Monday, July 09, 2018
Wednesday, June 06, 2018
2BHK Plan as per VastuShastra
Above Orientation of building as per Vastu Shastra.
As per vastushastra layout plan should divide in 81 part. each part have their own importance. The right utilization of part gives positive value regarding blase and wrong utilization gives negative value regards curse.At last when you plan to built your "Dream Home" it should considered in mind to choice right plan for your Family.
Saturday, October 18, 2014
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Tuesday, October 07, 2014
Tuesday, June 19, 2007
METHOD OF MEASUREMENT
- CLASSIFICATION METHOD OF MEASUREMENT
i) Wall panel, floor/roof slabs----------------------------In square metres
ii) Beams unit and columns, trusses, etc -----------------In running metres or numbers
iii) Channel unit and purlins------------------------------In running metres or numbers
iv) String or lacing courses, copings, bed plates, anchor blocks, plain window
sills, shelves louvers, steps, staircases, etc ---------------In running metres or numbers
v) Kerbs, edgings, etc ----------------------------------In running metres or numbers
vi) Solid blockwork ------------------------------------In cubic metres or square metres
vii) Hollow blockwork ----------------------------------In cubic metres or square metres
viii) Light weight partitions-------------------------------In square metres stating the thickness
ix) Door/window frames --------------------------------In running metres stating the size
x) Waffle units ------------------------------------------In square metres or numbers
xi) Water tank ------------------------------------------In numbers
xii)JALLIES --------------------------------------------In sq.metres of opening filled stating thickness
xiii) Fencing posts---------------------------------------In numbers or cubic metres
xiv) Folded slab-----------------------------------------In cubic metres
Failure Mechanisms
Failure Mechanisms:
Possible damaging effects of earthquakes on earth dams and embankments include:
• Slope failure because of inertial loading and/or softening of materials strength or liquefaction.
• Fault displacement under the foundation.
• Crest settlement of dam caused by settlement or by earthquake generated water waves in the reservoir.
• Permanent deformation of foundation soils or dam body.
• Sliding failure of an embankment composed of weak or liquefiable soils.
• Piping and erosion
Major contributors to earth dam failure are overtopping, piping, and structural failure.
Overtopping:
Overtopping is defined as uncontrolled flow of water over the crest of the dam or embankment. Non-overflow (other than spillway) portions of a dam are not usually designed for erosional effect of flowing water, overtopping may lead to failure of the dam due to excessive erosion or saturation of the downstream slope. Adequate spillway capacity should be provided to prevent such damages.
Piping:
Due to the pervious nature of earth dams, the dam body acts as pathways for water seepage. If such seepage is uncontrolled in terms of volume and velocity, and material used in constructing the dam body are not carefully selected, particles of soil with which the dam body is constructed may be taken into suspension by seepage water and carried away. In order to prevent such an occurrence, (a) the seepage gradient is kept well below the critical gradient, (b) the particle size distribution of the filter material used in constructing the dam body is carefully chosen to meet the filter criteria, and (c) hydraulic stability of dam core and potentially dispersive fine-grained soils within foundation is demonstrated with pin-hole tests. Additionally, there should be appropriate seepage control measures at the contact between dam and foundation such as: (a) drainage blanket for soil foundation, (b) removal of rock mass affected by excessive cracking or jointing at dam-foundation interface before dam construction, and (c) ensuring absence of slopes steeper than 10 vertical to 1 horizontal at dam-foundation interface.
Structural Failure:
Structural failure includes failure of upstream or downstream slopes of the dam, as well as cracking, deformation and settlement of the dam body that may lead to overtopping or a piping failure. Earthquake loading may trigger any one of the above failure modes or their combinations.
Defensive Design Measures:
Defensive design features should be incorporated in the foundation and embankment design of new dams regardless of the method of seismic analysis.
These features include (USACE 2004):
1. Additional dam height to accommodate the loss of crest elevation due to deformation, slumping, and fault displacement.
2. Crest details that will minimize erosion in the event of overtopping.
3. Wider transition and filter sections as a defense against cracking.
4. Use of rounded or sub-rounded gravel and sand as filter material.
5. Adequate permeability of the filter layers.
6. Near vertical chimney drain in the center portion of the embankment.
7. Zoning of the embankment to minimize saturation of materials.
8. Wide impervious cores of plastic (non-brittle) cohesive fine-grained soils to accommodate deformation.
9. Well-graded core and uniformly graded filter materials to ensure self healing in the event cracking should occur.
10. Stabilization of reservoir rim slopes to provide safety against large slides into the reservoir.
11. Ground improvement or removal and replacement of foundation material to mitigation liquefaction potential
12. Stabilization of slope adjacent to operating facilities to prevent blockage from slide associated with the earthquake.
13. Flaring embankment sections at the abutment contacts.
Installation of suitable features to prevent piping through earthquake generated seepage cracks.
Earthquake Loads:
For the design of intermediate dams or embankments and dams and embankments whose failure entails unacceptable level of risk, a two-tier seismic design approach is usually adopted so that (a) the dam or embankment remains operational following an earthquake that has a reasonable probability of occurrence during the service life of the facility with distress of a minor nature, and (b) the dam or embankment does not collapse following an earthquake that has a small probability or occurrence during the life of the facility.
The design earthquake for condition (a) usually corresponds to a probability of exceedance of 50% over the operational life of the facility. Such an earthquake is referred to as the Operational Basis Earthquake (OBE).
The design earthquake for condition (b) above is often specified as that having a probability of exceedance of 10% over the operational life of the facility. Such an earthquake is referred to as the Maximum Considered Earthquake (MCE).
Operational life of a dam or an embankment is usually 50 to 100 years. However, a longer operational life should be assumed in situations such as (a) a water-retaining dam that is not appropriately decommissioned at the end of operational life where there is an unacceptable downstream risk in the event of a dam break, and (b) a tailings dam retaining radioactive or other wastes that may pollute groundwater or jeopardize downstream public health and safety in the event of dam break.
Location:
Preference for Location:
Earth dams and embankments should be ideally located away from any potentially active fault or an area underlain by liquefiable or sensitive soils or abutments prone to static or seismic instability.
Design Measures:
If unavoidable, an earth dam or an embankment may be constructed over a fault or at a site underlain by potentially liquefiable or sensitive soils or between potentially unstable abutments only if (a) the dam is designed for the displacements and other dynamic effects of an earthquake that is likely to occur, and (b) potential failure is unlikely to lead to any loss of life and the risk associated with such a selection of site is acceptable area to assess their behavior during earthquake shaking, and how they might affect the ability of a structure to resist earthquake including evaluation of liquefaction potential, if appropriate. The investigation should focus on topics including:
1. Topographic conditions.
2. Description of geology
3. Composition and structure of foundation soils, soils from borrow area and bedrock
4. Principal engineering properties of the rocks and soils including grain characteristics, plasticity, compaction characteristics, shear strength, dispersivity and hydraulic properties
5. Geotechnical investigation would typically include drilling and sampling, in-situ testing (piezocone penetration test, Standard Penetration Test or Field Vane Shear Test, seismic velocity profiling) as appropriate.
Location
Earthquake damage to embankment can arise from two sources, actual ground rupture beneath the embankment and seismic shaking. Failure of a dam due to ground rupture is possible only when the dam is built over an active fault zone or across reactivated or newly activated landslide zone. The location of the dam over the fault zone should be reviewed at the time of site selection and appropriate measures should be taken in the design and construction of a dam over a fault. By far the more common problem in a dam design is to ensure that the dam will be stable under anticipated levels of seismic shaking.
Freeboard:
It is recommended to provide a freeboard of at least 2% to 3% of dam height, but not less than 2m if there is a potential for occurrence of landslides near the dam abutment within the slopes of the reservoir margins or 1m if there is a negligible landslide potential near the dam abutments.
Freeboard:
The freeboard of all embankment dams should be based on most extreme conditions expected for which the dam is designed. The maximum reservoir elevation is determined for the design flood, wind speed, fetch and expected wave run-up conditions. In general, overtopping of the dam is not acceptable. Ample freeboard should be provided to avoid the possibility of overtopping by (a) earthquake-generated water waves, (b) settlement and permanent deformation of crest due to liquefaction which may cause densification or loss of stiffness of the materials or fault rupture. In addition, it may be prudent to use riprap or other crest details that will resist erosion by a succession of overtopping waves.
Possible damaging effects of earthquakes on earth dams and embankments include:
• Slope failure because of inertial loading and/or softening of materials strength or liquefaction.
• Fault displacement under the foundation.
• Crest settlement of dam caused by settlement or by earthquake generated water waves in the reservoir.
• Permanent deformation of foundation soils or dam body.
• Sliding failure of an embankment composed of weak or liquefiable soils.
• Piping and erosion
Major contributors to earth dam failure are overtopping, piping, and structural failure.
Overtopping:
Overtopping is defined as uncontrolled flow of water over the crest of the dam or embankment. Non-overflow (other than spillway) portions of a dam are not usually designed for erosional effect of flowing water, overtopping may lead to failure of the dam due to excessive erosion or saturation of the downstream slope. Adequate spillway capacity should be provided to prevent such damages.
Piping:
Due to the pervious nature of earth dams, the dam body acts as pathways for water seepage. If such seepage is uncontrolled in terms of volume and velocity, and material used in constructing the dam body are not carefully selected, particles of soil with which the dam body is constructed may be taken into suspension by seepage water and carried away. In order to prevent such an occurrence, (a) the seepage gradient is kept well below the critical gradient, (b) the particle size distribution of the filter material used in constructing the dam body is carefully chosen to meet the filter criteria, and (c) hydraulic stability of dam core and potentially dispersive fine-grained soils within foundation is demonstrated with pin-hole tests. Additionally, there should be appropriate seepage control measures at the contact between dam and foundation such as: (a) drainage blanket for soil foundation, (b) removal of rock mass affected by excessive cracking or jointing at dam-foundation interface before dam construction, and (c) ensuring absence of slopes steeper than 10 vertical to 1 horizontal at dam-foundation interface.
Structural Failure:
Structural failure includes failure of upstream or downstream slopes of the dam, as well as cracking, deformation and settlement of the dam body that may lead to overtopping or a piping failure. Earthquake loading may trigger any one of the above failure modes or their combinations.
Defensive Design Measures:
Defensive design features should be incorporated in the foundation and embankment design of new dams regardless of the method of seismic analysis.
These features include (USACE 2004):
1. Additional dam height to accommodate the loss of crest elevation due to deformation, slumping, and fault displacement.
2. Crest details that will minimize erosion in the event of overtopping.
3. Wider transition and filter sections as a defense against cracking.
4. Use of rounded or sub-rounded gravel and sand as filter material.
5. Adequate permeability of the filter layers.
6. Near vertical chimney drain in the center portion of the embankment.
7. Zoning of the embankment to minimize saturation of materials.
8. Wide impervious cores of plastic (non-brittle) cohesive fine-grained soils to accommodate deformation.
9. Well-graded core and uniformly graded filter materials to ensure self healing in the event cracking should occur.
10. Stabilization of reservoir rim slopes to provide safety against large slides into the reservoir.
11. Ground improvement or removal and replacement of foundation material to mitigation liquefaction potential
12. Stabilization of slope adjacent to operating facilities to prevent blockage from slide associated with the earthquake.
13. Flaring embankment sections at the abutment contacts.
Installation of suitable features to prevent piping through earthquake generated seepage cracks.
Earthquake Loads:
For the design of intermediate dams or embankments and dams and embankments whose failure entails unacceptable level of risk, a two-tier seismic design approach is usually adopted so that (a) the dam or embankment remains operational following an earthquake that has a reasonable probability of occurrence during the service life of the facility with distress of a minor nature, and (b) the dam or embankment does not collapse following an earthquake that has a small probability or occurrence during the life of the facility.
The design earthquake for condition (a) usually corresponds to a probability of exceedance of 50% over the operational life of the facility. Such an earthquake is referred to as the Operational Basis Earthquake (OBE).
The design earthquake for condition (b) above is often specified as that having a probability of exceedance of 10% over the operational life of the facility. Such an earthquake is referred to as the Maximum Considered Earthquake (MCE).
Operational life of a dam or an embankment is usually 50 to 100 years. However, a longer operational life should be assumed in situations such as (a) a water-retaining dam that is not appropriately decommissioned at the end of operational life where there is an unacceptable downstream risk in the event of a dam break, and (b) a tailings dam retaining radioactive or other wastes that may pollute groundwater or jeopardize downstream public health and safety in the event of dam break.
Location:
Preference for Location:
Earth dams and embankments should be ideally located away from any potentially active fault or an area underlain by liquefiable or sensitive soils or abutments prone to static or seismic instability.
Design Measures:
If unavoidable, an earth dam or an embankment may be constructed over a fault or at a site underlain by potentially liquefiable or sensitive soils or between potentially unstable abutments only if (a) the dam is designed for the displacements and other dynamic effects of an earthquake that is likely to occur, and (b) potential failure is unlikely to lead to any loss of life and the risk associated with such a selection of site is acceptable area to assess their behavior during earthquake shaking, and how they might affect the ability of a structure to resist earthquake including evaluation of liquefaction potential, if appropriate. The investigation should focus on topics including:
1. Topographic conditions.
2. Description of geology
3. Composition and structure of foundation soils, soils from borrow area and bedrock
4. Principal engineering properties of the rocks and soils including grain characteristics, plasticity, compaction characteristics, shear strength, dispersivity and hydraulic properties
5. Geotechnical investigation would typically include drilling and sampling, in-situ testing (piezocone penetration test, Standard Penetration Test or Field Vane Shear Test, seismic velocity profiling) as appropriate.
Location
Earthquake damage to embankment can arise from two sources, actual ground rupture beneath the embankment and seismic shaking. Failure of a dam due to ground rupture is possible only when the dam is built over an active fault zone or across reactivated or newly activated landslide zone. The location of the dam over the fault zone should be reviewed at the time of site selection and appropriate measures should be taken in the design and construction of a dam over a fault. By far the more common problem in a dam design is to ensure that the dam will be stable under anticipated levels of seismic shaking.
Freeboard:
It is recommended to provide a freeboard of at least 2% to 3% of dam height, but not less than 2m if there is a potential for occurrence of landslides near the dam abutment within the slopes of the reservoir margins or 1m if there is a negligible landslide potential near the dam abutments.
Freeboard:
The freeboard of all embankment dams should be based on most extreme conditions expected for which the dam is designed. The maximum reservoir elevation is determined for the design flood, wind speed, fetch and expected wave run-up conditions. In general, overtopping of the dam is not acceptable. Ample freeboard should be provided to avoid the possibility of overtopping by (a) earthquake-generated water waves, (b) settlement and permanent deformation of crest due to liquefaction which may cause densification or loss of stiffness of the materials or fault rupture. In addition, it may be prudent to use riprap or other crest details that will resist erosion by a succession of overtopping waves.
Wednesday, June 21, 2006
Notes on EARTH DAMS
EARTH DAMS
1 Geometry
1.1 The downstream slope of earth dams without seepage control measures should be no steeper than 1 vertical on 3 horizontal. If seepage control measures are provided, the downstream slope should be no steeper than 1 vertical on 2 horizontal.
1.2 The upstream slope of earth dams should be no steeper than 1 vertical on 3 horizontal.
1.3 The side slopes of homogenous earth dams may have to be made flatter based on the results of design analyses or if the embankment material consists of fine grained plastic soils such as CL, MH or CH soils as described by the Unified Soil Classification System.
1.4 The minimum allowable top width (W) of the embankment shall be the greater dimension of 10 feet or W, as calculated by the following
formula:
W = 0.2H + 7; where H is the height of the embankment (in feet)
1.5 The top of the dam should be sloped to promote drainage and minimize surface infiltrations and should be cambered so that the design freeboard is maintained after post-construction settlement takes place.
2 Slope Stability
Where warranted and especially for new Hazard Class "C" dams, the department may require that slope stability analyses be provided for review. The method of analyses and appropriate factors of safety for the applicable loading condition. Earth dams, in general, should have seepage control measures, such as interior drainage trenches, downstream pervious zones, or drainage blankets in order to keep the line of seepage from emerging on the downstream slope, and to control foundation seepage. Hazard Class "A" dams less than 20 feet in height and Hazard Class "B" dams less than 10 feet in height, if constructed on and of erosion-resistant materials, do not require special measures to control seepage. In zoned embankments, consideration should be given to the relative permeability and gradation of embankment materials. No particle greater in size than six inches in maximum dimension should be allowed to be placed in the impervious zone of the dam.
3 Compaction Control and Specifications
Before compaction begins, the embankment material should be spread in lifts or layers having a thickness appropriate to the type of compaction equipment used. The maximum permissible layer thickness should be specified in the plans or specifications.
Specifications should require that the ground surface under the proposed dam be stripped of all vegetation, organic and otherwise objectionable materials. After stripping, the earth foundation should be moistened, if dry, and be compacted before placement of the first layer of embankment material. Inclusion of vegetation, organic material, or frozen soil in the embankment, as well as placing of embankment material on a frozen surface is prohibited and should be so stated in the specifications. For all dams, compaction shall be accomplished by appropriate equipment designed specifically for compaction. The type of compaction equipment should be specified in the plans or specifications. The degree of compaction should be specified either as a minimum number of complete coverage’s of each layer by the compaction equipment or, in the case of higher or more critical dams, based on standard test methods.
When the degree of compaction is specified as a number of complete coverage’s or passes, the final number of passes required shall be determined by the engineer during construction. In order to insure that the embankment material is compacted at appropriate moisture content, a method of moisture content control should be specified. For Hazard Class "A" dams less than 20 feet high, the moisture content may be controlled visually by a qualified inspector. Hand tamping should be permitted only in bedding pipes passing through the dam. All other compaction adjacent to structures should be accomplished by means of manually directed power tampers.
Backfill around conduits should be placed in layers not thicker than 4 inches before compaction with particle size limited to 3 inches in greatest dimension and compacted to a density equal to that of the adjacent portion of the dam embankment regardless of compaction equipment used. Care should be exercised in placing and compacting fill adjacent to structures to allow the structures to assume the loads from the fill gradually and uniformly. Fill adjacent to structures shall be increased at approximately the same rate on all sides of the structures. The engineer in charge of construction is required to provide thorough and continuous testing to insure that the specified density is achieved.
4 VEGETATION CONTROL - TREES AND BRUSH
4.1 Trees and Brush
Trees and brush are not permitted on earth dams because:
a. Extensive root systems can provide seepage paths for water.
b. Trees that blow down or fall over can leave large holes in the embankment surface that will weaken the embankment and can lead to increased erosion.
c. Brush obscures the surface limiting visual inspection, provides a haven for burrowing animals and retards growth for grass vegetation. vegetation can be established and the surface mowed. Stumps should be removed either by pulling or with machines that grind them down. All woody material should be removed to about 6 inches below the ground surface. The cavity should be filled with well compacted soil and grass vegetation established.
4.2 Grass Vegetation
Grass vegetation is an effective and inexpensive way to prevent erosion of embankment surfaces. It also enhances the appearance of the dam and provides a surface that can be easily inspected.
1 Geometry
1.1 The downstream slope of earth dams without seepage control measures should be no steeper than 1 vertical on 3 horizontal. If seepage control measures are provided, the downstream slope should be no steeper than 1 vertical on 2 horizontal.
1.2 The upstream slope of earth dams should be no steeper than 1 vertical on 3 horizontal.
1.3 The side slopes of homogenous earth dams may have to be made flatter based on the results of design analyses or if the embankment material consists of fine grained plastic soils such as CL, MH or CH soils as described by the Unified Soil Classification System.
1.4 The minimum allowable top width (W) of the embankment shall be the greater dimension of 10 feet or W, as calculated by the following
formula:
W = 0.2H + 7; where H is the height of the embankment (in feet)
1.5 The top of the dam should be sloped to promote drainage and minimize surface infiltrations and should be cambered so that the design freeboard is maintained after post-construction settlement takes place.
2 Slope Stability
Where warranted and especially for new Hazard Class "C" dams, the department may require that slope stability analyses be provided for review. The method of analyses and appropriate factors of safety for the applicable loading condition. Earth dams, in general, should have seepage control measures, such as interior drainage trenches, downstream pervious zones, or drainage blankets in order to keep the line of seepage from emerging on the downstream slope, and to control foundation seepage. Hazard Class "A" dams less than 20 feet in height and Hazard Class "B" dams less than 10 feet in height, if constructed on and of erosion-resistant materials, do not require special measures to control seepage. In zoned embankments, consideration should be given to the relative permeability and gradation of embankment materials. No particle greater in size than six inches in maximum dimension should be allowed to be placed in the impervious zone of the dam.
3 Compaction Control and Specifications
Before compaction begins, the embankment material should be spread in lifts or layers having a thickness appropriate to the type of compaction equipment used. The maximum permissible layer thickness should be specified in the plans or specifications.
Specifications should require that the ground surface under the proposed dam be stripped of all vegetation, organic and otherwise objectionable materials. After stripping, the earth foundation should be moistened, if dry, and be compacted before placement of the first layer of embankment material. Inclusion of vegetation, organic material, or frozen soil in the embankment, as well as placing of embankment material on a frozen surface is prohibited and should be so stated in the specifications. For all dams, compaction shall be accomplished by appropriate equipment designed specifically for compaction. The type of compaction equipment should be specified in the plans or specifications. The degree of compaction should be specified either as a minimum number of complete coverage’s of each layer by the compaction equipment or, in the case of higher or more critical dams, based on standard test methods.
When the degree of compaction is specified as a number of complete coverage’s or passes, the final number of passes required shall be determined by the engineer during construction. In order to insure that the embankment material is compacted at appropriate moisture content, a method of moisture content control should be specified. For Hazard Class "A" dams less than 20 feet high, the moisture content may be controlled visually by a qualified inspector. Hand tamping should be permitted only in bedding pipes passing through the dam. All other compaction adjacent to structures should be accomplished by means of manually directed power tampers.
Backfill around conduits should be placed in layers not thicker than 4 inches before compaction with particle size limited to 3 inches in greatest dimension and compacted to a density equal to that of the adjacent portion of the dam embankment regardless of compaction equipment used. Care should be exercised in placing and compacting fill adjacent to structures to allow the structures to assume the loads from the fill gradually and uniformly. Fill adjacent to structures shall be increased at approximately the same rate on all sides of the structures. The engineer in charge of construction is required to provide thorough and continuous testing to insure that the specified density is achieved.
4 VEGETATION CONTROL - TREES AND BRUSH
4.1 Trees and Brush
Trees and brush are not permitted on earth dams because:
a. Extensive root systems can provide seepage paths for water.
b. Trees that blow down or fall over can leave large holes in the embankment surface that will weaken the embankment and can lead to increased erosion.
c. Brush obscures the surface limiting visual inspection, provides a haven for burrowing animals and retards growth for grass vegetation. vegetation can be established and the surface mowed. Stumps should be removed either by pulling or with machines that grind them down. All woody material should be removed to about 6 inches below the ground surface. The cavity should be filled with well compacted soil and grass vegetation established.
4.2 Grass Vegetation
Grass vegetation is an effective and inexpensive way to prevent erosion of embankment surfaces. It also enhances the appearance of the dam and provides a surface that can be easily inspected.
Saturday, June 03, 2006
Erosion and Sediment Control actions (I)
Check Dam
When
· To stabilize constructed and existing flow corridors when flow is anticipated to exceed the erosive velocity.
· To control sediment in a stream in conjunction with a sediment sump.
Why
· To reduce water velocity minimizing erosion in flow corridors and channels.
· To temporarily protect vegetation during early stages of growth or permanently to reduce flow velocities.
Where
· Within and across an existing or constructed flow corridor.
Scheduling
· Around Year.
How
1. Configure check dams to site specific conditions. Utilize an engineer as necessary to determine the notched center dimensions and spacing between check dams based on channel slope, flow length, discharge, flow velocity, and soil type. Permanent check dams should be designed to pass, at a minimum, a 10‑year, 24‑hour storm at non-erosive velocity.
2. Permanent check dams should be constructed of clean rock placed on geo-textile fabric which has been toed in a minimum of 3 inches. Ninety percent of the rock should range between 2 to 4 inches for slopes less than 2 percent and 3 to 12 inches for steeper grades. The rock size should be large enough to stay in place during anticipated flows. When larger rock is used, place smaller aggregate immediately upstream to filter sediment and improve efficiency.
3. Temporary check dams that will experience low flow conditions can utilize pea-stone or gravel filled bags instead of rock over geotextile fabric. New commercially available technologies include prefabricated check dams that are effective and sometimes reusable.
4. When not engineered but used in series, the toe of the upstream check dam should be set at the same elevation as lowest point in the top of the downstream check dam.
5. The side slopes of the check dam should be 2 horizontal to 1 vertical or flatter or equivalent to the existing streambank slopes.
6. The middle of the dam should be a minimum of 9 inches lower than the outer edges, allowing flow to go over the depression in the center as opposed to around the sides where it could erode the banks.
7. The outer edges should be keyed into adjacent banks and extend to an elevation above the anticipated flow depth to prevent washouts.
8. Sediment sumps should be used upstream of check dams when working in sandy soils when excessive amounts of sediment is expected to accumulate.
9. Riprap should be placed immediately below the check dam to help dissipate the energy of the water flowing over the dam. In areas of higher velocities energy dissipation may be needed downstream of the check dam to prevent undercutting.
10. Temporary check dams should be constructed to handle the anticipated flow and sediment load until the site is stabilized. Aggregate filled bags are easier to remove than a rock check dam and the aggregate can usually be spread along the channel bottom when the check dam is removed. Aggregate meeting the gradation requirements of 6A is recommended; use nothing finer than pea-stone.
Maintenance
· Inspect check dams following each runoff event to ensure there is no piping under the structure or around the banks until the flow corridor has been stabilized.
· Initiate identified repair needs as soon as possible following inspection.
· Remove and properly dispose of sediment when it accumulates to 1/2 the check dam height. Spread sediment in an upland area and seed immediately.
· In some instances clogged stone must be cleaned to remain effective.
· Inspect downstream structures to ensure they have not been damaged or clogged with displaced rock or stone.
· After flow corridor or channel has stabilized remove accumulated sediment from behind the check dam. If check dam is temporary, remove check dam and then stabilize the area.
Limitations
· Check dams greater than two feet in depth at the center may seriously impact the flow characteristics of the flow corridor or channel and should not be used.
· Removal of rock check dams is labor intensive and expensive.
· Does not remove suspended clay and silt, therefore polymers may be needed.
When
· To stabilize constructed and existing flow corridors when flow is anticipated to exceed the erosive velocity.
· To control sediment in a stream in conjunction with a sediment sump.
Why
· To reduce water velocity minimizing erosion in flow corridors and channels.
· To temporarily protect vegetation during early stages of growth or permanently to reduce flow velocities.
Where
· Within and across an existing or constructed flow corridor.
Scheduling
· Around Year.
How
1. Configure check dams to site specific conditions. Utilize an engineer as necessary to determine the notched center dimensions and spacing between check dams based on channel slope, flow length, discharge, flow velocity, and soil type. Permanent check dams should be designed to pass, at a minimum, a 10‑year, 24‑hour storm at non-erosive velocity.
2. Permanent check dams should be constructed of clean rock placed on geo-textile fabric which has been toed in a minimum of 3 inches. Ninety percent of the rock should range between 2 to 4 inches for slopes less than 2 percent and 3 to 12 inches for steeper grades. The rock size should be large enough to stay in place during anticipated flows. When larger rock is used, place smaller aggregate immediately upstream to filter sediment and improve efficiency.
3. Temporary check dams that will experience low flow conditions can utilize pea-stone or gravel filled bags instead of rock over geotextile fabric. New commercially available technologies include prefabricated check dams that are effective and sometimes reusable.
4. When not engineered but used in series, the toe of the upstream check dam should be set at the same elevation as lowest point in the top of the downstream check dam.
5. The side slopes of the check dam should be 2 horizontal to 1 vertical or flatter or equivalent to the existing streambank slopes.
6. The middle of the dam should be a minimum of 9 inches lower than the outer edges, allowing flow to go over the depression in the center as opposed to around the sides where it could erode the banks.
7. The outer edges should be keyed into adjacent banks and extend to an elevation above the anticipated flow depth to prevent washouts.
8. Sediment sumps should be used upstream of check dams when working in sandy soils when excessive amounts of sediment is expected to accumulate.
9. Riprap should be placed immediately below the check dam to help dissipate the energy of the water flowing over the dam. In areas of higher velocities energy dissipation may be needed downstream of the check dam to prevent undercutting.
10. Temporary check dams should be constructed to handle the anticipated flow and sediment load until the site is stabilized. Aggregate filled bags are easier to remove than a rock check dam and the aggregate can usually be spread along the channel bottom when the check dam is removed. Aggregate meeting the gradation requirements of 6A is recommended; use nothing finer than pea-stone.
Maintenance
· Inspect check dams following each runoff event to ensure there is no piping under the structure or around the banks until the flow corridor has been stabilized.
· Initiate identified repair needs as soon as possible following inspection.
· Remove and properly dispose of sediment when it accumulates to 1/2 the check dam height. Spread sediment in an upland area and seed immediately.
· In some instances clogged stone must be cleaned to remain effective.
· Inspect downstream structures to ensure they have not been damaged or clogged with displaced rock or stone.
· After flow corridor or channel has stabilized remove accumulated sediment from behind the check dam. If check dam is temporary, remove check dam and then stabilize the area.
Limitations
· Check dams greater than two feet in depth at the center may seriously impact the flow characteristics of the flow corridor or channel and should not be used.
· Removal of rock check dams is labor intensive and expensive.
· Does not remove suspended clay and silt, therefore polymers may be needed.
Indian standard (IS) for Design of Dam
Indian standard (IS) for Design of Dam
- Criteria for Design of Solid Gravity Dams- I.S. 6512-1984.
- Guidelines for fixing spillway capacity –I.S. 11223-1985.
- Criteria for Earthquake resistant design of structures I.S. 1893-1984.
- Code of practice for stability analysis for earth dams- I.S. 7894-1975.
The Indian Standard IS: 11223-1985 “ Guidelines for fixing spillway capacity” gives the criteria for inflow design flood as under:
The seismic zone together with appropriate coefficients for use in such analysis is given in IS: 1983-84 “Criteria for Earthquake Resistant Design of Structures”.
The various design condition of analysis along with the minimum values of factors of safety to be aimed at and use of type of shear strength for each condition of analysis is given in I.S.:7894-1975 Code of Practice for stability analysis of earth dams .
IS:1893-1984. Criteria for earthquake resistant design of structures (3rd rev.).
Till specific reliable procedures become available for assessment of ice pressure, it may be provided for at the rate of 250 kpa applied to the face of the dam (I.S..6512-1984).
I.S. 1893-1984 “Criteria for Earthquake resistant design of structures” or similar Method.
As per Indian Standard IS:6512-1984 the compressive strength of concrete and masonry
The IS : 6512-1984 states that the factor of safety against sliding may be calculated on the basis of partial factor of safety in respect of friction (FQ) and partial factor of safety in respect of cohesion (Fc)
Wednesday, May 31, 2006
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