Buttress drains, also known as counterfort drains or trench drains, improve slope stability by controlling groundwater pressures through subsurface drainage.

This is achieved by reducing or maintaining adequate low pore water pressure on a potential failure surface, by providing a preferential pathway which encourages groundwater flow from the surrounding soil.

A buttress drain can be up to 6m deep, and comprises a perforated base-pipe, backfilled with free-draining material.

With appropriate design and construction, buttress drains can deliver significantly improved site stability at a moderate cost.

CLL’s ground improvement expertise allows us to recommend and create buttress drains – if this is the best option.

As with any soil stabilisation project, our ‘horses for courses’ approach determines the most cost-effective technique and technology to achieve the client’s requirements.

“Whether you call them buttress drains or counterfort drains, they’re the same thing.

“They’re often a great solution for unstable slopes, a way to make previously unusable land more productive.

“Buttress drains control groundwater pressures by subsurface drainage and can provide significant improvement to site stability at moderate cost.

“Drain spacing and depth is best assessed by a combination of analysis and practical experience.

“CLL has both, as well as the equipment to achieve the desired outcomes.”

Terry Donnelly