Investigation On The Effects Of Confining Pressure And Particle Size Of Shear Characteristics Of Calcareous Sand

With the development and construction of projects in the south China sea,island and reef projects have attracted much attention.In order to reduce costs and follow the principle of local materials,calcareous sand is used as an important construction material in island and reef projects,and its physical and mechanical properties have become a hot spot and difficult point in the field of research.With the development of research,the special shear characteristics of calcareous sand have attracted the attention of scholars at home and abroad.At present,the research on the shear characteristics of calcareous sand has achieved fruitful results,as a kind of granular material,calcareous sand particle size also has a significant effect on its shear characteristics,and the effect of particle size on its shear characteristics is still rarely studied,therefore,it is necessary to study the shear characteristics of calcareous sand with different particle size.Taking calcareous sand from a reef in the south China sea as the research object,this paper conducted a series of laboratory physical and mechanical tests on calcareous sand,focusing on the confining pressure effect and particle size effect of calcareous sand shear characteristics,and deeply understood the interaction forms between calcareous sand particles and the size effect of mechanical properties,The main contents and results are as follows:(1)The basic physical properties of calcareous sand were studied and analyzed.The particle analysis test,specific gravity test,relative compactness test and scanning electron microscope test were carried out on the calcareous sand samples,the results of particle analysis test showed that the suitable vibrating time of calcareous sand was 20 min,which belongs to silty sand;it was found by sem that there were many pores with different sizes and uneven distribution on the surface of calcareous sand particles.(2)For the study of different particle sizes and shear properties of calcareous sand under different confining pressure conditions,the six single particle group(5-2 mm,2-1 mm,1-0.5 mm,0.5-0.25 mm,0.25-0.075 mm,less than 0.075 mm)calcareous sand sample pine(relative compactness Dr=30%)and sample(relative compactness Dr=70%)under different confining pressure(50 k Pa,200 k Pa,400 k Pa,800 k Pa)under the condition of triaxial consolidation drained shear tests.The results show that,in the range of particle size of 5-0.075 mm,for loose samples,the confining pressure has a significant effect on the softening characteristics and dilatancy characteristics,but has no significant correlation with particle size.For dense samples,the influence of confining pressure on the softening characteristics of samples is gradually enhanced with the decreasing of particle size,while the influence on the dilatancy characteristics of samples is gradually weakened.(3)Based on triaxial shear test results,the introduction of relative softening coefficient of stress and dilatancy coefficient of strain softening characteristic and quantitative characterization of dilatancy characteristics,found that for different size of calcareous sand,with the increase of confining pressure,the specimen strain softening characteristic and dilatancy characteristic gradually weakened,and the confining pressure and stress relative softening coefficient and semilog linear correlated to the dilatancy coefficients along with the increase of confining pressure,different size of calcareous sand specimen strain softening characteristic and dilatancy characteristic gradually weakened,and confining pressure and stress relative softening coefficient and semilog linear correlated to the dilatancy coefficients.There was a critical confining pressure of strength and a critical confining pressure of volume variation in calcareous sand samples with different particle sizes,which made the characteristics of strain softening and dilatancy disappear.(4)The meso-generation mechanism of confining pressure effect and particle size effect of calcareous sand shear properties was discussed,The results show that under the same relative compactness condition,the critical confining pressure can be considered to be determined by the particle size of the sample and the crushing strength of the particle.Under the condition of low confining pressure(50 k Pa),the particle size group of 0.5-0.25 mm had the most significant crushing.