Influence Of Lateral Fill Load On Foudation Bearing Capacity Of High-Stacked Culvert

With the rapid development of the high-class highway in the mountainous area in our country during recent years, in order to satisfy the alignment standard of the high-class highway and the complex topography with lots of hills and ravines, high-stacking and deep-digging embankments will be constantly increasing. Because of the high-stacking areas generally locating constructed in the low-lying land, high-stacked culverts must be place for the sake of drainage.With the increasing of the high-stacked culverts in the mountainous area, the theory of the structure and foundation design under high embankments is not determined. Culvert disease continue to occur so the normal operation of highway is affected. In these diseases, the large part is due to improper ground treatment. Traditional design methods believe that the greater the stiffness of the foundation and subsoil, the more secure the upper structures. But the working status of the culverts is opposite in fact. The culverts constructed on the soft foundation generally used pile foundation to meet the requirements of the bearing capacity. Research found that all the culverts project which used pile foundation has been fully destroyed. In fact, as to culverts embedded in high embankments, high-fill is equivalent to a depth effect of culverts, can significantly improve the bearing capacity of foundation. 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, different damage of the culverts continue to occur 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 the improvement of filling effect on the bearing capacity is neglected. There is not a uniform theory to calculate the bearing capacity of high-stacked culverts, two dozen calculations of ultimate bearing capacity have been proposed, according to different theories can get different conclusions. Existing Code for Design of Building Foundation proposed that when the buried depth is greater than 0.5m, the bearing capacity of buildings should be amended, the embedded depth started from outdoor ground elevation. Existing Code for Design of Ground Base and Foundation of Highway Bridges and Culverts proposed that when the buried depth is greater than 3m, the bearing capacity of buildings should be amended, the embedded depth started from natural ground. According to different rules can get different standards in embedded depth of the starting.This paper collected the theories and methods which can be used to calculate ultimate bearing capacity of the high-stacked culverts now, and expatiated on several classical theories. Calculation principle, applied condition and localization were introduced for each theory.This paper deduced the improvement mechanism of lateral fill on the bearing capacity of high-stacked culverts with integral foundation. Then combining with the stress characteristics of the foundation soil, the soil force was analyzed, the general formulation of separated foundation bearing capacity considering lateral fill was deduced to point out the improvement mechanism of lateral fill.The high-embankment culvert foundation model tests were designed and completed. To separated foundation and integral foundation the model tests with different lateral fill heights were designed to simulate the silt clay foundation deformation in whole loading process. Analyzed the ultimate bearing capacity change rule with lateral fill, provided the experimental basis for engineering practice. The results showed that:1. The lateral fill as lateral load could increase the foundation soil shear strength, improve the foundation bearing capacity significantly. As to the silty clay, the growth of the lateral fill to the foundation bearing capacity is not unlimited. It firstly increases and then reduces, at last it tends to a constant when the fill height reach a certain critical point.2. To separated foundation the embedded depth should started from indoor ground elevation according to Code for Design of Building Foundation. To high-stacked culverts with integral foundation the embedded depth should started from bottom base.3. Not only the selected formula but also the impact of parameters provided by different test methods will be considered to calculate the foundation bearing capacity within the critical height.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.