Experimental Study On High Pressure Crushing Characteristics And Particle Shape Change Of Calcareous Sand

Calcareous sand is widely distributed on the continental shelf and coastline of tropical and subtropical seas between 30°N and 30°S,and is also widely distributed in the South China Sea.Calcareous sand is a kind of carbonate sediments rich in calcium carbonate particles or natural cements,which characteristics of irregular shape,low strength and internal void development,etc.It was well accepted that the mechanics of calcareous sands is significantly different from those terrigenous sand.With the advance of the Maritime Silk Road and the continuous expansion of the engineering scale in the Marine area,the high stress generated during the construction of large island and reef structures will inevitably lead to the particle breakage of calcareous sand as the foundation material.A large number of engineering practices have shown that particle breakage significantly affects the engineering mechanical properties of calcareous sand.Based on the calcareous sand sample taken from the waters of the south China sea in our country,through the indoor mesoscopic test analysis,reveals the microstructure morphology of calcareous sand characteristics,at the same time,calcareous sand is studied through macro unit tests in the characteristics of lateral confined compression crushing under the high stress,and analyzes the shape of the particle breakage parameter change rule,explore the method of the decrease of calcareous sand broken at the same time.The main work and achievements of this paper are as follows:1.The sphericity and convexity of calcareous sand with different particle sizes were obtained by using the image acquisition system and the geometric shape parameter calculation software,and the morphological characteristics of calcareous sand were quantitatively characterized.The results show that with the increase of particle size,the roundness and integrity of calcareous sand decrease gradually,and the particles tend to be irregular,while the surface edges and defects are more developed.2.Lateral confinement compression test of calcareous sand was carried out by using a modified high pressure consolidation instrument,and the compression test results were compared with those of Fujian sand(standard quartz sand).It is found that particle breakage level of calcareous sand is increasing with the loading stress.Particle breakage controls the compressive characteristics of calcareous sand under high stress.Under the same load conditions,the stress of a large number of particle breakage of calcareous sand is far less than the stress required by Fujian sand breakage,while when the stress level is equal,the compressibility and breakage of calcareous sand are higher.3.Lateral confinement compression tests of calcareous sand with different particle size groups and mixed particle size groups were designed.The effects of particle size and grade on the crushing characteristics of calcareous sand under lateral confinement compression were investigated.The quantitative relationship between the crushing rate and the particle size characteristic parameters and grading characteristic parameters was established.The results show that under the same termination stress,the compression of calcareous sand increases with the increase of particle size,and the relative breakage rate increases linearly with the mean particle size.In the process of good gradation,the stress required to reach the normal consolidation curve(NCL)increases gradually,while the compressibility and fragmentation decrease linearly and exponentially,respectively.At a higher stress(?16MPa),the influence of particle size and grade on the compressive characteristics of calcareous sand decreases sharply and even disappears,and the compressive deformation characteristics of the sample will be mainly controlled by particle breakage.4.The particle size evolution after particle crushing was tracked by particle dyeing labeling method,and the shape parameters of the particles with different particle sizes were calculated to reveal the change rule of the particle shape parameters in the particle size evolution process after particle crushing,and the change rule was explained in combination with the particle crushing model.The results show that after compression,the roundness and integrity of the residual particles(the particle size does not change)are significantly improved,and the particles tend to be round and the surface is smoother.The particle size generated in the form of crushing is slightly smaller than that before compression,and its roundness is reduced and the surface is rougher.The roundness and completeness of several small particle size generated in the form of fracture increase with the decrease of particle size.5.The effects of the incorporation of rubber particles and its content on the compression and crushing characteristics of calcareous sand were studied by the confined compression test.The results show that with the increase of the content of rubber particles,the converging stress of rubber sand with different initial pore ratios will be significantly reduced.In addition,the relative breakage rate of the sample decreases obviously after the addition of rubber particles,and the breakage rate of calcareous sand decreases more sharply with the increase of rubber particles content.