Study On The Static Properties And Particle Breakage Characteristics Of The Hydraulic Filling Calcareous Sand In South China Sea

Calcareous sand is a special geotechnical material composed of dead Calcareous limbs,shell debris and other marine biological skeleton in the ocean.Due to the complex sedimentary environment and the special mineral composition,Calcareous sand has significant engineering mechanical properties such as irregular in shape,porous,brittle,and often accompanied with cementation,which are strongly different from terrigenous quartz sand.To meet the needs for defense construction and the exploitation of oil and gas resources,China has launched a large-scale island and reef expansion project in the South China Sea.And Calcareous sand is used as the main filling materials for this project.Research results have proved that particle fragmentation can significantly affect the mechanical properties of Calcareous sand,and Calcareous sand can break up at low stress levels.Therefore,it is necessary to carry out in-depth research on particle fracture characteristics of Calcareous sand under load,which is of particular importance to the island reef reclamation project and infrastructure construction.In this paper,a series of drained and undrained triaxial consolidation shear tests are conducted on Calcareous sand.The effects on the mechanical properties of Calcareous sand are studied in detail,including the initial density,confining pressure(stress level),drainage conditions and other factors,and the intrinsic mechanism and influencing factors of particle breakage are identified.This paper also analyze the influence mechanism of particle breakage on the critical state of Calcareous sand.The research resultsof this paper will provide useful reference and technical support for the safe construction of basic engineering facilities such as docks,airports,and roads in the areas where the calcareous sand is widely distributed in the countries along the southern islands and reefs of the “21st Century Silk Road”.The main research contents are as follows:(1)A large number of triaxial shear tests were carried out to study the strength characteristics of Calcareous sand under different test conditions.The dilatancy coefficient and softening coefficient were introduced to quantitatively describe the stress-strain relationship,and the relationship between compactness,confining pressure and drainage conditions and their shear strength were analyzed.(2)To investigate the internal mechanism of particle crushing and reveal the effects of compactness,confining pressure,drainage conditions and plastic work on particle crushing of Calcareous sand,a screening test was conducted before and after the triaxial shear test.And the relative crushing rate index proposed by Einav was used to quantitatively analyze the degree of particle crushing in the triaxial shear test.(3)Based on the positional relationship of the critical state line in the q-p′ and e-lnp′stress spaces,the influence of the particle crushing on the critical state of Calcareous sand is analyzed.The relative particle crushing rate was used to draw the equivalent particle crushing line in the e-lnp′ stress space,and establish the relationship between the equivalent particle crushing line and the critical state line.