CIVIL ENGINEERING

Dewatering Methods

Methods of Dewatering

Ditches & sumps

Well point system

Shallow well system

Deep well system

Vacuum method

Electro-osmosis method

1. Ditches & Sump

Ditches & Sumps

• Simplest form of dewatering in shallow excavation in coarse grained soil.

• Shallow pits sumps are dug along the periphery of area drainage ditches.

• Water flows under gravity on the slopes.

• To avoid piping in the sump bottom because of upward flow an inverted filter is placed at bottom of sump.

Well Point System

Well Point system (cont….)

Well Point System

• More complicated than previous method,

• Flow is under gravity.

• Well point which is perforated pipe .5 – 1 m long & 5 – 8 cm in dia. is used.

• Conical steel drive point is attached at lower end of pipe with neoprine ball valve to allow jetting of water to pass through it for driving.

• Well points placed in a ring or row.

• Well points placed by jetting water through nozzle.

• Depth – 6 m, Spacing – 1-2 m.

Well Point system (cont….)

Deep Well System

Deep Well System

• Depth is more than 16 m.

• 15 – 60 cm hole is bored and casing with long screen 5 – 25 cm is inserted.

• Submersible pump with capacity ht 30 m pumping inserted near bottom.

DEEP WELL SYSTEM

• Used for fine grained, non cohesive soils like silty sands & other fine sands.

Electro-osmosis method

CIVIL ENGINEERING

COFFERDAM