| In the South China Sea,the distribution of calcareous sand is very common,and with the development of islands and reefs,it has been found that calcareous sand and terrestrial source sand have significant differences in mechanical properties.Calcareous sand has the properties of multiple internal pores,easy to break,easy to cement and irregular particle shape,which adversely affects its application in engineering.The reinforcement method of geosynthetics to reinforce the soil has been very mature,and it has shown good reinforcement effect in many reinforcement tests on terrestrial source sand.At present,there are few studies on the reinforcement of calcareous sand by geosynthetics.In this paper,the physical properties of calcareous sand were obtained through physical tests,and then two different geosynthetic materials were used to reinforce calcareous sand,and the stress-strain characteristics and bulk characteristics of geogrid reinforcement calcareous sand and geogrid reinforcement were studied by triaxial test.The influence of the number of reinforcement layers,test confining pressure,calcareous sand compactness and other factors on the static characteristics of calcium sand reinforcement of the two geosynthetics was analyzed,and the reinforcement effects of the two different geosynthetics were compared.The static characteristics of geogrid reinforced quartz sand and calcareous sand were compared.The parameters of the Duncan-Zhang E-B model of geosynthetics reinforced calcareous sand were obtained.The main research results are as follows:(1)Through physical tests,the maximum and minimum dry density,particle specific gravity and other parameters of calcareous sand used in the test were obtained.(2)The static characteristics of calcareous sand before and after reinforcement were studied by triaxial experiment,and the static characteristics of the two were compared.The shear strength of calcareous sand reinforced by geogrid and geogrid was higher than that of unreinforced calcareous sand,and the improvement effect increased with the increase of the number of reinforcement layers,confining pressure and compactness.Compared with geomesh,geogrid reinforcement of calcareous sand has a poor effect on improving strength,and geogrid reinforcement significantly improves the stress softening characteristics of calcareous sand,but geogrid reinforcement does not significantly improve it.The reason is that the mesh of the geogrid is large,and the restraining effect on calcareous sand is poor.The stronger the shear(shrinkage)characteristics of calcareous sand reinforced by geogrids and geogrids,the stronger the stress softening(hardening)characteristics.(3)Compared with quartz sand,calcareous sand has a larger stress-strain peak and more obvious stress softening characteristics.The reason is that the particles of calcareous sand are more irregular,have greater porosity,and are more prone to particle fragmentation.(4)The static and mechanical properties of geosynthetics reinforced calcareous sand are in good agreement with the Duncan-Zhang E-B model,so the Duncan-Zhang E-B model is used to fit the strength and deformation characteristics of geosynthetics reinforced calcareous sand.The results show that the failure ratio,internal friction angle and initial deformation modulus of calcareous sand increase with the increase of the number of reinforcement layers.The friction angle of the first,two-layer and three-layer geosynthetics increased by 5.3%,5.7% and 7.9% for calcareous sand and loose sand,respectively,and the increase amplitudes of calcareous sand dense sand,respectively6.0%、10.4%、13.9%;The friction angle of one-,two-layer and three-layer geogrids increased by 1.9%,4.9% and 5.8% of calcareous sand and loose sand,respectively The increase rates of calcareous sand dense sand were 4.0%,7.1% and 1 1.5%,respectively.Both reinforcement materials effectively improved the shear strength and deformation resistance of calcareous sand,and the effect of geomesh reinforcement of calcareous sand was better. |
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