Study On Dynamic Response Of Soft Soil Subgrade Based On FLAC^3D

Low liquid limit silt and silty sand soil are the most widely distributed in the coastal areas of China and the impact of the plain. The type of silt and silty sand grain size is more uniform, the particle size distribution is poor, and the water stability is poor, capillary development and other physical and mechanical properties. This type of silty soil is not suitable for the construction of buildings and structures of the foundation and subgrade site selection of objects because the permeability coefficient of this kind of soil is higher, and the permeability of the soil is stronger than that of the ordinary soil.However, with the rapid development of our economy, the big city group continues to expand the scale of each city and each city between trade exchanges have become increasingly frequent, increasing demand for Expressway and ordinary high grade highway. The economy of the coastal area and the central region is more and more urgent because of the dense population. But with the rapid development of highway inside and outside the province, the national highway mileage will continue to rise, in some geological conditions of poor regional planning highway route is inevitable, including in the soft soil area of the design and construction of the highway. However, due to the special physical and mechanical properties of the saturated silt and silty sand, the dynamic pore water pressure of the subgrade is rapidly increased under the action of earthquake, vehicle and other transient dynamic loads. At the same time, the drainage effect of this type of soil is poor, resulting in water pressure to dissipate. With the dynamic pore water pressure increasing, the effective stress decreases to zero, completely lost the shear capacity of the soil, the soil showed similar to liquid state known as liquefaction phenomenon. A series of damage caused by soil liquefaction, poses a great threat to people’s lives and property safety Therefore, combined with the specific geological data, starting from the mechanism of liquefaction of soft soil, through a series of calculation methods, specific research on soft soil subgrade liquefaction and deformation, can guide the engineering practice well. It is of great practical and practical significance to resist vibration liquefaction of soft soil foundation which is composed of low liquid limit soil such as silt or silty sand. This paper through the finite element software FLAC3D, analysis of the liquefaction characteristics of no reinforcement saturated soft soil subgrade based on the highway subgrade in Anhui Huaibei area of exploration data.Study on Soft Soil Subgrade in this paper mainly from the following two aspects, and obtain the corresponding conclusions:(1)Study on liquefaction of silty sand under different vibration loading.By decomposing the real seismic wave into the acceleration time history of different vibration direction, the soil layer is applied to simulate the liquefaction response of seismic waves in different vibration directions. The liquefaction degree and the distribution area of the roadbed can be obtained, by analyzing the result of numerical calculation:Compared with the bidirectional seismic load, the horizontal displacement and the vertical settlement of the subgrade are slightly difference when the action of the horizontal seismic load, at the same time liquefaction area and the effective stress change curve is not the same too. When the vertical seismic load is acting alone, it is not large, but the dynamic response of the subgrade is different when it is in the same time as the bidirectional seismic load. The results of the software model and the results of the experiment provide a reference, and can be used as the basis for approximate treatment.(2)Seismic dynamic response analysis of Subgrade under different dry density.In this chapter, the dynamic response of subgrade is studied by using the different dry density of the silty sand to change its initial in-situ stress and saturation density. Analysis results show that with the increase of dry density of silty sand subgrade, can the size and distribution have obvious change in scope of liquefied layer. With the increase of the effective stress, pore water pressure of fine sand layer increases with the dry density decreased gradually. The midpoint of the pavement settlement increases with the dry density decreased significantly, but the maximum heave embankment on both sides of the ground while the dry density increases.