chapter 5.pptx: drainage and irrigation engineering
Subsurface water Control methods (1).pptx
1. Subsurface water Control methods
• Various methods are there-
-depends on the type of engineering work involved,
-site conditions
- the purpose for controlling the water.
• Control methods can be reasonably grouped into
four categories
(i) Barriers
(ii) Liners
(iii) Wells
(iv) Drains. 1
2. Subsurface water Control methods
• Barriers - reduce both quantity and velocity of
subsurface water
• liners - prevent the movement of subsurface
water
• drains - reduces the quantity of water and
direct its movement.
• Dewatering wells - elimination of subsurface
water, is accomplished through the use of
wells.
2
3. Barriers
• Sheet pile cutoff walls, impervious cutoff
trenches and grouted or injected cutoff curtains -
common types of barriers.
• Example: earthen dams may incorporate a cutoff
wall or grout curtain in their foundation to reduce
the amount and speed of water flowing under the
structure.
• Type of barrier to use at a site is dictated as much
by subsurface conditions as by the type of
structure involved.
3
7. Slurry Cutoff trench
Types Applicability
Slurry Cutoff trench Suited for
construction of
impervious cutoff
trench below ground
water for stabilizing
trench excavation
7
10. Grouted or injected cutoff walls
Types Applicability
Grouted or injected cutoff
walls
Depth or character of
foundation materials make
sheet pile walls or cutoff
trench impractical.
Used in major hydraulic
structures
Used as a supplement below
cutoff sheeting or trenches.
10
13. Liners
• Liners are used to prevent the seepage.
• Prevent loss of water retained in a canal or
impoundment or keeping water out of an area
such as a waste disposal site to prevent
migration of contaminations.
• Bentonite and related clays are often favoured
as liners to prevent water from reaching
isolated waste.
13
14. Types of liners
1. Plastic liner- impervious liner formed by black
coloured polyvinyl chloride plastic film
2. Buried synthetic rubber liner- formed by synthetic
rubber
3. Bentonite seal- bentonite powder or in slurry form
used under water
4. Earth lining- lining of 2-4 feet thick of impermeable
soils used on bottom & sides
5. Thin compacted soil lining with chemical dispersant-
dispersant is used to minimize thickness of earth
lining, example- sodium tetra phosphate
14
15. Drains
• Effective drains depends on the relative permeability of the
drain materials and the surrounding materials.
• Besides the selection of the drain material must be such that
it must retain the migration of the fine particles from the
surrounding.
• The relative sizing of drain materials is critical to proper
operation. It must have a sufficiently greater permeability
than the soil it is protecting in order to intercept the
subsurface flow.
• At the same time, it must not permit excessive passage of
the smaller particles in the adjacent materials to avoid piping
of the soil or clogging of the drain.
15
17. Wells
• Well points accomplish the same purpose by being drilled
to a shallow depth and attached to a suction pump to draw
out the water.
• Pumping wells are necessary to achieve dewatering to a
greater depth
• Pumping wells are drilled and equipped in a manner nearly
identical to a well being developed as a water source.
• Horizontal wells depends on gravity to move water through
them. These wells are effective in maintaining cut slope
stability and in stabilizing landslides
17
