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Particle breakage and the corresponding change of morphology are two key factors governing the mechanical behavior of calcareous sands in offshore geotechnical engineering constructions. To reveal the characteristics of these two factors, oedometer tests on calcareous sands have been performed in this study. The materials were sampled from the South China Sea with a homogenous composition but different particle size ranges and relative densities. In these tests, the dynamic imaging analysis (DIA) by Microtrac PartAn3D and acoustic emission (AE) techniques were employed to investigate the evolution of particle morphology and characteristics of AE signaling associated with the material deformations, respectively. The compressive deformation of calcareous sands was mainly induced by the particle rearrangement and particle breakage which are effectively irreversible plastic deformations. The irregular particle shape has led to strong interparticle filling and interlocking effects, which affected the particle slippage and rearrangement significantly during the deformation. The intensity and type of AE-triggering micro-mechanical behaviors were characterized by AE ringdown counts (RDC) and peak frequency, respectively. The RDC values concentrated primarily in the compression stage and increased rapidly under the normal stress of 400–3200 kPa. The RDC values increased with the increase of particle size but decreased with the increase of initial relative density. The compressive deformation and breakage characteristics of calcareous sands are consistent with the existing acoustic emission laws. [ABSTRACT FROM AUTHOR]

To explore the fractal dimension, particle shape, and particle breakage of calcareous sand (CS) under multi-level ending pressure, a series of one-dimensional compression experiments along with microscope image recognition tests were performed. Test results demonstrated that compression behavior of CS was similar to that of silt soil for the reason that considerable particle breakage occurred under high-stress level. In unloading process, rebound index of tested specimens was in the range of 0.0027–0.0052 which suggested that irrecoverable plastic deformation consists of the main part of compression. The shape index sphericity ( S C ), aspect ratio ( A R ), convexity ( C X ), and overall regularity ( O R ) increased as increasing axial stress or decreasing average grain size. Besides, there existed a turning point of axial stress of 3200 kPa; these shape indexes increased rapidly first and then approached to a stable value after that. At present study, the surface and mass fractal dimension of tested specimens were in the range of 1.12–1.93 and 2.14–2.92, respectively. Both fractal dimension and relative breakage ratio increased logarithmically as increasing axial stress from 0 to 6400 kPa. In addition, an increase in the average grain size led to an increase in the relative breakage ratio and a decrease in fractal dimension which indicated that larger particles are more easily broken for the reason that the stress concentration between granular grains. Furthermore, there existed approximate linear relations between surface or mass fractal dimension with relative breakage ratio which might be helpful to quantitate the particle breakage of granular materials. [ABSTRACT FROM AUTHOR]

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