Engineering geology

Drainage of slides

Pore water pressure is critical to slide stability, so drainage is usually very effective, and is the only economical method to stabilize large landslides within natural slopes.
Surface drains: concrete diversion ditches intercept surface flows; drains on slides reduce infiltration.

Shallow drains: stone drains in trenches 1–2 m deep lined with geotextile; have limited effect by reducing soil water; granular fill in deepe counterfort drains also provides shear resistance.

Deep drains: most effective; mined adits with leaky walls and sealed floor, or boreholes with perforated casings, inclined to drain out from slide toe.
Relief wells: drain up or down through aquiclude; need pumping unless draining into a lower aquifer. Some London Clay slopes have been drained into lower sand, through 100 mm boreholes filled with sand in polypropylene tubing, on 2–5 m centres.
Interception tunnels: cut behind the slide to reduce groundwater inflow; used in 1800 to stabilize failing slopes of limestone and clay above the city of Bath.
Impermeable clays respond poorly to normal drainage.
Electro-osmosis, or heating with ducted hot air, can improve clay stability, but both are expensive.

Drainage of slides

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