Research On The Properties Of Interfacefriction Between Calcareous Sand Andstructure

With the need of marine development and protection,especially the exploitation of offshore oil and gas resources and the construction of islands and reefs in recent years,the construction of offshore engineering is in the ascendant.Calcareous sands are widely distributed in the South China Sea,which are different from quartz sands in terms of CaCO₃content,high porosity ratio,irregular shape and fragility.The interface friction characteristics of soil and structure have important application significance in engineering construction.Many experiments and studies on the interface between soil and structure have been carried out at home and abroad.However,there are few results on the interface between calcareous sand and structure.Therefore,it is necessary to study the friction characteristics of the interface between calcareous sand and structure.In this paper,the interfacial friction characteristics of coarse-grained calcareous sand are systematically studied through large-scale interfacial friction tests,and the effects of various factors on the interfacial friction characteristics are mainly studied.The variation of friction coefficients of different kinds of sand（calcareous sand,quartz sand）,different gradation,different initial relative density and different initial normal stresses under the conditions of soil-concrete interface and Soil-Steel plate interface are analyzed respectively.The experimental results show that the friction coefficients are independent of the initial normal stress within the normal stress range used by the test,but it is influenced by other factors..In addition,large-scale direct shear tests under the same conditions were carried out to study the effects of various factors on the internal friction angle under constant volume conditions.The experimental results show that the critical internal friction angle has nothing to do with the initial normal stress and initial relative compactness,but with the particle size distribution and the types of soils（calcareous sand and quartz sand）.Then,the relationship between the internal friction angle in critical state and the external friction angle in stable state under constant volume condition is explored.The large-scale interfacial friction test and large-scale direct shear test of coarse-grained sand are studied by using discrete element method.The displacement and rotation of particles in the numerical samples and the evolution process of micro-structural parameters are analyzed from the meso-level,and the similarities and differences between the meso-level of soil and soil,soil and structure interface are compared.The numerical test results show that there are similarities and differences in the mesoscopic level of the two numerical samples.Finally,the numerical analysis of the effect of particle breakage on the interfacial friction characteristics of calcareous sand is carried out.The results show that the particle breakage rate is related to the initial normal stress,and the distribution of particle breakage has a certain regularity.