Tilt test (geotechnical engineering)
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 (Figure). The angle with the horizontal at start of movement is the so-called tilt angle.
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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 (. The measured tilt angle will equal the friction of the friction of the discontinuity wall if the discontinuity in the sample is completely non-fitting. In other cases, the tilt angle will be a combination of the discontinuity roughness properties.