How can i obtain the CRR or CSR value from the UBC3D-PLM constitutive model?

Question

I am modeling tailing dams in plaxis and i need to obtain the CRR or CSR value to plot it versus the N1,60 value and generate the CRR or CSR V/S N1,60 value. 
 Thanks and regards to all

Stefanos Papavasileiou · Answer

Dear Sebasti&aacute;n, 
 
 The concepts of cyclic stress ratio (CSR) and cyclic resistance ratio (CRR) are used by semi-empirical procedures (e.g. Seed and Idriss, 1971; Youd et al., 2001; Idriss and Boulanger, 2014), aiming at estimating a factor of safety (FS) against soil liquefaction: FS = CRR / CSR. 
 The CSR involves the transformation of given earthquake-induced stresses into an &ldquo;equivalent&rdquo; series of shear stress cycles with uniform amplitude. According to the semi-empirical procedures, CSR can be computed at a given level of the deposit as: CSR = 0.65 tau-max / sigma&rsquo;v0, where tau_max is the maximum earthquake-induced shear stress and sigmav&rsquo;0 is initial vertical effective stress. Providing that the shear stress time-history at a given level is obtained, it is possible to determine tau_max and, given the initial vertical effective stress, to compute CSR. 
 Conversely, CRR is a measure of the soil&rsquo;s resistance to liquefaction and is typically estimated based on empirical correlations with field test results(e.g. Seed and Idriss, 1971; Youd et al., 2001; Idriss and Boulanger, 2014). Alternatively, it may be estimated based on the results of element laboratory tests using uniform loading conditions (e.g. Seed et al., 1975). 
 Although it is possible to simulate element laboratory tests in PLAXIS (e.g. using SoilTest facility) and obtain a measure of CRR for each level of the deposit following the guidelines proposed, e.g., by Seed et al. (1975), it is more usual to compute the liquefaction potential from a Finite Element analysis and, based on that, to obtain a measure of the shear resistance of soil to liquefaction in relation to the earthquake-induced shear stresses. 
 
 Note that the liquefaction potential is often computed based on the excess pore pressure ratio, ru, which can be inspected in PLAXIS Output. Note also that detailed guidelines on this procedure are provided here: https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/46050/site-response-analysis-and-liquefaction-evaluation .

Martin Hawkes · Answer

You will need to select some stress points at the start of the calculation. Plaxis will calculate the shear stress during the event and keep track of it at the points. When the analysis is completed you can use the curves to plot the shear stress at that point and get the maximum. 
 Martin

How can i obtain the CRR or CSR value from the UBC3D-PLM constitutive model?

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