Compression Test Study On Mechanics And Acoustic Emission Characteristics Of Calcareous Sand Considering Particle Breakage

In recent years,the Chinese government has paid more and more attention to the South China Sea,and the development of the South Island Reef and the construction of related marine projects have also advanced.Calcareous sand is widely distributed in the South China Sea and islands and reefs,and is the main foundation filler and building material in the construction of South China Sea marine engineering.Calcareous sand is a special rock and soil body formed by marine living coral debris and rich in carbonate materials such as calcium carbonate.The calcareous sand has the characteristics of multiple pores(including internal pores),extremely irregular shape and easy breakage.The engineering mechanical properties of calcareous sand are very different from ordinary land-based sand(such as quartz sand).Calcareous sand is prone to particle breakage under pressure,and the energy generated by particle breakage is released and propagated in the form of sound waves.Therefore,it is necessary to carry out research on the mechanical properties and acoustic emission characteristics of calcareous sand.Scholars at home and abroad have studied more on the macroscopic compression characteristics of calcareous sands,but less on the meso-crushing and acoustic emission characteristics.In this paper,based on the conventional calcareous sand compression test,the introduction of acoustic emission technology,combined with the statistical analysis of the avalanche dynamics of acoustic emission signals(combined with the relevant analysis experience summarized by the research group),carried out calcareous sand single particle compression and calcium Study on the mechanical properties and acoustic emission characteristics of the one-dimensional confined compression of the sand particles.The research content and main conclusions of this article are as follows:(1)Study on mechanical properties such as micro-breakage,strength and acoustic emission of calcareous sand single particle during compression.A precision tensile and compression loading table was used to compress the single particles of calcareous sand to study the effect of particle size on the strength,breakage and acoustic emission characteristics of the calcareous sand particles.The study found that during the compression and breakage of calcareous sand particles,the occurrence and expansion of cracks have a clear correlation with the force drop in the pressure curve,and the pressure signal has a clear correlation with the acoustic emission signal,but the acoustic emission signal is more sensitive accurate.As the particle size increases,the characteristic stress of single particles decreases,and the characteristic stress has a negative power law relationship with the average particle size,that is,large particles are more likely to break.The strength of calcareous sand particles follows Weibull distribution,and Weibull modulus m is between 1.6 and 2.2.The AE signal energy is subject to power law distribution,but the power law index of AE energy of calcareous sand with different particle sizes is different.(2)Study on the yield strength,stress deformation and particle breakage characteristics of calcareous sands during the process of lateral compression.By conducting the confined compression test on the particles of loose calcareous sand clusters,the end pressure,cluster particle size,gradation,loading rate,initial porosity ratio,unloading-reloading and sample height on calcareous sand stress deformation and particle breakage were studied.The influence of the characteristics,and compared with the results of ISO standard sand;and explore the relationship between the strength of single particles of calcareous sand and the lateral compression yield strength;the study found that during compression,the axial strain showed a rapid increase and slow The increase and eventually gradually stabilized,which is mainly related to the rearrangement of particles(including sliding and rolling),particle breakage,and rearrangement after particle breakage.It is pointed out that the particle strength controls the yield stress of calcareous sand.And the relative crushing rate index is used to analyze the crushing of the sample particles affected by various factors.(3)Research on the acoustic emission characteristics of calcareous sand group particles during lateral compression.By conducting the confined compression test on the loose calcareous sand cluster particles,the effects of the test termination pressure,cluster particle size,and loading rate on the acoustic properties of the calcareous sand were studied,and the relationship between the stress deformation and particle breakage characteristics of the calcareous sand and its acoustic emission characteristics was discussed.Correlation and comparison with the results of ISO standard sand;and explore the relationship between the acoustic characteristics of calcareous sand single particles and cluster particles during compression.The study found that the end pressure of the test,the particle size of the group and the loading rate all have different effects on the acoustic emission characteristics of calcareous sands,and the results are significantly different from the single particle compression results.It also reveals the close relationship between the acoustic emission energy spectrum and the sample particle breaking,which proves that the acoustic emission signal can better reveal the particle breaking state and degree inside the sample.By comparing the acoustic emission test results of standard sand,it is found that the calcined sand and the standard sand samples have different acoustic emission characteristics.