Abstract: Trapezoidal trench installing (TTI) culverts are widely used in highway and railway in mountainous area. However, there are currently no published standards for the design of the TTI culvert. The performances of embankment installation (EI) and trench installation (TI) culverts have been investigated by a number of researchers; but the study of performance of TTI culverts is less common. To understand the complex soil-structure interaction issues related to the design of TTI culverts, a numerical simulation is conducted to investigate the stress states and the soil arches in the backfill over the reinforced concrete box culvert installed in trapezoidal trenches. A theoretical model is established based on the numerical results; and the formula for calculating the vertical earth pressure acting on the culvert is deduced. The theoretical results are in reasonable agreement with the field test data and numerical results. Moreover, a parametric study is carried out to investigate the important influencing factors on the vertical earth pressure acting on the culvert. Research results show that the stress states on the TTI culvert is different from those of EI and TI culverts. Two layers of soil arches at different levels form in the backfill over the TTI culvert when the fill on the culvert reaches a certain height. The lower soil arches incur the vertical earth pressure concentrating on the top of the culvert. However, the upper soil arches covering the lower ones alleviate the concentration effect. The vertical earth pressure on the culvert is determined by the soil arching effect, which is affected by the height of backfill over the culvert, the slope angle and bottom width of the trench, the dimensions of the culvert and the properties of backfill.

Key words: culvert, trapezoidal trench, earth pressure, soil arch, theoretical analysis