Solve a ~ c

Problem $6\mathrm{.}15$CU triaxial compression tests were performed on two samples of a clayey soil containing $60\%$kaolinite and $5\%$illite$.$ The preconsolidation pressure for this soil was determined to be equal to $500$kPa$.$ Additional information about the soil includes: Gs $=2\mathrm{.}63$; smectite content ; nonclay material mostly composed of quartz and other silicates; and void ratio $=1\mathrm{.}021\mathrm{.}07.$One sample was isotropically consolidated to $125$kPa; the other, to $313$kPa before shearing. The results of the shearing stage of the test are shown in P$-$Figure $6\mathrm{.}5$and P$-$Table $6\mathrm{.}4.($a$)$Determine the OCR for each sample. $($b$)$Determine the undrained shear strength su$.($c$)$Estimate the critical$-$state friction angle of this soil.