CHAPTER III

BREAQ9fATER FOUNDATION

55

The principle function of a breakwater is to

provide the protection to make loading and unloading vesse' s

possible without risks of damage to the vessels or berthing

facilities resulting from wave and/or current action during

the process BRUNN,1981!.

The site selection for a breakwater is dependent

on the site selection of the entire port. Per Bruun �98l!

reported that "the choice of a particular location for the

establishment of a port depends upon many factors including:

l. Land requi rements.

2. Requirements to depth and space.

3. Requirements for the protection of the

harbor against wave action.

4. Current action

5. Sedimentation to the extent possible.

Richards, Ling and Gerwick �976! stated that

there are two methods in site selection, as follows:

a. Determined by the Structure:

In this method they summarized the methodology of

offshore site investigation as follows:

1. Select potential regions.

2. Compare. Select most desirable regions.

3. Select suitable areas within these regions.

4. Compare and select candidate areas.

5. Select suitable candidate sites within these

areas.

6. Compare. Rank the sites.

7. Select primary candidate sites.

8. Investigations 1 through 7 are based on

available information. At this stage limited

studies on primary candidate sites will be

performed.

9. Compare benefits of candidate sites with

environmental engineering costs.

10. Select prime site.

b. Determined by the Site

In the second method, the site is provided due to

the location of the facilities that the port will service.

This site will control the design and construction of these

structures.

Treadwell, Ridley and lagoon �986! reported that

"Consideration of regional geothechnical conditions early in

the site selection process may reduce costs significantly by

identifying sites which might require extensive variations

from anticipated designs in order to mitigate potential

geologic and seismic hazards. If such a site cannot be

avoided, knowledge of the potential hazards should result in

more realistic site investigation programs, analysis,

designs, and cost estimates."

In either method, complete and detailed

hydrographic surveys are necessary. This phase of the

investigation should be complete to the extent of

supplementing standard survey procedures with bottom

samplings, measurements of existing currents, and

measurements, if possible of amounts and directions of

materials transported by these currents. This data will:

l. Furnish information on foundation

conditions.

2. Provide a permanent record of conditions

prior to construction.

3. Through use of prior surveys, old charts,

maps, etc., indicate any changes the bottom

has undergone.

Foundation conditions must be known accurately in

order to properly design the breakwater to be constructed at

a particular site. The foundation analysis can be made by

means of probings, washborings or drillings. In the

majority of cases, the rock mound type breakwater is

normally selected, unless the bottom is so soft and of such

great depth that an excessive amount of rock would be

required to reach a satisfactory supporting medium. lagoon,

Sloan and Foote l9'74! reported " that a few instances have

been noted where settlement of the flexible portion of a

rubble mound structure with a concrete cap has resulted in a

hole or gap under the rigid cap." This has occurred both at

58

the Crescent City Outer Breakwater and the Hoyo Harbor

north jetty near Fort Bragg, Ca'ifornia.

Brunn �98l! reported that "Foundations for marine

structures deserve as much if not more careful study than

foundations for land structures. Wave forces acting against

a rubble structure have been found to attack the natural

bottom and the structure foundation even at depths usually

thought to be little affected by such forces. A rubble

structure may be protected from settlement resulting from

leaching, piping, undermining or scour, by a bedding layer

or blanket. Blanket mattress protection is explained in

more detail at the end of this chapter. Experience

indicates that using a bedding layer to protect foundations

of rubble mound structures from undermining is advisable

except where:

A. The depths of water are greater than twice

the maximum wave height.

B. The anticipated current velocities are

smaller than those necessary to move the

average size of foundation material, and

the material has suf f icient strength to

prevent settlement of the individual pieces

of stone.

C. The foundation is hard, durable material,

such as bed rack.

59

When large stones are placed directly on a sand

foundation at depths insufficient to avoid wave and current

action on the bottom as in the surf zone! and if an

adequate bedding layer is not provided, the rubble will

settle into the sand until it reaches the depth below which

the sand will not be disturbed by the currents. Actually,

this phenomenon is one of local liquefaction of the sand,

allowing the rock to settle while the sand flows out from

under it.

The planning phase of bathymetric survey will

involve an evaluation of the existing data available from

navigation and specific purpose charts. "Boat sheets"

usually provide sounding data in much greater abundance than

the published navigation chart, which is prepared from the

boat sheets made during the actual bathymetric surveys.

For general survey, side-scan sonar may serve to

cover the area rapidly and to identify natural or artifact

obstacles. Wide-beam echo sounders may be satisfactory for

general bathymetry. For these surveys, conventional

navigation using existing navigation networks may be

adequate for location control. On the other hand, detailed

site surveys may require a degree of accuracy and precision

that may not easily be obtainable using common state-of-the-

arts methods. ln these cases, precise depth determination

may necessitate the use of narrow-beam echo sounders and/or

deep-towed transducers; location control often will require

deploying a special navigation network.

Ships may utilize accurate electronic aids for

navigation, bottom-founded acoustic beacons, or other

methods of location control. Echo sounders or pressure

sensors deployed by submersibles may be effective for

accurate depth determination in limited areas. With the use

of inertial guidance and transponders on the sea floor, it

has become possible to make very accurate and detailled

surveys. However, these methods are very costly, and cannot

be used in the surf zone.

Identification of surface soil materials adequate

for some siting purposes may be obtained from nautical chart

bottom notations, from atlases published by hydrographic or

oceanographic agencies, and from the quality of seafloor

traces appearing on echograms.

Sampling methods can be approximately divided

according to penetration distances below the seafloar.

Surface sampling, to a depth of a few meters, can be

undertaken by grab-type samplers or short cores from a

stationary vessel. 8'ree-fall type short corers or grab-

samples can be taken f rom ships underway. Box gravity-type

corers often provide high quality short cores. Short cores

or grab samples can also be obtained from a submersible or

by divers.

61

Brown �971! suggested the use of a piston coring

device which can retrieve undisturbed samples of the ocean

bottom. This device can yield eleven ft. cores in soft

clays, six ft. cores in hard-packed sand, and one ft. cores

in stiff clays. Need3.ess to say, sampling of loose

surficial sediments is a very difficult task as the

structure cannot be preserved during sampling. Core

penetrometer tests may be used as an indication of the

relative density of sands.

Sampling to a depth of about 38 � 58 m is

conventionally done using marine-geological types of piston

corers. For all piston corers, if the piston is movable

relative to the bottom during the drive stroke, the piston

corer is dynamically operated. If the piston is fixed with

respect to the seafloor during the drive stroke, then the

piston cover operates statically. The latter method is

preferable.

FOUNDATION FAILURES

Foundation failures can be classified as follows:

1. Shear failures.

2. Migration of sand under wave and current

actions.

3. Scour.

4.Settlement

5. Liquefaction.

62

1. SOIL FAILURE DUE TO ITS OWN INSTABILITY:

SHEAR FAILURE OR LANDSLIDE

Underwater shear fai1ures can be initiated by

dynamic forces due to waves, earthquakes, and construction

operations. These shear failure,s once initiated can

propagate, leading to more extensive damage.

The shear strength characteristics of sands and

inorganic silt unless the soil is exceptionally loose! are

calculated by Terzaghi and Peck �967! as:

c = p � "w ! tan 8! = p tan �!Where:

c ~ shear strength

p = confining pressure

pore water pressure

0 ~ angle of internal friction

p = p � w = effective pressure

Figure �.1! shows a shear failure occurring

during the dumping of rock onto the seafloor. Such shear

failures are due to both the static load and the dynamic

shock, the later diminishing the effective shear strength

by causing a sudden rise in pore pressure.

63

Sea Water I eveI

Shows a shear failure occurring during thedumping of rock onto the seafloor. Such shearfailures are due to both the static and the

dynamic shock, the latter diminishing theeffective shear strength by causing a suddenrise in pore pressure.

Pigure 3.1:

SMEAR FAIL,URE DUE TQ STATIC I OAD AND DYNAMIC SMOCK

64

2. MIGRATION OP SAND UNDER WAVE ACTIONS SEEPAGE:

Rocking motion may induce seepage forces pumping

action! in the soil, resulting in tunnelling internal

erosion!. Soil compaction or drainage methods may be

possible solutions.

3. SCOUR

Massive breakwaters placed on the ocean floor

cause local changes in the current pattern in that

particular area. This can lead to local scouring,

especially i f the sea floor is a sandy bottom. Scour holes

can then affect the stability of the breakwater and cause

failure.

Scour is the removal of seafloor soils caused by

currents and waves: the potential for scour is particuarly

great in locations with sand and silt at to the seafloor.

Scour can result in removing vertical and lateral support

for the rock near the periphery, causing undermining of the

toe rock.

Zeevaert�957! reported that the spreading of

the rock mound because of erosion is a very important

phenomenon that may take place because of erosion at the

foot of the slope of partially submerged breakwaters on f ine

cohesionless sediments, such as fine sand. This phenomenon

is facilitated as the fine sand becomes loose during

spontaneous liquefaction. Let the figure 3.2 ! be the

65

slope of a partially submerged breakwater. As the crest of

the ~ater wave travels along the slope, the water fills up

the voids left in the rock mounds During the following

trough of the wave, because of the lower water level, the

water flows strongly out from the inside of the rock fill,

producing a strong erosion in the f ine sand at the base.

Therefore, the stability of the slope may be lost and

spreading may take place. Furthermore, the combined effect

of the uplift pressure and the horizontal force produced by

the rapid drawdown as the trough of the wave passes along

may eventually produce a total spreading of the fill. The

shearing strength at the base of the rock mound may be not

enough to counteract the internal water force developed in

the rock mound.

The grain size of cohesionless soil has a great

influence on the amount of scour; the larger the size, the

less the scour. The figure 3.3 ! represents a relationship

between flow velocity, particle transport and erosion

susceptibility as a function of grain size, Zeevaert,1957!.

66

E R 0 S l ON IN THE ROCK MOUND

Pigure 3. 2 Zeevaert,l957!

67

IOOO

O.lO.OOI O.OI O. I I

Par ficle Diometer mm!

I 00

Fig 3. 3 Zeevaert,1957!

IOOE

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TRANSPORT AND EROSION SUSCEPTIBILITY 4S

4 FUNCTION OF GRAIN SIZE 4ND FLOW VELOCITY

68

4. SETTLEMENT

When a heavy breakwater is constructed on fine

sand, silt and clay sediments, large settlements of the fill

may occur due to excessive loading of the soils. Settlement

may also be the result of exceeding the allowable mechanical

properties of shearing strength and compressibility of the

soft clay deposit, Zeevaert,l,957!.

Excessive settlements and shear failures may be

avoided by controlling the rate of deposition or even

carrying it out in stages! and by avoiding dynamic effects,

so as to allow the soil to gain in strength before it has to

resist the maximum load. Another solution that has proven

to be very effective is to widen the base course reducing

the slope ! and even placement of berms on either side of

the breakater so as to counter the shear forces under the

breakwater proper.

5. L l QUEFACTI ON

Liquefaction is a phenomenon in which a

cohesionless soil loses its strength, due to excessive pore

water pressure build-up during an earthquake, storm waves,

or shock, and acquires a degree of mobility sufficient to

permit local or area movements. The essential factors

influencing liquefaction potential are:

a. Soil Type grai n size distribution!

Uniformly graded materials are more

susceptible to liquefaction than well-graded

mater ial. For uni formly graded mater ial,

fine sands tend to liquify more easily

than do coarse sands.

b. Relative Density void ratio!. Loose sand

R 78 % ! may liquify.

c. Initial Confining Pressure.

The liquefaction potential of a soil is

reduced by an increase in confining

overburden pressure!.pressures

d. Intensity of Ground Shaking or Impact Shock.

e. Duration of Ground Shaking.

Although factors d. and e. can not be controlled,

factor c. can be increased by surcharge, and factor b. can

be improved by compaction. In the case of imported fill

material, factor a. may be controlled. In many other types

of projects other than breakwaters! various compaction

techniques are frequently carried out in order to prevent

liquefaction, since they are usually practicable and

economical.

Provision of drainage, so that the excess pore

water pressure can escape, is another solution. This can be

accomplished by placing a filter blanket of small rock on

sea floor.

In no case should a breakwater be used where the

strength of the bottom is not sufficient to support the load

without excessive settlement, as this may eventually result

in the failure of the breakwater due to uneven settlement.

However, it may be possible to consolidate the soft material

by a

l. Dumping rock until a stabilized base has

been built and allow it to settle for a

period of time prior to constructing the

upper part of the breakwater. Waiting allows

the remolding effect from the dumping of the

rock to dissipate and the clay to regain its

shear strength.

2. Placing a vide blanket of rock first, say

three times the width of the breakwater

base. The wide blanket will confine the

soil under the breakwater proper. Combined

with a period of waiting, the critical

strength at the edges of the dike will be

improved.

3. Excavate dredge! a trench to firm material

and refill with rock or other good

foundation material.

7l

Dredging could be done by one of the folloving types of

equi pment:

CuuesaELL

In this method a floating crane is employed,

with a clamshell bucket different sizes are

available!. This operation is very slow and

currents may partially refill these trenches

before the placing of the firm foundation

materials. Therefore, the trench may need to

have a supplemental cleaning operation just

prior ta placement of the rock. See figure

�.4! showing a clamshell dredging

operation. Another disadvantage of this

operation is that it is very difficult to

dredge the seafloor in an even and uniform

pattern. On the other hand a clamshell

dredge may be operated in moderate sea

states and even in the surf. It is not

depth limited.

~+F

gf

p

Figure 3.4: Clamshell Or> dying Opera . ion

73

HYDRAULIC DREDGE

There are many different types and sizes of

hydraulic dredges. Depending on the nature

of the sea, the depth and the work required

a specific type of hydraulic dredge may be

selected.

Figure �.5! represents a Cutter Suction Dredge of

the Beaver 4888 type.

Figure �.6! represents a Hydroland Cutter Suction

Dredge.

Figure �.7! represents a dredging operation

showing the drege Umpqua 'Fisher" loading a dump barge in

the San Francisco Bay.

Figure �.8! represents a "Seal" bucket dredge,

Umpqua, dredging in the San Francisco Harbour.

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78

DIFFERENT SOLUTIONS POR SOIL IMPROVEMENT TECHNIQUES TO

STRENGTHEN OFFSHORE FOUNDATIONS

Soil improvement techniques can be classified as

follows:

1. Vibro-compaction and vibro-displacement

compaction.

A. Blasting

B. Heavy duty penetrating vibrators

Terraprobe, Vibroflotation see figure

3.9 !, Toyomenka, Dutch Vibratory Probe,

Tomen! etc..!

C. Vibratory rollers surface compaction!

D. Compaction pile

E. Heavy tamping dynam i c consol idat 1 on!

also known as the "Menard Method"

2. Grouting and Injection

A. Particulate grout

B. Chemical grout

3. Preloading surcharging!. This may be

accompanied by wicks or sand drains to

facilitate drainage of the foundation soils.

4. Displacement. Rapid and continous dumping

can be used to create shear failures in the

weak surficial soils, so as to push a mud

79

wave ahead of the rubble fill.

The technique applicable to a specific project is

determined by a number of factors, especially the grain size

of the soil to be stabilized and the sea conditions at the

site.

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81

1. VIBRO~ONPACTION AND VIBRO-DISP~CEHENT CONPACTIQN

The basic concept of vibro-compaction is that

vibration and shock waves in loose saturated cohesionless

soils cause liquifaction followed by densification and

settlement accompanying the dissipation of excess pore water

pressures. The effectiveness of this method is greatly

reduced if there are more than 28% of silt or 5%, clay size

material, primarily because the hydraulic conductivity of

such material is too low to allow rapid drainage following

liquifaction.

Vibro-displacement compaction is similar to

vibrocompaction except that the vibrations are supplemented

by active displacement of the soil. Appendix B shows one

such system used to consolidate land fills: this could also

be applied in shallow water.

Blasting transmits shock waves through the soil

which momentarily liquefy it. Then as it drains and

reconsolidates, it acheives a higher densification and

strength.

Vibratory rollers act directly on the seabed and,

just as in dry land applications, result in densification of

the surficial soils.

Terraprobe and compaction pile give the vibration

to the probe or pile first, and then the vibration is

82

transfered to the soil. The stress wave excited at the pile

top may move through a pile without loss, because the

frictional resistance of water is negligible. Therefore,

vibration energy may be transmitted to the soil almost

completely.

The Japanese have carried out underwater

compaction using a sea bottom crawler tractor: this however

is of questionable applicability to the typical breakwater.

DYNAM ZC CONSOLIDATION

"Dynamic Consolidation" is the term used to denote

the method of compaction in which a large weight is

repeatedly dropped, so as to cause local shock waves. A

sudden rise in pore pressure is followed by liquefaction,

then reconsolidation in a more dense state.

The efficiency of dynamic consolidation will be

reduced in underwater operation due to the viscous damping

force of water.

Dynamic consolidation may work well in

consolidation of underwater fills up to 4 � 5 m thick.

Dynamic consolidation can be applied to a great range of

various soil types. It can be carried out in moderate sea

conditions. Figure �.ll! shows a schematic of the operation

procedures of such a system.

83

~Ee

84

BLASTING

Mitchell �976! states that, although blasting is

one of the most economical stabilization methods, with low

costs, it suffers the disadvantages of non-uniformity,

potential adverse effects on adjacent structures, and

dangers associated with the use of explosives in populated

areas, or near to other constructed facilities. In the

water, fish will be killed.

Nost of these methods for soil consolidation can

be applied to offshore breakwater foundations, depending on

the availability of equipment and the type of soil to be

compacted, and the sea conditions at the site.

Figure �.ll! shows the applicable grain size

ranges used in different stabilization methods. The ranges

vary from clay to gravel depending on the nature of the sea

floor material.

Figure �.12! displays a schematic of the

different methods of compaction mechanics described earlier.

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VIBRO FLUTATZON TZRRAP ROSE

COMPACTION PILE

Pigure 3.l2:A schematic of the different methods of compactionmechanics described earlier.

87

The following tables �11.1,2,3,4,5,! taken f rom

the Army Corps of Engineers design manual �976! represent

the different methods of soil stabilization for foundations

of structures. They detail the relationship between these

methods and the soil conditions, effective depth and the

area in which they can be most effective. They also note

the special material and equipment required for each method,

as well as their advantages and limitations.

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93

STABII IZXMG THE SEABED POUNDATXON

Experience in many breakwaters placed on seabed

sands shows that the surfici al layers may locally liquefy

during the dumping of the core rock, thus allowing the rock

to work down into the sand. Later, under service

conditions, the pore pressures may be increased by the

dynamic pounding of the waves, leading to local

liquifaction, settLement of the breakwater, and migration of

sand up into the core. This phenomenon has occured on the

Oregon coast and on the East Coast of India.

One solution, as prac, iced in India, is to place

an initial filter course of small rock, blanketing the sea

floor. Then the core rock is dumped on this. The Dutch, in

carying out their Delta Plan, have developed a number of

schemes, based on the principle of laying a filter carpet or

mattress on the seafloor sands. This mattress is designed

to initially protect the sands from scour and additional

loosening by wave action until the core can be placed. Then

the mattress functions as a filter, to provide relief of

pore pressure without upward miqration of the sands.

These practices of soil densification, followed by

laying of a filter mattress, are currently being carried out

in a very sophisticated manner on the Oosterschelde Storm

Surge Barrier in The Netherlands. This mammouth project

requires the construci ton of an underwater rock dike across

94

the mouth of the Eastern Scheldt. f.ater, caissons will be

set on the dike.

For the Oosterschelde Storm Surge Barrier, a

trench was first dredged in the unconsolidated sands, then

filled back with small rock. They then employed vibrating

probes to penetrate the loose underlying sands and compact

them by vibration. Figures �.13! and �.l4! show the barge

mounted plant and the sequence of operatio~.

Figure 3.l 3: 'lee U

Used iri

Sea i ~=or�.

Figure 3.14: Schematic Shcw inq The Rr. pCO Alps C'C ' AC Bh YGe .~.L 8 ~ YK

The second step involved the placement of a

protective layer of filter fabric mattresses weighted with

concrete blocks. Then the construction of submerged dike

followed. Appendix A illustrates a brochure describing the

filter assembly plant used in the Oasterschelde Storm Surge

Barrier.

The next section presents different methods of

placement of mattresses or filter cloth on the bottom of the

sea to prevent migration of sand or small soil particles

from foundation. These filter mattresses act to relieve the

pore pressures generated in the sands below during the

dumping of the breakwater core and subsequently by the

dynamic impact of breaking waves. They also serve to

protect the seabed from erosion and disturbance during the

initial periods of breakwater construction.

97

FASCINE MATTRESS WITH POLYPROPYLENK FILTRE CLOTH

The mattress consists of a polypropylene filter

cloth weight 788 g/sm! with fixed lashings polypropylene

ropes!, one layer of willow thickness 188 mm. when loose!

and two frameworks of wieps in the form of squares at 1 m.

centres.

The machine-made wieps have a circumference of not

less than 358 mm. throughout.

The total thickness of these mattresses is about

488 mm. including 8,488 t./sqm stone!.

These mattresses protect a sandy bottom far better

then fascine mattresses without filtre cloth.

They are practiced by the Deltaworks in Holland.

98

tigore3.l5: Nap of the Delta Works and Seacoast, Dikes ofThe Ne the r 3.ands

Figure 3.16: Placement of Filter Fabric Nattresses onSeabed

-jr=.:.:: j=='-:=! 1 -.,:==.i -::i =-.= ir-..::>j:=,-::-i::=:: ji==--.:j~j==..:=-Jl=-'==-- =4~~'-': J4~:=-Jj==~~&-==- =-= � �. =--=-'=-=" j.:=ii--=:="-~I==---!~3<<i== � '= jiQ=-==-!I=:= � '� I='= j jJI== = 1 +~i~~r=-..-- j'=- = i'=-: i=:=tj+=-='=-=

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BiFOUR WIEPS AND A LAYKII OF WILLOW.

FASCINE MATTRESS

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WIK P

wIE.P A <C' 4 LAYrOF " ' LO'hV

POLY P'.~OPYLK I'l

FILTRE-Q LQ'l i100 100

SECTION. 8.

Figure 3.17: Fascine Mattress With Polypropylene FilterCloth

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hphase l placed in position to start sinking

182

botton

phase g sinking of the sinking tube

phase 3 rarp i nq ad j ust i ng pontoonrarping and start stone dueping

phase 4 going on stone duaping sinking of adjusting tube adj pontoon inposition

XV e st ng rork

Figure 3.l9: Laying of Filter Fabric Mattress on Seabed:Installation Scheme

F i g u r e 3. 28: -'a y. r, g,< a - -.: e s s

F iqure 3. 2l: ~ay''nq Na tv.r ~s"=

l84

ADVANTAGES OFFERED BY PLASTIC FILTER FABRICS

The f iltering ability permeability and

particle retention! is factory controlled

and cannot be altered due to careless

placement.

2. They possess good tensile strength, thus

preventing rupture during subsequent rock

placement.

3. Quick visual inspection assures architects

and engineer the filter is in place as

designed. Screening and inspection of

graded material, and inspection of placement

to insure proper thickness and compaction

are eliminated!.

4. Permit greater opportunity for consistency in

filter design.

5. Geographic location and availability of

materials sand and gravel! are eliminated

as economic considerations in the design of

the filter system.

Relief of water presssure and prevention of loss

of soil is important in any design; it is especially

critical in a rock structure. Since a rock structure has no

independent strength, it depends upon the soil for its

l85

stability; if soil leaches thru the armoring units, the

structu=e will f ail.

Poly-Filter X, Filter-X, and Poly-Filter GB have

been successfully used to stabilize structures armored with

rock, sand-cement riprap, interlocking concrete block, and

Gabions.

Figures �.22! and �.23! illustrate a filter

fabric applied under a breakwater base.

The Architect/Engineer has difficUlty with conventionalfitter blankets in breakwater, jetty, or groin construction. since thelightweight stone is otten washed away before the heavier units arein a!ace. POLY&!LTER X / F!LTD X used as the base filter haseliminated this problem in many coastal projects.

tigure 3.22: Filter Fabrics Applied Under Breakwater

l87

ALT ER NATE TOETREATMENT

M LW. ~0.0'

M.L W. -2' PERMEASLE ROClC REVETMENT ALTERNATE TOETREATMENT

MLW ~ l

SPANlSN METHOO

Pigure 3.23: Filter Fabrics Applied Under Breakwater

APPLYING A SANDNASTIC CARPET ON THE SEABED

Another method of preparing the seabed is

illustrated by the figures �.24 and 3.25!. Zn this method

the converted ship by the name "Jan Heijmans"! lays large

sand-asphalt mattresses. Recent research reported by Prof.

C. Nonosmith at the University of California a5 Berkeley

indicates that rubber asphalt may produce a more flexible

and resilient matrix for the sand-asphalt carpet.

The asphalt layers can be applied under water at a

depth up to 28m �6 ft.! by a vessel equipped with asphalt

making machinery. The nylon carpeting is unrolled from a

trolley towed along the sea bottom. The carpeting has

pockets at regular intervals filled with sand for

ballasting. The ballasting of these underwater protective

layers is also done mechanically.

Appendix I represents some illustrations and

schematics demonstrating the sandmastic application process.

l89

~ESNC

tQStt ~ t ~ ~ ~ ~ o' + ~ ~~ ~ ~ ~ ~ S ~ !yee res a ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~S Iyvee r~~ a I~ ~ ~ ~ 0 0 I AI ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ OO ~ +~ y ~ ~ ~ ~ ~ ~ ~ ~~ 5 V i ~ ~ ~ ~ ~ t ~ ~ ~ ~ t +t ~ ~~ ~ ~ ~ 1 ~ ~ ~ ~ ~ ~ ~ ~ 92!~ ~ ~ ~ ~ A + t 0 ~ ~ ~ ~ ~ ~Ye ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ' ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ 0 ~ ~ ~ ~ t t ~ ~ y ~ ~ ~ ~ ~V V ~ ~ 4 ~ ~ ~ ~ ~ ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ ~ ~~ ~ ~ 92 ~ ~ ~~ V 4 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~92 ~ ~ ~ ~ ~ ~V Y~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ 4 ~ ~ ~ ~ ~ ~~ 0 ' ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~ 4 ~ ~ ~ ~ ~ ~~ ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~Ve ~ ~ e%eA o eoeo eAeA er

Figure 3.24: A Roller Trolley Used for Laying Nylon Cloth

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