Abstract: To support debris-flow disaster prevention and surface moraine modification by grouting consolidation in the Pulang Copper Mine, this study investigated the engineering mechanical properties of surface moraine. Shear strength, cohesion(c), and internal friction angle(φ)of moraines with different grain-size compositions were examined using a combination of small direct-shear apparatus and large-scale direct-shear equipment for coarse-grained soils. Soil skeleton theory and the Mohr-Coulomb criterion were applied to analyze the strength mechanism. The results show that as particle size increases, cohesion c first decreases and then rises, while the internal friction angle φ increases exponentially. The moraine samples exhibit elastic-plastic-creep behavior. Moreover, an increase in particle size and vertical pressure shifts the shear stress-strain curve from slight hardening to stress softening. As particle size increases, the load-bearing structure of the sample transitions from a fine-particle-dominated mosaic structure to a coarse-particle-controlled skeleton structure. Coarse particles progressively govern the shear strength of the sample, shifting the dominant resistance from cohesion-based to friction-based.