Abstract: Rock-soil aggregate mixture come from excavation is broadly used as filling in roadbed and foundation for its high density and convenience construction; affected by geology, rock-soil ratio, grain size distribution and other factors, the mechanical behavior of rock-soil aggregate mixture puts up obviously nonlinearity; additionally its intensity index can’t detect by routine tests, so that roadbeds or foundations filled with rock-soil aggregate mixture always occur a rather large differential settlement or slump, severely affecting the function of superstructure. To disclose its intensity character and variety rules with influencing factors, this study improved large scale direct-shear test, developed a large scale direct-shear test system, using this improved large scale direct-shear test system, carried out shear test on different kinds of rock-soil aggregate mixtures. The results show that the shear destroying rule of the mixture did not obey Coulomb law on high stress condition; its intensity should be discounted. Test results show the variety tendency of intensity index with influencing factors; the elementary rules of the friction angle varied with apiece influence factor are established. Test results also show that the character of native rock and rock-soil ratio of mixture have relatively bigger influence to the intensity index; the friction angle of hard rock mixture general is greater than that of soft rock mixture; rock-soil ratio has little influence on the intensity while the rock-soil ratio less than 30 %; the intensity of mixture increases with the increment of rock-soil ratio as parabolic curve, generally reach peak value at the ratio about 70 %.

Key words: rock-soil aggregate mixture, direct-shear test, shearing strength, rock-soil ratio