Study On Unified Calculation Theory Of Earth Pressure On Top Of Trench-buried Culverts And Positive-buried Culverts

Culverts have been widely used in engineering of water conservancy, railway, highway, municipal mine and energy. The vertical earth pressure on the top of culverts is a main force for the design of culverts and it is important to determine the earth pressure. The existing theory of culvert earth pressure is not perfect and there are large differences between each calculation result, which often cause troubles in the management. With the construction of basic installation, culverts are being used more widely. The study on the earth pressure of culverts is urgent. It is significant in reality and theory to perfect the theory of earth pressure on culverts.In this paper, the vertical earth pressure on the top of trench-buried culverts is studied systematically with the help of experiment under the condition of rigid culverts and foundation. Then the construction process of earth filling is simulated by FEM. Based on the settlement displacement of backfill by the experiment and FEM simulations, unified calculation theory of earth pressure on top of trench-buried culverts and positive buried culverts and regularity on the change of plane height of equal settlement are proposed for the first time. The calculation model and formulae contain factors such as trench geometry, foundation characteristics, nature of backfill and height-width rate of culverts. The unified calculation theory of earth pressure on the top of trench-buried culverts and positive buried culverts is formed.Experiment and FEM results show that layered backfill construction process caused special settlement displacement field. Under the condition of rigid foundation, the settlement at the top and the bottom of backfill is the smallest. The largest settlement changes with the backfill height and is located near the middle of it. When the backfill height is small, the largest settlement is beside the top of culverts. With the increase of backfill height and the effect of trench slope, largest settlement moves to the center line of the trench. The distribution of settlement displacement is the"W"shape at the level round culverts and is the"U"shape at the level far from culverts. The distribution becomes the"—"shape between them. The plane of equal settlement is located at the zone of"—".The settlement field form of backfill and the change of it prove the existence of the plane of equal settlement. The height of plane of equal settlement changes with the height of backfill and equals probably to 1.0- 3.5 times of the width of the culverts. It decreases and comes close to a constant as the depth of backfill increased. The height of plane of equal settlement increases when the width of trench increases, the slope becomes gentle or the height-width rate of culverts increases. It decreases when the angle of internal friction of soil or the Poisson's ratio increases.This paper proposes a uniform regulation of the change of coefficient of the earth pressure on top of trench-buried culverts and positive buried culverts. The coefficient of earth pressure decreases monotonously with the increasing depth of soil overlying culverts if trench width equals the outer width of the culverts and the side slope coefficient equals to 0, while the coefficient increases at first and decreases later if trench width exceeds the outer width of the culverts or the side slope coefficient is bigger than 0. The maximum coefficient appears at the depth close to the height of the initial plane of initial equal settlement. The coefficient of earth pressure increases and the change magnitude becomes smaller with the increase of width of trench and the decrease of slope coefficient. When the slope coefficient is larger than 5, the coefficient of earth pressure turns to a constant and trench-buried culverts becomes positive buried culverts.The influencing factors of earth pressure were studied quantitatively. The trench geometry size has the largest influence on the earth pressure. It can make the coefficient of earth pressure vary almost 100%. The foundation property, the ratio of high-width of the culverts and the deformation of the culverts influence the earth pressure equally. They can make the coefficient of earth pressure increase or decrease more than 30%. The earth pressure on square culverts is about 1.07 times as the earth pressure on circle culverts. The earth pressure of circle culverts decreases by 20% with the increase of the flexibility of circle culverts. The earth fill property slightly influences the earth pressure. It makes the coefficient of earth pressure increase or decrease by only 15%. All the factors will have a greater influence on the earth pressure when the trench becomes wider.