The Optimized Study On The Structure Of The High-Stacked Culverts

With the rapid development of the high-class highway in our country during the recent years, there are more and more high-class highways in the mountainous area. The highway in the mountainous area may cross the complex topography with lots of hills and ravines. In order to satisfy the alignment standard of the high-class highway, high-stacking and deep-digging embankments will be constantly increasing. Because of the high-stacking areas generally locating in the low-lying land, high-stacked culverts must be constructed in that place for the sake of drainage.With the creasing of the high-stacked culverts in the mountainous area, the design of the culvert structure has no standard graph to use with the height of fill over 15m. So the high-stacked culverts must be design separately. During the design of the high-stacked culverts, some culverts structure's dimensions are too conservative, causing the cost of the structure and the ground treatment greatly increasing. Other culverts structure's dimensions, because of the overemphasizing the arc effect of the soil, are a bit small, causing kinds of different damage of the culverts during the construction of the structure or after the soil-filling and adding the cost of reinforcement and maintenance. The fundamentality reason of these problems is that there is not a uniform theory to calculate the soil pressure on the top of the culverts. Up to now, about 20 methods are put forward to calculate the upper filled pipe soil pressure, and according to different theory can get different conclusion. The method of soil pole on the culverts which is adopted by the code for design of bridges and culverts is not a suit theory to calculate the soil pressure on the culverts. Otherwise the design of the culverts structure is also adopted the traditional load-structure method, which is not considering the influence to the mechanical characteristics of culverts caused by cooperation effect of culverts structure and soil.This paper collected the theories and methods which can be used to calculate the soil pressure of the high-stacked culverts now, and expatiated on several classical theories. Calculation principle, applied condition and localization were introduced for each theory. Because the finite element numerical analysis method has a better adaptability and can simulates different material character and outside load condition, so this paper adopts the finite element numerical analysis method to simulate the change rule of the soil pressure on the top of culverts in the construction process of filling layer by layer. After introducing the elasto-plastic constitutive relationship model, selecting suit geometry model and calculation parameter, and considering the construction process of filling layer by layer, this paper used the finite element software to simulate the soil pressure change rule on the top of reinforcement concrete culverts with the height of fill 20m. The result showed that the soil pressure on the culvert was bigger than the weight of the soil pole on the top of the culvert, and it was unsafe to design culverts according to the soil pole method in the code for design of bridges and culverts.The culverts which were designed by the traditional load-structure method could not reflect the practical mechanical characteristics. As interactive body, the culverts structure and surrounding soil must satisfy the force equilibrium condition on the interface, as well as the deformation compatibility condition. So culvert-soil cooperation effect must be considered, when analyzing the deformation and the mechanics of the culvert structure. This paper realized the culverts structure optimization through considering the culvert-soil cooperation effect. After introducing the elasto-plastic constitutive relationship model, this paper used the finite element software to simulate the structure mechanical characteristics of the hinge joint and the rigid joint between the cover slab and the culvert body. The tunnel invert could improve the mechanical characteristics of the tunnel structure. This paper changed the form of culvert bottom slab to be the invert type, and simulated the structure mechanical characteristics of the hinge joint and the rigid joint between the cover slab and the culvert body with the invert type bottom slab. The conclusions are as follow:1. By contrasting the structure mechanical characteristics of the hinge joint and the rigid joint between the cover slab and the culvert body, the result showed that the rigid joint structure could reduce the mid moment of the cover slab, and the minus end moment of the cover slab could transfer moment to the culvert body. Although the mid moment of the rigid joint culvert structure bottom slab was a bit bigger than the hinge joint structure, the end moment was smaller. The rigid joint structure made the culvert body under the effect of positive moment, improving the culvert body's mechanical characteristics. From the whole effect to the structure mechanics, the rigid joint structure was much better.2. By contrasting the structure mechanical characteristics of the hinge joint and the rigid joint between the cover slab and the culvert body with the invert type bottom slab, the result showed that the effect to the structure was closer to the structure without the invert type bottom slab. But the mid moment of the bottom slab was greatly affected by the invert type bottom slab.3. When the cover slab and the culvert body was connected by hinge joint, by contrasting the structure mechanical characteristics of structure without invert type bottom slab and structure with invert type bottom slab, the result showed that the effect to the cover slab could be ignored, and the structure with invert type bottom slab could reduce the mid moment and the end moment of the bottom slab. The moment at the bottom of culvert body was smaller in the structure with invert type bottom slab, but was bigger under the minus moment than the structure without invert type bottom slab. The structure with invert type bottom slab could improve the mechanical characteristics of the culvert structure.4. When the cover slab and the culvert body was connected by rigid joint, by contrasting the structure mechanical characteristics of structure without invert type bottom slab and structure with invert type bottom slab, the result showed that the effect to the cover slab could be ignored, and the structure with invert type bottom slab could reduce the mid moment and the end moment of the bottom slab. The culvert body moment under the positive moment of the structure with invert type bottom slab was smaller than the structure without invert type bottom slab, so the structure with invert type bottom slab could improve the mechanical characteristics of the culvert structure.The height of the fill on the top of the high-stacked culverts was big, so it requested the foundation of the culverts be much stronger to bearing the pressure. This paper contrasted the method of confirming the foundation bearing capacity in the code for design of building foundation and the code for design of bridges and culverts foundation. From analyzing the foundation ultimate bearing capacity of foundation, this paper derived the Prandlt foundation ultimate bearing capacity formula and the Prandlt-Reissner foundation ultimate bearing capacity formula. By contrasting the two formulas showed that the fill could improve the ultimate bearing capacity of the culverts foundation. The conclusion was that the fill could improve the bearing capacity of the culverts foundation, when the settlement of the culverts foundation satisfied the design request.