| Due to the hydraulic filtering effect during the construction period of the dredger,there exists some layers of calcareous silt with uneven thickness on the coral reef foundation.Apart from its low shear strength and high compressibility,the calcareous silt has the characteristics of poor stratification,high concealment and easy-mixed with sands on the spatial distribution,which can adversely affect the safety of the structure and the stability of the coral reef foundation.Based on the study of the basic physical properties and microstructure of calcareous silt,this paper takes remolded silt as the research object and conducts a lot of experimental research on its mechanical properties.In addition,the triaxial CD test of calcareous sand under different fines content is designed.Furthermore,the influence mechanism of finer content on the shear strength of calcareous sand was investigated from the perspective of particle morphology analysis.Finally,combined with the test and numerical analysis,the settlement deformation characteristics of foundation with silt interlayer under typical vehicle load are studied.Through laboratory experiments and theoretical analysis,the main conclusions are as follows:1?Through the on-site reconnaissance,the formation mechanism and occurrence state of calcareous silt are summarized.Compared with terrigenous silt,the mineral composition and microstructure of calcareous silt were analyzed,and the physical parameters of calcareous silt were obtained by conventional geotechnical experiments,especially,the applicability of the liquid-plastic limit test to the naming of calcareous silt was discussed.2?The indoor routine mechanical tests were carried out to reveal the compression and strength characteristics of calcareous silt.The stress-strain relationship and strength index of calcareous silt under different shear rates and compactness are analyzed.Furthermore,the shear behavior of CU triaxial tests for calcareous silt is controlled by samples'density.When the density of the sample changes from medium to dense state,the stress-strain relationship changes from micro-softening to obvious hardening,and the pore pressure strain curve changes from stable positive value then falling to negative.3?The static soil pressure coefficient test was carried out on the calcareous silt with the K0 consolidation instrument.The variation law of the K0 value of calcareous silt with water content,vertical stress under loading and unloading conditions is studied.Furthermore,by burying the earth pressure box under the roadbed,the K0 coefficient of the calcareous sand under the filling load is obtained.4?The morphology parameters of calcareous sand particles were obtained by electron microscopy and image processing software,and its morphological characteristics were quantitatively analyzed.Compared with the terrestrial quartz sand,the calcareous sand particles'shapes are much more irregular,which causes the weakening mechanism of the fine grain content to the shear strength of the calcareous sand to be different from that of the terrestrial sand.The tests results show that fines incorporation weakens the occlusion action between the calcareous sand skeletons,leading to a decrease in the shear strength,which results that the apparent cohesive force decreases linearly with the fines content,while the effective internal friction angle reaches a maximum at a certain fine particle content,and get gradually decreased as it rises.5?A typical road model of coral reef foundation is selected,and the characteristics of settlement deformation of silt-bearing foundation under vehicle load are analyzed.Results show that under the action of roller compactor,the settlement of the foundation increases linearly with the thickness of the silt interlayer.When the vibration working mode is started,the settlement of the foundation increases remarkably. |
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