Triaxial compression: triaxial compression test; SS: simple shear test; Meaning of regression metrics: Multiple R: Return the correlation coefficient of the data sets; R² (coefficient of determination), proportion of the variance in the dependent variable explained by the model; Adjusted R²: R² adjusted for the number of predictors; compensates for small sample sizes; Standard error: standard errors for Y estimate; df: degrees of freedom is the number of observations minus 2; F-statistic: Tests whether the regression model explains a significant amount of variance; p-value (F-test): Probability of observing the F-statistic if the model had no explanatory power; t-statistic: Tests whether an individual coefficient (e.g. slope) differs significantly from zero; and p-value (t-test): Probability of observing the t-statistic if the coefficient were actually zero