EARTH DAMS
INTRODUCTION:-
Dams which are constructed with earthen materials such as gravel, sand, silt and clay are called as earthen dams. Earthen dams are the most ancient type of embankments as they can be built with the natural and locally available materials with minimum processing. Earthen dams are preferred mostly since they are economical in construction and also the locally available materials are utilised and less skilled labour is required.
Classification of Earthen Dams:-.
Homogeneous embankment dam: The simplest type of an earthen embankment consists of a single material and homogenous throughout. A Purely homogeneous section is used when only one type of material is economically or locally available. These sections are used for low to moderately high dams.
Zoned embankment dams: Zoned embankments are usually provided with a central Impervious core, covered by comparatively pervious transition Zone, which is finally Surrounded by a much more pervious outer zone.
Diaphragm type embankment dam: Diaphragm type embankments have a thin Impervious core, which is surrounded by earth or rockfill.The impervious core,called diaphragm, is made of impervious soils,concrete, steel,timber or any other materials.
Causes of Failure of Earthen Dams:-
Earthen dams are less rigid and hence more susceptible to failure. They may fail due to improper designs, faulty construction and lack of proper maintenance etc. The various causes leading to failure of earthen dams are
Hydraulic failure:- About 40% of earth dam failure have been attributed to hydraulic failure under this category is due to
Seepage failure:-Uncontrolled or concentrated seepage through the dam body or through the foundation may lead to piping or sloughing and subsequent failure of the dam. More than 30% of the dams have failed because of these reasons.
Structural failure:- About 25% of dam failures have been attributed to structural failure. Structural failures are generally caused by shear failures, causing slides.
Design Criteria of Earth Dam:-
Functions and Design Requirements of Various Components Of Earth Dam:
The soils having high compressibility and liquid limit are not suitable as they are prone to swelling and formation
of cracks. Suitability of soils for construction of core for earth dam shall be as per IS:8826-1978.
b)Stability of u/s slope during sudden drawdown: The critical condition for u/s slope can occur when the reservoir is suddenly emptied.
Minimum desired factor of safeties for:-
In addition to basic design requirement, special design requirements such as
Instrumentation:
Different types of measurements are needed for monitoring the behavior of earth of rock fill dam and IS : 7436:1993 provides guidelines for choice of instrumentation and their location.Instruments required in earth dam are
DESIGN OF EARTH DAM/ROCK FILL DAM:
Note : The relevant slope stability calculations shall be checked and furnished
DESIGN OF HEAD SLUICE
The following basic parameters are required to take up the design of head sluices in Erath/Rock fill dams
Reference IS Codes for Earth dams:-
1. |
IS: 12169-1987 |
Criteria of Design of Small Embankments. |
2. |
IS: 8826-1978 |
Guide lines for Design of Large Earth and Rock Fill Dam. |
3. |
IS: 10635-1993 |
Free Board requirements in Embankment Dam- Guidelines. |
4. |
IS: 7894-1975 |
Code of Practice for Stability Analysis of Earth dam |
5. |
IS: 9429-1999 |
Drainage System for Earth and Rock fill dam. |
6. |
IS: 8237-1985 |
Code of Practice for Protection of Slope for Reservoir Embankment. |
REFERENCE OTHER BIS CODES
OTHER IS CODES for SPILLWAY,NON-OVERFLOW DAMS
SL. NO |
COMPONENT |
I.S.CODE No. |
1 |
Reservoir capacity-Maximum flood discharge SPF/PMF/5OO/1OOO/year flood and fixing of spillway capacity and considering gate inoperative condition. |
5477- 1971 11223- 1985 |
2 |
Site Selection |
6966- 1989 |
3. |
Permeability in rock below Gravity Dams |
11216- 1985 |
4. |
In-situ Permeability test |
5529- 1985 |
5 |
Selection of Spill ways and dissipators |
10137- 1982 |
6 |
Foundation treatment –Consolidation Grouting- Pressure grouting |
6066- 1994 |
7 |
Design Criteria of solid Gravity Dams – stability analysis, Load combinations, Loads, Factors of safety against sliding Fetch and free board computations |
6512- 1984 |
8 |
Hydraulic design of High Ogee Overflow Spillways Ogee Profile, U/S and D/S Quadrants, computation of Coefficient of discharge, provision of Breast wall etc., |
6934- 1998
|
9
|
Hydraulic Design of Bucket type Energy dissipator (a) Solid Roller (b)Slotted Roller (c)Trajectory Bucket |
7365- 1985
|
10 |
Hydraulic jump type stilling basins |
4997- 1968 |
11 |
Structural arrangement of energy dissipator for spillways |
11527- 1985 |
12 |
Drainage arrangements of Energy Dissipators,Spacing of contraction joints, size and spacing of half round pipes-details of no fine concrete blocks. |
11772- 1986 |
13 |
Water stops at transverse contraction joints in Spillways,NOF dams and at junctions of galleries |
12200- 2001
|
14 |
Construction of Spill ways-preparation of foundations and anchorage, maximum size of aggregates for different components, blocks lengths etc., |
11155- 1994 |
15
|
Galleries and other openings in dams –drainage gallery, inspection gallery, instrumentation gallery ,adits ,sump well and pump chambers ,stair wells, lift etc., general and structural design |
12966- 1990,1992 parts 1&2 |
16 |
Curtain Grouting from galleries –spacing ,depth of grouting ,size and inclination of grout holes-pressure of grouts etc., |
11293- 1993 Part-2 |
17 |
Shear parameters at interface of foundations of Dam with Rock.In-situ shear test on rocks |
7746- 1991 |
18 |
General construction of plain and R.C.C.for dams |
457- 1957 |
19 |
Aggregates ,Fine and Coarse for concrete |
383- 1997 |
20 |
HYSD bars and wires for concrete Reinforcement |
1786- 1990 |
21 |
Drainage system for gravity dams, their foundations and abutments (a)spacing ,size and depth of drainage holes (b)size of porous concrete and formed drains |
10135- 1985 |
22 |
Earth Quake resistant design of structures seismic zone, and computations, hydrodynamic forces and values at different elevations |
1893 - 1984 part-1- 2000 |
23 |
Dewatering during construction |
9759- 1981,2013 |
24 |
Extreme weather concreting (1)Hot weather (2) Cold weather |
7861- 1975, 2002 |
25 |
Temperature control of mass concrete for dams |
14591- 1999 |
26 |
Computation of seepage –provision of sump well and pump chamber-size of sump etc., |
4721- 2000
|
27 |
Radial gates –radius, trunion level etc., |
4623- 2000 |
28 (a)
(b)
(C)
(d)
(e)
(f) |
Instrumentation Location of measuring instruments in concrete & masonry dams. |
7436(part-ii) -1997 |
Selection ,splicing,installationand providing protection to the open ends of cables used for connecting type measuring devices in concrete and masonry dams. |
10334 -1982 |
|
Pore pressure measuring devices Electrical Resistance type cell, Vibrating Wire type cell. |
8282-1976, 1996, 1998,2001 (parts-1&2) |
|
Deformation measuring devices in concrete and masonry dams: part-1 resistance type joint meters. |
10434- 1982 (part-1) |
|
Seismic instrumentation for river valley projects |
4967- 1968, 2000 |
|
Instruments for temperature measurement inside dams –Resistance type thermometers |
6524- 1972, 1998 |
|
|
STRUCTURAL DESIGN |
|
1 |
Pier,Crest |
13551-1992 |
2 |
Bucket(roller/trajectory) |
7365-1985 11772-1986 |
3 |
Galleries,Adits,Sump well and pump chamber Stair well and Lifts |
12966-1990(part-2) |
4 |
Stilling basin |
11772-1986 |
5 |
Training walls and divide walls |
12720-1993 |
6 |
Walkway bridge-steel Concrete |
800- 1984, 1998 456-2000 |
7 |
Spillway bridge |
IRC codes |
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