Centrifugal Model Test Study On Bridge Approach Settlement Characteristics

Railway vehicle will run faster in the future.High-speed railway requires stricter ride comfort of track structure. As the two major projects of track foundation, when the train runs between the bridge abutment and soil embankment, it will easily cause the ride comfort problems just because of the stiffness and deformation properties differences in these two kinds of structures.During the high-speed railway construction, it is a big technical problem that make the settlement between the abutment and embankment transit uniformly under the condition of high embankment and special foundation such as soft soils and loose-soft soils,etc in order to ensure the strict ride comfort of track structure in high-speed railway. This thesis is depends on the construction of Beijing-Shanghai high-speed railway. Additional stress in bridge approach foundation is analysised, and the settlement characteristics between the abutment and bridge approach is discussed, and also the interaction between pile and soil structure is investigated by means of literature investigation, theoretical analysis,and centrifugal model test research. The main research conclusion in this paper are as follows:1.Through literature investigation, it is confirmed that the crux of the bridge approach matter is the nonuniform track stiffness and settlement, and these difference is harm to service performance of track structure, rolling stock, foundation under the rail.2.Based on the Boussineq equation of point load, a formula of calculating the additional stress in nature foundation of bridge approach is obtained by mathematical intergral. An example of normal embankment section shows that when the distance between the bridge approach and abutmen is greater than 20m long, the spatial distribution law of the additional stress in bridge approach foundation is the same as that in the ordinary embankment foundation3.The simulation problem of graded crushed stone in centrifugal model test is solved. The test results shows that the settlement of abutment and the bridge approach increased gradually with the increasement of the center to center spacing of the piles, but the sensitive degree in different section is different. Farther away from the abutment,more obviously the settlement change is. As the settlement control of embankment behind the abutment in high-speed railway is strict, it is proposed that the foundation treatment near the abutment area shoule be strengthened.4.Under the simulated condition that the abutment and embankment is once complete loading, the relationship between settlement and time in rigid abutment foudantion and soft embankment are the same, both of them can be forcasted by Weibull function. The center to center spacing of the piles change in foundation can affect the irregularity between the bridge and embankment from quantitative to qualitative. When the center to center spacing of the piles is not less than 4.5 times diameter, the irregularity behaves concave down, while the center to center spacing of the piles is less than 4 times diameter, the irregularity behaves upper convex.5.The center to center spacing of the pilse change in foundation can markedly affect the rigid pile mechanical characteristics under the soft embankment. When the spacing diameter ratio equals 4.5 and 5, there exists the negative friction around the pile, while the ratio is less than 4.5, the negative friction disappears. In order to play the bearing capacity of soil between pile,it is suggested that the pile spacing should not be too small.6,The center to center spacing of the piles change in foundation can also affect pile mechanical characteristics under the rigid pile cap.Force near the pile head gradually reduces with the increasement of spacing diameter ratio, while force near the pile end gradually increases with the increasment of spacing diameter ratio.There exists the negative friction under the condition that the foundation treatment with different the center to center spacing of piles.7.For ordinary pile foundation, additional stress gradually increases with the increasement of depth in plie length area, the additional stress is quite small in shallow layer, while in pile end area the stress increases significantly, the compression of soil between pile mostly happens in the area around pile end.8. The bridge-approach convergent settlement and the abutment horizontal displacement and inclination have a positive correlation. Based on the numerical simulation, the convergent settlement of the embankment at the distance of 20 meters from the abutment is proposed.