Abstract: Study on the microstructural change of granite residual soils (GRS) during compression is important to comprehend the influence of deformation mechanism and structure characteristics on soil mechanical characteristics and to establish relations between macroscopic behavior and microstructural characteristics of weathered soils. One-dimension compression tests were conducted on Xiamen GRS and scanning electron microscopy (SEM) was used to investigate samples under different loading conditions. Structural parameters enabling the quantification of particle assemblage and pore volume, morphologies and preferred orientations of GRS were gained. This study investigated these parameters during compression procedures, then the mechanisms of compression deformation were proposed. The results indicate that the effects of cementation played an important role on GRS. The compression curve showed an obvious turning point and approached ICL gradually after the load exceeding the pre-consolidation pressure. The compression of large pores contributed to deformation of natural soils, while deformation of reconstituted soils was mainly dependent on the transformation from large pores and meso pores to small pores. Particle assemblages of natural soils showed relatively low roundness value, while after one-dimension compression test, the particle assemblage shape showed remarkable tendency towards medium roundness. Compression deformation resulted in deflection of particle assemblages perpendicular to loading, facilitating the preferred orientation. The deformation mechanism of GRS is that the microstructure constantly rearranges and reorients into a more stable and orderly structure. The research provides theoretical support for foundation deformation analysis related to GRS.

Key words: granite residual soil, compression, microstructure, preferred orientation, pore, cementation