Abstract: Clay-sand mixture is widely used in dredger fill. The deformation of mixed soil foundation is closely related to its microstructure. To explore the microscopic mechanism of compression deformation of mixed soils, we analyzed in qualitative and quantitative scales the particle arrangement and pore distribution of clay-sand mixture samples before and after consolidation via compression tests, scanning electron microscopy (SEM) tests and Image-Pro Plus (IPP) image processing. Results revealed that with the increase of sand content, the void ratio of mixed soil reduced at first and then grew, and the compressibility decreased gradually. The sensitivity of each pore group to consolidation pressure is closely related to sand content. With the increase of sand content, the number of large and medium pores increased, and the contact mode between particles transferred from edge-face and face-face contact to point-point and point-face contact. Compression enhanced the compactness and orderliness of particle arrangement. Pore size tended to be smaller. The percentage of large pore area dropped up to 31.39%, which resulted in the expansion of middle pores; however, the impact on micro-and-small pores is not obvious. The directional probability entropy of soil particle is linearly correlated with sand content, while negatively linearly correlated with compressibility coefficient a_1-2. Lager sand content led to the more chaotic arrangement of mixed soil particles, larger directional probability entropy, and smaller compressibility. In conclusion, the change of microstructure parameters of particles and pores caused by different consolidation pressure and sand content ratio is the internal reason for the difference in the compression characteristics of mixed soil.

Key words: clay-sand mixtures, compression characteristics, microstructure, SEM, image processing, consolidation presscure, mixture ratio