TP-Growth and Development of Geotextile Containers

Case Studies Showing the Growth and Development of
Geotextile Sand Containers
An Australian Perspective

Mr S.J . Restall Mr L.A. J ackson
Soil Filters Australia Pty Ltd International Coastal Management
P O Box 727 P O Box 7196 G.C.M.C.
Southport, Queensland, 4215 Gold Coast 9726
Ph: +61 7 5539 3600 Ph: +61 7 5564 0564
Fax: +61 7 4439 4027 Fax: +61 7 5532 9147
e-mail: [email protected] e-mail: J [email protected]

Dr Ing. Georg Heerten Mr W.P. Hornsey*
Naue Fasertechnik GmbH & Co Soil Filters Australia Pty Ltd
Wartmuntsr. 1 D-32312 P O Box 727
Luebbecke Germany Southport, Queensland, 4215
Ph: +49 57 4140 0810 Ph: +61 7 5539 3600
Fax: +49 57 4140 0883 Fax: +61 7 4439 4027
e-mail: [email protected] e-mail: [email protected]

ABSTRACT

Soil Filters Australia Pty Ltd has been involved in the manufacture and
installation of geotextile containers in a variety of forms since early 1984, this
relates to 17 years experience in the field.
This paper outlines the historical development of the types of materials
used for geotextile containers and the diversity of applications in which these
containers are being used. The type of geotextile used for the containers varies
depending on installation conditions. This information has been compiled from
years of experience. The range of application for these products is extensive and
covers areas such as scour protection, groynes, berms, artificial reefs and
containment of hazardous materials.
The development of this form of coastal protection, has developed to such
a stage that in many cases it is no longer regarded as an alternative construction
method but rather the desired solution. This is not to say that there is not a great
deal still to be learnt from this type of protection
Initially the main emphasis was on hydraulically filled geotextile tubes
(typically 1.2m∅) used mainly as groynes to protect beaches. With time this
focus has changed to individual containers used in coastline protection and
marine structures (reefs).

Key Words: Geotextile, Containers, Tubes, Coastal, Australia




1 INTRODUCTION

A significant number of structures in the Australasian region have been
constructed using sand contained in geotextile forms over the last 20 years. The
practical experience has resulted in an evolution of the state of the art with
improved materials, design methods and construction methods. With the
increasing number of diverse community groups involved in the process of
consultation, planning and approval, in some cases geotextile structures are
providing solutions to coastal protection and improvement where traditional
materials and their impacts and costs have not been acceptable to the
community and approval authorities.
A range of coastal protection projects using sand filled geotextile
structures have been constructed in Australia at sites from estuarine to open
coast since 1985. Numerous identified sites are as listed below:

Green Island
Gold Coast Broadwater
North Kirra Groyne
Russell Heads
Lake Victoria
Maroochydore River and Beach
Kinka Beach
Great Keppel Island
Hamilton Island
Troubridge Island
Airlie Island
Towra Point
Belongil Spit
Stockton Beach
Motueka N.Z
Waihi N.Z.
Narrowneck Reef
Maroochydore Groyne

Selected benchmark projects have been evaluated and show the progression to
the present “state of the art”.
2 BENCHMARK PROJ ECTS

2.1 North Kirra Groyne


Fig. 1. North Kirra Groyne


2.1.1 Project location

North Kirra, Gold Coast, Queensland

2.1.2 Date constructed

September 1985

2.1.3 Principal

Gold Coast City Council

2.1.4 Description

120m long x 5m high sand-filled groyne

2.1.5 Cost

~Aus$350,000 (cost of the rock alternative was estimated at Aus$600,000)

2.1.6 Project objectives

A temporary structure was needed to retain nourishment to restore the eroded
beach, whilst long-term nourishment solutions were resolved to restore the long
eroded southern Gold Coast beaches. The eroded conditions of these beaches
had long been associated with the economic down turn of the immediate area
due to poor tourism figures.

2.1.7 Site conditions

Easterly facing open surf beach with an offshore max wave height of >12m.

2.1.8 Community requirements and constraints

As the site is a popular surfing area and site of the local surf life saving club,
therefore the structure had to be safe for swimmers and surfers. It also needed
to be removable if necessary after a permanent solution was implemented.

2.1.9 Construction techniques

The sand filled geotextile groyne was constructed of 100m long tubes
encapsulated in geotextile envelopes (Figure 2). To minimise risk during
construction, and to allow for erosion of the seabed after construction, the groyne
was constructed in a de-watered excavation following initial beach nourishment.
This construction technique required an all weather, around the clock program,
utilising a six-inch suction dredge pumping a series of one-metre diameter non-
woven geotextile tubes that in turn were completely encapsulated in geotextile
envelopes. In order to minimise the time spent on site sewing geotextiles
together to form the seeled envelopes, the encapsulating geotextile was supplied
pre-manufactured 115m long by 20m wide (5 standard roll widths) dispensed
from a hydraulically driven mandrill.
12.0 m
RL -1.5m
Terrafix 1200R
Encapsulating Envelope
1.2m dia. Sand filled Geotextile Tubes
Void between tubes
filled with dredged material


Fig. 2. Groyne X-Section



2.1.10 Geosynthetics used

Heavy duty UV stabilised non-woven staple fibre needle punched geotextile
(Terrafix 1200R
®
) with high tenacity polyester thread in all seams.

Table 1
Geotextile Tube & Geotextile Envelope Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
5.5mm 10 kN @ 60%
65kN/m XD
38kN/m MD
Min. 80% of
base fabric


2.1.11 Evaluation and comments

The project was ambitious in regards to the size of the structure and location in
an active surf zone. Conventional armour units were not an acceptable option
due to the cost and difficulty associated with the ultimate removal of rock or
concrete. This groyne was a success in terms of achieving its primary objective
of a safe temporary structure for beach stabilisation despite damage to the
seaward end due to vandalism. The groyne length was reduced by about 20m,
due to vandalism, before it was completely covered by a regional nourishment
scheme commenced in 1990.
Experience with vandalism lead to trials of coatings such as bitumen and
early patching techniques. As damage to a single long tube can have a
significant effect on the integrity of the structure there has been a trend away
from long tubes to smaller containers in order to isolate / mitigate damage.
Tubes still have an application where sufficient protection can be provided and
the techniques developed at North Kirra have been utilised on other tube
projects.
















2.2 Russell Heads



























Fig. 3. Aerial view of Russell Heads

2.2.1 Project Location

Russell Heads (Woolamaroo South), North Queensland. Boundered by Mutchero
Inlet River mouth at Constantine Point.

2.2.2 Date Constructed

1993 onwards

2.2.3 Principal

Local community

2.2.4 Description

250m long sand filled geotextile berms

2.2.5 Cost

Not Available

2.2.6 Project Objectives
Community based program to construct hydraulically filled tubes progressively as
a beach stabilisation structure.

2.2.7 Site Conditions

Russell Heads is a fragile residential peninsula that has endured sixty years of
recorded erosion influenced by a dynamic river system and seasonal cyclones.

2.2.8 Community Requirements and Constraints

The comparatively remote location limited resources and lack of government
funding presented a serious dilemma for the small Russell Heads community.
What was needed was a solution which would allow the community themselves
to construct the protection works and with very little expensive/specialist plant
requirements.

2.2.9 Construction Techniques

By combining their resources, the community constructed a small dredge
enabling them to install hydraulically 1.2m dia. sand filled geotextile tubes and
nourish the beach in a series of progressive “working bees”. This program has
continued for a number of years.

2.2.10 Geosynthetics used

Heavy duty UV stabilised non-woven staple fibre needle punched geotextile with
high tenacity polyester thread in all seams.

Table 2
Geotextile Tube Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
5.5mm 10 kN @ 60%
65kN/m XD
38kN/m MD
Min. 80% of
base fabric

2.2.11 Evaluation and Comment

The results of the resident’s actions have been positive. Several houses were
saved as a result of these works during cyclone J ustin in 1997.
Although the wave climate was such that displacement of the tubes
occurred, the inherent flexibility of the no woven needle punched material utilised
enabled re-alignment and settlement to follow scour contours and continue to
provide stabilising protection.

2.3 Maroochy River Groynes

Fig. 4. Maroochy River Groynes


2.3.1 Project location

Maroochy River, Maroochydore, Queensland

2.3.2 Date constructed

1994

2.3.3 Principal

Maroochy Shire Council

2.3.4 Description

50m long x 4m high sand-filled groyne

2.3.5 Cost

Aus$219,000

2.3.6 Project objectives

To put in place appropriate mechanisms to impede the increasing erosion and
river alignment. (Full details of the investigation are covered in the paper by
Coughlan and Mootoo 1995).

2.3.7 Site Conditions

The southern bank of the Maroochy River is a popular tourist destination fronting
a large Council operated Caravan Park, which has suffered severe erosion since
the 1980’s.

2.3.8 Community requirements and constraints

To ensure the nourishment and stabilisation process provided a ‘user-friendly’
amenity without spoiling the natural beauty and popularity.

2.3.9 Construction techniques

Two substantial groynes were constructed utilising sand filled geotextile tubes.
Each groyne was fifty metres long and the design incorporated an extensive
foundation layer to counter potential scour as indicated in the physical modelling.
The constructed height of over 4.0 metres utilising a multiple stack of 1.2
metre diameter tubes, incorporated a 30kN/m geogrid in the foundation layers
and first layer, fully encapsulating the respective layer to prevent the possibility of
lateral displacement (Figure 5).

1.2m dia. Geotextile Tubes
Geogrid
100mm Grout injected mattress


Fig. 5. Section through groyne structure

The tubes were manufactured from polyester staple fibre needle punched
geotextile, and were filled by Council day labour work crews in conjunction with
planned sand nourishment. Having learnt from the Kirra project where vandalism
compromised the integrity of the groyne as a long term solution the Council opted
to encapsulate the two groyne structures in a grout injected mattress for
additional resistance to vandalism and pedestrian traffic.

2.3.10 Geosynthetics used

Heavy duty UV stabilised non-woven staple fibre needle punched geotextile
tubes with high tenacity polyester thread in all seams. Tenax
®
LBO301 Bi-
oriented polypropylene geogrid and Fabri-form polyester woven multifilament
grout injected mattress
Table 3
Geotextile Tube Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
5.5mm 10 kN @ 60%
65kN/m XD
38kN/m MD
Min. 80% of
base fabric

Table 4
Geogrid Characteristics
Aperture
Tensile
strength
Elongation
40mm x 30mm
31kN/m XD
19kN/m MD
11%
16%

Table 5
Mattress Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
No information available


2.3.11 Evaluation and Comment

Six years after installation, the groyne structures are performing in accordance
with the design expectations, and the amenity of the area is vastly improved.
Wide beach widths are now the norm with no nourishment taking place. The
grout-injected mattress used to protect structure has prevented vandalism
however the fabric portion of the mattress has deteriorated substantially exposing
sharp grout edges and this could pose some health and safety risks to
pedestrians. This type of rigid cover/facing is not suited to a flexible geotextile
structures, hence the investigation into flexible hardwearing cover layers, such as
impregnated and composite fabrics which when combined provide strength,
elongation and high wearing and puncture resistance.

2.4 Stockton Beach Revetment


Fig. 6. Stockton Beach December 2000


2.4.1 Project location

Stockton Beach is located to the north of the Hunter River trained entrance in
Newcastle.

2.4.2 Date constructed

1996

2.4.3 Principal

Newcastle City Council

2.4.4 Description

48m long by 4.5m high double layer sand container revetment, at a 1.5H:1V
slope.

2.4.5 Cost

Aus$24,000 (materials only)

2.4.6 Project objectives

To provide temporary erosion protection to the Surf club. Severe erosion to the
beachfront at Stockton beach had placed the Stockton Beach Surf Lifesaving
Club in danger of collapse. Due to state government regulatory requirements an
interim measure was the only rapid solution whilst a coastal management plan
was finalised.

2.4.7 Site conditions

Exposed ocean beach with wave heights of greater than 5m.

2.4.8 Community requirements and constraints

A user-friendly aesthetically pleasing structure.

2.4.9 Construction techniques

The empty geotextile containers are placed in a filling frame and filled using an
excavator, the container is then sewn closed using a hand held sewing machine.
The containers are then lifted and placed using a modified rock grab, the rock
grab is modified in such a way as to limit the stress on the geotextile during the
lifting operation.
The containers when full were 1.5m x 1.1m x 0.4m and were laid in a
stretcher bond format to ensure maximum interlock at a 1.5H:1V slope. A self-
healing “Dutch Toe” was incorporated into the design to prevent scouring of the
toe of the wall during large storm events. The figure 7 shows the “as built” double
skin container layout and the self-healing toe detail.

1000
2152R (2 tonne)
Soft Rock Containers
terrafix 900R
Toe Detail
0.0 AHD
-1.0 AHD
terrafix 900R
2152R (2 tonne)
Soft Rock Container
2152R (2 tonne)
Soft Rock Container
Encapsulated self healing toe
Wall X-Section
Toe Detail
-1.0 AHD
terrafix 900R

Fig. 7. Wall Section & Self Healing Toe Detail

2.4.10 Geosynthetics used

2t Terrafix
®
Soft Rock
®
geotextile containers and Heavy duty UV stabilised non-
woven staple fibre needle punched geotextile (Terrafix
®
900R)

Table 6
Geotextile Container Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
5.3mm 7.0 kN @ 60%
42kN/m XD
27kN/m MD
Min. 80% of
base fabric

Table 7
Geotextile characteristics
Thickness CBR Burst
Tensile
strength
5.3mm 7.9 kN @ 60%
50kN/m XD
28kN/m MD




2.4.11 Evaluation and comment

This was the first of the engineered sandbag revetments constructed to protect
oceanfront properties. The option to construct in this manner was largely
influenced by the immediate need for protection of the site. The revetment was
built as a temporary/removable structure, as approvals for a permanent structure
would not have been issued without a full environmental assessment, into the
impact of the long term/permanent proposal. Time taken to prepare the
documentation and receive approvals for a permanent solution, i.e. the more
conventional rock wall approach, would have delayed the project for some
months and would undoubtable have lead the loss of the valuable surf lifesaving
club buildings. The loss of the structure was unacceptable to both the Newcastle
City Council (owners of the property) and the general public.
Despite the “temporary” nature of the structure, the non-woven geotextile
containers have withstood a number of storm cycles over five years of service.
This installation has outlived the original design requirements and met the
objectives of protecting the surf club whilst complying with providing a ‘soft’
interim solution to the total coastal management problem at this site. The “soft
solution has also proven popular with beach goers who find the structure a user
friendly option when compared with conventional rock and concrete structures.
To date no “permanent” works have been carried out and further extensive
works, using Sand Containers, have been proposed for the properties adjacent to
the site with construction due to begin in late 2002.
The success of this revetment has lead to a number of other areas such
as Belongil Spit at Byron Bay, Airlie Is in W.A, Troubridge Is in S.A. utilising
similar site appropriate techniques. The colour of the geotextile was important to
some clients who wanted the structure to blend in with the natural surroundings
to make the structure as unobtrusive as possible. The advantage on the
nonwoven geotextile in regard to this requirement is that the open structure traps
the local soil / sand and therefore takes on the colour of the surrounding area.
















2.5 Narrowneck Reef



















Fig. 8. Narrowneck Artificial Reef Aerial View

2.5.1 Project location

A narrow isthmus between Surfers Paradise and Main Beach, Gold Coast,
Queensland

2.5.2 Date Constructed

1999-2001

2.5.3 Principal

Gold Coast City Council

2.5.4 Description

400m x 200m Submerged reef

2.5.5 Cost

Aus$2.5M (The cost of rock was estimated at ~$5M)

2.5.6 Site conditions

Easterly facing open surf beach with an offshore max design wave height of
>12m.

2.5.7 Project objectives

The reef is an integral part of the Northern Gold Coast Beach Protection Strategy
whose aim was to widen and protect the northern beaches as well as enhancing
the surfing amenity. The reef would provide a low profile, near shore control point
to retain approximately 80,000m
3
of the 500,000m
3
of sand transported each
year to the north along this shoreline.

2.5.8 Community requirements and constraints

The public supported a user-friendly structure, the stakeholders identified at time
of design was the surfing community however now that the reef has matured the
fishing community is also making use of the facility. A condition of approval was
for modification and even total removal if required. The mega sand containers
facilitated these requirements.

2.5.9 Construction techniques

Nearly 400 mega sand containers varying from 3.0 metres to 4.6 metres in
diameter, were placed using a split hulled, trailing suction hopper dredge fitted
with computer interfaced DGPS. The containers were accurately filled utilising a
calibrated density metre, ensuring repeatability and consistency of the
construction. Containers were dropped in depths of water ranging from 3m to
11m, onto a sandy seabed.

2.5.10 Geosynthetics used

3 – 4.5m∅ x 20m (max 400tonne) Soft Rock
®
Mega Containers manufactured
from heavy-duty polyester

no woven geotextile (Terrafix 1200R
®
).

Table 8
Geotextile Container Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
5.3mm 10 kN @ 60%
65kN/m XD
38kN/m MD
Min. 80% of
base fabric


2.5.11 Evaluation and Comment

The ability to fill to a pre-determined shape and accurately place very large
geotextile containers at a very low unit cost was conclusively proven. During
construction total supplier and installer alike revised methodology, these
improvements were implemented to ensure the durability and longevity of the
structure.
Initially some failures occurred, during filling and release of the containers,
along the seams. With improvements to the calibration of the dredge feed and
container shape these types of failures were eliminated. Damage also occurred
to some containers during laying, generally due to contact with the dredge in
shallow water. Very effective underwater patching techniques were developed to
repair this damage. The holes are sealed with a silicone based adhesive and a
patch is screwed down over the hole, using nylon wall screws, to provide added
protection.
Various coatings were trialled for the crest bags with mixed success but
towards the end of the construction a durable composite (hybrid) material was
developed and tested with great success. Initial trials made use on a spray on
polyurethane coating of various thicknesses, however this product became rigid
once exposed to water and in fact made the products more susceptible to impact
and wave damage. The composite material, consisting of two layers of non
woven geotextile, used towards the end of the project allows entrapment of
approximately 4kg/m
2
of sand and shell particles within its structure, once the
geotextile is impregnated with these particles the puncture resistance of the
geotextile shows significant improvement.
The porus nature of the non woven geotextile makes it an ideal platform
for marine growth, within months the containers are covered with a thick growth
of seaweed. This structure is now host to a large number of marine creatures and
the reef has now become a popular fishing spot. An investigation into the
environmental impact of the reef on the marine life is underway at the moment.
Although some top up is still required, monitoring has shown a clear
salient at times and enhanced surfing conditions. Full details of the numerical
modeling for the design of the surfing wave break on the reef are covered in the
paper by Mead & Black; Design of the Gold Coast Reef for Surfing, Public
Amenity and Coastal Protection: Surfing Aspects (2001).
As construction progressed positioning of the dredge and placement of the
Mega Containers became more difficult as the wave characteristics changed
above the existing containers. This reinforced the concept that filling in place
would be very difficult if not impossible, concluding that the method adopted was
both effective and efficient.


2.6 Maroochydore Beach Revetment

2.6.1 Project Location

This beach is located at the dynamic mouth of the Maroochy River, Queensland
intersected by Pincushion Island.

2.6.2 Date Constructed

2000-2001

2.6.3 Principal

Maroochy Shire Council

2.6.4 Description

200m long by 2.5m high single layer sand container revetment, angle of repose
75 deg.

2.6.5 Cost

Not Available

2.6.6 Project objectives

Interim protection measures to stabilise the foreshore.

2.6.7 Site conditions

The mouth, continuing a trend identified in the late 80’s and early 90’s, reverted
to a more southerly discharge. During November 2000, the erosion problem on
Maroochy Beach had propagated to such an extent that the foreshore and
caravan park were likely to be threatened during the imminent cyclonic season
and king tides.

2.6.8 Construction techniques

Utilising two small excavators, (5 tonne and 8 tonne), 3000 nonwoven geotextile
units were filled and placed as a defence barrier in the dunal system.

2.6.9 Geosynthetics used

2t Terrafix
®
Soft Rock
®
geotextile containers and UV stabilised non-woven staple
fibre needle punched geotextile (Terrafix
®
600R)

Table 9
Geotextile Container Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
5.3mm 7.0 kN @ 60%
42kN/m XD
27kN/m MD
Min. 80% of
base fabric



Table 10
Geotextile Characteristics
Thickness CBR Burst
Tensile
strength
5.0mm 5.4 kN @ 60%
31kN/m XD
16kN/m MD


2.6.10 Evaluation and Comment

During the early months of 2001, king tides repeatedly tested the interim defence
barrier. Observations of direct overtopping during consistent 2m-wave attack,
proved that the stability of such structures was higher than expected. Some
undermining of the toe occurred during king tides and 3m swell in J anuary 2002
(Figure 9), which resulted in the settlement of approximately 35m of the wall.
Such conditions would have resulted in a failure of a rubble wall with the same
design (2.5m high 1.1m thick @ 15deg. off vertical). Toe protection of the
structure was identified as a very important feature of any wall, correct depth of
base and a self-healing toe (figure 7) will ensure the durability of the structure.

Fig. 9. King tides and 3m swell – J anuary 2002

The self-healing qualities of high elongation flexible Soft Rock
®
containers
have been proven. Some containers have been damaged but the integrity of the
structure has not been compromised, as the containers have been able to mould
themselves into the void left by the damaged container (Figure. 10).





















Fig. 10. Self healing characteristics of Soft Rock
®
wall

Although not the first application of its kind the success of the project
(withstanding severe storm attack) has lead to the construction of a groyne as
part of the works using innovative products and construction techniques.




















2.7 Maroochydore Beach Groyne


Fig. 11. Maroochydore Groyne November 2001

2.7.1 Project location

Maroochydore Main Beach, Sunshine Coast, Queensland

2.7.2 Date constructed

November 2001

2.7.3 Principal

Maroochy shire Council

2.7.4 Description

100m long x 2.5m high sand-filled groyne

2.7.5 Cost

Aus$210,000

2.7.6 Project objectives

To stabilise the Maroochydore main beach which had eroded by approximately
75m within 2 years. The structure had to be easily removable should it be
detrimental to the beaches north of the groyne.

2.7.7 Site conditions

Easterly facing open surf beach with an offshore max wave height of >10m.

2.7.8 Community requirements and constraints

As the existing Soft Rock
®
revetment wall was proving to be popular with
fishermen and the general public a similar structure was envisioned. This
structure would blend in with the natural sandy beach and would not form a
hazard to beach goers.

2.7.9 Construction techniques

The groyne consisted of 4 layers of containers stacked into a pyramid shape as
show in Figure 12. An 8t excavator was used to fill the containers while a 35t
excavator was used to place the containers.

2500 mm
5223PR Soft Rock Containers


Fig. 12. Section through groyne

2.7.10 Geosynthetics used

4.5t Terrafix
®
Soft Rock
®
geotextile containers manufactured from a composite
UV stabilised non-woven staple fibre needle punched geotextile (Terrafix
®
1209RP) with high tenacity polyester thread in all seams.

Table 11
Geotextile Container Characteristics
Thickness CBR Burst
Tensile
strength
Seam
Strength
11mm 12kN @ 60%
75kN/m XD
45kN/m MD
Min. 80% of
base fabric


2.7.11 Evaluation and comments

The geotextile sand containers and construction methods used in this project are
a result of the years of development into geosynthetic containers described as
described in the previous case studies.
For an exposed structure of this nature it was felt that the 2t containers
used on the revetment wall were to small and that the container size would have
to be increased substantially to ensure stability. The weight/size of the containers
were limited however to the capabilities of a 35t excavator as this type of
excavator is accessible to most contractors. The containers were be installed
using specially developed filling and placing apparatus designed to ensure
improved filling and simple handling of such large containers. The method of
lifting and placing containers with a modified rock grab, as with the 2t containers,
would have over stressed the geotextile and seams. The containers are filled in
the lifting/placement cradle and placed using the 35t excavator, no double
handling of the container is necessary. This method of placement is thought to be
the first of its kind in the world, which allows very accurate positioning with low
stress on the geotextile and seam’s (Figure 13).



Fig. 13. Placement using specialised equipment

The composite geotextile developed for the Narrowneck reef project was
used for all containers in the groyne minimising risk due to vandalism. After
7months of use only one incident of vandalism has occurred and was patched
using the screw down patch method described in the Narrowneck case study.
Specialised sewing equipment was developed for this project to ensure a high
strength seam on this thick puncture resistant geotextile (Narrowneck containers
have a different seam detail).
The groyne has performed exceptionally well and has withstood wave
heights of greater than the 3m design height, the council is now investigating the
construction of a further groyne based on this performance.

3 CONCLUSION

The use of geosynthetic containers in marine structures is a relatively new
science, however a great deal has been learnt from both the successes and
failures of these structures and the scope / limits of their application are yet to be
defined. The development of this field is unique in that it has relied on the close
collaboration between clients/consultants, contractors and manufactures to
provide the best solution.
Sand filled geotextile containers are a relatively new field of application for
geotextiles and with this new application comes new requirements for durability
and survivability. This poses the question: Are our current test methods adequate
to ensure effective specification of geotextiles? Being exposed to the elements
by a far higher degree than most other geotextile applications e.g. drainage and
separation, damage to geotextile sand containers used in marine structures,
whether it be by accident or vandalism is a serious threat to the durability and
longevity of these structures. There are very few tests available which a designer
can use to asses and compare the suitability of the various geotextiles used in
marine applications, this means that the designer must rely on past experience
which is likely to be limited or “gut feel” which is undesirable.
- Vandalism has been identified by a number of clients as the mode of
damage, which is of most concern. At present there are no indicator tests
available, that model puncturing of the bags using a sharp instrument,
hence there is very little information available to the engineer on which to
base the vandal resistance of the various geotextile. One solution may be
to modify the current ASTM D4833-00 puncture resistance test to from a
knife-edge thereby mimicking a knife cut by a vandal.
- Abrasion of geotextile containers is another area of concern particularly
in areas where coarse angular sand or coral debris is present and here
the German “Baudesanstalt fur Wasserbau” rotating drum test method is
recommended, as this test best replicates the abrasive near shore surf
environment.
The development of improved seaming methods is allowing larger
containers to be constructed, which can be subjected to higher stresses.
Improvements in seaming, filling, handling and placement techniques have
improved the quality of structures built and have also increased the diversity of
uses. Damage whether it be accidental or premeditated has prompted
development of hybrid geotextiles (used in the Narrowneck reef & Maroochydore
groyne projects) designed specifically for hostile marine conditions.
Containers can be manufactured to suit not only the physical application
but also to the equipment available to the contractor, hence their use is suited to
specialist installers who have access to split hulled barges (Narrowneck reef) and
to smaller contractors with limited resources (Russsel heads community
construction).

To summarise the views of Soil Filters Australia:

• Geotextiles structures can be successfully used to solve conventional
coastal problems and non-conventional challenges.

• Nonwoven sand filled geotextile structures adapt and conform readily to
changing site conditions.

• Design and construction approach requires specific consideration of site-
specific conditions and geosynthetic techniques. Factors such as vandalism
potential, abrasion potential of the beach sand, interface friction in a multi
layer structure etc must be addressed in any design.

• Durability is often higher than anticipated and continues to improve with
advances in Geotextile manufacturing techniques, related polymer science,
and container manufacturing methods.

• Sand filled geotextile forms can create an excellent foundation for a broad
diversity of marine species.

• In the event that something goes wrong in the complex field of sandy beach
systems, the geotextile sand containers can be easily removed compared to
other structures.

• In general there is a lack of specific test methods, which can be used to
specify geotextiles in marine applications.

• Geotextile structures are user-friendly features ideal for recreational
facilities such as beaches.

REFERENCES


German Federal Waterways Engineering & Research Institute, (1994).
Guidelines for testing of geotextiles in hydraulic engineering applications.

Heerten, Dr Ing. et al (2000). New Geotextile Developments with Mechanically
bonded Non Woven Sand Containers as Soft Coastal Structures. 27
th

International Conference on Coastal Engineering, Sydney, Australia, 16 – 21 J uly
2000, pp. 2342- 2355.

J ackson, L.A., (1987). Evaluation of Sand Filled Geotextile Groynes Constructed
on the Gold Coast. Internal Report for Gold Coast City Council.

Mead, S., Black, K., (2001). Design of the Gold Coast Reef for Surfing Public
Amenity and Coastal Protection: Surfing Aspects. J ournal of Coastal Research
No 19, The Coastal Education and Research Foundation (CERF), pp. 115-130

Mootoo, T., Coughlan, P. (1995), Sand Filled Geotextile Groynes as Bank
Erosion Protection within the Maroochy River Estuary, Sunshine Coast,
Queensland.

Pilarczyk, K.W., (2000). Geosynthetics and Geosystems in Hydraulic and coastal
Engineering. A.A. Balkema, Rotterdam, the Netherlands, 2000.