Embankment lecture 12
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Infinite and finite length of blanket A natural impervious blanket of large areal extent if available may be considered as a balnket of infinite length For a blanket of infinite length, the solution of equation (iv) is In this case for the convenience, the point x = 0 is taken at the downstream end of the blanket and hence h0 is the total loss of head through the blanket upto the end of the blanket. As a measure of the efficiency of a blanket of any length x (where x may be infinite or a finite length) a length Xr is considered which is known as equivalent resistance of the foundation and is defined below. It may be defined as the length of a prism of the foundation soil of thickness Zf and coefficient of permeability kf which under the loss of head h would carry flow equivalent to the flow which passes the blanket system under the same loss of head. Thus (2) Solution for finite length of blanket : For a blanket of uniform thickness and finite length of blanket ihe solution equation (iv) is which h is the loss of head through the blanket upto any point at a distance and hn is a constant for computing h. hn depends on the total head loss of the system of which the blanket is a part and on the ratio of the blanket to the remainder of system. * From equation (viii) at x - 0, h = 0, and hence in this case the point x = 0 is taken at the upstream end of the blanket. Differentiating both sides of equation (viii) with respect to x, we get
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CHECK STABILITY OF DAM FOR GIVEN SECTION
TOP WIDTH 7.5 M
HEIGHT OF DAM – 75 M
HEIGHT OF W.L. – 72 M
BATTER IS STARTING AT 45 M
PROJECTION FROM U.S 4.5 M
D/S PORTION LENGTH – 43.75 M
D/S SLOPE STARTED AT 12.5 M FROM TOP
D/S SLOPE 0.7 (H):1(V)
DRAINAGE GALLERY @ 48.7
5 M FROM TOE OF DAM
F Ф = 1.2
FC = 2.4
μ=0.7
SHEAR STRENGTH OF CONCRETE = c = 1400 KN/M^2
ΣV =
Weight of dam
(W1+W2+W3)
+
Vertical forces of water
(P1+P2)
–
Uplift Forces
(U1 + U2 +U3)
–
Vertical Acceleration of E.Q.
Moment of Weight Of Dam
(w1 + w2 + w3)
+
Moment of Weight of water
(p1 + p2)
-
Moment of water pressure
(p)
-
Moment of Uplift Forces
(U)
-
Moment of Inertia force
(vertical acceleration moment + Hori Acce.)
-
Moment Hydrodynemic Pressure
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PracticalProfileofSpillwaY
When the profile for the crest of the ogee spillway is plotted over the triangular profile the section of a gravity dam (non-overflow section) ,it is found that it goes beyond vie downstream face of the dam , thu requiring thickening of the section for the spillway .
However,this extra concrete can be saved by shifting the curve of the nappe in a backward direction until this curve becomes tangential to the downstream face of the dam .
Design of spillway
Design an ogee spillway for concrete gravity dam, for the following data :
(1) Average river bed level = 100.0 m
(2) R.L. of spillway crest =204.0 m
(3) Slope of d/s face of gravity dam = 0.7 H : 1 V
(4) Design discharge = 8000 cumecs
(5) Length of spillway = 6 spans with a clear width of 10 m each.
(6) Thickness of each pier = 2.5 m
If h/Hd is greater than 1.7 than high spillway so effect of velocity is neglected
The co-ordinates from x = 0 to x = 27.4 m are worked out in the table below :
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CHECK STABILITY OF DAM FOR GIVEN SECTION
TOP WIDTH 7.5 M
HEIGHT OF DAM – 75 M
HEIGHT OF W.L. – 72 M
BATTER IS STARTING AT 45 M
PROJECTION FROM U.S 4.5 M
D/S PORTION LENGTH – 43.75 M
D/S SLOPE STARTED AT 12.5 M FROM TOP
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5 M FROM TOE OF DAM
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FC = 2.4
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Weight of dam
(W1+W2+W3)
+
Vertical forces of water
(P1+P2)
–
Uplift Forces
(U1 + U2 +U3)
–
Vertical Acceleration of E.Q.
Moment of Weight Of Dam
(w1 + w2 + w3)
+
Moment of Weight of water
(p1 + p2)
-
Moment of water pressure
(p)
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Moment of Uplift Forces
(U)
-
Moment of Inertia force
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-
Moment Hydrodynemic Pressure
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PracticalProfileofSpillwaY
When the profile for the crest of the ogee spillway is plotted over the triangular profile the section of a gravity dam (non-overflow section) ,it is found that it goes beyond vie downstream face of the dam , thu requiring thickening of the section for the spillway .
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(2) R.L. of spillway crest =204.0 m
(3) Slope of d/s face of gravity dam = 0.7 H : 1 V
(4) Design discharge = 8000 cumecs
(5) Length of spillway = 6 spans with a clear width of 10 m each.
(6) Thickness of each pier = 2.5 m
If h/Hd is greater than 1.7 than high spillway so effect of velocity is neglected
The co-ordinates from x = 0 to x = 27.4 m are worked out in the table below :
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Section of an Earth Dam :
The design of an earth dam essentially consists of determining such a cross section
the dam which when constructed with the available materials will fulfill its required
tion with adequate safety. Thus there are two aspects of the design of an earth dam.
b) Foundation pervious to a moderate depth, after which impervious strata is available :
(c) Foundation pervious to a great depth:
CASE 2 ONLY FINE GRAVEL OR COARSE SAND IS AVAILABLE
PROVIDE DIAPHRAM TYPE DAM WITH SUITABLE ARRANGEMENTS
CASE 3
ONLY SILT AND CLAY IS AVAILABLE
NO CORE
ONLY IMPERVIOUS BLANKED AND ROCK TOE PROVIDES
SEEPAGE ANALYSIS
ASSUMPTIONS
FLOW IS – TWO DIMENTIONAL
Soil is INCOMPRESSIBLE SOIL
Soil is homogeneous and isotropic
Soil is fully saturated
Flow is steady
Darcys law is valid
Phreatic line – (seepage line)
Line within the dam section having positive hydrostatic pressure at below section and negative hydrostatic pressure at above section
Line has atmospheric pressure itself
Separation line of saturated and non saturated portion
Casagrande method of determining seepage line
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Water flowing over a spillway acquires a lot of kinetic energy because of the conversio of the potential energy into kinetic energy.
If the water flowing with such a high velocity is discharged into the river it will scour the river bed.
If the scour is not properly controlled it may extend backward and may endanger the spillway and the dam.
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FORCES ACTING ON GRAVITY DAM
The Bureau of Indian Standards code IS 6512-1984 “Criteria for design of solid gravity dams” recommends that a gravity dam should be designed for the most adverse load condition of the seven given type using the safety factors prescribed.
1. Load combination A (construction condition): Dam completed but no water in reservoir or tail water
2. Load combination B (normal operating conditions): Full reservoir elevation, normal dry weather tail water, normal uplift, ice and silt (if applicable)
3. Load combination C: (Flood discharge condition) - Reservoir at maximum flood pool elevation ,all gates open, tail water at flood elevation, normal uplift, and silt (if applicable)
4. Load combination D: Combination of A and earthquake
5. Load combination E: Combination B, with earthquake but no ice
6. Load combination F: Combination C, but with extreme uplift, assuming the drainage holes to be Inoperative
7. Load combination G: Combination E but with extreme uplift (drains inoperative)
Water Pressure (P) is the major external force exerted by the water stored in the Reservoir on the upstream face of the dam. It can be calculated by the law of hydrostatic pressure distribution; which is triangular in shape as shown in Fig. 3.3.
(a) When u/s face is vertical :
When the upstream face is vertical, the intensity of pressure is zero at the water surface and equal to γw • H at the base.
Earth quake pressure, Horizontal Component(PH) , (ii) Vertical Component(PV) = Weight of water in ABCD portion ,
2. Weight of the Dam :
The weight of the dam per unit length is given by the product of the area of crosssection of the dam and the specific weight of the Construction material, i.e. concrete, and masonary it acts vertically downwards at the centre of gravity of the section.
dam may be divided into smaller sections of simple geometrical shapes such as triangles,rectangles, etc.
weight of each of these acting at its centre of gravity may be considered.
Weight of any part of dam = cross-sectional area of that part x specific weight of material
3. Uplift Pressure :
Uplift pressure is defined as the force exerted by water penetrating through the pores, cracks, fissures within the body of the dam, at the contact between the dam and its
foundation, and within the foundation.
acts vertically upwards
it causes a reduction in the effective weight
Ice Pressure :
Ice pressure is exerted on a dam by a sheet of ice formed on the entire water surface of the reservoir, when it is subjected to expansion and contraction with changes in temperature.
The coefficient of thermal expansion of ice being five times more than that of concrete, the dam face has to resist the force due to expansion of ice. This force acts linearly along the length of the dam, at the reservoir level.
As per IS : 6512 - 1984, ice pressure may be taken equal to 250 kN/m2 applied to the face of the dam over the anticipated area of contact of i
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ENERGY DISSIPATORS
stilling basin
A stilling basin is defined as a structure in which a hydraulic jump used for energy dissipation is confined either partly or entirely.
Certain auxiliary devices such as chute blocks, sills, baffle walls, etc. are usually provided in the stilling basins to reduce the length of the jump and thus to reduce the length and the cost of the stilling basin.
Moreover, these devices also improve the dissipation action of the basin and stabilize the jump.
Chute Blocks :
These are triangular blocks with their top surface horizontal. These are installed at the toe of the spillway just at upstream end of the stilling basin.
They act as a serrated device at the entrance to the stilling basin. They furrow the incoming jet and lift a portion of it ab0ve the floor.
These blocks stabilise the jump and thus improve its performance, these also decrease the length of the hydraulic jump.
Basin Blocks or Baffle Blocks or Baffle Piers :
These are installed on the stilling basin floor between chute blocks and the end sill. These blocks also stabilise the formation of the jump.
Moreover, they increase the turbulence and assist in the dissipation of energy.
They help in breaking the flow and dissipate energy mostly by impact. These baffle blocks are sometimes called friction blocks.
Sills and Dentated Sills :
Sill or more preferably dentated sill is generally provided at the end of the stilling basin.
The dentated sill diffuses the residual portion of the high velocity jet reaching the end of the basin. They, therefore, help in dissipating residual energy and to reduce the length of the jump or the basin.
particular location of these blocks mainly depends upon the initial Froude number (F1) and the velocity of the incoming flow. The stilling basins are usually rectangular in plan. These are made up of concrete.
[A] U.S.B.R. Stilling basins :
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
Type I basin (F1 between 2.5 to 4.5)
Provide chute blocks and end sill
Length of basin = 4.3 y2 to 6.0 y2
Width of chute block = y1
Spacing = 2.5 y1
Height of chute block = 2y1
Length of chutes = 2y1
U.S.B.R. Type-II basin for F1 greater than 4.5 and v1 less than 15 m/sec.:
U.S.B.R. Type-Ill basin for F, greater than 4.5 and V1 greater than 15 m/sec :
Chutes and dentated sills provided
Baffle is not provided because of –velocity is high and cavitation is possible.
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
IS Type-Ill basin is usually provided with a sloping apron for the entire len
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STABILITY OF SLOPES SEEPAGE CONTROL MEASURES AND SLOPE PROTECTION
a finite slope AB, the stability of which is to be analyzed.
The method Consists of assuming a number of trial slip circles, and finding the factor of safety of each.
The circle corresponding to the minimum factor of safely is the critical slip circle.
Let AD be a trial slip circle, with r as the radius and O as the centre of rotation
Let W be the weight of the soil of the wedge ABDA of unit thickness, acting through the centroid G.
The driving moment MD will be equal to W x, where x, is the distance of line of action of W from the vertical line passing through the centre of rotation O.
if cu is the unit cohesion, and l is the length of the slip arc AD, the shear resistance developed along the slip surface will be equal to cu • l, which act at a radial distance r from centre of rotation O.
When slip is imminent in a cohesive soil, a tension crack will always DevelOP by the top surface of the slope along which no shear resistance can develop,
The depth of tension crack is given by
The effect of tension crack is to shorten the arc length along which shear resistance gets mobilised to AB' and to reduce the angle δ to δ'.
The length of the slip arc to be taken in the computation of resisting force is only AB', since tension crack break the continuity at B'.
The weight of the sliding wedge is weight of the area bounded by the ground surface, slip circle arc AB' and the tension crack.
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Hydraulic failures .... 40%
Seepage failures…….. 30%
Structural failures .... 30%
(1) Overtopping
(2) Erosion of u/s slope by waves
(3) Erosion of d/s slope by wind and rain
(4) Erosion of d/s toe
(5) Frost action
(1) Overtopping = the design flood is under estimated.
spillway capacity is not adequet
spillway gates are not properly operated
free board is not sufficient
excessive settlement of the foundation and dam
(2) Erosion of u/s slope by waves = The waves developed near the top water surface due to the winds, try to notch out the soil from the upstream face and may even, sometimes, cause the slip of the upstream slope.
Upstream stone pitching or riprap should, therefore, be provided to avoid such failures.
(3) Erosion of d/s slope by wind and rain = The rainwater flowing down the slope; may result in the formation of 'gullies' on the downstream slope thus damaging the dam which may generally lead to partial failure of the dam or in some cases it may cause complete failure of the dam.
Erosion of d/s toe : = Toe erosion may occur due to two reasons :
erosion due to tail water
erosion due to cross currents that may come from spillway buckets.
Frost action : = If the earth dam is located at a place where the temperature falls below the freezing point, frost may form in the pores of the soil in the earth dam.
When there is heaving, the cracks may form in the soil. This may lead to dangerous seepage and consequent failure.
Seepage failures : = Seepage failures may occur due to the following causes :
(1) Piping through the foundation
(2) Piping through the dam
(3) Sloughing of d/s toe
Structural failures :=
Structural failures in earth dams are generally shear failures leading to sliding of the tents or the foundations.
(1) u/s and d/s slope failures due to construction pore pressures
(2) u/s slope failure due to sudden drawdown
(3) D/s slope failure due to steady seepage
(4) Foundation slide due to spontaneous liquefaction
(5) Failure due to earthquake
(6) Failure by spreading
(7) Slope protection failures
(8) Failure due to damage caused by borrowing animals
(9) Failure due to holes caused by leaching of water soluable salts
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2. w index and 5 index
Dalton’s law of evaporation
The rate of evaporation depends upon the difference between the saturation vapour pressure in the air above
E= C(es-ea)
where c – coefficient depends upon barometric pressure
Es – saturation vapour pressure
Ea - Vapour pressure above 2 m height of water
Factors affecting
Temperature
Wind velocity
Atmospheric pressure
Nature of evaporating surface
Depth of water supply
Impurities in water
Energy budget method
LOW OF CONSERVATION of energy
Energy required is estimated by incoming outgoing, and stored energy in a specific time period
Total energy received from suns radiation = energy reflected + change in energy + energy required for evaporation
Energy budget method
most accurate method (evaporation is a function of the energy state of the water system)
difficult to evaluate all terms
energy balance equation has to be simplified
empirical formulas are used (although radiation measurements are preferable)
Water budget method
Characteristics:
Simple
Difficult to estimate Qd and Qs
Unreliable, accuracy will increase as Δt increases
Measurement et -
Direct measurement –
1 . Tank & lysimeter method
2. Field experimental method- no runoff no percolation
3. Soil moisture studies – gw deep
4. Integration method – laege area
5. Inflow and outflow studies
Infiltration rate
Infiltration capacity : The maximum rate at which, soil at a given time can absorb water.
f = fc when i ≥ fc
f = f 0when i < fc
where fc = infiltration capacity (cm/hr)
i = intensity of rainfall (cm/hr)
f = rate of infiltration (cm/hr)
Horton’s Formula:
This equation assumes an infinite water supply at the surface i.e., it assumes saturation conditions at the soil surface.
For measuring the infiltration capacity the following expression are used:
f(t) = fc + (f0 – fc) e–kt for
where k = decay constant ~ T-1
fc = final equilibrium infiltration capacity
f0 = initial infiltration capacity when t = 0
f(t) = infiltration capacity at any time t from start of the rainfall
td = duration of rainfall
Double Ring Infiltrometer
Infiltration indices The average value of infiltration is called infiltration index.
Two types of infiltration indices
φ – index (PHI INDEX)
w –index
PHI INDEX
- defined as average rate of rainfall such that excess volume of rainfall represents direct runoff
- unit is cm/hr or……
W INDEX
- average rate of loss (infiltration) averaged over whole storm period
- w index = P- Q- S
T
THUS phi index has to be some what than w index
IS 4987 - 1968
IN PLAINS – 520 km2
Elevation upto 1000 m – 260 to 390 km2
Hilly area – 130 km2
It is recommended that 10% of raingauge must be self recording type
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FORCES ACTING ON GRAVITY DAM
5. Wave Pressure :
Wind blowing over the water surface in the reservoir exerts a drag on the surface due to which ripples and waves are formed. The impact of these waves Produces a pressure on the upper portion of the dam. The magnitude of the wave pressure mainly depends on the dimensions of the waves which in turn depend on the extent of water surface and the wind velocity.
Silt pressure
The weight and the pressure of the submerged silt are to be considered in addition to weight and pressure of water. The weight of the silt acts vertically on the slope and pressure horizontally, in a similar fashion to the corresponding forces due to water. It is recommended that the submerged density of silt for calculating horizontal pressure may be taken as 1360 kg/m³. Equivalently, for calculating vertical force, the same may be taken as 1925 kg/m³.
Wind Pressure :
Wind pressure is required to be consider only on that portion of the dam structure which is exposed to the action of wind.
Normally wind pressure is taken as 1 to 1.5 kN/m2 for the area exposed to the wind pressure.
Wind pressure is not a significant force and therefore, sometimes, not considered in design of a dam.
Earthquake Forces (Seismic Forces) :
Earthquake or seismic activity is associated with complex oscillating patterns of acceleration and ground motions, which generate transient dynamic loads due to inertia of the dam and the retained body of water.
Horizontal and vertical accelerations are not equal, the former being of greater intensity.
The earthquake acceleration is usually designated as a fraction of the acceleration due to gravity and is expressed as α⋅g, where α is the Seismic Coefficient. The seismic coefficient depends on various factors, like the intensity of the earthquake, the part or zone of the country in which the structure is located, the elasticity of the material of the dam and its foundation, etc.
For the purpose of determining the value of the seismic coefficient which has to be adopted in the design of a dam, India has been divided into five seismic zones, depending upon the severity of the earthquakes which may occur in different places. A map showing these zones is given in the Bureau of Indian Standards code IS: 1893-2002 (Part-1) “Criteria for earthquake resistant design of Structures (fourth revision)”, and has been reproduced in Figure 28.
According to IS : 1893 - 2002, the design value of horizontal seismic coefficient
(Ah) may be determined by one of the two methods
(a) Seismic coefficient method
The total design lateral force or design seismic base shear (VB) along any principal direction shall be determined by the following expression.
Hydrodynamic Pressure :
Horizontal acceleration acting towards the reservoir causes a momentary increase ln the water pressure as the foundation and dam accelerate towards the reservoir and the water resists movement owing to its inertia.
The extra pressure ex
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The document describes the key components of a gravity dam and their functions. It discusses drainage galleries, which provide access to the dam interior and drainage. Shafts are vertical openings that provide access for equipment and instruments. The overflow section, also called the spillway, releases surplus water from the reservoir in a safe way. The non-overflow section is the rest of the dam where a road may be located. A power house is located at one end to generate electricity. Energy dissipation works reduce the velocity of water flowing over the spillway. Outlets below the spillway release water from the reservoir. Joints are included to aid construction and prevent cracks.
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Embankment lecture 2
The main components of an earth dam are as follows :
1. Impervious core
2. Pervious shell
3. Filter
4. Rock toe
5. U/S slope protection
6. D/S slope protection
7. Cutoff
core should not be less than 3 m and its height should be 1 m more than the maximum water level in the reservoir.
The upstream pervious zone provides free drainage during sudden drawdown. ,
Usually following types of filters are provided :
(1) Toe filter
(2) Horizontal drainage filter (blanket)
(3) Chimney drains
Such a filter is sometimes known as inverted filter or reverse filter.
Rock toe keeps the phreatic line well within the section and also facilitates drainage.
The following measures are taken to protect the slope.
(1) Rock riprap
(2) Concrete pavement
(3) Steel facing
(4) Bituminous pavement
(5) Precast concrete blocks
Cut off is required to
(1) reduce loss of stored water through foundation and abutments
(2) Prevent sub surface erosion by piping.
Cutoff may be provided in the following ways :
• by providing concrete cutoff wall
• by providing cutoff trench filled with impervious material
• by driving sheet pile
• by curtain grouting
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Embankment lecture 4
Section of an Earth Dam :
The design of an earth dam essentially consists of determining such a cross section
the dam which when constructed with the available materials will fulfill its required
tion with adequate safety. Thus there are two aspects of the design of an earth dam.
b) Foundation pervious to a moderate depth, after which impervious strata is available :
(c) Foundation pervious to a great depth:
CASE 2 ONLY FINE GRAVEL OR COARSE SAND IS AVAILABLE
PROVIDE DIAPHRAM TYPE DAM WITH SUITABLE ARRANGEMENTS
CASE 3
ONLY SILT AND CLAY IS AVAILABLE
NO CORE
ONLY IMPERVIOUS BLANKED AND ROCK TOE PROVIDES
SEEPAGE ANALYSIS
ASSUMPTIONS
FLOW IS – TWO DIMENTIONAL
Soil is INCOMPRESSIBLE SOIL
Soil is homogeneous and isotropic
Soil is fully saturated
Flow is steady
Darcys law is valid
Phreatic line – (seepage line)
Line within the dam section having positive hydrostatic pressure at below section and negative hydrostatic pressure at above section
Line has atmospheric pressure itself
Separation line of saturated and non saturated portion
Casagrande method of determining seepage line
Dam outlet works lecture 2
Water flowing over a spillway acquires a lot of kinetic energy because of the conversio of the potential energy into kinetic energy.
If the water flowing with such a high velocity is discharged into the river it will scour the river bed.
If the scour is not properly controlled it may extend backward and may endanger the spillway and the dam.
Final Project Report
The document discusses different types of dams classified by structure and materials, including gravity dams, arch dams, embankment dams, and barrages. Embankment dams, the most common type worldwide, are simple compacted earth structures that rely on their mass to resist forces. The document also describes various embankment dam types such as rock fill dams, concrete-face rock fill dams, and earth fill dams.
Concrete dam lecture 2
FORCES ACTING ON GRAVITY DAM
The Bureau of Indian Standards code IS 6512-1984 “Criteria for design of solid gravity dams” recommends that a gravity dam should be designed for the most adverse load condition of the seven given type using the safety factors prescribed.
1. Load combination A (construction condition): Dam completed but no water in reservoir or tail water
2. Load combination B (normal operating conditions): Full reservoir elevation, normal dry weather tail water, normal uplift, ice and silt (if applicable)
3. Load combination C: (Flood discharge condition) - Reservoir at maximum flood pool elevation ,all gates open, tail water at flood elevation, normal uplift, and silt (if applicable)
4. Load combination D: Combination of A and earthquake
5. Load combination E: Combination B, with earthquake but no ice
6. Load combination F: Combination C, but with extreme uplift, assuming the drainage holes to be Inoperative
7. Load combination G: Combination E but with extreme uplift (drains inoperative)
Water Pressure (P) is the major external force exerted by the water stored in the Reservoir on the upstream face of the dam. It can be calculated by the law of hydrostatic pressure distribution; which is triangular in shape as shown in Fig. 3.3.
(a) When u/s face is vertical :
When the upstream face is vertical, the intensity of pressure is zero at the water surface and equal to γw • H at the base.
Earth quake pressure, Horizontal Component(PH) , (ii) Vertical Component(PV) = Weight of water in ABCD portion ,
2. Weight of the Dam :
The weight of the dam per unit length is given by the product of the area of crosssection of the dam and the specific weight of the Construction material, i.e. concrete, and masonary it acts vertically downwards at the centre of gravity of the section.
dam may be divided into smaller sections of simple geometrical shapes such as triangles,rectangles, etc.
weight of each of these acting at its centre of gravity may be considered.
Weight of any part of dam = cross-sectional area of that part x specific weight of material
3. Uplift Pressure :
Uplift pressure is defined as the force exerted by water penetrating through the pores, cracks, fissures within the body of the dam, at the contact between the dam and its
foundation, and within the foundation.
acts vertically upwards
it causes a reduction in the effective weight
Ice Pressure :
Ice pressure is exerted on a dam by a sheet of ice formed on the entire water surface of the reservoir, when it is subjected to expansion and contraction with changes in temperature.
The coefficient of thermal expansion of ice being five times more than that of concrete, the dam face has to resist the force due to expansion of ice. This force acts linearly along the length of the dam, at the reservoir level.
As per IS : 6512 - 1984, ice pressure may be taken equal to 250 kN/m2 applied to the face of the dam over the anticipated area of contact of i
Dam outlet works lecture 3
ENERGY DISSIPATORS
stilling basin
A stilling basin is defined as a structure in which a hydraulic jump used for energy dissipation is confined either partly or entirely.
Certain auxiliary devices such as chute blocks, sills, baffle walls, etc. are usually provided in the stilling basins to reduce the length of the jump and thus to reduce the length and the cost of the stilling basin.
Moreover, these devices also improve the dissipation action of the basin and stabilize the jump.
Chute Blocks :
These are triangular blocks with their top surface horizontal. These are installed at the toe of the spillway just at upstream end of the stilling basin.
They act as a serrated device at the entrance to the stilling basin. They furrow the incoming jet and lift a portion of it ab0ve the floor.
These blocks stabilise the jump and thus improve its performance, these also decrease the length of the hydraulic jump.
Basin Blocks or Baffle Blocks or Baffle Piers :
These are installed on the stilling basin floor between chute blocks and the end sill. These blocks also stabilise the formation of the jump.
Moreover, they increase the turbulence and assist in the dissipation of energy.
They help in breaking the flow and dissipate energy mostly by impact. These baffle blocks are sometimes called friction blocks.
Sills and Dentated Sills :
Sill or more preferably dentated sill is generally provided at the end of the stilling basin.
The dentated sill diffuses the residual portion of the high velocity jet reaching the end of the basin. They, therefore, help in dissipating residual energy and to reduce the length of the jump or the basin.
particular location of these blocks mainly depends upon the initial Froude number (F1) and the velocity of the incoming flow. The stilling basins are usually rectangular in plan. These are made up of concrete.
[A] U.S.B.R. Stilling basins :
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
Type I basin (F1 between 2.5 to 4.5)
Provide chute blocks and end sill
Length of basin = 4.3 y2 to 6.0 y2
Width of chute block = y1
Spacing = 2.5 y1
Height of chute block = 2y1
Length of chutes = 2y1
U.S.B.R. Type-II basin for F1 greater than 4.5 and v1 less than 15 m/sec.:
U.S.B.R. Type-Ill basin for F, greater than 4.5 and V1 greater than 15 m/sec :
Chutes and dentated sills provided
Baffle is not provided because of –velocity is high and cavitation is possible.
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
IS Type-Ill basin is usually provided with a sloping apron for the entire len
Embankment lecture 7
STABILITY OF SLOPES SEEPAGE CONTROL MEASURES AND SLOPE PROTECTION
a finite slope AB, the stability of which is to be analyzed.
The method Consists of assuming a number of trial slip circles, and finding the factor of safety of each.
The circle corresponding to the minimum factor of safely is the critical slip circle.
Let AD be a trial slip circle, with r as the radius and O as the centre of rotation
Let W be the weight of the soil of the wedge ABDA of unit thickness, acting through the centroid G.
The driving moment MD will be equal to W x, where x, is the distance of line of action of W from the vertical line passing through the centre of rotation O.
if cu is the unit cohesion, and l is the length of the slip arc AD, the shear resistance developed along the slip surface will be equal to cu • l, which act at a radial distance r from centre of rotation O.
When slip is imminent in a cohesive soil, a tension crack will always DevelOP by the top surface of the slope along which no shear resistance can develop,
The depth of tension crack is given by
The effect of tension crack is to shorten the arc length along which shear resistance gets mobilised to AB' and to reduce the angle δ to δ'.
The length of the slip arc to be taken in the computation of resisting force is only AB', since tension crack break the continuity at B'.
The weight of the sliding wedge is weight of the area bounded by the ground surface, slip circle arc AB' and the tension crack.
Drop structure lecture 1
canal fall design . sarda type fall design steps cross regulator and head regulator, straight glasis fall with eazy animations
Irrigation water management
This document discusses irrigation water management and drainage systems. It covers the causes of waterlogging including over-irrigation, inadequate drainage, and obstruction of natural drainage. The effects of waterlogging like reduced plant growth and increased soil salinity are also outlined. Various measures to prevent waterlogging are then described such as controlling irrigation intensity, providing drainage systems, lining canals, and adopting better irrigation practices. Finally, the importance of properly-designed drainage systems to prevent and remedy waterlogging is highlighted.
ogee design
The document discusses the design of an ogee spillway for a concrete gravity dam. It describes how shifting the curve of the nappe spillway profile can save concrete by becoming tangential to the downstream dam face. It then provides sample calculations for designing an ogee spillway based on given parameters like discharge rate, dam dimensions, and river levels. These include calculating the design head, developing the upstream and downstream spillway profiles, and considering factors that affect spillway design.
check basin , furrow and border strip method
This document discusses three types of surface irrigation methods: border strip irrigation, check basin irrigation, and furrow irrigation. For each method, it describes what it is, when it is used, and key design aspects. Border strip irrigation uses long, graded strips separated by bunds to guide water down a field. Check basin irrigation uses rectangular plots surrounded by levees to pond water for crops that require submergence. Furrow irrigation uses small channels between ridges to irrigate row crops. The document provides details on layout, sizing, construction, and maintenance considerations for each method.
Irrigation Engineering
This document provides an overview of the course content for Irrigation Engineering (170602). It discusses key topics that will be covered, including the definition and purpose of irrigation, different irrigation systems and methods, soil-water-plant relationships, water requirements of crops, irrigation efficiency, irrigation channels, head works, cross drainage works, and canal regulation works. Assignments include topics on the methods of irrigation, irrigation channels, diversion head works, and cross drainage works. Students will prepare presentations on different types of canal falls. Exams will include a university external exam, mid-semester exams, and a practical internal exam based on the presentations. Reference books are also provided.
Embankment lecture 3
Hydraulic failures .... 40%
Seepage failures…….. 30%
Structural failures .... 30%
(1) Overtopping
(2) Erosion of u/s slope by waves
(3) Erosion of d/s slope by wind and rain
(4) Erosion of d/s toe
(5) Frost action
(1) Overtopping = the design flood is under estimated.
spillway capacity is not adequet
spillway gates are not properly operated
free board is not sufficient
excessive settlement of the foundation and dam
(2) Erosion of u/s slope by waves = The waves developed near the top water surface due to the winds, try to notch out the soil from the upstream face and may even, sometimes, cause the slip of the upstream slope.
Upstream stone pitching or riprap should, therefore, be provided to avoid such failures.
(3) Erosion of d/s slope by wind and rain = The rainwater flowing down the slope; may result in the formation of 'gullies' on the downstream slope thus damaging the dam which may generally lead to partial failure of the dam or in some cases it may cause complete failure of the dam.
Erosion of d/s toe : = Toe erosion may occur due to two reasons :
erosion due to tail water
erosion due to cross currents that may come from spillway buckets.
Frost action : = If the earth dam is located at a place where the temperature falls below the freezing point, frost may form in the pores of the soil in the earth dam.
When there is heaving, the cracks may form in the soil. This may lead to dangerous seepage and consequent failure.
Seepage failures : = Seepage failures may occur due to the following causes :
(1) Piping through the foundation
(2) Piping through the dam
(3) Sloughing of d/s toe
Structural failures :=
Structural failures in earth dams are generally shear failures leading to sliding of the tents or the foundations.
(1) u/s and d/s slope failures due to construction pore pressures
(2) u/s slope failure due to sudden drawdown
(3) D/s slope failure due to steady seepage
(4) Foundation slide due to spontaneous liquefaction
(5) Failure due to earthquake
(6) Failure by spreading
(7) Slope protection failures
(8) Failure due to damage caused by borrowing animals
(9) Failure due to holes caused by leaching of water soluable salts
Criteria for safe Design of Earth Dam :
Section of an Earth Dam :
The design of an earth dam essentially consists of determining such a cross section
the dam which when constructed with the available materials will fulfill its required
tion with adequate safety. Thus there are two aspects of the design of an earth dam.
Embankment lecture 1
The document discusses the design of embankment dams. It defines embankment dams as dams constructed of natural materials like earth or rockfill. It describes the different types of embankment dams including homogeneous dams, zoned dams, and diaphragm dams. It also discusses important design considerations for embankment dams like controlling seepage, providing internal drainage, and ensuring the shear strength of the soil is sufficient to resist failure. Pore water pressure in saturated soils is identified as an important factor that reduces the effective stress and shear strength of soils in embankment dams.
Design of Hydraulic Structure
This document discusses the key elements of dam engineering, including types of dams classified by function, material used, structural behavior, hydraulic design, and rigidity. It also covers critical dam components like spillways, which act as a dam's "safety valve," and spillway gates. Investigations are also conducted for dam design. Embankment dams and their components are specifically examined, along with causes of embankment dam failure and seepage analysis. Recommended references on the topics of irrigation, water resources, water power, and hydraulic structures are also provided.
Irrigation water management
This document provides an overview of irrigation water management concepts including irrigation efficiency, scheduling, and conveyance efficiency. It includes definitions of key terms like irrigation efficiency (Ei), which is the ratio of water used for crop needs to total water diverted. Overall system efficiency considers storage, conveyance, and application losses. Conveyance efficiency (Ec) is the ratio of water delivered to fields to the amount diverted. It is affected by losses from evaporation, seepage, leakage and unwanted vegetation. The document also provides examples of calculating irrigation requirements, soil moisture content, and efficiencies for different irrigation systems and crops.
Dam of india
The document discusses several major dams in India, including the Tehri Dam, Mullaperiyar Dam, Bhakra Dam, Hirakud Dam, Nagarjuna Sagar Dam, Sardar Sarovar Dam, Indirasagar Dam, Bhavanisagar Dam, Koyna Dam, Idukki Dam, Krishna Raja Sagara Dam, Mettur Dam, Srisailam Dam, Konar Dam, and Tungabhadra Dam. It provides details on their location, purpose, size, and other key facts.
Earthen Dams
Earthen dams are constructed using natural materials like clay, sand, gravel and rock. They are designed based on principles of soil mechanics. There are two main types - homogeneous and zoned. Zoned dams have an impervious core and outer shells. Components include the core, shells, rock toe, pitching, berms and drains. Stability requires the seepage line be within the downstream slope with minimum 2m cover. Common causes of failure are hydraulic (overtopping, erosion), seepage (piping through core or foundations) and structural issues like cracking. Proper design and construction can prevent these failures.
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2. w index and 5 index
Dalton’s law of evaporation
The rate of evaporation depends upon the difference between the saturation vapour pressure in the air above
E= C(es-ea)
where c – coefficient depends upon barometric pressure
Es – saturation vapour pressure
Ea - Vapour pressure above 2 m height of water
Factors affecting
Temperature
Wind velocity
Atmospheric pressure
Nature of evaporating surface
Depth of water supply
Impurities in water
Energy budget method
LOW OF CONSERVATION of energy
Energy required is estimated by incoming outgoing, and stored energy in a specific time period
Total energy received from suns radiation = energy reflected + change in energy + energy required for evaporation
Energy budget method
most accurate method (evaporation is a function of the energy state of the water system)
difficult to evaluate all terms
energy balance equation has to be simplified
empirical formulas are used (although radiation measurements are preferable)
Water budget method
Characteristics:
Simple
Difficult to estimate Qd and Qs
Unreliable, accuracy will increase as Δt increases
Measurement et -
Direct measurement –
1 . Tank & lysimeter method
2. Field experimental method- no runoff no percolation
3. Soil moisture studies – gw deep
4. Integration method – laege area
5. Inflow and outflow studies
Infiltration rate
Infiltration capacity : The maximum rate at which, soil at a given time can absorb water.
f = fc when i ≥ fc
f = f 0when i < fc
where fc = infiltration capacity (cm/hr)
i = intensity of rainfall (cm/hr)
f = rate of infiltration (cm/hr)
Horton’s Formula:
This equation assumes an infinite water supply at the surface i.e., it assumes saturation conditions at the soil surface.
For measuring the infiltration capacity the following expression are used:
f(t) = fc + (f0 – fc) e–kt for
where k = decay constant ~ T-1
fc = final equilibrium infiltration capacity
f0 = initial infiltration capacity when t = 0
f(t) = infiltration capacity at any time t from start of the rainfall
td = duration of rainfall
Double Ring Infiltrometer
Infiltration indices The average value of infiltration is called infiltration index.
Two types of infiltration indices
φ – index (PHI INDEX)
w –index
PHI INDEX
- defined as average rate of rainfall such that excess volume of rainfall represents direct runoff
- unit is cm/hr or……
W INDEX
- average rate of loss (infiltration) averaged over whole storm period
- w index = P- Q- S
T
THUS phi index has to be some what than w index
IS 4987 - 1968
IN PLAINS – 520 km2
Elevation upto 1000 m – 260 to 390 km2
Hilly area – 130 km2
It is recommended that 10% of raingauge must be self recording type
Concrete dam lecture 4
FORCES ACTING ON GRAVITY DAM
5. Wave Pressure :
Wind blowing over the water surface in the reservoir exerts a drag on the surface due to which ripples and waves are formed. The impact of these waves Produces a pressure on the upper portion of the dam. The magnitude of the wave pressure mainly depends on the dimensions of the waves which in turn depend on the extent of water surface and the wind velocity.
Silt pressure
The weight and the pressure of the submerged silt are to be considered in addition to weight and pressure of water. The weight of the silt acts vertically on the slope and pressure horizontally, in a similar fashion to the corresponding forces due to water. It is recommended that the submerged density of silt for calculating horizontal pressure may be taken as 1360 kg/m³. Equivalently, for calculating vertical force, the same may be taken as 1925 kg/m³.
Wind Pressure :
Wind pressure is required to be consider only on that portion of the dam structure which is exposed to the action of wind.
Normally wind pressure is taken as 1 to 1.5 kN/m2 for the area exposed to the wind pressure.
Wind pressure is not a significant force and therefore, sometimes, not considered in design of a dam.
Earthquake Forces (Seismic Forces) :
Earthquake or seismic activity is associated with complex oscillating patterns of acceleration and ground motions, which generate transient dynamic loads due to inertia of the dam and the retained body of water.
Horizontal and vertical accelerations are not equal, the former being of greater intensity.
The earthquake acceleration is usually designated as a fraction of the acceleration due to gravity and is expressed as α⋅g, where α is the Seismic Coefficient. The seismic coefficient depends on various factors, like the intensity of the earthquake, the part or zone of the country in which the structure is located, the elasticity of the material of the dam and its foundation, etc.
For the purpose of determining the value of the seismic coefficient which has to be adopted in the design of a dam, India has been divided into five seismic zones, depending upon the severity of the earthquakes which may occur in different places. A map showing these zones is given in the Bureau of Indian Standards code IS: 1893-2002 (Part-1) “Criteria for earthquake resistant design of Structures (fourth revision)”, and has been reproduced in Figure 28.
According to IS : 1893 - 2002, the design value of horizontal seismic coefficient
(Ah) may be determined by one of the two methods
(a) Seismic coefficient method
The total design lateral force or design seismic base shear (VB) along any principal direction shall be determined by the following expression.
Hydrodynamic Pressure :
Horizontal acceleration acting towards the reservoir causes a momentary increase ln the water pressure as the foundation and dam accelerate towards the reservoir and the water resists movement owing to its inertia.
The extra pressure ex
Concrete dam lecture 1
The document describes the key components of a gravity dam and their functions. It discusses drainage galleries, which provide access to the dam interior and drainage. Shafts are vertical openings that provide access for equipment and instruments. The overflow section, also called the spillway, releases surplus water from the reservoir in a safe way. The non-overflow section is the rest of the dam where a road may be located. A power house is located at one end to generate electricity. Energy dissipation works reduce the velocity of water flowing over the spillway. Outlets below the spillway release water from the reservoir. Joints are included to aid construction and prevent cracks.
Lecture 1-aerial photogrammetry
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Embankment lecture 2
The main components of an earth dam are as follows :
1. Impervious core
2. Pervious shell
3. Filter
4. Rock toe
5. U/S slope protection
6. D/S slope protection
7. Cutoff
core should not be less than 3 m and its height should be 1 m more than the maximum water level in the reservoir.
The upstream pervious zone provides free drainage during sudden drawdown. ,
Usually following types of filters are provided :
(1) Toe filter
(2) Horizontal drainage filter (blanket)
(3) Chimney drains
Such a filter is sometimes known as inverted filter or reverse filter.
Rock toe keeps the phreatic line well within the section and also facilitates drainage.
The following measures are taken to protect the slope.
(1) Rock riprap
(2) Concrete pavement
(3) Steel facing
(4) Bituminous pavement
(5) Precast concrete blocks
Cut off is required to
(1) reduce loss of stored water through foundation and abutments
(2) Prevent sub surface erosion by piping.
Cutoff may be provided in the following ways :
• by providing concrete cutoff wall
• by providing cutoff trench filled with impervious material
• by driving sheet pile
• by curtain grouting
irrigation water management
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Chapter 2 part 1 sprinkler
The document discusses various irrigation methods including sprinkler irrigation. It describes how remote sensing and GIS technologies can help with tasks like identifying land use patterns, crop nutrient deficiencies, optimal water levels for crops, and cropping patterns. The document also outlines the advantages and limitations of different irrigation methods such as sprinkler irrigation and subsurface irrigation.
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Embankment lecture 12
- 1. Infinite and finite length of blanket 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 1
- 2. (a) Infinite length of blanket : A natural impervious blanket of large areal extent if available may be considered as a balnket of infinite length For a blanket of infinite length, the solution of equation (iv) is v 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 2
- 3. where, h = loss of -head through the blanket up to any point at a distance x. h0 = loss of head through the blanket up to a point x = 0. 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 3
- 5. In this case for the convenience, the point x = 0 is taken at the downstream end of the blanket and hence h0 is the total loss of head through the blanket upto the end of the blanket. As a measure of the efficiency of a blanket of any length x (where x may be infinite or a finite length) a length Xr is considered which is known as equivalent resistance of the foundation and is defined below. 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 5
- 6. equivalent resistance Xr of the foundation : It may be defined as the length of a prism of the foundation soil of thickness Zf and coefficient of permeability kf which under the loss of head h would carry flow vi equivalent to the flow which passes the blanket system under the same loss of head. Thus 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 6
- 7. Also from equation (v), we have vii Equating the values of 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 7
- 8. (2) Solution for finite length of blanket : For a blanket of uniform thickness and finite length of blanket ihe solution equation (iv) is viii which h is the loss of head through the blanket upto any point at a distance and hn is a constant for computing h. hn depends on the total head loss of the system of which the blanket is a part and on the ratio of the blanket to the remainder of system. * 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 8
- 9. From equation (viii) at x - 0, h = 0, and hence in this case the point x = 0 is taken at the upstream end of the blanket. Differentiating both sides of equation (viii) with respect to x, we get 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 9
- 10. Again if Xr is the equivalent resistance of the foundation, we have from equation 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 10
- 11. If the length of the blanket is L then by substituting x = L in equation (ix) the value of Xr for the entire blanket is obtained. 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 11
- 12. Loss of head through the blanket : h0 is the loss of head upto the end of the blanket; H is the total reservoir head Xd is the base width of the impervious core 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 12
- 13. reduction in quantity of seepage due to provision of blanket : When no blanket With blanket 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 13
- 19. The value of constant 'a' is given by 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 19
- 20. The optimum length of blanket, 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 20
- 21. Let us vary the length of blanket as 25 m, 75 m, 100 m, 125 m, 151.78 AND infinite, and calculate the values of Xr , h0 and % reduction in the discharge. 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 21
- 22. Sample calculations for blanket length x =50 m, are given below 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 22
- 24. The results for other values of x are tabulated below. 1/27/2014 PREPARED BY V.H.KHOKHANI,ASSISTANT PROFESSOR, DIET. 24