PARTICLE EFFECT OF SHEAR ENERGY EVOLUTION OF GRAVEL-BLOCK SOIL IN THE MIDDLE REACHES OF THE YARLUNG ZANGBO RIVER

The widespread distribution of gravel-block soils in the middle reaches of the Yarlung Zangbo River poses significant challenges to engineering safety in the region. This study examines the influence of coarse particle content on the shear energy evolution of gravel-block soils through large-scale direct shear tests conducted on samples collected from the river valley. The results showed that as the coarse particle content increased, both cohesion and the internal friction angle initially decreased and then increased, with a critical transition observed at P₅=20%(where P₅ represents the mass percentage of particles larger than 5 mm). The total strain energy was found to increase with shear displacement. During the initial shear stage, elastic strain energy increased rapidly, while dissipative energy exhibited more significant growth in the later stages. Under low normal stress, dissipative energy decreased with increasing shear displacement in the early shear phase. At P₅=20%, both the total strain energy and elastic strain energy reached their minimum values during the compaction, elastic, and plastic shear stages, whereas dissipative energy peaked in the shear compaction stage. In samples with low coarse particle content, dissipative energy primarily consisted of energy consumed by particle rearrangement, interparticle friction, and minor particle breakage. In contrast, at higher coarse particle contents, dissipative energy was dominated by particle breakage, followed by frictional energy and minimal rearrangement energy. These findings provide valuable insight into the strength characteristics and energy evolution mechanisms of gravel-block soils in the Yarlung Zangbo River region, offering scientific support for engineering stability assessment in the area.