Study On Mechanical Characteristics Of Calcareous Sand Under Different Stress Paths

Due to the important geographical position and abundant oil,gas and fishery resources of the South China Sea,China has carried out large-scale reclamation and island-building projects there.The calcareous sandy soil formed through reclamation is a special geotechnical medium,which is very different from ordinary terrigenous sand.Geotechnical media is generally stress path dependent and calcareous sand is under complex stress conditions.Therefore,it is necessary to study the strength and deformation characteristics of calcareous sand under different stress paths.In this study,by conducting triaxial tests under different stress paths,performing acoustic emission monitoring during one-dimensional compression rebound tests and using Part An^3D observation system to compare the difference of the particle morphology of calcareous sands before and after the test,the stress-strain relationships under different stress paths,characteristics of strength and deformation can be analyzed and discussed.In addition,the compression rebound characteristics,characteristics of acoustic emission in the process of compression rebound,the variation characteristics of particle morphology before and after the tests can be analyzed.The main research contents and conclusions of this study are as follows:（1）The influence of stress path on the strength and deformation characteristics of calcareous sand particles was explored through triaxial tests under different stress paths.The results show that the consolidation pressure and stress path have significant effects on the volume strain,strength and particle breakage of calcareous sands.The difference of stress path is due to the difference of stress ratio,so the effect of stress path on the strength and deformation of calcareous sands is due to the change of stress ratio.Under the same stress path,the higher the consolidation pressure,the greater the peak internal friction angle,the higher the strength and the particle breaking degree,but the dilatancy of soil is inhibited.Under the same consolidation pressure,the strength and amounts of particle breakage of PL tests are at their maximum and increase with the principal stress.The peak deviator stress of TC tests is the smallest,the dilatancy is most obvious and the amount of particle breakage is the least.（2）The acoustic emission real-time monitoring test during the one-dimensional compression-rebound was carried out to study the compression-rebound and acoustic emission characteristics of calcareous sand.The compression deformation of calcareous sand is mainly the plastic deformation caused by the particle crushing.The particle size and particle shape have an effect on the compression and crushing of calcareous sand.Under the same pressure,the compression deformation and crushing amount increase with the particle size.The compressive deformation and amount of particle breakage increase with the particle size.The compression deformation and breaking characteristics of calcareous sand are consistent with their acoustic emission characteristics.The acoustic emission count rate of calcareous sand mainly appears in the compression stage of 800-3200 k Pa and increases with the particle size.The acoustic emission counting rate-time relationship curve of calcareous sand is in good agreement with the stress-time relationship curve,and the mechanical properties of calcareous sand can be reflected by the acoustic emission counting rate-time relationship curve.（3）Part An^3D particle morphology observation system was used to scan particles in the one-dimensional consolidation compression-rebound test and different stress path triaxial test.Particle morphological parameters before and after the tests were obtained.The results show that the morphology of particles in the grinding effect,or broken under the action of changed,but the sample of the whole particle morphology has not changed.The particle size distribution curves drawn according to the particle morphology parameters before and after the test are basically consistent with the particle size distribution curves drawn by the screening test.The particle fragmentation coefficient calculated by WEI method is consistent with the particle relative fragmentation potential calculated by Hardin method.