Tilt test (geotechnical engineering)

Tilt test

A tilt test is simple test to estimate the shear strength parameters of a discontinuity. Two pieces of rock containing a discontinuity are held in the hand with the discontinuity horizontal. The sample is slowly tilted until the top block moves. The angle with the horizontal at start of movement is the so-called tilt angle.

Tilt angle

The tilt angle is not directly comparable to the parameters measured in a direct shear test. Only if no cohesion (apparent or real) is present, the asperities do not break, and the two blocks contain a fitting discontinuity, the tilt angle equals the material friction plus the roughness i-angle (tilt angle = φ_material + i). The tilt angle equals the friction of the material of the discontinuity wall if the discontinuity in the sample is completely non-fitting (tilt angle = φ_material). In other cases, the tilt angle is a combination of the (apparent) cohesion and friction of the discontinuity.