Influence of loading method and stress level on the particle crushing of coral calcareous sand

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The relationship between particle crushing and grain group transformation under different loading conditions and stress levels of coral calcareous sand(CCS) from Xisha islands is investigated in this study. A series of tests were carried out,such as the oedometer test,triaxial compression test,simple shear test and cyclic shear test. The growth rate of particle crushing is adopted to analyze the crushing behavior of particles. The results indicate that the crushing growth rate of CCS decreases rapidly to zero with the increasing of loading cycles. The increasing of stress level accelerates the reduction of the growth rate of particle crushing,and arrives at the stable state of crushing sooner. It is proposed according to the test results that the particle crushing reaches its limit when the particle crushing growth rate is less than a small value. The limit value can be used in engineering practice. The mechanical parameters of the CCS corresponding to the limit value can be used as the extreme value in the design for the most unfavorable or most favorable situation in real project. Samples with higher contact force but insufficient relative motion between particles are lack of regularity in particle group transformation after crushing,while the samples with full relative motion between particles have the particle group transformation with obvious similarity and good regularity. The particle size of 0.25 mm is a critical point where the grain group content will be changed from variation to a stable growth state. The distribution of particle crushing can be divided into domains of particle size increasing and particle size losing. The particle size losing domain is correspond to the inflection interval of particle distribution curve under the same coordinate model of particle size.

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... e primary difference between one-dimensional compression, monotonic shear, and cyclic shear is that the relative motion between calcareous sand particles is limited and the contact force is large. e distribution law of particle size range is similar under different loading modes, but the distribution of new particles produced during particle breakage is different [70]. In addition, existing studies primarily focus on the size range of fine-grained (calcareous sand) in coral reef sediments and rarely consider the related research on the mechanical properties of calcareous gravel particles [19,71]. ...
... Furthermore, Huang et al. [79] believed the influence of relative density and normal stress on shearing and particle breakage evolution characteristics of calcareous sand, and found that the particle breakage primarily occurred from 0.50 to 2.00 mm, resulting in small particles ranging from 0.25 to 0.50 mm ins size. e proportion of particles smaller than 0.25 mm was almost unchanged, which is consistent with Qin et al. [69] and Ji et al. [70]. Wei et al. [80,81] mainly studied the formation of shear bands, particle breakage evolution, and the shear mechanical behavior of fiber reinforced calcareous sand, and put forward the function model for the relative particle breakage and final shear strain, normal stress, initial sand particle size distribution, maximum particle size, and shear rate. ...
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In order to better understand the particle breakage mechanics and characterization methods of calcareous sand, the particle breakage characteristics of calcareous sand in one-dimensional compression tests, isotropic compression tests, triaxial shear tests, and ring shear tests are reviewed and analyzed. The results show that the mechanism of shear crushing is essentially different from compression crushing. Compared with one-dimensional compression, it is easier to break calcareous sand under triaxial shear. In the shearing process, the particle breakage of calcareous sand will not continue indefinitely. The gradation tends to be stable and controlled by confining pressure and shear strain. The characteristic particle size measurement method for particle breakage is simple and has limitations. The description method using the particle size distribution curve is more comprehensive, but it is impossible to compare the crushing degree of particle with different particle sizes, and a suitable measurement method needs to be proposed.
... It has been well recognized that the mechanical properties of coral sands are quite different from those of silica sands [9,33]. Coral sands are characterized by high porosity, high angularity, low breakage strength [14,17,39], and time-dependent behavior [17,29]. As a peculiar soil medium, the mechanical properties of coral sands will affect the safety and reliability of engineering construction [4,28,39]. ...
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A series of one-dimensional dynamic compaction tests were conducted on coral sands with different impact energies. Effects of impact energy on the compressibility and crushing of coral sands were assessed in terms of the evolutions of axial deformation, particle size distribution, void ratio, relative breakage index and fractal dimension. The test results indicate that the axial deformation of coral sand specimen and the duration time of impact loading increase nonlinearly with an increase in impact energy, while decrease remarkably with an increase in the number of repeated loading. The void ratio of coral sands under dynamic compaction reduces from 1.56 to 0.86 as the singe impact energy increases from 10 to 160 J, demonstrating that dynamic compaction could effectively consolidate the coral sand specimen. The particle size distribution of coral sands under dynamic compaction tends to a well-grated distribution with the coral particles in the diameter size range of 2.36–4.75 mm primarily fragmentizing into smaller ones with size ranges of 1.18–2.36 mm and 0.6–1.18 mm. The relative breakage index of coral sands under dynamic loading grows approximately linearly with an increase in the input impact energy. The fractal dimension of coral sands under dynamic compaction increases monotonously and the corresponding slope decreases as the impact energy increases.
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