Sheet Piling

Sheet piling can be used to repair damaged canals in Germany as well as prevent Venice from sinking! Be it metro rail projects, power projects, ports or bridges – sheet piling is useful. Sheet piling is a method which is used to retain soil and water. Whenever there is need to excavate soil for foundation/basement work, sheet piles are required to secure soil from collapsing. While constructing bridge piers in river/sea, there is need to retain water outside as inside waterless area is required. This can be achieved by using sheet piling wall and then pumping out water from inside.
Application: They are designed to create rigid barrier for earth or/and water, while resisting the lateral pressure of these (water, earth/soil) bending forces. The shape or geometry of a section contributes to structural strength. Hence, it can act as a retaining wall or structure. It can be used in place of retaining and diaphragm walls. It has wide applications in civil engineering/ foundation engineering field as sheet piling can be driven in almost all soil conditions. Special site conditions where sheet piles are ideal are: In water (river/sea), no water pumping is allowed, uniform ground conditions. Faster speed, total project cost and time reduction, easy to use, adapt to any shape/size and reusability are the features which give extra edge over other technologies.
Importance: This technology is very useful in India. In metro cities like Mumbai, Delhi, Chennai and Kolkata, there is an acute shortage of space for car parking. A new concept of ‘multiple basements’ is picking up and plans are to go 8.0-12.0 meter (3-5 floors) below ground level. Hence to retain such huge soil sheet piling is used. For instance, in case of Delhi Metro Rail Project, sheet piling for 12 m deep excavation is used. For one of the power projects, excavation up to 20 m from ground level (more than the height of a 7-storey building) is at planning stage. “Do you think it is possible without using sheet piling,” asked Zain Nathani, Director, Nathani Industrial Services Pvt. Ltd. This technology is extremely popular in developed countries. In general, their per capita steel consumption is very high, he added.
Innovations: Sheet piling is an old method, but there have been innovations. Earlier they were using wooden sheet piles but they have certain limitations. Now we have sheet piles which we can roll up to 36 m single piece and 750 mm in width. Even vibration technology is the latest happening in sheet piling which has the following advantages: Fast, efficient, low noise emission, environmentally-friendly, wide range of applications, adaptable to different carrier system, penetrating all types of rammed section without damaging. This system is very flexible and there is lots of scope for the technology. “Soon, more economical systems will be available for the Indian market,” said Nathani. Even 36 m deep sheet piles are available and can extend the length of a wall from a few meters to thousands of meters. On an average, one can construct 200 sq. m. of sheet pile wall in eight hours shift.
Sheet piles are available in four different materials viz. steel, wood, aluminium, PVC. However, steel sheet piles are more popular and commonly used throughout the world. It is more popular due to following reasons: Faster installation, reusability, easy to cut or lengthen, low height with high stability, scrap value, techno-commercial suitability, adaptability to take any shape/size.
Sheet piling consists of three main components: Sheet pile section/rammed section, driving equipment (which consists of a vibrator unit, power pack and clamming device in case of vibrator), crane/excavator for holding a vibrator unit.
Sheet piling can be designed as a temporary structure or as a permanent structure. It depends upon the application, its requirements and site  conditions. Permanent structures can last up to/ above 100 years if they are designed and maintained properly. Being a steel section, it is one of the most durable and possesses high strength.
Some typical applications of permanent sheet piling are: Water engineering: Ports (quay walls/ dock construction/dolphins), water eng. structures (locks/weirs/inlets-outlets), waterways (berth/ scour protection/retaining wall). Pollution control: Landfills (vertical sealed enclosure/tank enclosures), contaminated sites, noise abatements, water protection, (pumping stations/securing embankments). Construction & Transport: Road & rail (support walls/ramps/sunken roads/ ground water retention/noise protection walls.
Some typical applications of temporary sheet piling are: Civil engineering: Foundations/site excavations/underground parking; transport, bridge abutments. Excavation for soil replacement.
Sheet piling is manufactured from steel slabs using hot rolling process. This slab passes through lots of rolling applications and finally it is converted into required sheet piles profile/shape. Interlocks are the heart of sheet piling which provide mechanical bonding between two sheet piling.
Driving is the first activity in sheet piling for which you can use vibro hammer. This vibro hammers are mounted on crane/excavator depending upon the length of sheet pile, weight of section, soil condition, site constraints, etc. Sheet piling is lifted using clamping device and then vibrations are created in soil.
Fixed to a rammed section, a top vibrator induces vibrations to the ground. The soil surrounding the rammed section reaches a state of liquefaction, thus reducing surface friction and tip resistance between section and soil. The section is pushed down easily by low penetration forces i. e. by dead weight of the system.
Sheet piling will work out to be a cheaper option if you take into consideration total cost of the project. You can save precious time, as well as ease at work will help to adopt this technology. Reuse is the prominent feature of sheet piling which gives edge over the other technologies. It can be used again and again which will give huge savings and lastly, it does have scrap value.
The cost of sheet piling depends upon application, profile, length, etc. Hence it varies from site to site. Roughly the cost (including driving) starts from Rs 9,500 per sq. m. The cost is for one time use. If you use sheet piles 3-4 times, the cost can be curtailed down to Rs 4,000-Rs 4,500. The cost of sheet piling mainly depends upon international steel prices, import taxes, etc.
The Indian government is not promoting the technology. Custom duty to the extent of 38 per cent is applicable which makes imported sheet piling costlier.

Stop Venice from sinking!

MOSE (Modulo Sperimentale Elettromeccanico) is the name of the project to prevent Venice from sinking. The world-famous lagoon city is regularly inundated, and is built on thousands of oak pilings.
This wooden foundation is unsound and has subsided by half a meter over centuries. At the same time, the level of the Adriatic Sea is also rising. The Plaza San Marco is often flooded, the walls of palaces, churches and apartments are saturated with water. The dykes built to protect Venice from floods are too weak.
Preliminary work for three giant gates to the Adriatic Sea has been in progress since 2003. These involve modules filled with water that, in the event of flooding, are electromechanically filled with air so that they rise up from the sea bottom to hold back the water. The MOSE project will cost around 6 billion euros, and should be finished in 2011, with the help of ThyssenKrupp GfT Bautechnik. The three planned Venetian tidal fortifications, with a length of up to 1,600 metres, are architectural masterpieces.
(This part of the article is contributed by Mumbai-based Nathani Industrial Services Pvt. Ltd that deals in steel and alloy scrap, solid fuels to the steel, power and cement industries, steel sheet piling, etc.)