CVE 515
EMBANKMENT DAM ENGINEERING
ENGR S.O ODUNFA
DEPT. OF CIVIL ENGINEERING
UNIVERSITY OF AGRICULTURE,
ABEOKUTA
Introduction
• A dam is an obstruction placed across a river
or stream to perform certain function
Types of Dams
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Storage dam
Diversion dam
Detension dam
Multipurpose dam
Classification of Dams
• Based on constructional materials we have
• Earthfill dam – made up of locally material
• Rockfill dam – composed of rocks of all sizes to
provide stability and impervious membrane
for water seal.
• Concrete gravity dam
• Concrete arch dam
Earth and Rockfill Dams
• Further classifications
• Homogeneous – Constructed of only one
materials usually of sufficiently impervious
materials
• Zoned – Composed of a central impervious
core flanked by zones of considerably pervious
materials called shells.
• Diaphram – Involves the use of a pervious
materials to form a water barrier.
Principles of analysis and design for
earth and rockfill dams
• Site investigation
• Reconnaissance study – To identify the
needed data.
• Site apprasial – Functional suitability of a site
must be governed by the balance between its
natural physical characteristics and the
purpose of the reserviour catchment
hydrology
• Study of certain parameters of the
environment so that their normal behaviour
can be built into the dam. E.g
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Stream flow records
Flood records
Wind records
Ground water data
Evaporation rates
Rainfall and temperature records
Water quality records,etc
Dam Site Evaluation
• The nature of the soil and rock formations
present,critical to formations integrity is to be
proved by subsurface exploration.
• Based on all these imformation, analysis and
design would follow
Feasibility Report
It is prepared at the conclusion
of the reconnaissance survey
and interpretes all available
information and data.
Materials for Construction
• Earthfill dam – Locally materials
• Rockfill dam – Rocks of all sizes are used for
stability and impervious membrane for water
seal.
Methods of Constructions
• Rockfill Dam
• Rock placed in layers – Materials are dumped
on the embankment surface and pushed over
the advancing construction face with a
buldozer
• Dumped in high sluiced lift – The material is
dumped down the sloping face of the
construction lift and sluiced with high
pressure water jets from monitors. The fines
and smaller rocks are deposited at the top of
the lift and the larger rocks slide and rolled
down the face of the slope to the lower part
of the lift.
• Earthfill Dam
• Excavate the materials
• Hauling to the dam,
• Mixe to predetermine water content and
unformity of properties
• Sread it in layers and
• Compact to desire density
Advantages of construction in layers
• Rock with a higher percentage of fines can be
placed, there is less danger segregation of
fines accumulations
• Embankment obtained is more denser,
uniform and less compressible
• It can be built with any slide slope inclination
but rockfill dumped in high lift is placed on the
angle of repose of the materials
• etc
STABILITY
• The stability of an embankment lies in its
ability to resist shearing stresses created by
external applied loads such as reservoiur
water pressure and internal forces caused by
the soil mass and embankment slope
Stability of Downstream slope during
steady seepage
• Examine the most critical condition i.e when
the reservouir is full and the seepage is taking
place at full rate
• Draw the flow net and determine the points of
intersections of equipotentiallineswith failure
arc
• Get the critical arc
• Calculate the shear strength developed on the
slices and find the net shear strength
Seepage and Drainage
• Seepage is the ease at which water flows
through the soil and this is possible due to the
presence of voids within the soil particles.
• Permeability is the property that allows the
flow of water/fluid through the soil.
• The flow of water through the soils is assumed
to follow Darcy’s law:
• Q/t = KAH/l
• Where Q = Quantity of water flowing
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t = time for quantity Q to flow;
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K = coefficient of permeability for the
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soil
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A = area of cross section through
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which the water flows;
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H = hydraulic head across soil
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l = length of flow path through soil.
• Seepage can be effectively study by the use of
flow nets
• Flow net is a pictorial representation of the
path of flow through a soil.
• Flow net comprises of
• flow lines and equipotential lines
• Construction of flow net
Control of Seepage
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Through embankment:Rock Toe/filter and
Horizontal blanket methods
Through foundation:Impervious cut offs and
Chimmy drain methods
Performing monitoring
• Maintenance – periodic and
• Daily routing maintenace
Reservoiur Design Studies
• Types of reservoiurs
• Storage reservoiurs – To retain excess water
flow in a natural sream or river during raining
season
• Service/Distribution reservoiur – used in water
supply system where water stored in it is used
to supplement the water supply when the
demand exceed the water pumping rate