Experimental Study On Dynamic Characteristics And Microstruture Of Marine Soft Soil Under Cyclic Loading

The site formed by blowing sand reclamation usually has thick layer of marine muddy soft soil.The poor engineering properties of soft soil have a great influence on the seismic action because coastal areas are seismically active belt.For this reason,from the perspective of engineering earthquake disaster reduction,this paper study on dynamic characteristics of Beihai's marine soft soil by dynamic tri-axial tests under the influence of three different factors.The soil samples before and after cyclic loading were subjected to mercury injection test and scanning electron microscopy.The change of microstructure and the influence of three elements on microstructure were studied qualitatively and quantitatively.Therefore,the relationship between the microstructure characteristic parameters and the macroscopic properties parameters is established and the mechanics of soil displacement and deformation can be explained by micro level.The main results of this paper are as follows:(1)Beihai's marine soft soil is sandy clay and the main mineral compositions are quartz and kaolin.Under the vertical press,the vertical settlement deformation of artificial sample preparation is up to 44%and settlement deformation rate of artificial sample preparation gradually slow down and ultimately stabilizes,as the load levels increased.The preparation of marine soft soil samples has the characteristics of large porosity and high saturation(2)With the increase of the dynamic load amplitude,dynamic deformation of Beihai's marine soft soil evolve from the elastic steady state to the plastic expansion state and different factors have different effects on soil dynamic characteristics.The increase of consolidation ratio can reduce the strength and rigidity of marine soft soil and the effect of consolidation ratio on soil deformation is relatively small.The increase of the confining pressure can obviously improve the anti-deformation ability of the soil and reduce the energy consumption of the energy in the soil.When the vibration frequency is between 0.05Hz and 1Hz,the stress-stain curve shows hyperbolic stable.When the vibration frequency is 2Hz,the stress-stain curve shows hardening characteristic.The lower the vibration frequency,the more conducive to the development of dynamic deformation.And the frequency reduction can weaken the soil strength and stiffness.(3)According to the pore characteristics of marine soft soil,the aperture is divided into four grades in the mercury injection test.The original aperture shows a single peak distribution and medium pore occupies the largest proportion in the total pore.By contrast,it is found that the total pore volume of soil samples increased after cyclic loading,but it is still mainly dominated by medium pore.And the distribution of pore space in each group is changed,among which the medium and small pores content decreased but large pores content increased.The larger the consolidation ratio,the smaller the large pores content and the smaller the total pore volume.The increase of confining pressure can reduce the pore volume.The effect of vibration frequency on pore distribution is more complicated under the coupling of various factors.(4)The qualitative and quantitative results of SEM image show that Beihai's marine soft soil is a kind of frame-mosaic structure that is mainly surface-to-surface contact with marginally surface-side contact.The basic unit body is mainly composed of flat particles of laminated pieces of 'clay domain' stackers.The stackers are indented in space and form an overhead-mosaic pore whose development is obvious.Most of them present striped fissures.Their shape is very irregular and their connectivity is poor.The soil structural units show a certain orientation under the larger vertical press.(5)IPP software has been used to extract structural parameters of each unit from SEM binary image,analyzing the change of microstructure under the influence of three elements.Combined with the dynamic characteristics of Beihai's marine soft soil,the process of microstructure evolution can be concluded by studying the evolution of the microstructure of the soil before and after cyclic loading:elastic deformation-stress yield-plastic deformation.The relationship between the characteristic parameters of the pore structure and the macroscopic characteristic parameters is established,and the influence mechanism of each factor on the dynamic characteristics of the soil is analyzed from the microscopic point of view.