Shear behavior of filled discontinuities

All rock masses contain discontinuities. In some situation behavior of the rock mass is controlled by sliding on discontinuities and some discontinuities are filled with deposits and soil. High deformability and low shear strength are typical behavior of exhibited by this type of discontinuities. So the shear stress-strain behavior and shear strength parameters of filled discontinuities are of practical importance in the optimal and safe design in tunneling and mining. These parameters are related to the type, thickness and moisture of content of filling and also surface roughness of the host discontinuities, it is therefore essential to at least understand its typical behavior under the interactive effects of these controlling components. To study the behavior of filled discontinuities a series of laboratory shear tests were conducted on model filled discontinuity. The physical model used in these tests consists of silty-sand as infilling and plaster as discontinuity blocks. Experimental variables include infill thickness, moisture content of infilling, normal stress. The shear tests were conducted on simple shear direct apparatus under strain controlled condition and in large scale. Laboratory tests result indicate that in low ratio of infill thickness over amplitude of roughness (t/a) the maximum shear strength of discontinuity is depend on shear strength of block but with increasing the ratio of t/a the maximum shear strength of discontinuity decrease and it is depend on infill material as in t/a equal 2, shear behavior is the same as shear behavior of infill material.