The monotonic shear tests are carried out to investigate the mechanical properties of rock mass joints with the second-order asperities

which simulated by small regular saw tooth; and gypsum material is used to simulating rock mass joint samples. Five artificial joint samples with different heights of second-order asperities are tested under low normal stress

which keep constant during the tests. Characteristics of shear strength and deformation are analyzed; an interpretation of the joints failure modes is given. Based on the experimental results

it can be found that the second-order asperities have important influence on the shear mechanical properties of joints

and the mechanical properties are different from the joints with first-order asperities only

for which shear stress vs. shear displacement curve just has one peak shear stress; by contrast

the joints with second-order asperities have multi-peak shear stress

which decreases gradually one after one with the increase of shear displacements. As well

the dilatancy curves of the joints with second-order asperities show wave shape. With the increase of second-order asperities height

peak shear strength increases; the failure modes appear wearing

many-times shearing of asperities

and one-time shearing failure of asperities.