RETAINING WALLSCASE STUDY: WORLI SEA FACE

TOPICS COVERED:

(1) GENERAL STUDY OF RETAINING WALLS

(2) STUDY OF SEA WALLS

(3) SITE STUDY : WORLI SEA FACE

(4) SITE PICTURES

Batter

Drainage

HoleToe

A GENERAL STUDY OF RETAINING WALLS

Retaining walls are usually built to hold back soil

mass. However, retaining walls can also be constructed for

aesthetic landscaping purposes.

Gravity retaining wall

GL1

GL2

BACK

SOIL

Shown alongside is the

broad classification of the

different types of retaining

walls.

(1) Gravity walls

(2) Piling walls

(3) Cantilever walls

(4) Anchored walls

The additional categories

are indicated in the flow

chart.

APPLICATIONS OF RETAINING WALL

A RETAINING WALL MAINTAINING THE DIFFERENCE

BETWEEN THE ELEVATIONS OF THE GROUND

SURFACE.

RETAINING WALL OF A BASEMENT

APPLICATIONS OF RETAINING WALL

A TUNNEL PORTAL

MAINTAINING THE

LEVEL BETWEEN A

HIGHWAY AND A

CONTOUR LAND

WHAT IS EARTH PRESSURE?

Earth pressure is the pressure exerted by the retaining

material on the retaining wall. This pressure tends to

deflect the wall outward.

Types of earth pressure :

Active earth pressure or earth pressure (Pa)

Passive earth pressure (Pp).

Active earth pressure tends to deflect the wall away from

the backfill.

Passive earth pressure is the highest limiting lateral

pressure developed at the onset of shear failure by wall

moving in the direction opposite to the direction of

acting earth pressure

Pa

GL

Variation of Earth pressure

PP

TYPES OF FAILURES IN

RETAINING WALLS

INTRODUCTION TO SEA WALLS

Seawalls are generally massive concrete structures emplaced along a considerable

stretch of shoreline at urban beaches.

The rubble mound seawall is generally designed to consist of three layers. Viz.

core, secondary layer and an armour layer (Fig.1). 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.

Seawalls are vertical or near

vertical shore-parallel structures

designed to prevent upland

erosion and storm surge flooding.

NEED FOR SEA WALLS The best natural protection against erosion is an adequate beach on which waves expend their energy.

Creation of beach is rarely possible due to economic reasons. As such, the engineering structures like seawalls, revetments, offshore breakwaters, etc. are adopted for coastal protection. Rubble mound seawall is more commonly used measure in India for combating coastal erosion.

Various methods to prevent beach erosion are briefly indicated below :

(a) Seawalls, revetments, anti-sea erosion bunds

(b)System of jetties – shore connected

(c)System of offshore breakwaters - away from the shore

DESIGN DETERMINATION OF SEA WALL

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 exact 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 flat bed

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.

Advantages Disadvantages

•Long term solution in comparison to soft beach

nourishment.

•Effectively minimizes loss of life in extreme events and

damage to property caused by erosion.

•Can exist longer in high energy environments in

comparison to ‘soft’ engineering methods.

•Can be used for recreation and sightseeing.•Forms a hard and strong coastal defense.

•Very expensive to construct.

•Can cause beaches to dissipate rendering them useless

for beach goers.

•Scars the very landscape that they are trying to save and

provides an ‘eyesore.’

•Reflected energy of waves leading to scour at base.

•Can disrupt natural shoreline processes and destroy

shoreline habitats such as wetlands and intertidal

beaches.

•Altered sediment transport processes can disrupt sand

movement that can lead to increased erosion down drift from the structure.

AN OLD MAP OF MUMBAI

LOCATION OF SITE:

WORLI SEAFACE :

(1) ONE OF THE SEVEN ISLANDS OF OLD BOMBAY, WORLI IS CURRENTLY A PART OF SOUTH MUMBAI, EXTENDING FROM HAJI ALI TO PRABHADEVI.

(2) THE BRITISH HAD ESTABLISHED A FORT IN THIS AREA: THE WORLI FORT, IN AROUND 1675. SINCE THEN WORLI SEA FACE HAS BEEN STRATEGIC FOR NAVAL SECURITY.

(3) WHILE THE GRAVITY RETAINING WALL AT THE SEAFACE DATES BACK TO THE SAME TIME, RENOVATIONS IN TERM OF VALUE ADDITION HAVE BEEN DONE FROM TIME TO TIME.

(4) FOR EG. THE DEVELOPMENT OF A PROMENADE AND RECENTLY, THE TETRAPODS(LIKE IN MARINE DRIVE) WERE ADDED IN WORLI SEA FACE ABOUT 3 TO 5 YEARS BACK.

SCHEMATIC SECTION: The schematic section of the wall shows the type of

retaining sea wall constructed.

The aim of constructing this wall was to protect the shore from erosion and to protect areas of human habitation, conservation and leisure activities.

Concave structure introduces a dissipative element.

The curve can prevent waves from overtopping the wall and provides extra protection for the toe of the wall

Curved seawalls aim to re-direct most of the incident energy, resulting in low reflected waves and much reduced turbulence.

SITE PICTURES

A tetrapod is a four-

legged concrete structure

used as Armour unit on

breakwaters. The

Tetrapod's shape is

designed to dissipate the

force of incoming waves

by allowing water to flow

around rather than

against it, and to reduce

displacement by allowing

a random distribution of

tetrapod to mutually

interlock.

The random rubble piles

are a toe protection

measure for the retaining

wall.

The original stone retaining wall is strengthened with concrete

and clad with a 1-meter wide granite stone seat. This feature

has made the stretch a popular hang-out spot, rather than just

serving the purpose of being a retaining wall.

One can clearly see the gravity-type stone retaining wall, which

was presumably constructed by the British. The concrete

layering is distinctly visible.

The junction where the

retaining wall meets the

Bandra-Worli sea link

terminal

Sea level rise creates an issue for seawalls worldwide as it raises both the

mean normal water level and the height of waves during extreme weather

events, which the current seawall heights may be unable to cope with

NEW TECHNOLOGIES In 2011, the BMC had proposed the revitalization of the

shores between Mahim and Worli by extending the

beachfronts from 3 m to 50 m.

The existing seafronts would be protected by employing

GEOTEXTILE BAGS. These are sacks filled with sand,

which will be set up linearly along the shore, leaving

some place for the sand to accumulate in the desired

shoreline.

The main applications are:

• flood control and protection

• reinforcing existing dikes/shoreline structures

• erosion control

• storage of contaminated sediments

Geo-textile bags are produced from woven textiles with

very good filtration properties and high tensile

strengths that will resist to pump pressures, handling

and total weights.

THANK YOUGARIMA RAJPUT 41

MANASVI RANE 42

RITHIKA RAVISHANKAR 43

SHIVALI SANAP 44

SUVOJIT SEN 45