The following are the results of four drained direct shear tests on undisturbed normally consolidated clay samples having a diameter of 50 mm. and height of 25 mm.
![336_b4ea50c2-69e3-4dcc-aa78-411f8e87cfe8.png](https://secure.tutorsglobe.com/CMSImages/336_b4ea50c2-69e3-4dcc-aa78-411f8e87cfe8.png)
Draw a graph for shear stress at failure against the normal stress and determine the drained angle of friction from the graph.