Design of Groins

7/27/2019 Design of Groins

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Structural design of rubble mound groins/ breakwaters

S.A. Sannasiraj

Professor, Department of Ocean Engineering, Indian Institute of Technology Madras

Chennai 600 036, India. Email: [email protected]

Abstract

Groins play an important role in the shore protective measures. In comparison with other

protective measures such as sea walls or artificial beach nourishment, groins initiate the

natural beach development. In this paper, the structural design of groins is detailed. The main

criterion in the design is the stability of armour blocks for the design wave climate. The

importance of various characteristic layers of a typical groin is discussed.

1.0 Introduction

The shoreline is a dynamic line which frequently changes its course due to the action

of waves and near shore currents. The change in the shoreline profile is mainly due to the

alongshore or cross-shore sediment movements. The cross-shore sediment movements only

influence a particular region and would stabilize the coasts soon. However, the alongshore

sediment movement is a perennial problem. For an equilibrate shore, the net sediment

transport would be insignificant. If the net sediment transport along any shore line is either

positive or negative, then that shore line would be subjected to either erosion or accretion. If

the boundary between the land and sea shifts towards seaward with time, then the process is

accretion. If the shift is towards landward, the shoreline recedes due to erosion.

The rate of erosion or deposition depends on composition of shore zone and exposure

to erosive forces. There are two basic causes which initiate erosion. One is due to the forces

of nature acting along the shoreline and the next, due to the actions of man-made coastal

development activities. The most significant natural erosive force is wind-driven wave action

in combination with water level changes due to tides, wind set-up and sea-level rise. The

man-made activities can interfere with the continuing shore processes such as interruption of

littoral drift patterns, deflection of shore current patterns, removal of sediments by dredging

and modification of wave regimes through reflection from and diffraction around structures.


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There are many types of coastal protection measures such as sea walls/ dikes, mound

breakwaters, groins, detached breakwaters and sand nourishment.The size, type and location

of coastal protection depends on the actual needs, benefits expected from the methodology,

effect on adjacent shorelines and more importantly economy. In this paper, groin as an

effective shore protective measure is considered. A row of groins constructed on an eroding

part of the coast would locally reduce the longshore sediment transport capacity and thus the

coastal erosion. In this process, basically the erosion areas are shifted to less harmful

situations or spreaded into longer distances so that the erosion effect would not be felt.

The design on the layout of groins with particular reference to our Indian coasts are

presented in this workshop. In this paper, the structural design of groins is presented.

Although the proper structural design of groins would not guarrentee the functionalachievements of the groins, it requires great attention. This is because many of the groins and

breakwaters have failed due to the defective design in this respect.

2.0 Structure of groins

Groins like breakwaters can be constructed using rubble stones, pre-cast concrete

units or blocks, rock-filled timber cribs and gabions, steel sheet pile, timber sheet pile, and

grout filled bags and tubes. A typical rubble-mound groin cross section is shown in Fig. 1. An

armour layer at the top protects the other layers beneath it from washing away. Thus, the

armours have to be designed to withstand under severe environmental forces. And, an inner

core layer of smaller size stones prevents any sediment to seep through the groin section.

Depending upon the requirements, there may be few (none to two) under-layers between

armour and core layers. The stones in the under-layer are chosen in such a way that it will not

fit through the voids of its immediate overlaid layer.

The groins are often provided with rubble toe protection that serves as a scour blanket

to prevent undermining and thereby a reduction in lateral stability. Unlike in the breakwaters,

the toe protection for the groins would be provided on both sides of its section. This is

because the wave attack would be from any direction. The entire cross section would be

placed over the filter layer blanket, which is laid on the seabed. The filter layer evenly

distributes the entire weight of the structure into the seabed and hence, it is the foundation for

the groin super structure. And also, the filter layer prevents the seabed materials seeps into

the core layer and bigger stones to settle into soft sands.


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Fig.1 Conventional rubble mound groin

3.0 Structural design

3.1 Forces acting on Groins

3.1.1 Wave forces.

The rubble mound groin is preferably used at exposed sites because of a rubble-mound structure's ability to withstand severe wave loads and to decrease wave reflection.

Moreover, the risk of scouring and formation of strong rip currents along rubble groins is

reduced. Most rubble mound groins are designed with quarry stone as armor and it is heavy

enough to be stable under a selected design wave height.

3.1.2 Current forces

Currents can exert forces on rubble-mound groins both as longshore currents flowing

over low groins and as seaward flowing rip currents along a groins flank. However, current

caused forces are usually small when compared with the forces due to waves. Normally the

stone weight necessary for stability against currents will be much less than the stone weight

necessary for stability against wave action.

3.1.3 Buoyancy forces

The effective weight of rubble stone would be reduced due to the buoyancy force in

proportional to the submerged volume of the stone.

3.1.4 Frictional resistance

Frictional resistance induces parallel to the slope, either upward or downward, but

contrary to the direction of the wave force. The condition of instability occurs if the friction isinsufficient to neutralize the other forces parallel to the slope.

Crest width

Design low water

Limit of wave runup

Design high water

Toe layer

Core layer

sea bed

Filter layer

Secondary layer

Armour layer


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3.1.5 Other forces

A groin might experience impact forces due to wave-carried debris and small craft

collisions. The magnitude of these forces is difficult to predict because the cause of the

impact and the mass of the impacting body are not known a priori. If debris is suspected to be

a problem, appropriate levels of conservatism should be included in the design.

A groin may have to be designed to withstand forces that might occur only during

construction; e.g., the groin may have to carry construction equipment or there may be

surcharge due to temporary fill. These forces may be critical and exceed forces due to other

more routine causes such as waves and currents.

3.2 Armour layer

The outermost armour layer protects the entire structure from the wave action. It

dissipates the wave energy through its porosity. This armour layer can be formed either using

natural rock debris or concrete blocks depends on the size of the armour units required to

withstand against the wave action, the availability rocks and its quality. The concrete blocks

can be from simple cube forms to highly interlocking tetrapods, accropods and core-locs. The

armor unit size thus depends on the design wave characteristics.

3.2.1 Stability criteria

There are hardly any standards available for the design of armour units except an

attempt from European standards. However, the design of armour units has been carried out

from the experiences of physical model studies and the field observations. Some empiricalformulae have been developed from experimental work to find the suitable size of unit which

allows the block to withstand the wave-induced forces. The main governing parameter of the

armour layer stability is the stability number (Ns) which is defined by,

50)1( nwss

D

HN

=

(1)


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whereHis the design wave height; s is the unit weight of armor stone; w is the ratio of unit

weight of water and, Dn50 is the nominal median diameter of the stones. The nominal median

diameter is related to the median weight W50 by,

35050 nsDW = (2)

From Eq. (1),

33

3

50)1/(

sws

s

N

HW

=

(3)

The stability (amount of movements) of the armour unit is related to the value of Ns.

Stone motions are, in general, not expected on conventional rubble mound groins. For stable

groins, the value of Ns ranges between 1 and 4. The armour unit size can then be estimated

using either Hudsons formula (Hudson, 1958) or from the findings of Van der Meer (1988).

3.2.2 Hudsons formula

The size of the armour stones is commonly estimated using the widely accepted Hudson

formula and the same is recommended by CERC (1984). Hudson (1958) established the

stability coefficient (KD) for different types of armour units from physical model tests underregular waves. These values are given as a function of the damage. For the design of rubble

mound groins, a damage percentage of 0-5% is acceptable to have no motion of stones. The

stability coefficient thus can be correlated to the weight of the armour units and the slope

(angle, with the horizontal) in which the units are laid. The suggested KD values for

different structure slopes, in general, satisfies the stability criteria of N s in the range of 1~2.

cot3Ds KN = (4)

In this method, the weight of the individual stones (W) is proportional to the cubic power

of design wave height (HD) for a given structure slope () and the type of stones/ blocks and

is given by from Eq. (3) and (4),

cot13

3

=

w

sD

Ds

K

HW (5)


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Table 1 provides the stability coefficient for different types of stone/ concrete blocks for use

in a trunk section. The corresponding coefficients for head sections are more conservative

because head sections directly face the wave action from all the directions.

3.2.3 Van der Meers formula:

Van der Meer (1988) suggested stability criteria as function of more parameters than

in the Hudsons formula based on physical model tests using irregular waves. This would

make it more difficult to apply. A stability criterion is estimated using the damage level S,

relating the erosion area in a cross section (A, m2) and the mean diameter of stones (Dn50, m)

[van der Meer and Heydra (1991)].

2

50nD

AS= (6)

For the rubble quarry stone, the stability criteria under the action of breaking waves are given

below.

For plunging waves ( < c):

1

2.61

2.0

18.0

50

=

N

SPD

H

nw

s(7)

For surging waves ( > c):

P

nw

sN

SP

D

H

cot0.1

1

2.0

13.0

50

=

(8)

In the above formula, many variables were introduced such as the number of waves, N, the

permeability (P) of the surface and the surf similarity parameter, which relates the slope to

the wave steepness H/L.

LH

tan= (9)

And, ( ) 5.01

31.0 tan2.6 += Pc P (10)


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The condition of no damage introduced by Sin the van der Meers formula leads to

a value ofNs nearly 1 ~ 2. If one notice the differences in both Hudsons formula and van der

Meers formula, they differ only in extreme wave condition. On comparing Eq.(5) and Eqs.

(7 & 8), KD defined by Hudsons formula is explicitly defined in terms of the permeability

coefficient and wave steepness in the van deer Meers formula. As the wave intensity

increases from surging to plunging, the importance of slope was given due consideration by

increasing its power of influence.

The armour layer slope should be equal or greater than 1V:1.5H. Hudsons formula

[Eq. (5)] is applicable for armour units of nearly uniform size and the overtopping of waves is

not allowed. For graded riprap armour stone, in the modified Hudsons formula, the weight of

the armour stones, W50 represents weight of 50% size in the gradation. In the graded armourlayer, the maximum weight of graded rock is 1.25 W50 and the minimum weight of graded

rock is 0.75 W50. And, the stability coefficient has to be modified on conservative side and

the recommended values are 1.3 and 1.6 for depth at the toe of the structure less than 6.0m

and greater than 6.0m respectively. These coefficients were chosen based on allowable 5%

damage criteria. However, graded stones are not recommended if the design wave height

exceeds 1.5m.

Table 1. Recommended KD values for the estimation of armour unit size

KDArmour units N

BW NBW

Slope

Cot Porosity (P)

%

1 NR 2.9 1.5 3.0

2 2 4 1.5-3.0 37

Rough angular

quarry stone

>3 2.2 4.5 1.5-3.0 40

Graded rough

angular stone

---- 1.3 1.7 1.5-5.0 37

Tetrapod 2 7.0 8.0 1.5-3.0 50Dolos 2 15.8 31.8 2.0-3.0 63

Cube

(modified)

2 6.5 7.5 1.5-3.0 47

Note: BW breaking wave; NBW non breaking wave.

3.3 Under layer

The purpose of one or more under layers in between the armour and core layers is toprevent smaller stones in core seeps through the voids of armour units. This criterion is met if


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the first under-layer stone weighs W50/10 to W50/15 where W50 is the median weight of the

armor stone. This criterion assumes that the stone in the under layers has approximately the

same unit weight as the armor stone. By this criterion, the second under-layer stone should

weigh approximately W50/100 to W50/150. For the groin system, one under-layer is

recommended. To prevent smaller stones in the under-layer escape through the pores of

armour layer, the following filter design criterion need to be followed for graded stones.

D15 (cover) 5 D85 (under) (11)

where, D15 (cover) is the diameter exceeded by the coarsest 85% of the layer immediately

above the underlayer and, D85 (under) is the diameter exceeded by the coarsest 15% of the

underlayer.

3.4 Core layer

The core layer supports the protective armour cover and any other additional under

layers. It prevents sediments passing through the groin. The size of stone in core layer would

be W50/200 to W50/4000 (CERC, 1984) following single underlayer. If there is more than one

underlayer, the weight of core stones may further be reduced.

3.5 Toe layer

The stone weight needed for stable toe protection can be determined from the stability

against the scour arise under the armour stones. This requirement dictates that the weight of

toe layer stones should be equal to the weight of underlayer stones, ie. W50/10. The minimum

width and height of the toe berm is about 3kDn50and 2 kDn50 respectively. Here, k is the

layer coefficient and approximately, it can be taken as 1.0.

A scour apron in addition to the above toe layer width is required if the wave down

rush reaches the toe layer. An additional toe-berm should be provided if the bearing failure is

possible.

3.6 Filter Layer

The massive rubble stone structure should be stable against disintegration due to

excessive settlements due to leaching, undermining or scour due to wave and current induced


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turbulence and quick soil conditions, particularly on sandy beds. Filter or bedding layer is

required to retain the groin structure while passing large volumes of water through it. The

filter layer should satisfy,

D15 (filter material) 5 D85 (foundation soil) (12)

The filter layer thickness should not be less than 300mm to ensure that the bottom

irregularities are completely covered. Geotextiles can be considered instead of filler

materials. The lower limit of filter materials normally is specified by its median size to avoid

placing very small stones comparable to the sediments.

The stone size gradation of each layer as a percent of the mean stone size is given in

Table 2.

Table 2. Stone size gradation in a graded rubble design

Layer Stone size Gradation (%)

Armour layer W50 75 to 125

Underlayer W50/10 to

W50/15

70 to 130

Toe layer W50/10 to

W50/15

70 to 130

Core W50/200 to

W50/4000

30 to 170

Filter layer 100mm to

W50/6000

30 170

3.7 Thickness of armour/under Layer

The thickness of a single armour or under layer, t is equal to the mean diameter of

stones in that particular layer. However, if there are n number of layers, then the thickness is,

50nDnkt

= (13)

where, k is the layer coefficient in the range of 1.0 (for dolos) to 1.15 (for rough quarry

stone).

The placing density of rubble stones is expressed in terms of required number of

armour units (Nr) for a given surface area,A.

3/2

50

)100/1(

n

r

D

Pkn

A

N = (14)

where, P is the average porosity of the armour layer given in Table 1.


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3.8 Crest width

The crest width, r is the maximum of the following: First depends on the minimum

number of stones (ns) required. CERC (1984) suggests minimum number of stones as 3. Next,

the width depends on the degree of overtopping and the groins are designed as non-

overtopping structure to avoid sediment by passing. The last criterion demands from the

functional aspect during the construction and after use. For groins, the access on the top of

the groins is not mandatory after construction. Hence, the minimum required crest width

would be equal to the wheel base of the crane used for the construction to place the stones in

the slope.

),max( 50 trequiremenonconstructiDknr ns = (15)

3.9 Crest elevation

The rubble mound groin height or the crest elevation is an important parameter in the

groin design. It depends on the maximum possible wave height (Hmax) that would come

across during the lifetime of the groin, wave run-up (R), the free board (FB) requirement and

the permissible overtopping of water.

Hence, crest elevation above the maximum high water line =Hmax+R + FB (16)

The free board is an additional safety provided to the groin to avoid overtopping of

waves and temporary water level setup submerges the groin during the storm cyclones. A

typical value of 1.5m may be assumed for groins. If suitable storm data were available, FB

should suitably be increased from the storm-surge data.

3.9.1 Wave run up

The wave run-up over the groin slope is calculated from the design wave height (H)

and the structure slope ().

2HR= (17)

The wave run-up according to van der Meer and Stam (1991) is given including the

frequency of the wave.


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HR 83.0= (18)

3.10 Design Procedure

Fig. 2 presents the overview of the design procedure of groins. For the preliminary groin

design under the stability criterion, the following steps needed to follow for an adequate groin

section.

a. Determine the water level range for the site.

b. Determine the wave heights.

c. Select suitable groin configurations.

d. Select suitable armor unit type and size (rubble mound/ concrete units and toeprotection).

e. Determine the potential run up to set the crest elevation.

f. Determine the amount of overtopping expected which should not be more than the

allowed.

g. Develop cost estimate for each alternative.

The most critical design elements are a secure foundation to minimize settlement and toe

protection to prevent undermining. Both of these are potential causes of failure of such wallsapart from the main cause of stability of armour units against waves.

>>>> >>>> Hs, Tp, Hmax

Wave history wave spectra Characteristic

wave parameters

Transform offshore wave climate into shallow water

Long term extreme wave statistics

Design wave climate

Preliminary design calculation of armour stability and other layers

Model tests of preliminary design

Final design

Fig. 2 Design procedure of groins


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4.0 DESIGN OF GROINS AT KANYAKUMARI DISTRICT

PWD, WRO, Madurai division, proposed the construction of seven groins at different

sites in the Kanyakumari district following the shore erosion affecting the fishing villages at

Simon Colony, Vaniyakudi, Kurumbanai, Periyakadu, Kovalam, Arokiapuram and Enayam.

The design of various structural components such as armour stone, toe mound and filter bed

layer are detailed below. The core layer and under layers, if any, were also been suggested

based on the design of armour stones.

The main parameters in the design of groin cross section are the water depth and the

design wave height. The various cross sections need to be designed in different water depths

from the shoreline to the tip of the groin. As the general alignment of the groin is along shore

normal, the offshore tip of the groin is subjected to severe wave action from all the possibledirections. Thus, the armour slope of a head section (offshore tip) is adopted flatter than

(1V:2.5V or higher) a typical trunk section. The following sections present typical designs in

water depths of 4.0m and 6.5.

4.1 For a water depth of 4.0 m

Design wave

The design water depth can be calculated from the mean water depth, tidal level and the

water level set up during the storm.

Design water depth = 4m + 0.5 m for storm and tide corrections

= 4.5 m

The maximum possible sustainable wave height in a particular water depth is,

Maximum wave height, Hmax = 0.78 x water depth

= 0.78 x 4.5 = 3.51 m

In the calculation of armour weight, the design wave height, represented by significant wave

height is needed to be established.

Significant wave height, Hs = Hmax / (1.6~2.0)

1.95 m

Armour unit (rubble)

Hudson formula was used for the estimation of the stable weight of armour rubble

stone, W50 from Eq. (5). The following rubble characteristics were assumed. The unit weight

of sea water, w was 1.025 t/m3. The stone available in the near by quarries were rough and


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angular stones with a unit weight, s of 2.65 t / m3. Hence, the stability coefficient, KD was

adopted to be 2.0 from Table 1. This coefficient is for the severe wave climate existing at the

site, i.e., wave breaking on the groin. For trunk section, an armour slope of 1V:1.5H (cot

=1.5) was suggested.From Eq. (5),

W50 = 1650 kg

The nominal median diameter of stones corresponding to the armour rubble stone

weight can be calculated using Eq. (2).

Dn50 = (W50/ s)1/3

= 0.86 m say 1.0m.

Then, the thickness of armour layer (t) can be calculated using Eq. (13). The suggested

number of armour layers was two (n = 2) and the layer coefficient was 1.0.

t = 2.0 m

Hence, 1.25t to 2.0t armour stones in two layers of thickness 2.0 m was provided.

Under-layer

The under-layer stone weights should be one-tenth of armour stone weight (W50/10).

Hence, the under-layer was provided with the stone weighing about mean weight of 125 to

200 kg. From Eq. (13), for two layers of similar under-layers, the layer thickness was 1.0.

Core

Core layer comprises the core part of the groin. Only one under-layer was proposed

for the groins. Hence, the core layer which is below the under-layer should be one-tenth of

under-layer stone weight so that the rubbles in the core would not penetrate through the top

layers. A stone weight of W50/100 can be used which is about 12.5 to 20kg. However, for

practical limitations as well as to serve the purpose of core to avoid silt to pass through the

groin sections, a wider range was usually suggested.

Filter layer

Filter layer or bedding layer acts as a foundation to support the entire structure. The

stones of 10mm to 50 kg were provided as bedding layer to a thickness of 0.5 m.


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Toe mound

A toe mound is to be placed on both sides of the groin for preventing the sliding of the

stones and protecting the groin from slope failure. A toe mound of 3.0 m top width and 2.0 m

height with 1:1.5 side slopes was provided. The toe mound can be built using the stones

similar to under-layer as the armour was supported by the toe mound.

4.2 Design details of groins

Fig. 3 and Fig. 4 present typical cross-sectional details of the groin designed for

Kanyakumari coast in the water depths of 3.0m and 5.0m. Table 3 provides the design details

at various water depths up to 5.5m.

For a water depth above 6.5m and up to 8.0m, the concrete cubes as armour stones

were suggested as shown in Fig. 5. Later, based on the constructional difficulties and the

operational expenses, it was decided to use rough angular stones. Fig. 6 presents the

redesigned groin section in a water depth of 7.5m.

Fig. 7 depicts a typical head section of the groin. The head section directly faces the

wave action and hence, the slope was made flattened compared to the trunk sections. Table 4

presents the design details of the head section using concrete cubes and using random rubbles

as armour units. In the revised design using rubble stones, the slope was flattened to 1:2.5

compared to the concrete cubes in 1:1.5 slope.

Fig. 3. Typical cross section of groin in a water depth of 3.0m


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Fig. 4. Typical cross section of groin in a water depth of 5.0m

Table 3. Typical design details for trunk section up to a water depth of 5.5m

Trunk section 0m to 1m water

depth

1m to 3m water

depth

3m to 5.5m water

depth

Wave Height up to 0.7m Up to 1.0 m Up to 2.5 m

Crest elevation (m) + 3.5 + 3.5 + 3.5

Crest width (m) 4 4 4

Armour layer 300-500 kg (2 layers

of thickness 1.1m)

3001000kg(2 layers

of thickness 1.5m)

500-2500kg(2 layers

of thickness 2.0m)

Slope 1:1.5 1:1.5 1:1.5

Under layer Nil Nil 50-250 kg (thickness

1.0m)

Core layer 1 to 150 kg 1 to 150 kg 1 to 150 kg

Filter layer

(thickness 0.3 m)

1 kg - 50 kg 1 kg - 50 kg 1 kg - 50 kg

Toe 50 100 kg 150 50 kg 250 to 1250 kg

Toe width (m) 3.0 3.0 3.0

Toe height (m) 1.0 2.0 2.0


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Table 4. Comparison of design details of a head section using concrete cubes and rubble

stones as armour units

Fig. 5. Typical cross section of groin using concrete cubes in a water depth of 8.0m

Fig. 6. Modified cross sectional detail of groin using rubble stones in a water depth of6.5m to 7.5m

Head section Concrete cubes Concrete cubes

Crest elevation (m) + 4.5 + 4.5

Crest width (m) 4.0 4.0

Armour layer 2500 kg in 2 layers of

thickness 2.0m

2000 to 3000 kg in 2 layers of

thickness 2.0 m

Slope 1:1.5 1:2.5

Secondary layer 50-250 kg of thickness 1.0m 50-250 kg of thickness 1.0 m

Core layer 1 150 Kg 1 150 Kg

Filter layer 1to50 kg of thickness 0.30 m 1 to 50 kg of thickness 0.30 mToe 250 to 1250 kg 250 to 1250 kg

Toe width (m) 3.0 3.0

Toe thickness (m) 2.0 2.0

3.03.0

1:1.50

23.5

66.5

050

4.0

1.0

3.00.75 3.0 23.5

BEDDING LAYER OF 1 Kg TO 50 Kg OF STONES

1.00.753.0 3.0

SEA BED

ARMOUR LAYER OF 2.0 m TK, 2000 Kg to 3000 kg STONES IN TWO LAYERS

SECONDARY LAYER OF 1.0 m TK, 50 Kg TO 250 Kg STONES

(75% shall be 2500 Kg to 3000 Kg and 25% shall be 2000 Kg to 2500 Kg)


SLOPE1:2.550 SLO

PE1:

2.5

0

(1 Kg TO 150 Kg STONES)

MSL

CORE MATERIAL

50

50

4.0

TOE MOUND OF

250 Kg TO 1250 Kg

MSL


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Fig. 7. A typical head section of a groin in a water depth of 7.5m

4.0 Concluding remarks

The fundamental to the design of groins is the determination of topography,

hydrography, still water characteristics and wave characterisitics. The structural parameters

include the properties of armour units such as shape, dimensions, specific weight, weight of

individual units, porosity, thickness and interlocking qualities etc. The determination of still

water level includes tidal elevation at the site, storm surges and subsequent wind setup.

The ability of a groin to withstand environmental loads is based mainly on the wave

climate, the rock density and the size of armour stone. The size reduction of individual pieces

due to abrasion or breakage may lead to damage of the structure and possibly even failure. It

has been observed that the volume loss of armour stone due to abrasion during the life time of

a groin can be quantified and that material properties can be related to the wave climate and

the structure consideration into a damage model. However the problem of armour stone

breakage due to in service motion is not yet tackled and the determination of stone

movement, stone velocity and the probability of stones breakage still need further work.

Last but not least, even though the sectional design has been carried out using stability

criteria using the widely adopted Hudsons formula, it is however suggested to verify the

stability of the armour layer from a physical model study. None of the empirical model would

be equivalent to the stability test using scale down models.

SLOPE1:2.5

35.25

SECONDARY LAYER OF 1 .0 m TK, 50 Kg TO 250 Kg STONES

23.5


BEDDING LAYER

4.0

1 Kg TO 50 Kg OF STONES

(1 Kg TO 150 Kg STONES)CORE MATERIAL

3.0 250 Kg TO 1250 Kg

1.03.03.0 0.75

SEA BED

TOE MOUND OF

M SL

ARMOU R LAYER OF 2 .0 m TK, 2000 Kg to 3000 kg STONES IN TWO LAYERS



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References

Hudson, R. Y. (1958). Design of Quarry-Stone Cover Layers for Rubble-Mound

Breakwaters; Hydraulic Laboratory Investigation. Research Report No 2-2, US Army

Engineer Waterways Experiment Station, Vicksburg.

CERC, Coastal Engineering Reseach Centre (1984). Shore Protection Manual, vol. I & II.Department of Army, US Army Corps of Engineers, Washington DC, USA.

Van der Meer, J. (1988). Rock Slopes and Gravel Beaches Under Wave Attack. Delft

Hydraulics Laboratory, Ph.D. Dissertation.

Van der Meer, J. W., and Heydra, G. (1991). Rocking armour units: Number, location and

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Publications no. 454, Delft hydraulics, Netherlands.

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Design of Groins