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Asked: September 25, 2020In: Construction

Can a random rubble masonry retaining wall withstand the high impact of water during floods?

aviratdhodare
aviratdhodare

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Can a random rubble masonry retaining wall withstand the high impact of water during floods, if the walls are built on both sides of a canal. And how can we check if the design of the wall was sufficient?

  1. aviratdhodare

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    Added an answer on September 29, 2020 at 5:09 pm

    You start asking about ‘High Impact’ from flood waters. Generally flood waters is not High Impact unless a dam collapses or you have an extreme flash flood. Usually if you are at a canal you will have fast water eroding the base of the wall or pushing the rubble masonry wall as the water goes througRead more

    You start asking about ‘High Impact’ from flood waters. Generally flood waters is not High Impact unless a dam collapses or you have an extreme flash flood. Usually if you are at a canal you will have fast water eroding the base of the wall or pushing the rubble masonry wall as the water goes through the canals.

    To check if the design of the wall is sufficient see if any design calculations were filed with the local municipality or water agency. The calcs should identify the design water speed and height. If no calcs then you need an engineer to review the construction of the wall.

    If you can’t afford an engineer first look at the base of the wall. Is there exposed dirt, is erosion already occurring? Look for photos from a few years ago to see if the wall has changed. Check the upstream ends of the walls on both sides. Are they flared out and do they extend below grade into the earth. If the rubble is just on the surface at the upstream then as the fast water rises it will undermine the wall and it will fail one piece at a time.

    A random rubble masonry wall can survive a flood if correctly designed but the only way to know for sure is to have another engineer review the wall.

    Usually a RR retaining wall is constructed in embankments (above the linings) of canal when the lateral force from the soil behind is considerably high due to various factors. During the floods, this force will exert more pressure. If the slope and base width of the wall is not designed properly, it will fail. Hence the design parameters should include this eventuality. (Max. Lateral pressure with a minimum factor of safety 1.50). Sometimes there is no need for cement mortar and the tiny gaps will be help full to act as weep holes.

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Asked: July 24, 2020In: Construction

What is a Floor Area Ratio (FAR)?

DevilAVRT
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What is a Floor Area Ratio (FAR)?

  1. aviratdhodare

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    Added an answer on October 10, 2020 at 3:05 pm

    What does FLOOR AREA RATIO mean: FAR is a technical term used in Urban Planning that determines the total built-up space of the building on a plot of land. Generally, the FAR of the City or the Area is fixed by the government, based on various parameters like infrastructure, population or populationRead more

    What does FLOOR AREA RATIO mean:

    FAR is a technical term used in Urban Planning that determines the total built-up space of the building on a plot of land. Generally, the FAR of the City or the Area is fixed by the government, based on various parameters like infrastructure, population or population growth. These you will understand once you are going through this issue.

    So by Definition FLOOR AREA RATIO (FAR) is the ratio of BUILDING’S TOTAL COVERED AREA to THE SIZE OF THE PLOT on which it is built.

    BUILDING’S TOTAL COVERED AREA is the Gross Floor Area.

    Formula for FAR

    FAR = TOTAL COVERED AREA (ALL FLOORS)/ AREA OF PLOT.

    For e.f. If there are 4 Floors and each Floor is of 5000 Sq feet, then the Total Covered Area of all the Floors is 20000 Sq Feet and the size of the plot is 10000 Sq Feet, then FAR = 20000/10000 = 2. In some areas it is mentioned as % i,e, 200% or somewhere it is mentioned simply 200. So if it is 200 then it means the FAR of the City or Area is 2, meaning one is authorized to build up the covered area 2 times to that of the plot area.

    But Generally FAR is fixed by the government, for particular City or Area and the FAR can be used to calculate the Total Covered Area that is built on a plot of land.

    NOTE: There is one more term FLOOR SPACE INDEX i.e. FSI. The meaning of FAR and FSI is the same. There is a difference of only denoting these two. FAR is always mentioned in percentage. For e.g. the FAR of any City / Area is 200% then the FSI of the same City / Area will be denoted as 2.0.

    Let us understand with the help of an illustration as in the image below:

    For e.g. the total Plot Area is 10000 Sq feet

    CASE 1: If FAR of a place is 0.5, then the total area to be built up is allowed only 5000 sq feet.

    OPTION A: One can construct in 50% of the plot area, only one floor of 5000 sq feet. So FAR = 5000/10000=0.5

    OPTION B : One can construct in 25% 2 Stories of 2500 sq feet of each. So FAR = (2X2500)/10000=5000/10000 = 0.5

    What is Floor Area Ratio (FAR)? | Seattle's Land Use Code

    CASE 2: If FAR of a place is 1.0, then the total area to be built up is allowed only 10000 sq feet.

    OPTION A: One can construct in 100% of the plot area, only one floor of 10000 sq feet. So FAR = 10000/10000=1.0

    OPTION B : One can construct in 50% of the plot area ,2 Stories floor of 5000 sq feet. So FAR = (5000 X 2) /10000 = 10000/10000=1.0

    OPTION C : One can construct in 25% 4 stories of 2500 sq feet of each. So FAR = (2500 X 4) /10000=10000/10000 = 1.0

    CASE 3: If FAR of a place is 2.0, then the total area to be built up is allowed only 20000 sq feet.

    OPTION A : One can construct in 100% of the plot area ,2 Stories of 10000 sq feet each. So FAR = (10000 X 2 )/10000 = 20000/10000=2.0

    OPTION B : One can construct in 50% of the plot area ,4 Stories floor of 5000 sq feet. So FAR = (5000 X 4) /10000 = 20000/10000=2.0

    OPTION C : One can construct in 25% 8 stories of 2500 sq feet of each. So FAR = (2500 X 8) /10000=20000/10000 = 1.0

    So if you know the FAR, you can calculate the total covered area that can be built on the plot.

    How much open area you have to leave or how much area can be built up depends on the zoning and planning regulations also. For e.g. how much area to be left for:

    • Setback.
    • Parking
    • Ground Coverage or Maximum Ground Coverage.
    • Height Restrictions

    FACTORS URBAN DEVELOPMENT AUTHORITY CONSIDER WHILE DECIDING FAR:

    • The current population of the City / Area: When the population of the City / Area is high, the FAR is also high, it means the government is intending for Vertical Development as compared to the spread-out development,
    • Population Growth: If the population growth rate is high, then also the FAR of the City / Area is high
    • Infrastructure: Infrastructure also plays a key role while deciding the FAR of the City / Area. If Infrastructure is low then FAR will be kept low otherwise there will be pressure on infrastructural facilities viz, water, power supply, transport etc. If Infrastructure of the City / Area is already high and developed by the government relative to population density, then FAR can be kept at a higher level by the Authorities.

    Note: If in the City / Area, the infrastructure is low but the population is growing at a faster rate, then the government has to increase the infrastructure and FAR has to be kept higher to accommodate the high growing population.

    So when FAR increases the Population Density of the City / Area increases.

    IMPACT OF HIGH FAR:

    • Higher Population Density
    • Stress on Infrastructure
    • Better Profitability for Developers
    • High Land Value
    • Better Walkability

    IMPACT OF LOW FAR:

    • Lower Population Density.
    • Better Per Capita Infrastructure
    • Reduced Profitability for the Developers.
    • Low Land Prices.
    • Long Travel Distances
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Asked: May 28, 2020In: Construction

Which are the Methods or Reference codes for the casting of Precast Piers for Metro Construction particularly?

poojan
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Which are the methods or reference codes for the casting of precast piers for metro construction particularly?

  1. AdityaBhandakkar

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    Added an answer on October 19, 2020 at 7:52 am
    This answer was edited.

    Hi, Following are some Codes used in Pune metro constructions(INDIA). IRS IRC IS AASHTO Indian Railway Standards(IRS) IRS - Bridge Rules for loading (Min. of Railway) IRS - Code of practice for Steel bridges. IRS - Code of practice for plain, reinforcement and prestressed concrete for general BridgeRead more

    Hi, Following are some Codes used in Pune metro constructions(INDIA).

    1. IRS
    2. IRC
    3. IS
    4. AASHTO

    Indian Railway Standards(IRS)

    IRS – Bridge Rules for loading (Min. of Railway)

    IRS – Code of practice for Steel bridges.

    IRS – Code of practice for plain, reinforcement and prestressed concrete for general Bridge construction, latest revision.

    IRS – Code of practice for the design of substructures and foundation of bridges. Indian Roads Congress (IRC) Standards (with Latest Revisions, Addendum &Corrections) IRC 5: 1985 Standard Specifications and Code of Practice for Road Bridges, Section I – General Features ofDesign IRC 6: 2000 Standard Specifications and Code of Practice for Road Bridges, Section II – Loads and Stresses IRC 10: 1961 Recommended Practice for Borrow pits for Road Embankments Constructed by ManualOperation IRC 18: 1985 Design Criteria for Prestressed Concrete Road Bridges (PostTensioned Concrete) IRC 19: 1977 Standard Specifications and Code of Practice for Water BoundMacadam IRC 21: 1987 Standard Specifications and Code of Practice for Road Bridges Section III – Cement Concrete (Plain and reinforced) IRC 22: 1986 Standard Specifications and Code of Practice for Road Bridges, Section VI – Composite Construction for RoadBridges IRC 24: 1967 Standard Specifications and Code of practice for Road Bridges, Section V – Steel Road Bridges IRC 36: 1970 Recommended Practice for the Construction of Earth Embankments for Road Works IRC 37: 1984 Guidelines for the Design of FlexiblePavement IRC 45: 1972 Recommendations for Estimating the Resistance of Soil below the maximum Scour Level in the Design of Well Foundations ofBridges IRC 48: 1972 Tentative Specifications for Bituminous surface Dressing using Pre-coated Aggregates IRC 75: 1979 Guidelines for the Design of HighEmbankments IRC 78: 2000 Standard Specifications and Code of Practice for Road Bridges, Section VII (Parts 1 and 2), foundations and substructure Standard Specifications and code of practice for Road Bridges, SectionIX – Bearings Part I & II: Bearings (Metallic and elastomeric) IRC 87: 1984 Guidelines for the Design and Erection of False Work for RoadBridges IRC: SP 11 1958 Handbook of quality Control for Construction of Roads and runways. IS: Codes: National building code SP 7: 1983 Bureau of Indian Standards IS 73: 1992 Paving Bitumen IS 215: 1995 Road Tar IS 217: 1988 Cutback Bitumen IS 226: 1975 Structural steel (standard quality) IS 269: 1989 33 grade Ordinary Portland Cement IS 278: 1978 Galvanised steel barbed wire for fencing IS 280: 1978 Mild Steel wire for general engineering purposes IS 281: 1991 Mild Steel siding door bolts for use with padlocks IS 383: 1970 Coarse and fine aggregates IS 432: 1982 Mild steel and medium tensile steel bars and hard-drawn steel wire for concrete reinforcement (Part 1) Mild steel and medium tensile steel bars (Part 2) Hard-drawn steel wire IS 455: 1989 Portland slag cement IS 456: 2000 Code of practice for plain and reinforced concrete IS 457: 1957 Code of practice for general construction IS 515: 1959 Natural and manufactured aggregates for use in mass concrete IS 516: 1959 Method of test for the strength of concrete IS 650: 1991 Standard sand for testing cement IS 800: 1984 Code of practice for general construction in steel structures IS 814: 1991 Covered electrodes for manual metal arc welding of carbon and carbon manganese steel IS 815: 1974 Classification coding of covered electrodes for metal are welding of structural steel IS 823: 1964 Code of procedure for manual metal arc welding of mild steel IS 875: 1987 Code of practice for design loads (other than earthquake) for buildings and structures IS 1077: 1992 Common burnt, clay building bricks IS 1080: 1986 Design and construction of shallow foundation in soil (other than the raft ring and shell) IS 1161: 1979 Steel tubes for structural purposes IS 1239: 1990 Mild steel tubes, tubular and other wrought steel fittings (Part 1) Mild steel tubes (Part 2) Mild steel tubular and other wrought steel pipe fittings IS 1322: 1993 Bitumen felts for waterproofing and damp-proofing IS 1343: 1980 Code of practice for Prestressed concrete IS 1489: 1991 Portland Pozzolana Cement IS 1732: 1989 Dimensions for round and square steel bars for structural and general engineering purposes IS 1785: 1983 Plain hard-drawn steel wire for prestressed concrete (Part 1) Cold-drawn stress-relieved wire (Part 2) As drawn wire FOREIGN STANDARDS ASTM D-297 Methods for Rubber Product Chemical Analysis ASTM D-395 Compression set of vulcanized rubber ASTM D-412 Tension testing of vulcanized rubber ASTM D-429 Adhesion of vulcanized rubber-metal ASTM D-573 Accelerated ageing of vulcanized rubber by the oven method ASTM D-624 Tear resistance of vulcanized rubber ASTM D-797 Young’s Modulus in flexure of elastomer at normal and subnormal temperature ASTM D-1149 Accelerated Ozone cracking of vulcanized rubber ASTM D-1559 Test for resistance to plastic flow of bituminous mixtures using Marshall Apparatus ASTM D-2166 Test methods for Unconfined Compressive Strength of Cohesive Soils ASTM 0-2172 Extraction, quantitative, of bitumen from bituminous paving mixtures ASTM 0-2240 Indentation hardness of rubber and plastic using a Durometer ASTM 0-2434 Test methods for the permeability of Granular Soils ASTM 0-3080 Method for the direct shear test of soils under consolidated drained condition ASTM E-11 Specification for wire cloth sieve for testing purpose AASHTO OM 57-80 Materials for embankments and sub-grade AASHTO OM 147-67 Materials for aggregate and soil (1980) base and surface courses AASHTO OM 282-80 Joints sealants, not poured, elastomeric type, (ASTM: D 3406) for Portland cement cure rate of pavements

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Asked: July 13, 2020In: Construction

What is the object of pointing? Describe the operation of pointing.

DevilAVRT
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What is the object of pointing? Describe the operation of pointing.

  1. nikeetasharma

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    Added an answer on September 30, 2020 at 6:49 pm

    Pointing :- It is the art of finishing the mortar joints in the exposed brick or stone masonry with suitable cement or lime mortar, in order to protect the joints from weather effects and also to improve the appearance of building structure. Pointing is a type of front of the house exposed finish onRead more

    Pointing :- It is the art of finishing the mortar joints in the exposed brick or stone masonry with suitable cement or lime mortar, in order to protect the joints from weather effects and also to improve the appearance of building structure. Pointing is a type of front of the house exposed finish on masonry work.

    Object of pointing :- The main object of the pointing is to maintaining the joints of the structures. Pointing being cheap can be adopted in places of low rainfall. Pointing gives resisting power to the bricks and stones used in construction towards weather conditions.

    Operation of pointing :-
    1. All the mortar joints (on the masonry face required to be pointed) are raked out by a special pointing tool to a depth of 15 to 20 mm, so as to provide an adequate key for the fresh mortar used for pointing.
    2. All the loose mortar and dust are removed by brushes.
    3. The joints and wall surface are washed with clean water, and then kept wet for few hours. The joints so prepared, are filled with suitable mortar with a small trowel.
    4. The mortar is well presses into the joints to form a close contact with the old interior mortar joints and all excess mortar sticking to the sides are scraped away.
    5. The finished pointing work is kept wet for about 3 days when lime mortar is used for pointing and for 10 days when cement mortar is used for pointing.

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Asked: July 7, 2020In: Construction

Can Infrared thermography be used to inspect cracks in a building?

Ancy Joby
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Can Infrared thermography be used to inspect cracks in a building?

  1. Komal Bhandakkar

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    Added an answer on September 7, 2020 at 5:38 pm
    Can Infrared thermography be used to inspect cracks in a building?

    Basically, infrared thermography is one of the non-destructive technique that measures the radiation emitted by bodies in the thermal infrared band of the electromagnetic spectrum.S Formation of cracks due to anomalies in the coating material or associated with the substrate elements. The diagnosisRead more

    Basically, infrared thermography is one of the non-destructive technique that measures the radiation emitted by bodies in the thermal infrared band of the electromagnetic spectrum.S


    • Formation of cracks due to anomalies in the coating material or associated with the substrate elements.
    • The diagnosis needs to establish the causes of cracks and identify the existing topography as well as the degree of damage.
    • The study indicates a strong dependence on the variations of surface temperature and sun incidence with no agreement about the criteria regarding the best time to make the thermographic inspection in day or night
    • The use of thermography to study cracks, detachment, and humidity are still being performed on an experimental basis.
    • Thermography is used to observe the location of cracks
    • Nowadays, the weather conditions in the country where the studies are being performed are an important variable in the process and results since they involve differentiation of heat flux for each study.
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Asked: July 10, 2020In: Construction

What are Refractory Bricks and mention it’s types?

Shivan
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What are refractory bricks and mention it’s types?

  1. nikeetasharma

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    Added an answer on October 8, 2020 at 9:40 pm

    A fire brick, firebrick, or refractory is a block of ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency. There are mainlyRead more

    A fire brick, firebrick, or refractory is a block of ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency.

    There are mainly three varieties of refractory bricks;

    a) Acid Refractories
    i. Ordinary Fire Bricks
    ii. Silica Bricks
    iii. Ganister Bricks

    b) Basic Refractories
    i. Magnesite Bricks
    ii. Dolomite Bricks
    iii. Bauxite Bricks

    c) Neutral Refractories
    i. Chromite Bricks
    ii. Carborundum
    iii. Chrome Magnesite Bricks
    iv. Spinal Bricks
    v. Forsterite Bricks

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Asked: July 17, 2020In: Construction

Can quarry dust be replaced with sand in concrete?

fathima
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Can quarry dust be replaced with sand in concrete?

  1. Komal Bhandakkar

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    Added an answer on September 8, 2020 at 11:13 pm
    Can quarry dust be replaced with sand in concrete?

    Yes, correct. Sand can be replaced by Quarry dust without any problem. Based on several references, I concluded that sand can be replaced by Quarry dust without highly compromising its durability property. By the experimental investigation, 40% replacement of sand with Quarry dust shows maximum compRead more

    Yes, correct.

    Sand can be replaced by Quarry dust without any problem.


    • Based on several references, I concluded that sand can be replaced by Quarry dust without highly compromising its durability property.
    • By the experimental investigation, 40% replacement of sand with Quarry dust shows maximum compressive strength and later on, it will decrease after increasing percentage of Quarry Dust in the sand.
    • Workability of concrete decreases as increasing the percentage of Quarry dust
    • Quarry dust is Waste. If we use quarry dust as a replacement of sand, then waste will ultimately reduce.

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Asked: September 25, 2020In: Construction

What is the correct procedure of designing surplus weir in irrigation?

nikeetasharma
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Give the correct procedure of designing surplus weir.

  1. aviratdhodare

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    Added an answer on September 28, 2020 at 11:36 pm

    Surplus weir (waste weir): It is a concrte or masonry structure constructed to dispose off excess water from an irrigation tank. It is a safety device in the tank. Full tank level (FTL): It is the highest level up to which water could be stored in the tank. Excess water will go out through the surplRead more

    Surplus weir (waste weir): It is a concrte or masonry structure constructed to dispose off excess water from an irrigation tank. It is a safety device in the tank.

    Full tank level (FTL): It is the highest level up to which water could be stored in the tank. Excess water will go out through the surplus weir. Fixation of this level depends on the availability/demand of water.

    Max water level (MWL): It is the max level of water allowed in the tank. MWL is higher than FTL. The difference between MWL & FTL is the spillage or head on crest of surplus weir Fixation of this level depends on the submergence of land due to back water.

    Tank bund level (TBL): It is the top level of the liqd of the bund & is equal to MWL + freeboard.

    Abutment: The walls that flank the edge of a weir and which support the banks on each side of the weir. The length of the abutment is generally kept same as the base width of weir. The top level of the abutment is kept at tank bund level.

    Wing wall: A wall on a weir that ties the structure into the bank in continuation of the abutments. Wing walls are provided both on the u/s and d/s sides on both the banks to ensure smooth entry and exit of water away from the tank.

    Return wall (Return): These are provided at right angles to the abutment at the end of wing wall and extend into the banks to hold the back-fill.

    Splay: Horizontal deviation of wall. Ex: 1 in 3, 1 in 5, etc.

    Batter: Vertical deviation of wall. Ex: 1 in 8, 1 in 12, etc.

    Hydraulic gradient, Saturation gradient (or) Seepage gradient: It is the head loss
    (energy loss) per unit length in the direction of flow traveled by water particle through soil. Ex: Saturation gradient 4:1, it means to dissipate energy of 1m, water should travel a distance of 4 m in the soil

    Catchment area(watershed area, drainage area, drainage basin or basin or
    catchment): It is a portion of land which catches the rain and produces runoff through a one outlet.

    Free catchment: Entire runoff in the catchment will be passed direct to tank. It means water from catchment area is not go to other tank or channels, and it should directly goes to one tank.

    Intercepted catchment: Part of runoff will be intercepted and stored by the u/s side tank(s) within the catchment.

    Combined catchment: Entire runoff in the catchment will be shared by group of tanks or a chain of tanks which comes under the same catchment.

    D/S Apron of the surplus weir: Depending upon the foundation particulars, and the levels of U/S and D/S ground at the location of the work, any one of the following types can be adopted.

    Type A → Horizontal masonry apron – when fall height < 75 cm

    Type B → Sloping apron

    Type C → Similar to B but with rough stone sloping

    Type D → Stepped apron – when fall height ⩾ 75 cm

    Location of surplus weir: It is desirable to locate the surplus weir at or near the flank of the tank bund and connected to it, and also at a place where it is possible to drain the surplus waters below the work away from the tank bund falling into its natural watercourse. The cost of works should be minimum.

    Design a surplus weir for a minor tank forming a group of tanks with the following data:
    Combined catchment area                                                      = 25.89 km2 (35 km2)
    Intercepted catchment area                                                   = 20474 km2 (10 km2)
    Top width of the bund                                                             =2m (2m)
    Side slopes of the bund                                                           = 2:1 both sides (2:10n both sides)
    Top level of bund                                                                      = +1450 (+ 12.50)
    Maximum Water Level (MWL)                                             =+ 12.75 (+ 10.75)
    Full Tank Level (FTL)                                                              = + 12.00 (+ 10.00)
    General ground level at the site                                             =+ 11.00 (+ 9.00)
    Ground level slopes off to a level in about 6 m distance) = + 10.00 (+ 8.00 in about 6 m dist)
    The foundations are of hand gravel                                      = + 9.50 (+ 7.50)
    Saturation gradient                                          = 4:1 with 1 m clearcover (4:1 with 1m clearcover)
    Provision is to be made to store water up to MWL in-times of necessity

    Components to be designed

    (1) Estimation of flood discharge entering the tank (Q) :
    Combined catchment area (M) # 25.89 km2
    intercepted catchment area (m) = 20.71 km2
    Assuming Ryve’s coefficient(C) =9 and c = 1.5
    Flood discharge (Q) = CM2/3 – cm2/3
    Q = 9 (25.89)2/3 — 1.5 (20.71)2/3 = 78.77 — 11.32
    Q = 67.45 m3/s

    (2) Length of surplus weir (L):
    Assuming the flow over a surplus weir is identical to that of flow over a rectangular weir then discharge is given by Q = 2/3 CdL √2g h3/2
    where, Q = 67.45 m3/s, cd = 0.562 (assuming), g = 9.841 m/s2
    h = MWL – FTL = 12.75 — 12.00 = 0.75 m, L — Length of the water way
    67.45 = 2/3 x 0.562 x L √2×9.81 (0. 7s)3/2 → L=62.75 m ≈ 63.00 m (say)
    Since temporary regulating arrangements are to be made on top of weir to store water at times of necessity.
    The dam stones of size 15 x 15 x 125 cm are at 1m clear internals keeping top of the stone at M.W.L.
    The no. of openings will be = 63, The no. of dam stones required = 62
    ∴ The overall length of surplus weir between abutments = 63 + (62 x 0.15)
    = 72.30 m
    However, provide an overall length of 75 m.

    (3) Height of the weir (H):
    Crest Level = FTL = +12.00
    Top of dam stones (top of shutters) = M.W.L = + 12.75
    Ground level = + 11.00
    Hard soil at the foundation is + 9.50.
    However, taking foundations about 0.50 m deep into hard soil and fix up foundation level at + 9.00
    Assuming foundation concrete is 60 cm thick
    Top of foundation concrete = + 9.60
    Height of weir above foundations (H) = 12.00 – 9.60 = 2.4m

    (4) Crest width of weir (a):
    a = 0.55 (√H + √h) = 0.55(√2.4 + √0.75) = 1.3m

    (5) Base width of weir (b):
    The base width is determined based on moment considerations. i.e., based on the magnitude of stabilizing and destabilizing moments.
    Stabilizing moments are caused by self weight of the weir which is given by
    M = γw /12 = [{(G+15)H + 2.5S}b2 + a(GH – H – S)b – ½a2 (H +3S)]
    Where, γw = Unit weight of water = 1000 kg/m3
    G = Specific gravity of masonry = 2.25
    H = Height of the weir = 2.40 m
    a = Crest width of weir = 1.30 m
    b = Base width of the weir = ?
    S = h = height of shutter above weir crest = 12.75 – 12.00 = 0.75 m
    Destabilizing moments (M,)
    Mr = γw (H + S)3 / 6
    Equating both the moments: M,=M
    Mr = (2.4 + 0.75)3 / 6 = 1 /12 [{2.25 + 1.5)2.4 + 2.5 x 0.75} b2 + 1.3 (2.25 x 2.4 – 2.4 – 0.75)b – ½ (1.3)2 (2.4 + 3 x 0.75)]
    Solving, b = 2.4 m

    (6) Abutments, Wing walls and Returns:
    The top width of abutments, wing walls & returns will all be uniformly 0.50 m with a front batter of 1 in 8. Diag in attachment.
    Abutment (AB)
    Length of the abutment = width of bund = 2m
    The top level of the abutment is kept at TBL = + 14.50
    Bottom level of the abutment = top of foundation level = + 9.60
    Height of the abutment = 14.50 — 9.60 = 4.90 m
    Bottom width= 0.4 x height = 0.4 x 4.90 = 1.96 m = 2.00 m (say)
    Top width 2 0.5 m (assuming), Front batter = 1 in 8
    Wing walls:
    U/S Wing Wall:
    BD is called u/s wing wall
    Section at B:
    Same as the section of abutment
    Wing wall from B to C is sloping and
    Top level of C = M.W.L + 30 cm = 12.75 + 0.30 = 13.05
    Section at C:
    Top Level at C = 13.05
    Bottom level = 9.60
    Height of wing wall = 13.05 – 9.60 = 3.45 m
    Bottom width = 0.4 x height = 0.4 x 3.45 = 1.38 = 1.40 m (say)
    Top width from B to C is the same as 0.5 m.
    But, bottom width gets slowly reduced
    from 2.00 m at section at B to 1.40 m at Section C:
    From C to D wing wall is horizontal. Therefore, Section at D = Section at C
    U/S Return (DE):
    Section at E = Section at D
    U/S transition:
    In order to give an easy approach, the u/s side wing wall may be splayed at 1 in 3.
    D/S wing wall:
    AF is called d/s wing wall.
    Section at A: Same as the section of abutment. The Wing wall from A to F will slope down till the top reaches the ground level at F.
    Section at F:
    Top of wing wall at F = + 11.00
    Bottom of wing wall = + 9.60
    Height = 11.00 – 9.60 = 1.40 m
    Bottom width = 0.4 x 1.4 = 0.56 m
    However, provide a minimum of 0.6 m
    D/S return (FG):
    The same section at F is continued for FG also
    D/S transitions:
    Provide a splay of 1 in 5.

    (7) Aprons of the weir:
    i). U/S Apron: Though apron is not required on the u/s side of the weir, a puddle clay apron is usually provided to minimize the seepage under the weir.
    ii).D/S Apron: Since the ground level is falling down to +10.00 in a distance of about 6m. Then, the fall is (12.00 – 10.00) = 2.00 m > 0.75 m therefore provide a stepped apron (Type D) Diagram in attachment. The stepping may be done in two stages.
    (a) The length of the Apron: The length of the apron should be adequate to avoid piping problem.
    [Maximum uplift will be occurred when water level on U/S is up to top of dam stone (M.W.L.) and no water on D/S (+10.00))
    Max. Uplift head = 12.75 – 10.00 = 2.75 m (max. energy to be dissipated)
    Assuming a hydraulic gradient of 1 in 5
    The length of the creep required = 2.75 x 5 = 13.75 m
    The length and thickness of apronts to be designed.
    The length of the creep = AB + BC + CD + DE + EF = 1.40 + 0.60 + 3.00 + DE + 1 (Assuming EF = 1 m)
    This length should not be less than 13.75 m, if the structure is to be safe.
    13.75 = 1.40 + 0.60 + 3.00 + DE + 1 → DE = 7.75 m = 8.0 m (say)
    Provide total length of solid apron ts 8 m.
    First step in 3 m and second step in 5 m length.
    (b) Thickness of solid apron: The maximum uplift on the apron is felt immediately above the point D. (i.e., at point K)
    Assuming the thickness of apron at point K = 80 cm = 0.80 m.
    Then the level of K = 11.00 – 0.80 = 10.20
    The length of the creep from A to K = 1.4 + 0.6 + 3 + 0.6 + (10.20 – 9.60) = 6.20 m
    Head loss in percolation along the path up to the point K = 6.20/5 = 1.24 m
    Residual head exerting uplift under the apron at point K = 2.75 – 1.24 = 1.51 m
    Thickness of apron required = Residual head / Sp. gravity = 1.51/2.25 = 0.67 m
    Provide 20% of more thickness as a safety
    Then thickness of apron required = 0.80 m
    So, provide the first solid apron as 80 cm thick.
    The second apron can be similarly checked for a thickness of 50 cm.

    8) Talus: At the end of d/s side apron, a nominal 3 to § m length of Talus (i.e., rough stone apron) with a thickness of 50 cm may be provided as a safety mechanism.

     

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