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In recent years, it has been demonstrated that diffuse or irregular sources of pollu­tion, like runoff, constitute significant contamination points in the natural drainage system. In most cases one has to take appropriate measures to control this pollution. In general, the environmental aspect of a road project nowadays constitutes an in­tegral and fundamental part of […]

Water that has been collected from runoff or from sub-surface drainage systems has to be disposed of. The simplest means is to route it to a naturally occurring surface waterbody (stream or lake). Often a retention pond (see Section 13.4.8.1) is interposed between the water coming out of the highway and the outflow into the […]

In colder climates, deep drains (“cut-off’ drains) are used to reduce local frost damage by intercepting the flow of groundwater and seepage water under the road structure, usually where there is a crossfall (see Section 13.4.4). The depth is usually at least the design frost depth (e. g. in Finland, this is between 1.5 and […]

In excavated areas and cuttings where the longitudinal slope is more than 3%, a longitudinal water flow may appear fed by water from under the pavement that is Water*………………. ……………….. table with drain ^ | separate from the flow in channels, gutters and gully’s. In these cases, the inclusion of pavement underdrains (Fig. 13.26), installed […]

Drains can be placed as a trench or fin at the toe of a cutting, between the cutting and the pavement construction (Fig. 13.23). These act to lower the water in the cutting both increasing the stability of the slope and also reducing the water arriving at, and the pore water pressure in, the foundation […]

Drainage masks provide control of emerging water (e. g. a spring line) on a slope’s face with a geotextile covered by hand-placed rock (Fig. 13.21). The material used for a drainage mask should be angular and should comprise 100-500 mm sized stone. The rock provides improved slope stability both by allowing the reduction of pore […]

This kind of drainage is installed with the aim of controlling waters emerging from earthworks, which includes not only the water that appears at the base of the exca­vations but also the flow coming from excavated slopes. Five types of systems can be used: 13.4.4.1 Drainage Layers These consist (see Sections 13.3.4 and 13.3.6) of […]

Transverse drains are similar in construction to lateral drains, except that they run perpendicular or slightly skewed to the centreline of the carriageway (Kasibati & Kolkman, 2006). They are mostly used to drain water that may infiltrate into the road bases and sub-bases at joints, see Fig. 13.18 (FHWA, 1980). It is important to provide […]

So-called “Californian Drains” are sometimes used. These consist of parallel and closely-spaced tubes, arranged vertically or sub-horizontally. The tubes can be perforated or grooved and are installed into natural ground or fill. The main objective of such drains is the reduction of pore water pressure in a certain area, in order to lower the water […]

Fin drains or drainage screens are also longitudinal drains, manufactured from com­posite materials. Their essential make-up is of two geotextile faces that provide a filter function between the surrounding ground and a rigid plastic core that is sandwiched between the geotextile faces — see Fig. 13.16c. The so-called “drainage core” is, typically, formed of a […]