**Abstract**

A great deal of weathered granite soils are distributed in mountainous areas around the world. With further improvements to the civil engineering, more and more construction infrastructures (roads, railways, dams, etc.) in mountainous areas will be built. Making full use of weathered granite soils, a type of special geomaterial, can alleviate the shortage of building materials in mountainous areas. Weathered granite soil has its own unique physical and mechanical properties, e.g., disintegrative, easy weathering, and particle breakage. In this chapter, a large number of field investigations and laboratory tests (including X-ray diffraction, sieving, heavy compaction, and large-scale triaxial) have been carried out. The process of weathering, the influence factors on particle breakage, and the mechanical properties of compacted weathered granite have been discussed. The results show that particle gradation, mineral content, blows per layer, and stress level have a significant effect on the particle breakage characteristics of weathered granite soils. The experimental results show that the product of the stress ratio at shear failure *M*<sup>f</sup> and the stress ratio at characteristic state point *M*<sup>c</sup> is not a constant but a power function of an average main stress *p* due to particle breakage. Hereby, the constitutive model of weathered granite soils was proposed.

**Keywords:** weathered granite soils, weathering mechanism, particle breakage, mechanical behavior, modified strength condition, constitutive model
