Study On Vertical Soil Pressure On The Top Of Trenching Conduit Based On Stiff Foundation

The conduit buride in fill has been applied widely in fields such as water conservancy, transportation, municipal engineering and energy sources. It is divided mainly into two types: trenching conduit and projecting conduit. It is reported that there is some troubles in the management constantly. Although there are many formulae about vertical soil pressure on the top of trenching conduit, there are some limitation exist in them. The method calculated the vertical soil pressure on the top of trenching conduit is not recommended in present load code for the design of hydraulic building structures. In this paper, based on the model testing in the house, researches is done deeply and systematically on the vertical soil pressure on the top of trenching conduit using finite element analysis and theoretical analysis.A series of testings on the model are done about trenching stiff conduit based on the stiff foundation and sand soil. The boundary conditions are respectively rectangle section groove with different width, trapezoidal section groove with fixed width of bottom that equals to twice diameter of the conduit and different slope of trough wall, the condition of positive buried conduit. The result involves the earth pressure on the top of conduit and the displacement of the earth with the different height of backfill. The coefficient of vertical earth pressure on the top of conduit is calculated according to the experimental results. The change rule is got by analysis and comparison. The coefficient of vertical earth pressure on the top of trenching conduit changes nonlinearly followed the height of backfill and is related to the section of the groove. When B/D=1.5, the coefficient of vertical earth pressure on the top of conduit buried in rectangle section groove is decreased monotonously; When B/D≥2, the coefficient of vertical earth pressure on the top of conduit buried in rectangle section groove is increased at first and decreased later. The coefficient is increased while the groove is wider at the same hight of backfill. The coefficient of vertical earth pressure on the top of conduit buried in trapezoidal section groove is increased at first and decreased later and increased while the slope of groove is gentler.The model testings were simulated with the data in the testing by the software ANSYS. It is clear to see that the software is reliable for calculating the vertical earth pressure on the top of conduit. Then, the pressure on the top of flexible conduits was calculated. It is concluded that the interaction of backfill and conduit should considered when the vertical earth pressure was calculated. Relative stiffness ratio of soil and conduit—a_S can reflect the influence on vertical earth pressure produced by stiffness of soil and conduit. The vertical earth pressure on the top of flexible conduit could be calculated by reducing the pressure on stiff conduit filled in same condition. The reducing coefficient has been got through the FEM results. When a_S equal to 0.005, the vertical earth pressure on the top of flexible conduit is about 70 percent of stiff conduit.The theory of Marston-Spangler is basis of methods with which calculating the vertical earth pressure on the top of trenching conduit. The theory considers the weight of earth is supported by the conduit subtracting the friction between the wall and the earth, and there is little with the backfill on both sides in supporting the weight of the earth above. This does not accord with the fact. So a new calculation model of earth pressure on the top of trenching conduit has been established in this paper according to the results of experiment and EFM. Some formula were deduced and the theory of M-S has been modulated.