Sheet piles are widely used for cofferdams due to sheet piles structural strength, interlocking capability that provides a water tight system.

Sheet piles are preferred too due to their ability to penetrate many types of ground.Thus achieving deep penetration which provides resistance to inward movement at the bottom of the excavation.

The ability to achieve deep penetration in permeable soil also has the advantage of cutting off water infiltrating into the excavation.

Most common available sheet piles can be used, sheet piles like the Larssen and Frodingham are widely used to form cofferdams. In fact, some contractors combine the different sheet piles utilizing the strength of each types/make of sheet piles to achieve an effective cofferdams.

Figure 1 - Cantilever Single Sheet Pile Wall

Sheet piles cofferdams can be of many types depending on the construction requirement and site conditions. An example of a simple cofferdam can be just a single layer of sheet piles cantilever above the working area. Normally this is used in low water heads or the required excavation is not too deep. Such a cofferdam is shown in Figure 1.

Figure 2 - Single Sheet Pile Wall with embankment

Should deeper excavation be required, an earth embankment can be left in front of the sheet piles. This is shown in Figure 2. Single sheet piles wall can be strutted across to the opposite sheet pile wall to form an enclose working area. Fewer struts are used if excavation is not deep. On the other hand if deeper excavation is required, than more struts are used and the cofferdams had to be strutted at different levels too. This is shown in Figure 3.

Figure 3 - Strutted Single Sheet Pile Walls

When the excavation area is too wide for strutting, than a more massive cofferdams can be constructed by utilizing double layer of sheet piles wall. The sheet piles wall are tied together or can be formed into interlocked cellular cells with filled with rock debris or earth infill between the sheet pile walls. This form a massive self supporting cofferdams that can keep exterior water at bay and the working area dry for construction works. This is shown in Figure 4.

Figure 4 - Double Wall Cofferdams

For resources related to sheet piling visit Sheet Piling Resources

One of the popular use of sheet piles is for the construction of cofferdams. Before that,

What are cofferdams?

From the definition below, you can also note the usefulness of cofferdams on many types of situation such as construction, ship building and even archaeology works.

However regardless of the use, the main function of a cofferdam is to provide a dry area to work and to prevent the entry of water into the working area when work is in progress. Cofferdams can be constructed in many ways but in modern civil engineering works, they are now mostly constructed using sheet piles.

The installation of sheet piles is highly configurable that it can be install on and into water. Off-course there will be a slight differences between land installation and on water.

According to Wikipedia Cofferdams are :-

A cofferdam is an enclosure within a water environment constructed to allow water to be displaced by air for the purpose of creating a dry work environment. Commonly used for oil rig construction and repair, bridge and dam work, the cofferdam is usually a welded steel structure that is temporary, typically dismantled after work is completed. Its components consist of sheet piles, wales, and cross braces.

The cofferdam is also used on occasion in the shipbuilding and ship repair industry, when it is not practical to put a ship in drydock for repair or alteration. An example of such an application is certain ship lengthening operations. In some cases a ship is actually cut in two while still in the water, and a new section of ship is floated in to lengthen the ship. Torch cutting of the hull is done inside a cofferdam attached directly to the hull of the ship, and is then detached before the hull sections are floated apart. The cofferdam is later replaced while the hull sections are welded together again. As expensive as this may be to accomplish, use of a drydock may be even more expensive. See also caisson.

Cofferdams have also been used to recover ships sunk in shallow waters, such as the USS Maine, or Robert de LaSalle’s La Belle.

Why is steel sheet piles widely used for cofferdams?

This is because of sheet piles structural strength, the water tightness due to its ability to be interlocked and also its ability to be driven to deep penetration in most types of ground. The ability to be driven deep into the ground is important as this gives resistance to inward movement “caving in” at the bottom of the excavation and sufficient cut-off to prevent infusions of water into the excavated/working area.

Common sheet piles used construction of cofferdams are Larssen and Frodingham. The Larssen has a U type section are very popular sheet piles used in cofferdams. This is because of their good design which includes interlocking capability and that they can be driven deep with minimal problem.

When used as in a cofferdams, the sheet piles have to resist both the soil and water pressure which acts on it from outside. This pressure increases with excavation depths. Thus to resist these pressures, the internal of the cofferdams are braced. Proper bracing is important to maintain the integrity and safety of the internal working area.

The construction of cofferdams begin by marking out the location and the shape of the cofferdam. This job is done by the surveyor. Thereby the work of driving sheet piles can start. Methods of driving sheet piles are mentioned in this post “the-installation-of-sheet-piles” During driving and pitching of the sheet piles, ensuring verticallity is very important. Guides are used to ensure proper driving. On land guides can be 2 pairs of guide wailing. One pair at ground level while the other at a higher level. This guides can made into a trestle so that it can be easily shifted as sheet piling work progresses.

However for driving over water, the wailing guides are supported by timber or steel piled stagings constructed into the water. Thus comparing to working in ground, more preparation and setting up is involved when working over water. Sheet piles are driven from a floating barge which has to be anchored to prevent it from drifting due to water current.

Single Wall Cofferdam

Sheet piles are driven either one by one successively which is also known as single driving or can be in echelon or in panel methods. Cofferdams can be either single-wall or double-wall design. A single wall cofferdam consist of one layer of sheet piles only as the picture above shows.

Double Wall Sheet Pile Cofferdam

In double-wall, there are 2 layers of sheet piles. The space between the sheet piles are filled with soil or granular materials. A double wall cofferdam can resist greater pressure than a single wall cofferdams.

Some times a very large cofferdam can be constructed from smaller circular cofferdams known as cells. These cells are constructed very close to one another.  One can find such huge cofferdams in used in large project like dams construction where rivers need to be diverted. Attached picture show cellular cofferdams under construction.

Large Circular/Cellular Cofferdams

Below more pictures of circular sheet piling cells formed from interlocking sheet piles and Larssen sheet piles are the popular ones used.

Cellular Cofferdams

Sometime for short length of sheet piles of about 6 to 8 meters, they can be installed using a small hydraulic powered vibratory hammer attached to a heavy excavator.

The bucket of the excavator had been removed and in it’s place a vibratory hammer is placed. It will be powered by the hydraulic system of the excavator.

This video below shows a vibratory hammer mounted to an excavator arm. It’s installing a sheet pile walls. Most likely the wall is to stabilize the ground behind the sheet wall. Infront of the wall is an open excavation.

Now as mentioned earlier in my earlier post it is not a good practice to install sheet piles by banging the steel sheet piles using the excavator bucket. Doing this may cause damage to the sheet piles and as well to the excavator bucket. If you see a dented excavator bucket, then you are sure that the excavator may had been subjected to abuse beyond what the excavator had been designed for.

However, if the sheet piles are not made of steel but of vinyl sheeting ( easily recognizable from it’s clean white color ) than the installation can make use of the excavator bucket. Like this video below shows. Sometime when difficult ground is encountered, the area where the vinyl sheet piles are to be installed may be loosen using water jet prior to installation. Vinyl sheet piles are popular near water areas like sea wall, river banks due to it’s non corrosive nature. Here is a video on how vinyl sheet piles are installed with an excavator bucket.

Ensuring proper and correct interlocking between sheet piles is one of the key and crucial requirement during the installation of sheet piles. Usually this is done manually and can be rather tricky if the the sheet piles need to be interlocked at a height.

Thus this required the hosting of both man and sheet pile high up from the ground to get the job done. And this can be dangerous due to the height involved and difficult too as the person ensuring the proper interlocking of the sheet piles has to communicate with the crane operator from a height.

Further more it will be virtually impossible to do this when there is strong cross winds. Now a company had come out with an ingenious solution.

N A gadget called the “Universal Sheet Pile Threader” solves all the inconvenience and problem as mentioned above. It is completely safe and require only two men ( one infront and the other behind the sheet pile) to install the gadget and done on ground level (thus very safe)

Watch the video below to see how this gadget work.

Following the first post of How to install sheet piles, this is the continuation of the fist post on the same subject of sheet piles installation.

Sheet piles can also be installed or driven by drop hammer. The drop hammer can be single acting or double acting ones. They are powered by disel, compressed air, steam or hydraulic.

The hammers usually operate with a false leader or piling frame. An example of which is shown in the video below.

In the video, you can see that the person is first checking on the alignment and verticality of the sheet pile before giving the go ahead.

Do note that in the second part of the installation, the installation process produces vibration which cause some crest of sand to flow down ( on the middle right of the video).

And between double acting hammers and single acting hammers, double acting are generally preferred for speed and efficiency, and this type performs well in most types of ground conditions but specifically in sandy and gravelly soils.

But single acting hammers are preferred when heavy driving is required. The heavier weight and slower velocity of the single-acting hammer can transmit a higher energy into driving the piles.

When sheet piles are driven by drop hammers, it is important to protect the heads of sheet piles during installation.

There are a number of ways to install sheet piles. The methods are

1. Using a vibratory hammer
2. Hydraulic powered drop hammer
3. Diesel power drop hammer
4. Hammering with the bucket of an excavator (Not recommended as this can damage the sheet piles and the excavator bucket)

Starting wiht the vibratory hammer, the sheet piles are first grabbed with the hammer jaws. Once in position, the sheet piles are installed using vibration.

The vibration produced by the vibratory hammer is used to loosen the soil and allowing the installation of the sheet pile through penetration into the ground with it’s own and the hammer’s weight.

The vibratory hammer is usually powered by large electric motors. The vibratory hammer is usually hoisted using a crane. Sammler vibratory hammer can be adapted to an excavator boom.

Below is a video on the installation of sheet piles using a vibratory hammer. The hammer is hoisted using a crane.

From the well known Larssen, frodingham sheet piles and to sheet piles manufactured from Japan, sheet piles technology can be said to be well established. It is documented that sheet piles had been used in civil engineering works for close to two hundreds years.

Sheet piling consists of a series of panels with interlocking connections driven into the ground with impact or vibratory hammers to form an impermeable barrier. Sheets can be made from a variety of materials such as steel, vinyl, plastic, wood, recast concrete, and fiberglass. It is steel sheet piles that this site will concentrate on. It is in the early 20th century that steel sheet piles to becomes  mainstream, thanks to a German by the name of  Mr Tryggve Larssen .

What are the technology of sheet piles application?

As sheet piles formed an interlocking wall, it’s application can be used in retaining purpose and can be adapted to jobs requirement like : -

* Cofferdams
* Ground Water Diversion/Control
* Barrier for Ground Water Treatment Systems
* Retaining Walls
* Containment Walls
* Flood Protection
* Coastal Protection
* Tunnel Cut and Cover
* Bulkheads and Seawalls
* Weir Walls
* Slope Stabilization
* Baffle Walls

The picture below is an example of a coffer dam. Notice that the cofferdam is being installed by a crane floating on a barge. ( image source :-

Cofferdams can be used on land and in water. The shapes can be of any configuration depending on the structures to be built.

There are many advantages applying the technology of sheet piles . One major advantage is the installation of sheet piles, removed the need for open cut excavation. Open cut excavation required large amount of material to be removed. Using sheet piles, excavation is limited to the exact spot where only excavation is require for work to be done. Thus this minimize waste disposal problems.

The next benefit of applying the technology of sheet piles is the sheet piles are removable once the work is completed. In this sense, the sheet pile is used temporary as a retaining wall while the actual work is done.

Sheet piles can be permanent too as they can be part of the permanent strurtures. As an example, in the construction of basement, the basement wall can be casted with the sheet piles wall. Thus this eliminates the need for exterbal form works for the wall as the sheet piles formed the external form work.

Generally topography and ground water does not hinder the use of sheet piles, thus is is another benefit of applying the technology of sheet piles to construction works with uneven topography and high water table. Finally, using sheet pile, they can be installed to various shape formation required by the designers.

The photo below show the use of temporary sheet piles for retaining purpose, allowing excavation to take place. The excavator at the lower level is excavating down. The orther excavator is installing sheet pile.

Since the first usage of steel sheet piles in the early part of the 20th Century, sheet piles had evolves into one of the most versatile tools in the arsenal of civil engineering. With modern steel manufacturing techniques and improve in technology, modern steel sheet pile are stronger, lighter and versatile.

Improvement is not only in the manufacturing of the sheet piles but also in the installation techniques. In this post we will touch on the different types of steel sheet piles or the sections as commonly known. I will touch on the installation at a later post.

Nowadays steel sheet piles evolves into other sections forms. Starting from the common U-section, sheet piles now comes in Z-section, Flat or Arch section. Flat or straight-web piles are used to form cellular cofferdams.The other sections are used in a wide variety of situation in civil engineering works.

Regardless of the type of sections, steel sheet piles are mostly hot formed with occasionally some cold rolled. The difference is that cold-formed steel shapes are formed at room temperature, while hot-rolled steel shapes are formed at elevated temperature. From a design point of view, cold-formed steel is much thinner than hot-rolled steel.

As can be seen in the attached diagrams, the dimension of sheet piles are labeled b, h, a and e, except for the flat section sheet piles. They represent the Width, Depth, Web Thickness and Flange thickness respectively. In the flat section sheet piles, the width is labeled L and the depth W. The thickness is labeled as e. Theses dimension varies and by doing so sheet piles can have various strength.

If you look up at any tables of the sheet piles property example Larssen sheet pile, you will notice that the web thickness is thinner than the flange. The web is thinner to allow it to be worked more easily to form the interlocking. Further more designers had calculated before hand the optimum thickness of both the web and flange before the sheet piles are made. Both thickness affect the strength of the sheet piles. Again if you look at sheet piles tables, the strength is represented by the “Moment of Inertia” and the “Section Modulus”.

U- Section Sheet Piles

A U-section sheet pile is in the form of the letter U, with a deep depth and wide width. The depth becomes twice when interlocked.

Z-Section Sheet Pile

A Z-section sheet piles, looks like a slanted letter Z with equally deep depth when interlocked.

Flat Section Sheet Piles

The flat section sheet piles have neligible depth. Essentially its a flat sheet of steel with interlocking features on both sides.

Arch section sheet Piles

The Arch section sheet piles is a U shape with a shallow depth. The shallow depth resulted in an arch shape section.

Let’s start with Larssen sheet piles. Larssen set of sheet piles are famous and well known to civil engineers worldwide. Their reliability, versatility and strength in all types of condition as retaining structures has beenwell proven and documented many times over.

Here is a little bit of history of this famous sheet pile. In 1902, Mr Tryggve Larssen, State Chief Engineer at the City of Bremen in Germany, developed the world’s first steel sheet pile, which has U section with riveted interlocks. Thus this how the name of this sheet pile comes about.

Larssen U Section Sheet Pile

The interlocking idea on both sides of the sheet pile came about In 1914. This is still utilized all over the world as the most popular steel sheet pile section.

One of the oldest Larssen U pile is displayed at Giken Kochi Head Office to remind us of the historical background of U steel sheet pile. The picture below is a typical larssen sheet piles stacked together.

The interlocking system mentioned above can be seen from the photo on the left. On both the sides of the sheet piles have U shapes which can be used to interlock to another sheet pile.

The interlocking system creates a water tight and increase the strength the sheet pile structures. Be it cofferdams or earth retaining systems.

Here is a diagram thats show how interlocking is done.

Image source :-

Image1 – www.steelcom.com.au/images/sheet-pile-larssen-u-section-small.jpg

Steel Sheet Piles -A Brief Introduction

Steel sheet piles are interlocking steel panels driven into the ground to form a wall. The installation of sheet piles can be carried out with impact or vibratory hammers. Sheet piling has been used in the construction industry for years.

Steel sheet piles are used in temporary works such as forming a temporary wall to support excavation in soft or water logged soil for the construction of cofferdams or basement. Steel sheet piles can also be used to form permanent retaining walls especially those used for river bank strengthening and in the construction of jetties. They can also be used to form part of the permanent wall of building basement where they are casted together with the basement concrete wall.

The three common forms of steel sheet pile walls are the Larssen/Larseen, Frodingham and straight web piles. All these have interlocking joints that can formed an effective water seal. Straight web piles are mainly used to form cellular cofferdams. Steel sheet piles can come in various lengths of up to 18m.

Beside steel the sheet can be made from a variety of materials such as vinyl, plastic, wood, recast concrete and, fiberglass. The most recent addition to the sheet pile family is the vinyl sheets. These vinyl sheets, with imperious sealants, have made this a very attractive technology for the cutoff or containment of contaminated groundwater flow in the environmental industry.