Compression Characteristics And Gradation Optimization Model Of Calcareous Sand Based On Fractal Theory

The calcareous sand is a kind of sedimentary material widely existing in the South China Sea.Due to its physical properties such as multi-angle,porous,irregular shape and easy breakage,large settlement or uneven settlement may occur during the compaction treatment of calcareous sand foundation in actual construction.and a large number of particles may be broken due to its fragility during engineering activities.The engineering characteristics,especially the research of compression features,is particularly important.Considering the need to improve the compression characteristics of calcareous sand itself to meet the engineering needs,this paper,based on fractal theory,conducts experimental research on the compression characteristics of calcareous sands with different gradations,and further based on the experimental results.The evolution law and generation mechanism of calcareous sand compression behavior characteristics are discussed in depth,and a gradation optimization model and a calcareous sand compression characteristic prediction model are established with the yield strength of calcareous sand as the characteristic index.The main tasks of this research are as follows:(1)By introducing fractal theory,samples with fractal dimensions of 2.4,2.5,2.6,and 2.8were configured,plus the original sample(D=2.67),and five kinds of samples were subjected to constant loading rate indoor lateral line compression test.The test results show that under a certain initial relative density,with the increase of the initial fractal dimension,the compressive index of the sample decreases linearly,the particle size of the sample decreases,and the yield strength increases nonlinearly.And the change trend of the compression characteristics of calcareous sand is obviously related to the relative compactness.In the case of high relative compaction,the feedback of secant modulus,yield strength and compression index to the change of sample gradation is compared with low relative compaction.situation is more sensitive.(2)A particle breakage characterization method based on fractal theory is established.The method is constructed with reference to the description of Hardin’s relative breakage potential.In theory,this method can better reflect the particle-scale breakage than the relative breakage potential.Through the analysis and comparison of the test data,it is found that the description of the crushing law of calcareous sand particles by the two crushing indexes is roughly the same,indicating that the particle crushing decreases with the increase of the fractal dimension,and increases with the increase of the relative compactness,and The change trend of particle breakage with the increase of fractal dimension is different under different relative compactness.(3)A prediction model for the compression characteristics of calcareous sand was constructed,including a prediction model for yield strength and a prediction model for compression index,and the model fits well.In the study of yield strength,it is found that there is a “boundary fractal dimension”,before this value,the increase of fractal dimension has a weak effect on the yield strength of the specimen.After this value,the increase of the fractal dimension will lead to a significant increase in the yield strength of the specimen.On this basis,the relationship between the “boundary fractal dimension” and the initial relative compactness was further analyzed,and a gradation optimization model was constructed.The increase of yield strength has a significant effect,and when the initial relative compactness is less than 0.38,it is difficult to effectively improve the yield strength by adjusting the initial gradation.In view of this situation,the compaction should first be increased to more than 0.38,and then the initial gradation adjustment should be carried out.can effectively increase the yield strength.