关键词: 干湿循环, 红土, 压汞试验, 扫描电镜, 微细观结构, 力学性质

Abstract: To investigate the multi-scale effect of degrading mechanical properties of laterite soils under dry-wet cycling, we conducted mercury intrusion tests, scanning electron microscope tests, micro-fracture tests, and triaxial compression tests, focusing on analysis of the damage to the micro-meso structure of a remolded laterite soil and its deterioration of macroscopic mechanical properties. And the multi-scale mechanism of soil mechanical property degradation is explored. Results show that: (1) the micro-structure of remolded laterite is damaged by dry-wet cycles obviously: its gradation becomes slightly denser and most of the particles are modified closer to the spherical shape. The frequency of particle orientation is modified, but it is overall isotropic with a dominant orientation only locally. The probability distribution index of particle area increases and transforms to that of smaller particles. The total pore volume increases and small pores transform into medium and large ones. This increase is involved in pore transformation, serving as the main source of more medium and large pores; (2) Under dry-wet cycling, the evolution of remolded laterite meso-cracks experiences three stages: crack initiation of humidification, development with the cycling, and later stableness. The development of fracture rate and fracture width mainly occurs in the initial five cycles and is stabilized in the late stage; (3) Owing to the action of dry-wet cycles, the shear strength of remolded laterite degrades significantly. The cohesion decreases in an inverse ￠S￠ type, which occurs in the initial five cycles and tends to be stable later. The internal friction angle decreases linearly to a small extent. Based on the results above, the multi-scale mechanism of remolded laterite mechanical properties deterioration can be summarized. The expansion potential of total pore volume, matrix potential of pore expansion and penetration weakening, cementation strength weakened by dissolution of cement material, and particle structure modified by repeated water migration under the action of dry-wet cycling － all these factors together cause damage to soil microstructure and then make the micro-cracks expand into meso-cracks, resulting in degraded soil integrity and deteriorated macroscopic mechanical properties.

Key words: dry-wet cycle, laterite, mercury intrusion test, scanning electron microscope (SEM), micro-meso structure, mechanical property