| Geotechnical constitutive modelling, which studys stress-strain relations laws of soil, is an important theoretical basis for geotechnical engineering disciplines, and provide a theoretical basis and guidance for the analysis and design of geotechnical engineering. Sandy soil has a wide distribution in our country. Scholars at home and abroad have carried out a number of studies on sand’s basic mechanical properties and established a wide variety of constitutive models. In recent decades, many new hydraulic and power projects, high-rise buildings and traffic engineering are springing up, bringing a lot of new geotechnical problems, such as sand fiber reinforcement and cyclic accumulated deformation of sands. Fujian sand is a representative kind of sand for experiment in our country. In this paper, a series of static and dynamic triaxial tests were carried out to study the fiber reinforcement and cyclic accumulative deformation properties of Fujian sand, and constitutive models were developed based on the test datas.Fiber reinforcement is a new type of fiber reinforced soil improvement technique. Studying the stress-strain relationship laws of fiber reinforced soil and establishing the associated mechanical model are not only beneficial for forecasting the strength and deformation characteristics of fiber reinforced soil, but also to provide a reference for the engineering design of fiber reinforced soil. The current works about the theories of fiber reinforced soil mechanical models and calculations are still not mature. In this article, a constitutive model of fiber reinforced soil is developed considering the fiber reinforced soil as a kind of composite material comprising of basic phase and fiber phase, which is based on modified Cambridge model and linear elastic model respectively. A reasonable strength model is introduced as the failure criterion for the fiber reinforced soil and fiber reinforcement weakening at large strain is also taken into account. At the same time, launched a fiber volume fraction of1%of the reinforced sand consolidated drained triaxial shear tests, the two-phase constitutive model was validated. Then the two-phase constitutive model is validated by a series of triaxial consolidated compression tests of fiber reinforced sand with1%volume fraction of fiber and provide good agreement with experimental data.In recent years, the development of offshore wind power industry is soaring. The foundations of offshore wind turbines are often subjucted to cyclic loads such as wind, waves, currents and even earthquakes. Under long-term cyclic loads, it is tend to produce cyclic accumulative deformation of the soils around foundation, which affecting the normal operation of offshore wind turbines. In this paper, a series of cyclic triaxial compression and tension tests of saturated sands under drainage condition have been carried out, to study the influences of dynamic stress level, initial mean stress, initial static stress ratio and initial density on the accumulative deformation characteristics of Fujian sand, fingding that when dynamic stress, initial mean stress and initial static stress ratio increases and initial density decreaces, the cyclc accumulative deformation is smaller. A double logarithmic linear relationship between the axial accumulative strain and cycles was obtained from cyclic triaxial tests and all the factors were included in the first cyclic accumulative axial strain. After that, the relationship between the first cyclic accumulative axial strain and the initial mean stress and deviatoric stress levels were analyzed. Finally, a explicit model for the accumulation of strain in saturated sand is developed based on a reasonable explicit model for the accumulation of strain in saturated soft clay in which the definition of deviatoric stress level was properly corrected and a strength theory of sand associated with relative density was introduced in it. The explicit model was verified by the data of cyclic triaxial tests. |
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