Drainage plays an important role in highways by improving the long-term stability of earthworks, retaining structures and pavements. This Report, one of a series on drainage studies, deals with a study of the performance of slope drains in an old cutting in London Clay. The slope drains were installed in 1981, and monitored until 1988. During this period, there was no deterioration in performance. The drains substantially reduced the water table within the cutting slope. They were not effective, however, in eliminating a perched water table associated with more permeable soil near the surface. The water table reduction was in accordance with theory. There has been no sign of further instability in the cutting since the drains were installed, although several potential failure mechanisms were identified. The geotextile filter used as wrapping for the granular filter material in the drains showed no signs of significant damage or deterioration. The presence of a layer of wet clay adjacent to the geotextile, and also ground movements during excavation for the drains, could be relevant factors at some sites. (Author/publisher).
Abstract