BY ROUTHU SATYANARAYANA

CHIEF ENGINEER (Retd.)Former Advisor (Designs), and Member Technical Advisory Council

GOVERNMENT OF A.P

Andhra Pradesh Human Resources Development InstituteInduction Training Programme to Newly Recruited AEEs

7th September 2017 at ETC, Srikalahasti

Design of Concrete and Masonry Dams

HYDRAULIC DESIGN STRUCTURAL DESIGN

DESIGN CRITERIA

HYDROLOGY

HYDROLOGY – DESIGN CONSIDERATIONS

➢ Every Artificial Storage Is Potential Hazard To Downstream Life And Property And Cause Upstream Submergence

➢ An Important Function Of The Flood Disposal Is To Reduce The Hazard To Negligible Or Acceptable Level

➢ Choice Of Dam● Solid Masonry/Concrete Dam Is More Permanent● But Adoptability Limited By The Foundation Strength ● Earth Dams Are More Suitable For Locations Rock Is Met

With At Greater Depths.

HYDROLOGY – DESIGN CONSIDRATIONS

➢ Probable Maximum Flood (PMF)The Flood That May Be Expected From the Most Severe

Combination of Critical Metrological and Hydrological Conditions That Are Reasonably Possible in the Region. It is Computed Using the Probable Maximum Storm (PMS) Which Is the Upper Limit

➢ Standard Project Flood (SPF)It Is Computed Using the Standard Project Storm (SPS)

Ignoring the Very Rare Storms

➢ Return Period FloodA Flood With a Return Period of “T” Years

DESIGN PARAMETERS

➢ Full Reservoir Level (FRL)

➢ Maximum Water Level (MWL)

➢ Minimum Draw Down Level (MDDL)

➢ Free Board

➢ Storage Characteristics / Reservoir Geometry

➢ Spillway Capacity

➢ Tail Water Rating Curve

➢ Sedimentation 100 yearsContinued …

HYDRAULIC DESIGN ➢ Design Of Overall Dimensions & Profiles

For Satisfactory Hydraulic Performance Of Head Works

● Water Way / Spill Way● Spillway Profile ● Energy Dissipation● Foundations ● Uplift Pressure● Internal drainage & galleries● Protection Works continued…

HYDRAULIC DESIGN ➢ Spillway Capacity depends on Inflow flood &

capacity of downstream channel● Designed for two floods (Intensities) : with

and without 10% gates inoperative conditions● Large floods of 25 years close succession and● SMF/ PMF By providing● Breaching section● Auxiliary spillway● Flood routing● Pre-depletion and● Surcharge storage continued…..

HYDRAULIC DESIGN ● Shape Of The Spillway:

• Similar To The Nap Substituting The Sharp Crest

• To A Jet Corresponding To The Maximum Flood

• D/S Face Usually Curved At The Base To Reduce Erosion

• Coefficient Of Discharge Depends On:• Shape Of The Crest• Depth Of The Over Flow• Depth Of Approach• Tail Water Level And Submergence Of Tail Water

• Inclination of Upstream Face

➢ Energy Dissipation ● Selection Of Dissipater Based On

• Head • Discharge Intensity• Tail Water Level• Velocity & Froud’s Number• Bed Rock / Bed Material

● Hydraulic Jump Type Of Stilling Basin Is Preferred In Alluvial Soils To Confine Dissipation Within

➢ Energy Dissipation ● Type Of Energy Dissipaters

• Hydraulic Jump Type Stilling Basins● Horizontal Apron Type● Sloping Apron Type

• Bucket Type Dissipaters● Solid Roller bucket And Slotted Roller Bucket● Trajectory Bucket

• Jet Diffusion & Free Jet Stilling Basins

Continued …

➢ Energy Dissipation

• Hydraulic Type Of stilling basin● Kinetic energy causes turbulences and is ultimately

lost as heat energy• Provided on week bed rock, clays & loose gravel• Stilling basin level least 300mm below d/s bed level

• Basin length 5 to 6(D2-D1)• Appurtenances, chute blocks, basin blocks & end sill

• Basin I – Froude number more than 4.5 and velocity less than 15m/s

• Basin II – Froude number more than 4.5 and velocity more than 4.5m/s

Continued …

Energy Dissipation • Solid roller bucket and slotted roller type of energy dissipaters

● Sound rock to with stand higher velocities ● Tail water depth in excess of sequent depth● Energy dissipation occurs due to formation of two

complementary elliptical rollers.● Surface rollers (anticlockwise) in bucket proper● Ground rollers (clockwise) on the d/s of bucket● Bed d/s side of the bucket to be lowered 1.5m

below lip level for a length of 15m to minimize the churning action of ground rollers and joined to original bed with a slope of 1:3

Continued …

➢ Energy Dissipation • Solid roller bucket and slotted roller type of energy dissipaters

● All the gates of the spillway to be operated equally ● The velocity entering the bucket 20m/s● Discharge per meter width exceeds 45cumecs● To design the bucket invert level, radius of bucket and the

lip angle● Bucket lip width 1.0m and with d/s slope of 1in 10● Minimum concrete thickness 1.5m above foundation grade ● Reinforcement 20mm/16mm at 300mm● Anchor bars 25mm dia 3.0m long at 1.5mm staggered● Lateral spreading of jet will occur in slotted roller bucket.

Continued …

Energy Dissipation • Trajectory bucket type of energy dissipaters

● Tail water depth is insufficient for formation of hydraulic jump.

● Sound rock to withstand the impact and high velocity jet ● The velocity entering the bucket 10 to 45m/s● Very little energy dissipation with in the bucket.● The energy is imparted to the channel bed below● Design of the bucket pre-supposes formation of large

craters or scour holes at the zone of impact of jet initially● To design the bucket invert level, radius of bucket and the

lip angle● Bucket lip width 1.0m and with d/s slope of 1in 10 bucket.

Continued …

Energy Dissipation • Trajectory bucket type of energy dissipaters

● Lip level above tail water level● Bucket invert elevation close to bed level to form ground

roller ● Sufficient straight reach down stream● Concrete apron for 15m d/s bed and concrete the loose

pockets further down stream ● Provide training wall 10m beyond end sill & 1.5m above

TWL● Minimum thickness 1.5 m above foundation grade● Anchor anchors 25mm .3.0m long at 1.5m c/c staggered● reinforcement 20mm/16mm at 300mmc/c.

…

FOUNDATION • The area under and adjacent to dam, affected or be affected by

loading, scour, or leakage, and a good foundation to:● Ample strength to withstand the weight of the structure● Prevent sliding ● Tight enough to prevent excessive leakage● Uplift must be reduced as much as possible● To pass discharge from spillway and out lets without any

damage down stream sidePrevention of uplift by:● Consolidation grouting● Grout curtain on upstream face● Adequate drainage arrangements etc.,

…

TYPICAL LAYOUT

STRUCTURAL DESIGN – GRAVITY DAM➢ Stability Is Checked Against

● Sliding ● Overturning ● Unit Stress In Concrete & Foundations

➢ Designed To Resist Following Forces & Moments ● Dead Loads● Live Loads Due To Road Way● Impact & Braking Forces● Temperature Forces● Dead & Live Loads Due To Gates, Stop Logs Etc.

Continued …

➢ Designed To Resist Following Forces & Moments ● Wind Forces● Buoyancy / Uplift● Differential Hydro-static Pressure● Seismic Forces● Hydro Dynamic Forces● Water Pressure On Closed Gate● Wave Pressure● Thermal Loads● Silt Loads

➢ Designed For Following Load Combinations

● A – Construction Condition – Dam Completed

But No Water On U/S & D/S

● B – Normal Operating Condition - FRL

Condition Dry Weather Tail Water, Normal

Uplift, Ice And Silt

● C – Flood Discharge Condition – MWL

Condition, All Gates Open, Full Tail Water

Level, Normal Uplift And Silt

➢ Designed For Following Load Combinations

● D – Combination A with earth quake.

● E - Combination B with earth quake but no ice.

● F - Combination C , but with extreme uplift.

● G - Combination E, but with extreme uplift

➢ Divide walls

● Provide to separate different type or different

levels of energy dissipation.

● Top width not less than 1.5m

● Minimum depth of anchorage thickness of divide

wall

● Minimum steel 20mm dia at 250 c/c both ways

➢ Galleries

● Provided for all dam heights more than 10m● Minimum size 1.5m x 2.5m, normal 2.0m x 2.5m● Located 3.0m away from upstream face and● Minimum 1.5m concrete cover over foundation

grade● Inspection gallery at every 30m height● 300mm dia ventilation shaft at every alternate block● 200mm dia formed drain at every 3.0m spacing

➢ Concrete Mix Design● Selection Best Combination Of Ingredients To

Produce Desirable Properties Of Fresh And Hardened Concrete

● With Adequate, But Not Excessive Workability (W/C)

● Compressive Strength And Durability● Other Factors Effecting:● Size, Shape, And Grading Of Aggregate● Quality And Quantity Of Cement● Water● Batching And Transportation & Placement● Compaction And Curing.

TABLE I

Minimum cement content, max. w/c ratio And min. grade of concrete of different

exposeres with normal weight of aggregates of 20mm nominal maximum size

Sl no. Exposure

Plain concrete Reinforced conctrete

min. c.c max. w/c min. gr. min. c.c max.w/c min. gr

kg/cum of cement kg/cum of cement

1 2 3 4 5 6 7 8

1 Mild 220 0.60 - 300 0.55 M20

2 Moderqate 240 0.60 M15 300 0.5 M25

3 Severe 250 0.50 M20 320 0.45 M30

3 Very severe 260 0.45 M20 340 0.45 M35

4 Extreme 280 0.40 M25 360 0.4 M40

TABLE II

Adjustment to minimum Cement contents for aggregates other than 20mm nominal maximum size

Sl no. Nominal max. aggregate size Adjustment to min. cement content in tabl. 1

mm kg/cum

1 10 40

2 20 0

3 40 -30

➢ Construction Foundation ● Much More Is Learnt During Construction Than At Design

Stage● Foundation Exploration Is A Continuous Process● Last 500mm, Just Before Concreting ● No Blasting With In 30m● Foundation Slope Upwards Down Stream Direction● Surface Cleaning And Roughening By High Velocity Air

Water Jet, Wet Sand Blasting, Stiff Broom, Pickers Etc.,● Concrete Mix Design On Strength Requirement● Max. Height Of Single Pour 2m In Layers Of 50cm.● Difference In Level Of Adjacent Blocks Not Exceeding 10● Crest Surface Irregularities Not Exceeding 6mm

Continued..

➢ Construction Foundation ● Pouring Temperature Of Concrete 15 To 20

Centigrade ● Concrete Poring From D/S To U/S● Avid Cold Joints, Provide Anchor Bars If Necessary● Anchor Hole Size 1.5 Times The Diameter Of Bar● Avoid Excessive Vibration ● Contraction Joint Spaced At 15-25m C/C● Grouting –To Fill Openings To Render Impervious,

To Improve Strength, Elasticity And Form Curtail Flow From U/S To D/S

➢ Construction Supervision ● Relationship With A Contractor Is A Very Important For

Success Of A Project● Unwise To Award Contract To A Price Much Below The

Price Estimate. In Such Case Examine The Bid Carefully● Once Work Awarded, Utilize All His Experiences And

Judgment To Help Contractor Plans And Economic Methods Of Construction

● While Extending All Assistance, Specific Procedure To Do The Job Left To The Contractor

● Not To Insist Arbitrarily To Do The Job In One Way Only

Continued…..

➢ Construction Supervision ● Engineer In Charge To Obtain Well In Advance Each Phase

Of Construction Plan Schedules To Carry Out The Work● Lack Of Co-operation Or Antagonism Between The Two

Result In Unnecessary Delays And Higher Costs

HYDRAULIC MODEL STUDIES

➢ Two & Three Dimensional Model Studies Shall Be Carried Out To Confirm The Hydraulic Performance Of The Waterway, Layout, Distribution Of Flows & Sufficiency Of Protection Works

THANK YOU

CONSTRUCTION QUALITY FAILURE, ANALYSIS & EFFECTIVE RECTIFICATIONS

IN IRRIGATION PROJECTS

➢ CASE STUDIES● Foundation Failures

● Structural Failures

● Failures During Maintenance

BUGGAVANKA PROJECT ➢ A Medium Irrigation Project Near Cudappah Town (AP)➢ Constructed Across Buggavanka➢ Command Area - 5953 Ha (12,850 Acres)➢ Construction Period - 1986 – 1998➢ Capacity Of Reservoir - 14.32 M Cum (0.505TMC).➢ 57m Long Ogee Spillway - 4 Nos. x 12m x 6m Radial Gates➢ Maximum Flood Discharge - 929 Cumecs (32,800 c/s)➢ Spillway Crest Level - + 180.00 m➢ Full Reservoir Level - + 186.00 m➢ Road Level - + 189.00 m➢ Right Side NOF (Masonry) - 93m➢ Earth Dam - 1320m On Left & 590m On Right

➢ Reservoir First Impounded During October’ 1998

POSSIBLE CAUSES OF DISTRESS – SPILLWAY & NON OVERFLOW SECTION

➢ Curtain Grouting / Pressure Grouting Was Not Carried Out In

Drainage Gallery Portion

➢ Drainage Holes Were Not Provided

➢ Curtain Grouting Was Not Extended Into Core Wall Junction

Of Spill Abutment And Earth Dam

OCTOBER 2001 FLOODS➢ Heavy Precipitation Was Received In The Catchments Of

Buggavanka & Mulavagu (A Tributary Of Buggavanka)

➢ Heavy Devastation Occurred In Cuddappah Town & Many

Deaths Were Reported

➢ The D/s Side Protection Works Were Damaged & Deep Scours

Observed On D/s Side Of Spill Channel

➢ Hydraulic Jumps Moved Out Of Stilling Basin & Shooting

Flows Observed On D/s Side

OCTOBER 2001 FLOODS

➢ Further Detailed Investigation

● Bore Holes Were Drilled At 200m C/C Along The Center Of The

Dam & Logged

● Permeability Tests Were Conducted Below COT At Every 3m

Depth Intervals Upto The Depth Where The ‘K’ Value Is Observed

To Be Less Than 5 Lugions

● ‘V’ Notches Established Along The Toe Drain

● Seepage Through The Earth At Various Locations With Reference

To Reservoir Levels Were Noted & Plotted On A Graph

● Hydraulic Model Studies (Geometric Mode) Carried Out On The

Spillway At APERL (Hyderabad)

FINDINGS & REMIDIAL MEASURES

➢ SPILLWAY● The Maximum Flood Discharge Of 1053 cumecs Through Spillway

Was Observed Against The Designed Flood Discharge Of 949 cumecs

● The Spillway Was Provided With One Extra Gate (3+1)● Spillway Was Adequate To Handle 100 Yrs Return Flood● Curtain Grouting (Pressure Grouting) Was Carried Out Through

Foundation Gallary● Drainage Holes Drilled And Pumps Installed To Pump Seepage

Water● 3 D Model Studies Indicated Inadequate Energy Dissipation &

Recommended Secondary Stilling Basin Of 40m Length● Surplus Channel Was Excavated Upto 1 Km Length To Dispose

1134 cumecs (40,000 cusecs) Of Discharge

FINDINGS & REMIDIAL MEASURES

➢ Authors Visit To Dam Site In March’ 2006

● Grouting Along The Earth Dam Was Completed Between Chainage 600m

And Chainage 1320m Including Core Wall

● The Reservoir Level Was At +179m, One Meter Below Crest

● The Entire D/s Side Of Spill Channel, D/s Of Return & Toe Drain Of Earth

Dam Were Observed To Be Dry

● The Seepage Was Quite Visible On The Ungrouted Reaches

● Bubbling Effect Had Completely Disappeared

● The Reservoir Did not Receive Any Water In 2006

BV PROJECT SPILLWAY

Stilling Basin Extension

PANNA AHOBILA BALANCING RESERVOIR (PABR) – TBPHLC (STAGE-II)

➢ Constructed Across Pennar➢ District - Ananthapur➢ Gross Reservoir Capacity - 11.10 TMC➢ Net Capacity Of Reservoir - 10.77 TMC➢ 103.54m Long Spillway - 7Nos. x12.23mx8.6m Radial Gates➢ Maximum Flood Discharge - 4596 Cumecs (1,62,310 c/s)➢ Spillway Crest Level - + 434.34 m➢ Water Spread - 27.56 SqKm➢ Length Of NOF - 331.46m➢ Length Of Earth Dam - 2060 m

➢ Construction Started In 1979 & Completed In 1994

PANNA AHOBILA BALANCING RESERVOIR (PABR) – TBPHLC (STAGE-II)

➢ Construction Of Spillway & NOF Blocks Stopped Intermittently In 1982, With Each Block At Various Levels

➢ Works Resumed In 1988-89, After A Span Of 7 Years

➢ The Delay & Long Gap Led To Cold Joints

➢ Impounding Of Water Started First Time From Nov’ 1993

OBSERVED DISTRESS – Non Over Flow Dam➢ Leakage Was Observed On The D/s Face Of Spillway & NOF.

➢ Cement Slurry Grouting Under Pressure Was Taken Up In

Spillway & NOF Blocks 6 & 9 During November 94.

➢ During January 1995, Heavy Leakage Was Observed On D/s

Side Face Of The NOF In Blocks 6 To 12 And Drain Gallery

Through Porous Pipes.

PABR DAM

NOF Section

PABR DAM

NOF Section

FINDINGS – NOF DAM

➢ Leakage Points Were Observed In NOF At Various Locations

➢ In Addition Small Jets Of Water At The Penstock Anchor Block

Were Observed

➢ Leakage Was Observed On D/s Face Of Spillway At The Junction

Of The Pier

PABR LEAKEGES IN NOF

PABR LEAKAGES IN NOF

FINDINGS - SPILLWAY

➢ Leakage Was Observed On Lower Tangent Point Of Spillway

Bucket In Block 17

➢ Small Seepage D/s Face Of Blocks 19th Part To 25 And The Entire

D/s Face Below +426.00m

➢ Leakages In Foundation Gallery

➢ Gushing Of Water Through Porus Concrete Drainage Pipes &

Foundation Drains

➢ At Joints Of 10,11,& 12th Block Water Was Observed To Be

Gushing Through U/s Face

EXPERT COMMITTEE – REMIDIAL MEASURES

➢ A Committee Was Constituted By Govt. Of AP To Suggest

Remedial Measures & Monitor The Work

➢ After Detailed Examination, Committee Suggested Remedial

Measures

● Curtain Grouting Was Proposed Through Foundation Gallery Of Spillway &

NOF

● Drainage Holes Drilled & Drainage Connected

● Cement Slurry Grouting Was Proposed Through The Body Of The NOF,

1.5m Away From U/s Side Face

● Grout Holes (Primary) To Be Drilled At 3m Intervals

● Secondary Holes 1m Away On D/s At 3m Intervals Staggered & Grouted

● Test Holes Were Suggested At 10% Of The Holes

EXPERT COMMITTEE – REMIDIAL MEASURES REVIEW

● Work Executed Between 2002-2005

● Water Stored Upto Crest Level, I.e. +434.34m

● Water Jets Completely Stopped

● Wetting Is Noted At One Or Two Places

● Jetting Is Observed At Lower Tangent Point Of Spillway In

Block 17

● Tin Sheet Of Seepate Noted On RNOF Between 19 & 25th

Block Below +430.00m

● Treatment Incomplete

THANK YOU