(Solved): Can you please show how to answer part A with the graph? and how to use the line of best fit method ...

12.4 During a subsoil exploration program, undisturbed normally consolidated silty clay samples were collected in Shelby tubes. (13.4 in \( 10 \mathrm{~cd} \).) Following are the results of four drained, direct shear tests conducted on the clay samples with each having a diameter of \( 63.5 \mathrm{~mm} \) and height of \( 32 \mathrm{~mm} \). 13.4 During a subsoil exploration program, undisturbed normally consolidated silty clay samples were collected in Shelby tubes from location \( A \) as shown in Figure 13.62. FIGURE \( 13.62 \) a) Graph shear stress at failure vs. normal stress (5 points) b) Determine the drained angle of friction for the silty clay soil by using the line best-fit the shear stress at failure vs normal stress data. (5 points) Note: You may determine the drained angle of friction by using only one test results at a time and then report the average value. This method will lead to large errors sometimes. Best-fit method will effectively utilize all the data points and eliminate possible errors. c) Determine the shear strength of the clay in the field at the location A (5 points, hint: use Mohr-Coulomb failure criteria).