Rock-soil aggregate mixture is broadly used in roadbed

dykes and dams for its favorable engineering properties. Shear strength of the mixture becomes the most important mechanical index for stabilization and deformation analysis because it always occurrs shear failure along the weakness surface in filler. However

it is difficult to determine the shear strength for the complexity composition

non-regularity frame distributing of the mixture

and restriction of current measure instrument. This study carried out shear test on different kinds’ and different dmax rock-soil aggregate mixtures by using the improved shear test instrument

determined the intensity of the mixture conveniently; meanwhile

reappeared the actual shear surface; and further more

directly measured the gurgitation data of the surface. According to the principle of fractal geometry

the surface has well fractal property; the gurgitation data was used to calculate the fractal dimension of the shear surface by program that based on cover method of triangle prism superficial area. Finally

the relationship

between shear strength of the mixture and the fractal dimension of shear surface

is established so as to forecast the strength of the mixture quickly.