Abstract: TBM excavated materials are mainly composed of fine sand and needle-flake-shaped rock blocks. The deformation and strength characteristics of TBM excavated materials,which belong to poor graded soil,with large variation in rock block proportion,unique soil structure,are quite different from other types of soil-rock mixtures. Based on the field surveys and 3D laser scanning technology,the shape and structural characteristics of the TBM excavated materials from the Duoxiongla Tunnel in the eastern Himalayas were quantified. This paper proposes a discrete element direct shear model construction method,which is suitable for TBM excavated materials. The large-scale indoor direct shear test combined with PFC^3D discrete element numerical simulation were used to reveal the macroscopic mechanical behavior and mesoscopic deformation and failure mechanism of TBM excavated materials under different rock block proportions. The results show that the shape of rock blocks in the TBM excavated materials is similar to cutter disk,bar,and disc. After the manual stacking process,the angle between the long axis direction of the rock blocks and the horizontal plane is mainly distributed in 0°~20°,and the soil structure shows significant spatial orientation. With the increase of rock content,the structure of TBM excavated materials transforms from suspended dense structure to skeleton dense structure,and finally transforms into the skeleton void structure,resulting in a significant increase in the occlusion,nesting,and self-locking between the rock blocks. Therefore,the rotational freedom of the rock is greatly limited. The macroscopic deformation characteristics of specimen change from shear shrinkage to shear dilatation,and its shear strength shows a trend of slow growth at first,then a slight decrease,and finally a large increase. In addition,according to PFC^3D simulation results,the internal particle movement form has changed from "soil-rock linkage" to "soil-rock around" with the increase of rock content. The number of force chains decreases linearly,and the mean force chain strength increases gradually. The strong force chain gradually played a supporting role in the model. On the whole,the distribution of the shear zone also gradually approaches from the "S"-shaped distribution to the linear distribution,and the thickness of the shear zone becomes thinner obviously. Overall,this paper will make up for the insufficiency of the current research on the needle-flake-shaped soil-rock mixture,and provides theoretical support for the stability analysis and risk assessment of the TBM waste dump.