Geoflex applications
There are a large variety of applications of Geoflex sheet piles. They can be classified as:- cut-off barriers
- shore protection
- retaining walls
Cut-off barriers
Geoflex can be used as cut-off barrier to isolate contaminated areas from the environment. The lock can be provided with a hydrotite swelling cord to minimise the leakage. Since thesheet piles are supported by soil on both sides, there is minimal horizontal load on the sheetsand a profile with a very low strength rate can be used. Since PVC is not resistant against allchemicals, especially some hydrocarbons, it cannot be used at all circumstances. For thoseareas where hydrocarbons are present HDPE Geolock panels can be installed.Another cut-off barrier application is to seal dikes and avoid perforation by rodents. In thiscase the chemical resistance is no issue and the strength of the sheet piles can increase thestability of the dike. Geoflex can be used to avoid inundation of the ground under locks orother piled structures that retain soil with different groundwater levels.
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Shore protection
Geoflex can be used as facing, revetment, bulkhead or flood protection. The sheet piles are used to prevent erosion of the shore line by wave or tidal action. The design should be basedon extreme tidal differences. Excessive water pressure behind the wall should be avoided tominimize the load on the sheet piles. Also wave action should be incorporated in the design.Shore protection walls should be anchored if the backpressure of th ground exceeds themaximum load. At flood protection application, higher maximum stresses are allowed sincethe amount of creep will be limited due to the temporary nature of the load. Geoflex is also anexcellent product to stabilise revetment systems. The riprap used to protect the shoreline canbe set and washing out of fines is avoided.
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Retaining wall
Also behind retaining walls the water level in the ground should be controlled by a drainage system to limit the active load. Especially at retaining walls the expected rate of bendingshould be taken into account, since the sheet piles are visible over the total retaining heightand large deformations are not always acceptable. Geoflex is also extremely suitable to construct emergency platforms along highwayembankments. It is very simple to install without heavy equipment.
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Special applications
Geoflex can also be used for a number of applications where traditional materials are used. As retaining wall under a concrete quay construction Geoflex will have a life time of over 100years without loss of strength.Small overflows or dams in rivers can be made with Geoflex possibly in combination with avalve that controls the water level..Geoflex in combination with a low berm, creates an environmental solution that has a attractive appearance. These environmental banks give animals the possibility to escape fromthe canal.
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Installation of Geoflex sheet piling
There are a large number of techniques to drive Geoflex sheet piles. The system used is largely depending on the circumstances like:
• Sheet pile lengthl;
• Soil conditions;
• Obstructions;
• On shore or off shore;
• Water depth.
This means that there is no standard installation system available. We can however provide two basic techniques:
• Driving the sheet pile directly;
• Driving a steel supporting sheet pile
Driving the sheet pile directly can be done with a standard pneumatic hammer or a light vibrator with or without a clamp. This system is only suitable for driving at light conditionsand to a limited depth. For heavy conditions and installation from 4 m up to 8 depth it isadvisable to used a steel support sheet pile with exactly the same shape as the Geoflex sheet.Harder soil can be penetrated and installation is speeded up because the hammer does nothave to be disconnected from the steel guiding sheet pile.
Please follow the following steps carefully:
• Store the sheet piles so that the locks cannot be damaged or compressed. It will make installation almost impossible if the male lock cannot be easy inserted in the femalelock.
• Set up a driving guide system, to provide support of the sheets during installation.Two driving guides make installation even more efficient and accurate.
• Put two sheets together to speed up installation and achieve better support from the
temporary driving guides
• See that the installation is done in the right direction. This means that the female is
installed over the male lock.
• Clean the female lock with high water pressure if necessary
- See that the installed sheets are plumb. Attach the last driven pile to the guide or attach a clamp to the sheet and keep it tensioned upwards during installation of the nextsheet.
- Put the sheet in the steel sheet pile guide and position it above the last driven pile
- Drive the sheet gently in the plumb direction.
- Water jetting can be used to ease installation.
- If obstructions are occurred it may be advisable to loosen up the soil by a trenching machine before installation.
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| Installation by vibrator with flat plate | Installation with pneumatic hammer and water jetting |
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| Installation by vibrator and rig with steel sheet pile guide | Installation by vibrator with flat plate |
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| Installation by vibrator and rig with steel sheet pile guide. | Installation by vibrator and rig with steel |
Geoflex physical properties
Geoflex is a 300 mm wide extrusion profile. This means that the raw PVC pellets are melted and pressed through a die. The regular shaped profile is then cooled of in water and cut andthe desired length. The process guarantees a constant quality and steady sizes. The sheets areprovided with a male and female lock that match perfectly and create a high strengthconnection. The lock is designed with the following philosophy.
- no geotextile needed to prevent erosion of soil particles
- a certain rotation makes curved shapes possible
- no edge profiles necessary to make right angles
- two different configurations possible with one profile
The different configurations give the engineer the possibility to choose between several sheet pile shapes with a large range of flexural strength.
Geoflex mechanical properties
All mechanical properties are based on extensive testing on extruded PVC profiles. Design should however not only based o the strength properties of the material. Deformation shouldbe taken into account as well.
Comparison PVC, steel and hard wood
Steel has much better mechanical properties than PVC. It is ten times stronger than PVC and the tensile modulus is even 80 times higher. So in strength and especially in deformation steelbeats PVC in every way. There are however some significant advantages for PVC as well.PVC is a very good electric insulator which gives excellent lightning protection. Alsoaluminium boats like PVC sheet piling much more than steel because of absence ofelectrolyse in a salt environment.
Steel is subject to corrosion. In underground conditions acorrosion rate of 0.015 mm/side/year has to be incorporated in the calculations. In someenvironments with chemicals of salt water, these rates may even much higher. A totalcorrosion of 0.09 mm can occur in tidal zones, thus decreasing the strength of light weightsheet-pile in 50 years with 90%, while PVC keeps its design strength during that period.
The flexural strength of hard wood is almost 50% of the strength of PVC while the tensile modulus is approx. 7 times higher. Hard wood is however subject to decay because ofweathering and biodegradation. Only the most durable types have a lifetime of more than 25years. Ten year old PVC sheet pile installations have still no signs of significant degradationin the material, while both steel as well as hard wood are subject to a much faster degradation.Since PVC has to be designed on deformation rather than on strength there will always be asurplus in strength left after decades.
PARTNERS
Project partners in Europe "Cofra":
