Sheet Pile Wall Considerations

Sheet pile wall types, construction methods, advantages and disadvantages are described in this article.

Sheet-pile walls are widely used for both large and small waterfront structures, ranging from small pleasure-boat launching facilities to large dock structures where ocean-going ships can take on or unload cargo. A pier jutting into the harbor, consisting of two rows of sheet piling to create a space between that is filled with earth and paved, is a common construction. Sheet piling is also used for beach erosion protection; for stabilizing ground slopes, particularly for roads; for shoring walls of trenches and other excavations; and for cofferdams. When the wall is under about 3 m in height it is often cantilevered; however, for larger wall heights it is usually anchored using one or more anchors. The resulting wall is termed an anchored sheet-pile wall or anchored bulkhead.

Sheet pile wall types

1. Wooden Sheet Piles

1. Wooden sheet piles
   Wooden sheet piles are made in various sizes and forms. The nature of site conditions determines the choice of a particular type. If the water-tightness is required to a great extent, lapped sheet piling is used. In this case, each pile is made up of two planks, either spiked or bolted to one another. Thus if only earthen banks of small height are to be supported, a single or double row of planks properly erected will perform the function of sheet piling. If complete water tightness is desired or pressure of the retained material Wakefield or tongue and grooved sheeting is generally used. To facilitate the driving of the piles, they are usually beveled at foot. This not only assists in driving but also prevents bruising, if the piles encounter hard stratum
2. Wakefield piles
   This type of pile is made with three planks, 5 cm, 8 cm or 10 cm in thickness. The planks are nailed together with the middle plank offset forming a tongue on one edge and a groove on the other. The planks are connected by using a pair of staggered bolts at 80 cm center to center at intermediate points. The triple lap piles prove stronger in driving. There is no wastage in forming the tongue and groove joints and the piles have less tendency to warp. Timber sheet piles have light weight and as such the equipment required for pile driving is also light. This is considered to be an important advantage timber piles have over piles of other materials.

2. Steel sheet piles

Steel sheet pile is a rolled steel section consisting of a plate called the web with integral interlocks on each edge. The interlocks consist of a groove, one of whose legs has been suitably flattened. This flattening forms the tongue which fits into the groove of the second sheet. Commonly used steel sheet piles types are:

1. Larssen shapes
   

   

2. Z-type shapes
3. Straight web section

3. Concrete

1. Precast concrete sheet piles
   Precast concrete piles are made in square or rectangular cross-section and are driven similar to wooden piles to form a continuous wall. The interlock between two piles is normally provided with the help of tongue and groove joint. The tongue and groove extend to the full length of the piles in most of the cases. An alternative method of providing joint between two piles is shown below. In this method, after the piles are driven to the required. depth, the joint is grouted with cement mortar 1: 2 (1 cement : 2 sand).

   

   The piles are reinforced to avoid formation of cracks due to rough handling or shrinkage stresses. In order to reduce the possibility of damage due to driving impact, the stirrups should be spaced closely near the top and bottom of the piles. The piles are normally bevelled at their feet to facilitate tightly close driving of a pile against the already driven one.
   Reinforced concrete sheet piles are bulky and heavy and as such they are gradually being superseded by prestressed concrete piles.

2. Prestressed concrete sheet piles
   On account of the numerous advantages the prestressed concrete members have over the conventional type of reinforced concrete members, prestressed concrete sheet piles are commonly used for sheet piling jobs. Similar to concrete sheet piles, they are reinforced on both the faces so that they could be handled from either side. They are comparatively lighter in weight, more durable and economical in the long run. They are advantageously used in sea water, since the danger of cracking of concrete is negligible and also the corresponding danger of corrosion of pile reinforcement is reduced.

4. Light-gauge aluminum sheet piles

5. Vinyl sheet piles

6. Fiberglass sheet piles

Construction Methods

In the construction of sheet-pile walls, the sheet pile may be driven into the ground and then the backfill placed on the land side, or the sheet pile may first be driven into the ground and the soil in front of the sheet pile dredged. In either case, the soil used for backfill behind the sheet-pile wall is usually granular. The soil below the dredge line may be sandy or clayey. The surface of soil on the water side is referred to as the mud line or dredge line. Thus, construction methods generally can be divided into two categories (sheet pile wall types):

1. Backfilled structure
2. Dredged structure

The sequence of construction for a backfilled structure is as follows:

1. Dredge the in situ soil in front and back of the proposed structure
2. Drive the sheet piles.
3. Backfill up to the level of the anchor, and place the anchor system.
4. Backfill up to the top of the wall.

For a cantilever type of wall, only Steps 1, 2, and 4 apply. The sequence of construction for a dredged structure is as follows:

1. Drive the sheet piles.
2. Backfill up to the anchor level, and place the anchor system.
3. Backfill up to the top of the wall.
4. Dredge the front side of the wall.

With cantilever sheet-pile walls, Step 2 is not required.

Advantages:

Steel sheet piling is the most common because of several advantages over other materials:

1. Provides high resistance to driving stresses.
2. Light weight
3. Can be reused on several projects.
4. Long service life above or below water with modest protection.
5. Easy to adapt the pile length by either welding or bolting
6. Joints are less apt to deform during driving.

Disadvantages:

1. Sections can rarely be used as part of the permanent structure.
2. Installation of sheet piles is difficult in soils with boulders or cobbles. In such cases, the desired wall depths may not be reached.
3. Excavation shapes are dictated by the sheet pile section and interlocking elements.
4. Sheet pile driving may cause neighborhood disturbance.
5. Settlements in adjacent properties may take place due to installation vibrations

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