The location of highways and other routeways is influenced in the first instance by topography. Embankments, cuttings, tunnels and bridges (viaducts) can be constructed to carry roads and railroads with acceptable gradients through areas of more difficult terrain. Obviously, the construction of such structures increases the difficulty, time and cost of building routeways. Nonetheless, the distance between the centres that routeways connect has to be considered. Although geological conditions often do not determine the exact location of routeways, they can have a highly significant influence on their construction.

As highways are linear structures, they often traverse a wide variety of ground conditions along their length. In addition, the construction of a highway requires the excavation of soils and rocks, and stable foundations for the highway, as well as construction materials. The ground beneath roads and, more particularly, embankments, must have sufficient bearing capacity to prevent foundation failure and also be capable of preventing excess settlements due to the imposed load (Kezdi and Rethati, 1988). Very weak and compressible ground may need to be entirely removed before construction takes place, although this will depend on the quantity of material involved. For instance, if peat is less than 3 4 m thick and is underlain by a soil with a satisfactory bearing capacity, such as gravel or dense sand, then the peat may be removed prior to the construction of a road or, more particularly, an embankment (Perry et al., 2000). In some cases, heave that occurs due to...