For all earthwork slopes, rainfall will enter the underlying soil through the surface, in quantities which depend on the soil type, topography, and vegetation cover. Slope drainage can control the movement of surface water and also the subsurface pore water pressure in the slope. Drainage can be very effective if installed at the correct location on or within the slope. In the long term, systems need to be designed with maintenance operations in mind so that a sustainable system is installed with a design life comparable to the 60 year design life of a highway slope.
The report reviews the distribution of pore water pressures within a slope measured by TRL at a number of sites on highway schemes and follows with a critical assessment of the applicability of different slope drainage techniques. The report concludes with best practice guidance in the design and maintenance of the various drainage systems. The increased use of surface water channels and a more proactive bioengineering approach are recommended in the design of slope drainage systems. These methods offer the advantages of ease of inspection, reduced maintenance costs and a sustainable technique.

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