1

Design of Rubble Mound Seawall

A THESIS

Submitted in partial fulfillment of the requirement for the award of degree of

MASTER OF TECHNOLOGY IN DREDGING AND HARBOUR

ENGINEERING

BY

SHAILESH SHUKLA

Under the guidance of

K. Muthuchelvi Thangam Scientist B

INDIAN MARITIME UNIVERSITY

VISAKHAPATNAM 530005

DATE: 06.12.2013

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DECLARATION

I hereby declare that the work described in this thesis has been carried out entirely by me in the

school of Naval Architecture and Ocean Engineering, Indian Maritime University, Visakhapatnam

campus and further state that it has not been submitted earlier wholly or in part to any other

University or Institution for the award of any degree or diploma.

SHAILESH SHUKLA

3

Indian Maritime University

Visakhapatnam campus

CERTIFICATE

This is to certify that the thesis entitled Design of Seawall submitted by SHAILESH SHUKLA

to the Indian Maritime University for the award of the degree of Masters in Technology is a bonafide

record of project work carried out by his/her under my supervision. The contents of this thesis, in

full or in parts have not been submitted to any other institute or University for the award of any

degree or diploma.. In our opinion, the thesis is up to the standard of fulfilling the requirements of

the Masters degree as prescribed by the regulations of this Institute.

The project has been carried out at Indian Maritime University, Visakhapatnam.

K. Muthuchelvi Thangam External Guide

Project Guide

Scientist B

SMDR

IMU, VISKHAPATNAM

Place: Visakhapatnam

Date: 06.12.2013

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ACKNOWLEDGEMENTS

First of all, I thank Almighty GOD for showering his blessings without which all my efforts would

have been in vain. I wish to express my heartfelt gratitude and indebtedness to our Director Sir for

the facilities provided to successfully carry out this project. I sincerely thank my project guide Mrs.

Muthuchelvi Thangam for her encouragement, support and sincere guidance.

Last but not least, I express my sincere thanks to my classmates and friends for their co-operation

and encouragement.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS 4

TABLE OF CONTENTS 5

LIST OF FIGURESAND TABLES 6

CHAPTER -1 INTRODUCTION 7

1.1 PROBLEM DEFINITION 7

1.2 AIM AND OBJECTIVE 7

1.3 PLAN OF WORK 8

CHAPTER -2 INTRODUCTION TO SEA WALLS 9

CHAPTER -3 DESIGN PRINCIPLES 19

CHAPTER -4 DESIGN OF SEAWALL 25

REFERENCES 31

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List of Figures

Figure Figure no. Page no.

Site location 1.1 7

Vertical and curved seawall 2.1 11

Types of seawall 2.2 11

Action of waves on seawall 2.3 12

Failure of vertical seawall 2.4 13

Location of seawall b/w high

and low water

2.5 14

Seawall with toe protection 2.6 15

Filler layer damage 2.7 15

Overtopping of waves 2.8 16

Pockets in armour layer of a

Seawall

2.9 17

Seawall layout 3.1 24

Proposed seawall location 4.1 25

Proposed area in 2003 4.2 25

Proposed area in 2013 4.3 26

Significant wave height 4.4 26

Mean wave period 4.5 27

Modal of seawall 4.6 30

List of Tables

Table content Table no. Page no.

Table for KD 3.1 21

Table for K 3.2 22

Table for Total weight of the

structure

4.1 29

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CHAPTER 1

INTRODUCTION

1.1 PROBLEM DEFINITION

The Earths climate system is changing. All aspects of the climate are affected, including

temperature, ocean levels and rainfall patterns. The global average temperature is rising, mostly due

to increased greenhouse gas concentrations stemming from use of fossil fuels and land clearing. Sea

level rise creates an issue worldwide as it raises both the mean normal water level and the height of

waves during extreme weather events. Sea level rise increases the risks coastal communities face

from coastal hazards such as floods, storm surge, and chronic erosion. Coastal erosion is already

widespread, and there are many coasts where exceptional high tides or storm surges result in

encroachment on the shore, impinging on human activity. If the sea rises, many coasts that are

developed with infrastructure along or close to the shoreline will be unable to accommodate erosion.

An upside to the strategy is that moving seaward (and upward) can create land of high value which

can bring the investment required to cope with climate change. Sea walls are probably the second

most traditional method used in coastal management.

1.2 AIM AND OBJECTIVE

The aim of the project is to prevent destruction of property by the sea waves during high tides by the

construction of a seawall. The project involves design of 1550 m long seawall at the area where the

habitat is prone to coastal hazard here in this case is coastline near Alappuzha(Kamalapuram),

Kerala.

Fig 1.1: Site location (Source: Google Earth)

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1.4 PLAN OF WORK

Plan of work here involves choosing the right appropriate location for the construction of seawall, a

place close to habitat and infrastructure where sea is making advancement and beach is getting

depleted. Upon selection the location the requisite data of the area required for the designing of the

seawall is to be obtained. Keeping in mind the design procedure and criteria the data is processed to

design a seawall.

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CHAPTER 2

INTRODUCTION TO SEA WALLS

2.1 SEA WALLS:

2.1.1 DEFINITION

A seawall is a structure built on the beach parallel to the shoreline. Seawalls can be large or small,

high or low, and constructed of a range of materials including wood, plastic, concrete, rock,

construction rubble, steel, old cars, aluminum, rubber tires, and sandbags.

2.1.2 THE PROBLEM: COASTAL BUILDING AND SHORELINE EROSION

Shoreline erosion is the term used to describe the natural process of shoreline retreat where the

beach changes its location but retains its shape. The problem arises when shore line retreat meets

human obstacles, such as houses, highways, the seawalls placed to protect those houses and

highways. These obstacles block shoreline retreat; the beach is squeezed up against these objects,

which causes it to narrow and leads to a reduction in sand supply to adjacent beaches.

When coastal buildings or roads are threatened, the typical response is to harden the coast with a

seawall. Seawalls run parallel to the beach and can be built of concrete, wood, steel, or boulders.

Seawalls are also called bulkheads or revetments; the distinction is mainly a matter of purpose. They

are designed to halt shoreline erosion caused primarily by wave action. If seawalls are maintained,

they may temporarily hold back the ocean from encroaching on shoreline development. In spite of

their ability to hold back the ocean, when waves hit a seawall, the waves are reflected back out to

sea, taking beach sand with them and eventually causing the beach to disappear. Moreover, seawalls

can cause increased erosion at the ends of the seawall on an adjacent beach that is not walled.

2.1.3 SEAWALLS EFFECTIVENESS

Seawalls, if properly engineered and constructed for a particular situation, are effective at saving

beachfront property, provided the severe disadvantages they impose are acceptable. They can be

effective in protecting beachfront property from a retreating shoreline and, if high enough and strong

enough, can protect a backshore area against the onslaught of storm waves. They may retain a low

fill, but they are intended primarily to withstand and to deflect or dissipate wave energy. If a

communitys only priority is to preserve beachfront buildings then seawalls will effectively

accomplish that goal. Seawalls protect only the land immediately behind them, offering no

protection to fronting beaches.

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2.2 CLASSIFICATION OF SEAWALLS

Seawalls can be classified as:

Rigid

Flexible

Semi-flexible.

2.2.1 RIGID

A rigid seawall could be a gravity wall, sheet piling, a caisson or a concrete revetment. They have a

compact nature with a minimum plan area with the tendency not to harbour rubbish. However, they

can fail by a single large wave, toe erosion (undermining) or geotechnical instability (overturning) -

catastrophically. Mostly rigid seawalls tend to be highly reflective to incoming waves which can

result in accelerated sand loss in front of the wall during a storm, and delay beach rebuilding

following a storm. To protect the foundations of a rigid seawall from undermining, rock scour

blankets, gabions, etc. can be used. It is also possible to found the structures at depth on non-erodible

materials. However, theres a general tendency away from rigid structures due to their cost and risk

of catastrophic failure.

2.2.2 FLEXIBLE

Flexible seawalls are constructed from quarry rock, shingle and specially manufactured concrete

units. They are not as compact as rigid seawalls but they can withstand striking deformation without

total failure occurring. The failure is progressive rather than catastrophic. Flexible seawalls are also

less reflective than rigid structures. A disadvantage is the tendency to harbour rubbish because of the

broken nature of their surface.

2.2.3 SEMI-FLEXIBLE

A combination of the characteristics of rigid seawalls and flexible seawalls are the semi-flexible

seawalls. They are compact but may not fail as easy as rigid seawalls

2.3 TYPES OF SEA WALLS:

2.3.1 CURVED SEAWALLS

Curved seawalls mirror the shape of a wave as it moves towards land. The sweeping design

dissipates the impact of the wave by deflecting it upwards, away from the bottom of the structure.

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These walls are usually made from poured concrete and are designed to reduce scour which means

the removal of sediment from around a structure, which weakens it at the base of the wall.

2.3.2 GRAVITY SEAWALLS

Seawalls that rely on heavy materials to give them stability are known as gravity seawalls. Gravity

seawalls are built in areas where strong soil runs right up to the coastline; the seawall is anchored,

using this strong soil as a foundation. These walls are susceptible to shearing around the base, a

process in which internal components of a structure move across each other as a response to stress.

Gravity seawalls usually have extra reinforcement around the base to counteract shearing.

Fig 2.1: Vertical wall and curved concrete wall

Fig 2.2: Types of seawalls (Source: seawall design construction and performance Gary Blumberg)

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2.3.3 STEEL SHEET PILE SEAWALLS

Steel sheets, interlocked and anchored deeply into the ground, are frequently used as seawalls in

areas less intensively battered by the sea. Steel sheet pile seawalls are usually anchored both into the

ground beneath them and to a bank of earth or bluff behind them. The weight of this earth acts as a

reinforcement to the wall; water retained in this bank of earth can be drained through openings in the

wall.

2.3.4 CONCRETE BLOCK AND ROCK WALLS

Walls constructed from concrete blocks and rocks mounted on a manmade slope are generally

lower-cost operations than other seawall types, but they do not last as long. A mound made of rubble

and rock is constructed, and heavy boulders made of concrete or stone are anchored into position.

The shape of the slope dissipates the force of the wave by guiding it up a gentle slope, while the

irregular boulders with gaps between them absorb the force by dividing the main wave into lots of

smaller channels.

2.4 FACTORS AFFECTING SEAWALL

For coastal protection works rigid structures should normally be avoided and the flexible structures,

which dissipate energy, should be adopted. In case of rigid structures, if unavoidable, may be

provided with slope and vertical face should in any case be avoided. The vertical face leads to the

reflection and scouring and subsequently failure of the wall. The vertical rigid retaining wall is

normally mistaken with the seawalls. However, it should be kept in mind that the function of the

seawall is to dissipate the wave energy and allow formation of beach in front of it. As such, the

sloping rubble mound seawall is the most suitable type of seawall.

Fig 2.3: Action of wave on seawall

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Fig 2.4: Failure of vertical wall

The rubble mound seawall is generally designed to consist of three layers that are core, secondary

layer and an armour layer. A minimum of two layers of stones (units) in the armour and secondary

layer is always necessary. While the thicknesses of these layers are determined by the size of stones

used, the levels including that of the core are determined based on maximum water level, design

wave height, wave run-up, permissible overtopping and method of construction.

2.4.1 POSITION OF THE SEAWALL

For locating the seawall, determination of the beach profile and the water levels are important. The

highest and the lowest water levels at the site must be known before evolving a design. The highest

water level helps in deciding the crest level while the lowest water level guides the location of the

toe. The bed slope in front of a coastal structure also has an important bearing on the extent of

damage to the structure and wave run up over the structure. With steeper slopes, damage to armour

stones is more as compared to flatbed slope. The wave run-up is also higher on steep bed slopes.

The seawall should be located in such a position that the maximum wave attack is taken by the

armour slope and the toe. The seawall, if located above the high water level contour, the waves will

break in front of the structure causing scouring and subsequent failure of the seawall. The increase in

the depths would cause higher waves to break on the coastline aggravating the erosion problem. It

should be kept in mind that seawall is for dissipating the wave energy and not merely for avoiding

inundation of the land.

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Fig 2.5: Location of Seawall between High Water & Low Water

2.4.2 UNDER DESIGN OF ARMOURS

Various factors contribute to render the armours provided in a seawall ultimately inadequate to

withstand the wave action at a given spot. Underestimation of maximum water level, incorrect

information of beach slope considered at the design stage, steeping of foreshore after the

construction of seawall, presence of a large number of smaller stones than design size (armour size

could vary from 0.75 W to 1.25 W such that 50% of the stones weigh more than W, where W is

design-size) are a few of them. In case of seawalls provided with a large percentage of undersized

armour, there has been considerable displacement and dislocation of armours. Stones having

excessively rounded corners attribute to repetitive displacements and consequent attrition and

abrasion which have been possibly compounded by poor quality stones. The stones in the lower

reaches have been excessively subjected to such forces. The displacement of the armours has

resulted in the exposure of secondary layer, which is from the section that has created small pockets

of breaches completely exposed to the fury of waves.

2.4.3 TOE PROTECTION

Toe protection is supplemental armouring of the beach or bottom surface in front of a structure,

which prevents waves from scouring and undercutting it. Factors that affect the severity of toe scour

include wave breaking (near the toe), wave run-up and backwash, wave reflection and grain size

distribution of the beach or bottom material. Toe stability is essential because failure of the toe will

generally lead to failure throughout the entire structure. Toe is generally governed by hydraulic

criteria. Scour can be caused by waves, wave induced currents or tidal currents. Design of toe

protection for seawalls must consider geo-technical as well as hydraulic factors. Using hydraulic

considerations, the toe apron should be at least twice the incident wave height for sheet-pile walls

and equal to the incident wave height for gravity walls.

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Fig 2.6: Seawall with Toe Protection

2.4.4 INADEQUATE OR NO-PROVISION OF FILTERS

Many rubble mound structures have failed due to no or inadequate provision of filter underneath. As

a consequence, the insitu soil is leached resulting in the collapse of the structure. In a typical case of

a seawall the crest of which subsided due to removal of fill material by overtopped water, there is no

proper filter between the sloping fill and the seawall. In some cases, the toe of the seawall sank over

the years due to inadequate filter and removal of insitu bed material. With the failure of the toe,

armours in the slope, which were otherwise intact, were dislodged by gravity and wave forces. These

stones occupied the toe portion and sank further due to the absence of filter. Thus the failure is

progressive and renders the seawall ineffective within a short period, if not attended promptly. In

situations such as these, the reformation of the profile to design slope alone would not be adequate.

It is necessary to provide a proper filter before reforming the section, which could be done by

dumping additional stones or retrieving some of the displaced stones.

Fig 2.7: Inadequate Filter Layer Exposed After Damage to Seawall

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2.4.5 OVERTOPPING

Underestimation of design wave or the maximum water level leads to excessive overtopping of

seawalls and eventual failure particularly when the freeboard is inadequate. Such failures also lead to

the failure of leeside slope and damage to reclamation, if any. This calls for not only proper

estimation of waver un-up and the crest level of the seawall, but for also providing proper filter

between the backfill and the seawall. It is also necessary to provide facilities for drainage of

overtopped water, which otherwise will find its way through seawall itself causing further damage.

There are instances where the reclamation fill in the lee has shown local depressions. Subsurface

fill/soil has been removed in the process of draining of overtopped water. In situations where it is not

possible to raise the level of seawall crest to avoid overtopping, it is advisable to provide a deflector

to throw a part of the overtopping water back to the seaward slope of the seawall. As mentioned

earlier, the leeside fill and the seawall core (or secondary layer) should be sandwiched by an

appropriate filter and adequate drain be provided for safe discharge of overtopped water. However,

some of the seawalls are designed as semi-submerged bunds, which allows overtopping at the higher

Water Levels. A proper care needs to be taken to prevent damage to the crest and the leeside slope

during the design of such seawalls

Fig 2.8: Overtopping of Waves over Seawall

2.4.6 ROUNDED STONES

The in-place stability of an armour unit which is distinct from the overall stability of a rubble mound

structure, but which is an essential prerequisite for the same, is dependent, interalia on the

interlocking achieved at placement of armors. In order to achieve efficient interlocking, the rock

should be sound and the individual units should have sharp edges. Blunt or round edges result in

poor interlocking and hence poor stability (lower stability factor KD), other conditions remaining the

same. Rounded stones result in lower porosity and are less efficient in dissipation of wave energy.

Lower stability factor necessitates a higher weight in a given situation, which renders the structure

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costlier. The in-place stability of such units is highly precarious and sensitive to small disturbances.

Hence such stones should not be used in rubble mound structures.

2.4.7 WEAK POCKETS

Several weak spots are often present in rubble mound structures, which maybe attributable to

reasons such as lack of supervision, quarry yielding smaller stones or deliberate attempts to dispose

of undersized stones etc. The failure thus initiated could lead to the failure of the structure as a

whole.Concentration of stones much smaller than the required armour should therefore be avoided at

any cost, lest the entire structure, however carefully executed, can become functionally ineffective.

Fig 2.9: Pockets in armour Layer of a Seawall

2.5 DESIGN PROCEDURE

The usual steps needed to design an adequate and efficient rubble mound seawall / revetments are:

Determine the water level range for the site

Determine the wave heights

Determine the beach profile after the storm condition / monsoon

Select the suitable location and configuration of the seawall

Select suitable armour to resist the design wave

Select size of the armour unit

Determine potential run-up to set the crest elevation

Determine amount of overtopping expected for low structures

Design under-drainage features if they are required

Provide for local surface runoff and overtopping runoff and make any required provisions for

other drainage facilities such as culverts and ditches

Consider end condition to avoid failure due to flanking

Design toe protection

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Design filter and under layers

Provide for firm compaction of all fill and back-fill materials. This requirement should be

included on the plans and in the specifications. Also, due allowance for compaction must be

made in the cost estimate

Develop cost estimate for each alternative.

Provision for regular maintenance and repairs of the structure.

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CHAPTER 3

DESIGN PRINCIPLES OF SEAWALL

3.1 DESIGN WATER DEPTH:

The primary factor influencing the wave conditions at the harbor site is the bathymetry in the

general vicinity of harbor.

Water depth will partly determine whether a structure is subjected to breaking, non-breaking,

or broken waves.

The maximum and minimum water depths at each section must be evaluated taking into

account the tidal range and the storm surge effect.

3.2 DESIGN WAVE:

The most important single factor controlling the design of seawall will be the Design wave.

The design wave must be so chosen that the seawall during its construction and throughout

its intended service life has a sufficiently low probability of failure both in terms of

unacceptable damage and collapse.

Shore protection manual (1984) specifies that H1/10 (average of the highest one-tenth of the

waves) should be used as the design wave height for rubble mound seawall instead of

H1/3(significant wave height) as recommended in earlier editions.

3.3 CREST ELEVATION:

The crest level is very important for the total cost, since the total volume of the seawall is

approximately proportional to the second power of the total height of the seawall.

The crest level should be as low as permitted by the functional requirements and stability of

armor units on crest and the lee side. Reduced crest level would mean overtopping when high

waves and high water levels occur. Whether overtopping will occur or not will depend on the

wave run-up and for rubble slopes.

3.4 SLOPE ANGLE:

Side slopes are generally as steep as possible to minimize the volume of core material and to

reduce the reach of cranes working from the crest.

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However it may be possible to develop a less steep slope if the cranes operate from a barge.

Slopes are typically within the range 1V:1.5H to 1V:3H and influence the amount of

interaction between armor units.

As the angle increases, the contribution to stability from friction and interlocking also

increases due to the squeezing or increase in slope-parallel forces applied by adjacent units.

There is however a corresponding decrease in the slope-perpendicular component of self-

weights. This implies optimum slope angles for maximum interaction and stability.

3.5 WEIGHT OF ARMOR UNIT:

Hudson (1959) considered the stability of an individual armor unit subjected to wave action

and assumed that the disturbing forces could be type of drag and lift caused by the wave

motion which tends to move the armor unit.

The stabilizing forces were considered to be mainly the submerged weight of each unit.

3

31 cot

HaW

K SGD

W = weight of individual armour unit in primary cover layer (t).

a = Unit weight of armor unit (t/m3).

H = design wave height (m).

SG = Specific gravity of armor unit relative to the water at the structure site.

= Angle of structure slope measured from horizontal in degrees.

KD = Stability coefficient that varies primarily with the shape of the armor unit.

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Table 3.1: Table for KD value (Source: EM 1110-2-1614)

3.6 CREST WIDTH:

The crest width depends greatly on the degree of overtopping permitted. Where there is no

overtopping, crest width is not critical.

Shore protection manual (1984) recommends as a general guide that the minimum crest width

should equal the combined widths of three armor units.

1/3W

B nKa

B = Crest width

n = number of stones or armor units (n=3 is recommended).

K = layer coefficient.

W = weight of primary armor unit.

a

= unit weight of armor unit.

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3.7 THICKNESS OF ARMOR LAYER:

The thickness of the cover and under layers required can be determined from the following

formulae:

1/3W

r nKa

r = Average layer thickness.

n = number of armor units in thickness comprising the cover layer.

K = Layer thickness.

W = weight of individual armor unit.

a = unit weight of armor unit.

Fig 3.2: Table for K(Source: EM1110-2-1614)

3.8 SECONDARY COVER LAYER:

The purpose of the secondary core layer is to prevent core material from being washed out

through the voids of the primary armor layer and at the same time provide a good foundation

for the heavier units of the primary armor layer.

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The secondary cover layer also should act as a temporary protection to the core before

primary armor is laid.

Shore protection manual recommends the stone sizes in the secondary layers to be W/10 to

W/15 and a minimum thickness corresponding to two stone layers.

3.9 CORE:

The purpose of the core is following:

To form a substantial portion of the total volume of the rubble mound seawall in order to

utilize the quarry run which is available as a byproduct of the quarrying for secondary and

primary armor stones.

To provide a satisfactory foundation for the secondary and primary armor layers, and for any

cap stone or cap wall on top.

To provide a relatively impermeable barrier to the transmission of wave energy, and

To form a suitable working platform from which the secondary and primary armor layers can

be constructed.

The weight of core will vary from W/100 to W/400. A highly impermeable core may prevent

wave transmission through the structure but because of pore pressure build up, is likely to

have an adverse effect on the stability of the cover layers.

The influence of core permeability on the wave transmission and stability suggest that a

densely packed but fairly permeable core, a limit may be specified on the minimum size of

the material to be used. This is also necessary to avoid wash out of core material.

3.10 BOTTOM ELEVATION OF PRIMARY COVER LAYER:

The armor units in the cover layer should be extended down slope to an elevation below

minimum still water level equal to the design wave height.

3.11 TOE BERM:

Seawalls exposed to breaking waves should have their primary cover layers supported by a

quarry stone berm.

The quarry stone in the toe berm should be of weight W/10 to W/15. The width of the toe

berm must be such as to hold at least three stones and thickness must be such as to have two

stone layers. The toe berm is generally intended to provide safety against foundation failure

and hydraulic stability of the structure.

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3.12 BEDDING LAYERS OR FILTER LAYERS:

Wave action against rubble mound seawalls creates enough turbulence within the structure

and in the underlying sea bed that may result in sucking of soil into the structure. This may

cause settlement of structure.

A filter blanket or a bedding layer is a good precaution against such settlement.

Geotextiles filters may also be used. In case of clays and silts, it will be necessary to provide

a coarse sand layer first before placing the filter blanket or bedding layer.

The bedding layers must extend well beyond the toe of the structure.

The weight of filter layer varies from W/1000 to W/6000.

Grain size of sand used is 100 mm.

Fig: 3.1: Seawall layout (Source: CWPRS Technical Memoranda for Seawall)

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CHAPTER 4

DESIGN OF RUBBLE MOUND SEAWALL

4.1.1 Length and location of Seawall

Fig: 4.1: Proposed seawall location

Length of seawall is: 1.55 Km

Latitude and Longitude: . . E

Location: Kamalapuram / Alappuzha / Kerala / India.

4.1.2 Criteria for Site Selection:

The area near Kamalapuram has been selected for the construction of seawall because of the gradual

erosion along the coast. The following has been shown with the help of satellite imagery below.

Fig 4.2: Proposed area in 2003

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Fig 4.3: Proposed area in 2013

4.2 Determining significant wave height and wave period

Significant wave height:

Fig 4.4: Significant wave height (Source: Panoply software data analysis)

The wave height obtained is 1.524 m. The significant wave height is obtained by analyzing

cumulative data from 2003 to 2013.

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Wave Period:

Fig 4.5: Mean Wave Period (Source: Panoply software data analysis)

The mean wave period is 7 sec. The wave is determining by analyzing data from 2003 to 2013.

4.3 DESIGN PROCEDURE:

Design conditions:

Depth of water (d) = 3.224 m

Time period of the wave approaching the

seawall (T) (assumed)

= 7.468 sec

Armor unit = Rough quarry stone

Unit weight of quarry stone = 2.65 t/m3

Structure slope = 1 in 1.5

Shape = Symmetrical

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Weight of armor unit:

3

31 cot

HaW

K SGD

KD = 2 (for rough quarry stone)

a = 2.65 t/ m3

w = 1.025 t/m3

= 1 in 1.5

Cot = 1.5

H = 2.524 m

Crest width:

Minimum crest width should equal the combined width of 3 armor units.

n (number of armor units) = 3

1/3W

B nKa

B = 3.31 m

Armor layer thickness:

1/3W

r nKa

n = 2

Armor layer thickness (r) = 2.2068 m

W = 3.56 T

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Secondary cover layer:

Thickness of secondary layer is same as armor layer and weight varies from 0.356 T to 0.237T.

Quarry stones are used as secondary layer.

Core layer:

The weight of core layer varies from 0.0356 T to 0.0089 T.

Gravel is the material used here.

Filter layer/ bedding layer:

The weight of filter layer varies from 0.00356 T to 0.000593 T and sand size of 100 mm is used.

Toe berm:

The weight of toe berm varies from 0.356 T to 0.237T.

Width = 2xHs = 3.05 m

Depth = 0.4 d = 1.29 m

Height of the structure = Thickness of Armour layer + Thickness of Under layer + Depth of Toe

berm + Thickness of Bedding layer

= 2.2068 + 2.2068 + 1.2896 + 1

= 6.7 m

Table 4.1: Table for Total weight of the structure

NAME OF

LAYER AREA ( M

2) UNIT WEIGHT

(T)

LENGTH (M) TOTAL WEIGHT

(T)

(AREA*WT*L)

Armour Layer 33.0131 3.56 1550 182,166.286

Under Layer 20.6802 0.356 1550 11,411.334

Core Layer 6.3770 0.0356 1550 351.88

Toe Berm 2*3.9345 = 7.869 0.356 1550 4342.114

Filter Layer 30 0.00356 1550 165.54

Weight of the structure = 198,437.15 T

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Design obtained from above calculation:

Figure 4.6: Model of seawall

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Reference:

Technical memorandum on guidelines for design and construction of seawalls, May, 2010,

Central Water & Power Research Station, Pune.

Design of Coastal Revetments,Seawalls, and Bulkheads, EM 1110-2-1614

Evaluating theCondition of Seawalls/Bulkheads -Coastal Systems International, Inc.

European Centre for Medium-Range Weather Forecasts (ECMWF) http://www.giss.nasa.gov/tools/panoply/

Harbour and Coastal Engineering S. Narasimhan & S. Kathiroli.