Strength failure case histories

Olson, S.M. and Stark, T.D. Liquefied strength ratio from liquefaction flow failure case histories. Canadian GeotechnicalJoumal, 39, 629-647, 2002. 

Robertson (2010) added three flow failure case histories to the Olson and Stark (2002) database and proposed a correlation that utilizes cone penetration test measurements (normalized net tip resistance, Qt , and normalized friction ratio, F ) to define a contractive-dilative boundary and a correlation to estimate liquefied strength ratio using equivalent clean sand normalized net tip resistance, Qm.cs- These correlations are shown in Fig. 20. Robertson (2010) also recommended that the liquefied shear strength be limited to the drained shear strength of the soil. 

Residual Strength of Liquefied Soils, Fig. 21 Comparison of liquefied strength ratios for field and laboratory data. Flow failure case histories from Olson and Stark (2002). Laboratory data include only Type A (contractive) response where... 

Seed (1987) first proposed to back-analyze liquefaction failures to estimate liquefied shear strengths. However, as discussed by Olson and Stark (2(X)2), there were a few limitations and inconsistencies in the back-analyses performed by Seed (1987). Seed and Harder (1990) expanded the work by Seed (1987), and their resulting correlation is stiU used in practice. Olson (2001) nearly doubled the number of back-analyzed case histories (from 17 to 33) used by Seed and Harder (1990) and performed kinetics analysis for 10 of the 33 case histories with sufficient documentation. This database has been widely used by numerous researchers (e.g., Idriss and Boulanger 2(X)7 Robertson 2010) for evaluating liquefied shear strengths and strength ratios. 

Figure 16 presents a correlation proposed by Seed and Harder (1990) between liquefied shear strength and (NOeo-cs based on the back-analysis of 17 liquefaction flow failures and liquefaction-induced lateral spreads. Seed and Harder (1990) updated the work from Seed (1987), adding a few case histories and considering the kinetics of failure for an unknown number of cases. This correlation remains widely used in practice for estimating the liquefied shear strength. 

The degradation of the composite laminates can be modelled as simple strength criteria for fibres or matrix, before delamination occurs. Eigure 9.19 shows the test force history for a 200 x 200 mm plate and the various numerical EE (77) predictions (Davies et al. [42]), The hnear elastic case does get the time of the event but underestimates the peak force by a factor of 3. The damaged EE prediction overestimates the force but does get the departure from the linear solution correctly. The fuUy degraded solution (with much fibre failure) does match the experimental history. Delamination was confined to one interface near the mid-plane as the C-scan image indicates. 

Stress and strain at failure are readily calculated from the sample geometry in both cases. If failure has not occurred with 5 percent deflection strain, this is usually reported as the flexural yield strength. In practice, results depend on the heat history of the sample, extent of fusion, uniformity of dispersion, and freedom from surface cracks. Generally, molded specimens yield higher values than those die-cut from pressed sheets or actual articles of commerce. 

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