Soil Mechanics-II Earthen Dames Dr. Attaullah Shah ground

Components of a Dam

Types of Earthen Dams

DAMS Classifications based on type and materials of construction Criteria for selection of best dam type: 1. Feasibility -topography, geology, and climate (& its effect on materials) 2. Cost -availability of construction materials near the site; accessibility of transportation facilities Types Materials of Construction A. Gravity Concrete, rubble masonry B. Arch Concrete C. Buttress Concrete, also timber & steel D. Embankment Earth or rock

Foundation Requirements Strong foundation Minimal differential settlement No bearing capacity shear failure Sand/Gravel or rock Low hydraulic conductivity Silt and/or Clay, non-fractured rock

DAMS GRAVITY DAMS Gravity dams are dams which resist the horizontal thrust of the water entirely by their own weight. They use their weight to hold back the water in the reservoir. Can be made of earth or rock fill or concrete.

-Depends on its own weight for stability DAMS Gravity -Depends on its own weight for stability -Usually straight in plan although slightly curved Forces on Gravity Dam 1. Gravity (weight of dam) W = V x γ = (volume)(specific weight of material) (lb) = (ft3)(lb/ft3) 2. Hydrostatic pressure Hh = γ h2 / 2 (horizontal component) (lb/ft) = (lb/ft3) (ft)2 /2 where, h = depth of water at that section γ = specific weight of water Hv = γ V / h (vertical component) (lb/ft) = (lb/ft3) (ft3) / ft Where, V = volume of the dam at that point

DAMS Gravity Forces on Gravity Dam 3. Uplift the water under pressure that comes b/t dam and foundation and results in upward (uplift) forces against the dam h1 = depth of water @ upstream face, aka “heel” (higher) h2 = depth of water@ downstream face, aka “toe” (lower) γ = specific weight of water t = base thickness of dam. 4. Ice pressure pressure created by thermal expansion exerts thrust against upstream face of the dam 5. Earthquake forces results in inertial forces that include vertical motion, oscillatory increase, or decrease in hydrostatic pressure (all put force against dam) DAMS

DAMS GRAVITY DAMS Causes of Failure: 1. Sliding along horizontal plane (shear failure) net force > shear resistance at that level 2. Rotation about the toe 3. Failure of material

DAMS Gravity Dams Friat Dam

DAMS Gravity Dams Tygart Dam, West Virginia

DAMS ARCH DAMS Curved dam which is dependent upon arch action for its strength. Transmits most of horizontal water thrust behind them to the abutments by the arch action. Thinner and requires less material than any other type of dam. Used only in narrow canyons.

DAMS ARCH DAMS Arch dams includes: *series of horizontal arches *series of vertical cantilevers Load distribution Most of load carried by Near bottom of dam cantilevers (Known as Trial Load Near top of dam arches Method) I. Constant-center (Constant radius) best for U shaped canyons II. Variable-center (Variable radius, constant-angle) best for V shaped canyons

DAMS ARCH DAMS Boundary Dam, Seattle

DAMS ARCH DAMS Salmon Creek Dam, Alaska

DAMS BUTTRESS DAMS Buttress dams are dams in which the face is held up by a series of supports. Buttress dams can take many forms -- the face may be flat or curved. Usually, buttress dams are made of concrete and may be reinforced with steel bars.

DAMS BUTTRESS DAMS sloping membrane that transmits the water load to a series of buttresses @ right angles to axis of dam -Increased formwork & reinforced steel compared w/gravity dam -Less massive than gravity dam (requires 1/3 to 1/2 as much concrete) -Use on weaker foundation -Same forces as gravity and arch dams, however, ice pressures not as prevalent; gaps b/t buttresses relieve majority of uplift forces Types Water Supporting Membrane 1. Flat-slab flat, concrete-reinforced slabs 2. Multiple-arch series of arches

DAMS BUTTRESS DAMS Daniel-Johnson Dam, Quebec

DAMS BUTTRESS DAMS Bartlett Dam, Colorado

DAMS EMBANKMENT DAMS Embankment dams are massive dams made of earth or rock. They rely on their weight to resist the flow of water, just like concrete gravity dams.

DAMS EMBANKMENT DAMS Types: 1. Simple Embankment (homogeneous throughout) (upstream less permeable material) 2. Impervious Foundation 3. Impervious Core (Zoned embankments)

DAMS EMBANKMENT DAMS Generally have some sort of water proof insides (called the core), which is covered with earth or rock fill. Water will seep in through the earth or rock fill, but should not seep into the core. The water will seep into the core material and should stop at the seepage line. Forces on Embankment Dams: 1. Force of the water (main force) 2. Uplift force

DAMS EMBANKMENT DAMS Wolf Creek Dam, Nashville

DAMS COFFER DAMS temporary structures (sheet-pile, water-tight) that allow construction operations diverts flow from construction areas until work completed

Hoover Dam • 726.4 feet high .. • 1,244 feet across at the top .. • 660 feet thick at the base .. • 45 feet thick at the top .. • weighs 6.6 millions ton ... • 17 generators giving it the capacity to produce over 2,000 megawatts • can store up 2 years 'average' flow from the Colorado River ... • total storage capacity can be measured in 30,500,000 acre feet ...

Hoover Dam