| Granular soil material is widely used in civil engineering fields, and as the basematerial of various kinds of geotechnical engineering. Under high stress level staticand dynamic load, granular soil will produce particle breakage. Particle breakage willusually results in more compressibility and less strength for granular soil material,which could cause large deformation and resulting in instability and failure of thewhole structure. So the research on particle breakage of granular soil material causedmore and more attention. Due to its special material composition and sedimentaryenvironment, its engineering mechanics properties have significant differences withthe ordinary terrigenous sand. Its irregular shape, porous, frangible, compared withquartz sand is much easier to produce grain breakage. Calcareous sand are widelydistributed in the south China sea, along with the construction of national defense andto the south China sea oil and gas resources exploration, mining, modern engineeringquantity will be increased, the size will be bigger, as the foundation of the bottom ofthe sea of calcareous sand under stress level is very high, often accompanied by alarge number of particle breakage. So the research on the mechanical properties ofcalcareous sand is especially important, and want to make a full understanding ofcalcareous sand mechanical properties, must conduct systematic study on the particlebreakage characteristics.This article take a series of physical and mechanical properties tests to study thebasic mechanical properties and grain breakage characteristics of calcareous sand.Specific research contents and conclusions are as follows:(1) The basic physical properties of calcareous sand were analyzed. Thecalcareous sand used for tests was uncemented, mainly consist of marine biodetritus,particle shape was highly irregular. Carbonate content in its mineral composition isgreater than95%. By electron microscope scanning to observe the microscopicstructure found that it has a lot of small openings.(2) The compression characteristics of calcareous sand were analyzed. Throughone dimensional compression test, found that the compression properties of calcareous sand were similar to normal consolidated clay. The yield point stressdecrease with the particle size increases. One-dimensional compression under thesingle particle size of calcareous sand particle breakage increases with the increase ofparticle size.(3) The shear characteristics of calcareous sand were analyzed. Calcareous sand’sstress-strain characteristics under direct shear tests were similar to ordinaryterrigenous sand, irregular particle shape caused its high internal friction Angle, andinternal friction Angle increases with the increase of particle size. Calcareous sand intriaxial tests, the stress-strain relationship changes over the level of stress. In triaxialconsolidation drainage test, shear dilatancy in lower effective confining pressure,grain breakage increase with the increase of effective confining pressure, graduallydisappear of its dilatancy effect, show the reduction. The particles breakage featuresof calcareous sand under triaxial test was studied, the increase of the shear stress andnormal stress can aggravate grain breakage. Strength characteristics of calcareoussand under triaxial test are discussed in this paper, the effective internal friction Angleis increased with the increase of effective principal stress decreases, within the scopeof the stress for the test, the ultimate residual strength value is around33°.(4) A series of ring shear tests on the grain breakage characteristics of calcareoussand were analyzed. Different shear displacement of ring shear tests were taken toprove the existence of the limit of particle breakage, and determined its sheardisplacement to limits grain breakage state. For different particle size of calcareoussand ring shear tests, studied the effect of particle size on the ultimate states ofparticle breakage. The relative breakage rate is proportional to the particle size. Fordifferent initial grading of calcareous sand ring shear tests, the better the calcareoussand size distribution is, the ultimate states of the broken relative breakage rate issmaller. Different stress levels on ring shear tests with calcareous sand were analyzed.The calcareous sand is obtained to the ultimate states, the broken relative breakagerate within a certain stress level is proportional to the stress level, stress level hasreached a certain degree of its influence will gradually disappear. The mobilisedstrength is unaffected by the particle breakage, the residual strength is around33°.(5)The characterization of quantity-particle size distribution fractal model, basedon the screening results and laser particle size analysis of calcareous sand after ringshear tests, respectively to calculate the fractal dimension. |
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