The methodology of designing high highway embankments over weak and compressible clay subsoil is shown in this paper. Excess pore water pressures will generate in the subsoil and may compromise stability. It is important for any project to design a proper timetable for the use of vertical and horizontal drains to accelerate subsoil consolidation. Our design method could be used in conjunction with the observational method using field measurements during construction of embankments. Design calculations were made by using the program FLAC, which is an explicit finite difference method, that may analyse plastic flow, even if peak strength is reached and softening is developed. It is possible to simulate compressible transient, quasi-static mechanical processes coupled to fluid flow process - consolidation. The author's elastoplastic constitutive relation was implemented into FLAC, to model the effective stress-strain relationship and to judge embankment stability. Plastic strain increments are divided into a plastic expansive (dilatation) component and plastic collapse (compression) component. These strain components are calculated separately. Each plastic component has own yield and plastic potential function and plastic memory. Plastic memory is used for correction of parameters used in the yield and plastic potential functions, which determine the next increment of plastic deformation.


A typical problem for Czech Highways in Moravia in the Czech Republic is construction of high highway embankments over weak and compressible subsoils. Calculated highway embankment heights were 8.8 m, 11 m, 12m, 13 m and 15 m. Embankments are constructed over weak and compressible fluvial soft normally consolidated clay, fluvial gravel and sand and a subsoil of a Miocene marine over consolidated clay deposit or similar profile without gravel and sand. The water level is very often about 1–3 m under ground surface. Some embankments are located near or in ponds.

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