# 4.9 Problems

1. The following data presents the results of triaxial tests performed on a dry samples of cohesionless fine sand from the Frio formation in the Gulf of Mexico Basin:

 Confining pressure Pore pressure Peak deviatoric stress [MPa] [MPa] [MPa] 3.4 0 7.1 6.9 0 20.6 10.3 0 29.7

1. Plot the maximum principal effective stress as a function of for the three experiments. Fit a line that goes to the intercept (0,0) and calculate the shear strength parameter .
2. Replot the data as Mohr circles, calculate the shear angle and plot the shear yield line. Does the shear yield line intersect the Mohr circles?

2. The file Triaxial-1500psi-raw.dat (uploaded to Github) contains data from a triaxial test performed on a sandstone in dry conditions ( = 0 psi). is the confining pressure, is the deviatoric stress (), is the axial strain, and is the radial strain.
1. Plot deviatoric stress and strains as a function of time (two plots). Mechanical experiments are usually performed at constant strain rate or constant stress rate. Which case is this? What is the rate?
2. Plot deviatoric stress as a function of axial strain. Compute loading Young modulus at 25% of the peak stress and the unloading Young moduli for the two unloading cycles. Comment on the difference.