Study on shear stress - shear strain nonlinear response of wide-graded saturated coral soil site in dynamic centrifugal test

As an important soil for port engineering and military and civil facilities construction sites in tropical and subtropical areas, there is a lack of knowledge about the cyclic shear stress - shear strain behavior of coral soils under near-real site conditions and bottom-up transfer of earthquakes. Based on the advantages that the dynamic centrifugal test can simulate the site stress distribution, drainage conditions, and earthquake transmission of the site more realistically, a typical horizontal saturated coral soil site model test is carried out. The spatial and temporal distribution characteristics and evolution laws of cyclic shear and stress shear strain in coral soil sites are discussed. The correlation between cyclic shear stress, shear strain, and the development of excess pore water pressure ratio are compared, and the relationship between the dynamic shear modulus and damping ratio with shear strain and the development model of coral soils with different burial depths is solved and analyzed. The results show that the shear stress-shear strain hysteresis loops evaluated by inverse analysis have good smoothness, continuity, and regularity, and with the increase of the number of cycles, the hysteresis loops are gradually tilted to the horizontal and the area is enlarged, which is an obvious characteristic of strength softening. Under the same load, the shear stress increases with the increase of burial depth, and the shear strain increases firstly and then decreases with the increase of burial depth and increases with the increase of load intensity, and under the sinusoidal load of 0.05g~0.3g, the shear strain is mainly concentrated in 0.01%~2%. The correlation between the shear stress and the excess pore water pressure ratio with the burial depth is not obvious when the load strength increases gradually, but the increase of the excess pore water pressure ratio has a certain constraint on the increase of the shear stress with the burial depth. While the distribution of shear strain and excess pore water pressure ratio is remarkably consistent with the buried depth. When the pore pressure ratio exceeds 0.6, the shear strain will increase significantly. The dynamic shear modulus increases with the increase of buried depth and decreases with the increase of shear strain with good regularity. The damping ratio decreases with the increase of buried depth, and the relative dispersion is larger, which is related to the calculation method and the strong nonlinear liquefaction. The maximum shear modulus is significantly lower than that obtained by the unit test, and the dynamic shear modulus ratio of coral soils in a typical horizontal saturated site is more consistent with the Martin-Davidenkov model.