A large-span buried concrete culvert, which is 10 m height and 15,3 m wide, is designed in 14,3 m high embankment over fluvial soft normally consolidated clay in the depth of 0,3 - 4,8 m and a subsoil of a Miocene marine over consolidated clay deposit. Flexible concrete culvert has three joints and its thickness is between 30 and 50 cm. It was necessary to calculate precisely the soil-structure interaction during gradual construction of embankment, after subsoil consolidation and under embankment surface traffic loading. Design calculations were made by using the program FLAC, which is an explicit finite difference method, that may simulate compressible transient, quasi-static mechanical processes coupled to fluid flow process - consolidation. The proper shape of the culvert and necessity of sandy gravel backfill extension around the culvert was tested during soil structure interaction modeling to reduce lining bending moments. Before large-span culvert calculation was necessary to optimize design of embankment, in which is culvert projected. The proper timetable, combination of horizontal free draining layer, vertical drains to accelerate subsoil consolidation, geogrid reinforcement inside a horizontal free draining layer and proper embankment shape had to be designed.
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