Shear Strength of Tire Shreds

Direct shear test results are given in figure 1.

Figure 1. Shear stress vs. horizontal deformation for Pine State Recycling tire shreds tested in direct shear box (Humphrey, et al., 1992)

Figure 2 compares failure envelopes for low stress levels (less than about 2000 psf).  These failure envelopes are non-linear and concave down.  Tests on 0.5-in and 1-in tire shreds at higher stress levels produce failure envelopes that are approximately linear.  For high stress tests, using a failure criteria of 15% axial strain, Ahmed (1993) obtained cohesion intercepts from 572 to 689 psf and friction angles from 15.9 to 20.3 degrees.

Figure 2. Comparison of failure envelopes of tire shreds at low stress levels

References:

            (21)Humphrey, et al, 1992

            (9)Cosgrove, 1995

            (20)Benda, 1995

Procedures

A direct shear apparatus and ASTM D 3080 or a triaxial shear apparatus can be used to measure the shear strength of tire shreds.  When testing tire shreds, larger sample sizes have to be used than are necessary for other soils.  This is due to the larger particle size of tire shreds.  Large triaxial shear apparatuses only have limited availability, so tests are generally completed on 1-in or smaller tire shreds.  The triaxial shear apparatus also shouldn't be used for tire shreds with protruding steel belts.

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