2. Objectives
On completion of the module you should be
capable of:
โข describing the various types of dam
construction
โข describing the provision of spillways and river
diversions
โข planning detail surveys for damsite design
โข planning dam wall monitoring surveys
โข reading and understanding the plans and
drawings associated with dam construction
3. Introduction
The material covered in this lecture is specific
to dam construction.
It is assumed that the concept of control and
detail surveys is already known by the student
4. Dams
Dams are constructed for one or more of the
following purposes:
โข Storage of water for urban supply
โข storage of water for farm irrigation
โข flood mitigation
5. Dams
โข A watertight seal placed in a river in order to
create a lake or reservoir by impounding the
stream flow
โข Must be stable under all loading conditions
โข must resist
โ hydrostatic pressures on its upstream face
โ destructive influences of water perculation and
possible uplift due to it
6. Investigation for Dams
Factors to be considered include:
โข Geological conditions
โ effect the location and construction of the
foundations, abutments, dam itself, and spillways
โข long and short term stream flow
โข rainfall and storage reservoir characteristics of the
proposed dam catchment
โข access road
7. Investigation for Dams
Factors to be considered continued:
โข local availability of earth and rock materials
and their suitability for dam construction
โ or as concrete aggregates
โข degree of permeability of the rock formation
on which the dam is to be placed
โ may affect hydrostatic uplift pressures and the
degree of grouting necessary to control it
8. Investigation for Dams
Factors to be considered continued:
โข planning for river diversion to occur while the
dam is being constructed
โ cutting a temporary channel which by-passes the
dam itself
โ installation of large pipes under the dam
9. Investigation for Dams
Factors to be considered continued:
โข provision of sites for:
โ water intake structures and pumping stations for
water supply dam
โ Penstocks ( inlet tower )
โ power station in the case of hydro-electric
facilities
10. Investigation for Dams
Factors to be considered continued:
โข an Environmental Impact Study
โ short and long term effects of of the proposed
reservoir and the construction operations on the
region
โ aesthetics, plant and animal, ecology, fish
preservation and public amenity of the reservoir
and downstream reaches
โ noise and dust hazards in construction
โ effects of the dam on the regional micro-climate
11. Types of Dams
Dams are classified by the materials of which
they are constructed:
โข earth
โข earth and rock
โข rock
โข concrete
12. Types of Dams
The first three can be subgrouped as
embankment dams whilst there are also
several different types of concrete dams:
โข Embankment
โ earth - earth and rock
โ rock
โข concrete
โ solid gravity - concrete arch
โ arch-gravity - hollow gravity
โ prestressed concrete
14. Embankment Dams - Earthfill
Dam composed
entirely of
soils
Thomson Dam, a 166 metre high earthfill and
rockfill dam
15. Embankment Dams - Earthfill
โข Fine grained impervious material
โข only moderate stability, necessitating flat
side-slopes
โข protect slopes from erosion by layers of
rock rip-rap
16. Embankment Dams - Earthfill
โข Symmetrical zoned material
โข somewhat steeper slopes
โข most common type
17. Embankment Dams - Earthfill
โข Hybrid of types A and B
โข large upstream impervious section
โข transition zone
โข downstream pervious zone
โข may be used when rapid reservoir draw
18. Embankment Dams - Earthfill
Process of dam construction:
โข All vegetable matter and organic material is cleared
from the dam site
โข grout holes for the cut-off curtain are drilled to a
depth where the grout curtain will effectively seal
off the seepage of water beneath the proposed dam
19. Embankment Dams - Earthfill
Process of dam construction:
โข The holes are filled with cement-water at
sufficient pressure to force it into rock fissures
beneath the dam foundation
20. Embankment Dams - Earthfill
Process of dam construction:
โข When placing the embankment layers of soil
should be kept horizontal, but graded slightly
from the centre to the sides
โข layers should be approx
โ 150mm after compaction for impervious core
โ 225mm for outer pervious zones
21. Embankment Dams - Earthfill
Process of dam construction:
โข Protection of the embankment from
upstream wave action
โ stone rip rap commonly used
โข prevention of erosion on dry downstream
side
โ grass, stone or concrete
โข No earth dam should be overtopped from the reservoir,
spillways are provided to discharge excess water from the
reservoir
22. Embankment Dams - Earthfill
Crotty Dam, an 82 metre high concrete-faced
rockfill structure.
23. Embankment Dams -
Embankment
between the clay core and the rock fill both upstream and downstream of
the core. In foreground drilling rigs are being used to drill grout holes
in the conglomerate, sandstone and shale foundation. Grouting is used
to fill open cracks in the foundation rock so water cannot leak out of
the dam and is carried out by pumping grout (a mixture of cement and
water) under pressure into holes drilled in the foundation rock.
Windamere Dam under construction,
a 69m high, Earth and Rock Fill Dam
Brown clay core in centre of photo with light
grey andesite rock fill both upstream (left)
and downstream (right) of clay core. Note
the narrow zones of dark brown filter
material
24. Embankment Dams - Embankment
or Concrete
Provided suitable materials are available
embankment dams often offer a more
economical alternative to concrete
structures
The inability of the abutment materials to take the
thrust from a concrete dam may dictate the
construction of an embankment dam
however many sites are suited to concrete dams
26. Concrete Dams - Solid Gravity
Straight or curved relying on its weight for
stability
โข Concrete using large aggregate ( 150mm to
225mm maximum size )
โข dam is made up of individual vertical blocks
with construction joints
โ later grouted to prevent leakage
27. Concrete Dams - Solid Gravity
Warragamba Dam, 142 metre high concrete
gravity dam
28. Concrete Dams - Buttress
Sloping concrete slab
supported on a
number of buttresses
โข Massive buttress occurs when the
buttresses touch
29. Concrete Dams - Arch
Upstream curvature
transmitting the
majority of its load
onto the abutments
โข Base thickness < 60% of its height
โข where base thickness > 60% of its height, the dam is
essentially a curved gravity dam
โข suited to deep, narrow gorges of strong abutment
material
โข constructed in blocks- appropriate shrinkage gaps
and construction joints
30. Concrete Dams - Arch
โข Gordon Dam in Tasmania is a 140 metre
high concrete arch dam
31. Concrete Dams - Arch Gravity
Combination of gravity and arch dams
curved gravity dams
32. Concrete Dams - Hollow Gravity
Rely upon their weight for stability
for watertightness, an impervious reinforced
concrete membrane supported by
buttresses securely keyed into sound rock
โข Include
โ slab and buttress, with inclined membrane
โ massive buttress, touching buttresses
โ conoidal, with a plane upstream face and identical
massive buttresses
โ multiple-arch, membrane is a series of arches as
distinct from a slab
33. Concrete Dams - Prestressed
Downstream curvature
dam subjected to compressive forces before
filling
after filling, tensile stresses resulting in the
dam are counteracted by the already
existing compressive forces
34. River Diversion
Before the dam can be constructed, diversion
of the river is necessary
Satisfactory handling of the stream flow during
construction is vital to the success of the work
cost of river diversion must be compared with the risk
of all or parts of the new dam in peak flood
conditions
types of diversion
tunnel, flume, concrete or steel pipeline and open channel
36. Spillways
โข When dams are designed provision needs to be
made to cope with large floods. Spillways are built
to provide a path for floodwater to flow over or
around the dam
โข Spillways on concrete dams are usually
constructed to allow water to flow over the
top.
โข Spillways associated with embankment dams
are built to take the water around the side of
the dam and away from the downstream face.
37. Spillways
โข Overflow Spillway
โ overflows a special section of the dam itself
โข Byewash Spillway
โ separate open flood channel cut through a nearby
saddle and with a small weir at the upstream end
โข Side-Inlet Spillway
โ located on the steep side of the gorge
โ direction of flow is parallel to the crest of the river
โข Drop-Inlet Spillway
โ water enters via a horizontal lip, drops through a vertical
or sloping shaft and discharges through a horizontal or
gently sloping culvert
39. Spillway Gates
โข Allow control over the level of fill of the reservoir
โข Used for three reasons:
โ to reduce the cost of the dam
โ to reduce the inundation of land in the reservoir area
โ to reduce the downstream flood damage
โข Three types
โ sliding gates - shutters running grooves
โ roller gates - employ rollers on the shutters
โ radial gates - form an arc pivoting on a trunion bearing
40. Outlet
โข Necessary to make provision for the discharge of
water as and when it is required for irrigation etc.
โข Separate outlet required
โ commonly a pipe passing under or through the
dam, with discharge controlled by valves
41. Damsite Surveys
โข Study of existing topographic maps and aerial
photographs will indicate possible dam sites.
โข An estimate of catchment area and storage
capacity can also be made
โข Surveys required
โ contour survey
โ watershed traverse
โ stability of site
โ cadastral surveys
42. Dam Site Surveys -
Contour Survey
โข Following selection of a possible site an aerial
survey should be undertaken to provide a more
detailed contour of the storage area
โข Typical scale, 1 : 10000 with a 2m contour interval
โข Allows more accurate computation of storage
capacity
โข if the site is feasible, the survey provides a more
concise design location of the dam wall
โข marks placed during the control survey for photo
control also provides control for all future surveys
43. Dam Site Surveys -
Watershed Traverse
โข Where insufficient information exists to
accurately determine the catchment area, it may
be necessary to carry out a watershed traverse
44. Dam Site Surveys -
Stability of Site
โข Dam must be positioned where it will be stable and
where the storage area does not have excessive
underground leakage
โข Soil and rock features must be carefully examined
โข Large dams require test pits, bore holes and detailed
geological survey
โข small dams may require only test holes to determine
sub-surface features
โข the position of each investigation must be accurately
located
45. Dam Site Surveys -
Cadastral Surveys
โข Land to be inundated is resumed by the
constructing authority
โข Cadastral surveys required to delineate the land to be resumed
โข Surveys will also be required to close roads
passing through inundated land
46. Surveys in Dam Wall Area
โข General location of dam wall has been decided
from earlier surveys
โข Further surveys are required within this area to aid final design and computation of volumes of excavation and fill
- detail surveys
- definition of dam wall on plan
- location of limits of dam on ground
- by-wash
- clearing of site
- pipeline surveys
- road access
- pumping stations
47. Surveys in Dam Wall Area -
Detail Surveys
โข More intense geological and soil surveys are
carried out
โ ensure absence of geological faults
โ determine required depth of stripping
โข Detail and contour survey locating all topographic features, test-bores
etc.
โ total stations or GPS
โ scale 1 : 1000, contour interval 1m
48. Surveys in Dam Wall Area -
Definition of Dam Wall on Plan
โข Following consideration of all factors, it is now
possible to to define the centreline of the dam wall
on the contour plan
โ also, working to specified batters, the extent of the
earthworks can be plotted on the contour plan
49. Surveys in Dam Wall Area -
Definition of Dam Wall on Plan
โข Crest RL 550m
โข 5m wide pavement on top
โข batters 2:1
50. Surveys in Dam Wall Area -
Locate Dam Limits on Ground
โข Stability of dam is dependent on
โ foundations,
โ materials used, and
โ method of construction
โข Foundations
โ remove all unsuitable material or unstable
material from within the limits of the dam wall
โข Requires definition of the limits of the wall marked on the ground
โ toe of batters require pegging
51. Surveys in Dam Wall Area -
Grout Curtains
โข Grout is pumped down drill holes bored along the
centreline and on either side of it
โข Centreline must be marked before actual construction
commences
52. Surveys in Dam Wall Area -
By-Wash
โข The downstream face of an embankment dam will
scour if water flows over the dam crest
โข an outlet or by-wash channel is necessary to allow
excess water to flow around the dam wall to be
discharged away from the dam wall
โ large dams normally have a large concrete channel
โข The horizontal and vertical position of the by-wash must
be defined on the ground
53. Surveys in Dam Area -
Clearing of Site
โข Usual to clear the dam storage area of vegitation
and tree cover prior to filling of the dam
โข Requires definition of the limits of the dam storage area marked on the ground
โ running the contour equal to full storage level
54. Surveys in Dam Area -
Additional Surveys
โข Pipeline alignment and sections from dam to
consumer
โข pipeline easement surveys
โข access roads to dam site, and
โข surveys for siting and constructing pumping
stations
55. Surveys in Dam Area -
Stability of Dam Wall
โข Monitoring surveys
โ to determine if any horizontal or vertical movement
occurs after construction and in later years
โ unusual movement may indicate dam failure
โข Fix permanent marks along the crest of the dam
wall and over the downstream face
โข regular control surveys required
โ must be able to identify small movement of say
3mm in horizontal or vertical
56. Small Dams
โข Contour survey of pondage area is undertaken by
ground survey rather than aerial survey
โข only test bore-holes are used to determine sub
surface features with respect to site stability
investigations
โข by-wash need only be a grass channel
57. Proposed Earth Dam, General Arrangement
and Detail (Sheet 1 of 6)
โข Plan of Works Area
โ dam centreline
โ by-wash
โ Drop Inlet
โข Longitudinal Section
โข Embankment - Type Section
โข Storage Capacity Diagram
58. Proposed Earth Dam, General Arrangement
and Detail (Sheet 1 of 6) - Plan of Works Area
59. Proposed Earth Dam, Plan of Storage Area
(Sheet 2 of 6)
โข Control Traverse
โข horizontal control
โ datum, permanent marks
โข vertical control
โ datum, bench marks
โข full storage level
โข test holes, test Pit Logs
60. Proposed Earth Dam, Standard 600 * 100
Drop Inlet (Sheet 5 of 6)
โข Typical Abutment Plan and elevation
โข By-Wash Location Plan
61. Proposed Earth Dam, Setting Out Survey
(Sheet 6 of 6)
โข Assist with setting out batter points