the test is able to detect minor changes in soil fabric and thus is sensitive to stress history, cementation, bonding and aging, all factors which increase liquefaction resistance. The current SPT and CPT based methods, which do not account for the effects of aging, underestimate the South Carolina Coastal Plain soil’s resistance to liquefy (e.g. cyclic resistance ratio (CRR)) by as much as 60%.

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