Direct Shear Test - Soil Properties: Testing, Measurement, and Evaluation - page 384

Figure 23-7 Curve of Maximum Shear Stress versus Normal Stress

[D] Curve of Maximum Shear Stress versus Normal Stress

Using results of the direct shear test for which data are given in this
example (i.e., a normal stress of 604 lb/ft 2 and maximum shear stress of
1,522 lb/ft 2 ), an initial point on the curve of shear stress versus normal
stress can be plotted (see Figure 23-7). Using similar results of two
additional direct shear tests performed on other specimens at different
normal loads for which data are not given in this example (but for which
results are listed), two additional points on the curve can be plotted and
the best straight line drawn through these points. The angle between
this straight line and a horizontal line is measured to be 17°, and the
value of shear stress where the straight line intersects the ordinate is