Oaks Designer Resource Guide 6.0

Drainage Design and Water Considerations

Improper management of surface water can cause erosion. When water infiltrates the Gravel Fill or Reinforced Soil Zone, it can overload a wall. Drainage swales made of low to negligible permeability materials such as clay, plastic liners or concrete can divert water around the back of the wall (see below). Scuppers can provide for controlled flows over the crest of the wall, but they need to include proper erosion control features at the toe of the wall. Drainage inlets can collect water and direct it towards storm water facilities or out the face of the wall.

WATER CAN INCREASE THE PRESSURE BEHIND A WALL BY 2.5 TIMES!

Groundwater can weaken foundation soils supporting the wall, clog drain pipes , and increase external loads on the wall. Blanket or chimney drains may be required to divert groundwater around the wall structure (see below). When using walls for shoreline stabilization or erosion/sedimentation control along stream banks, some unique considerations need to be addressed in the wall design, such as: erosion at the toe of the wall; potential build up of hydrostatic pressure behind the wall (especially when rapid water level draw down occurs); the forces of waves and ice sheet flows exerted on the face of the wall.

POTENTIAL GROUND WATER DETAIL

Separation geotextile (Required at top of gravel fill, optional at back)

Grade surface to prevent ponding

Low-permeability soil

Coping Unit Standard Unit

Compacted Native Backfill (Where appropriate) or Imported Fill

WATERFRONT APPLICATION

300mm (12”) Gravel Fill (free-draining aggregate)

High Groundwater Elevation

Compacted Native Backfill (Where appropriate) or Imported Fill

Separation geotextile (Required at top of gravel fill, optional at back)

Slope may vary

Finished Grade

Geosynthetic Reinforcement

H x 0.7

Low-permeability soil

Coping Unit Standard Unit

300mm (12”) Gravel Fill (free-draining aggregate)

Chimney Drain (Extended H x 0.7 or maximum elevation of ground water rise, whichever is greater)

Blanket Drain 150mm (6”) Min.

100mm (4”) Dia. Minimun Drainpipe (set elevation to drain) Separation Geotextile around leveling pad and blanket/chimney drain

Erosion Protection (designed by others)

High Water Elevation

Geosynthetic Reinforcement

Backfill with free-draining aggregate to 300mm (1’) above high water elevation

NOTE: A minimum of 600mm (2’) of embedment is recommended in shoreline or channel wall applications

Separation Geotextile

150mm (6”) minimum compacted granular-base leveling pad wrapped in separation geotextile 100mm (4”) diametre minimum drainpipe. Outlet through front face every 15m (45’)

150mm (6”)

Separation geotextile under erosion protection

675mm (27”)

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APPLICATIONS AND SOLUTIONS

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