Soldier pile and lagging walls in deep excavations

Soldier Pile Walls: Information, Advantages & Disadvantages

Soldier pile and lagging walls, commonly known as soldier piles, are some of the oldest forms of retaining wall systems used in deep excavations. Soldier pile walls have successfully being used since the late 18th century in metropolitan cities like New York, Berlin, and London. The method is also commonly known as the "Berlin Wall" when steel piles and timber lagging is used. Alternatively, caissons, circular pipes, or concrete piles can also be used as soldier piles but at an increased cost. Timber lagging is typically used although reinforced concrete panels can be also utilized for permanent conditions. Soldier pile walls are formed by:

1. Constructing soldier piles at regular intervals (6 ft to 12 ft, typical)

2. Excavating in small stages and installing lagging.

3. Backfilling and compacting the void space behind the lagging.

Moment resistance in soldier pile and lagging walls is provided solely by the soldier piles. Passive soil resistance is obtained by embedding the soldier piles beneath the excavation grade. The lagging bridges retain soil across piles and transfer the lateral load to the soldier pile system.

Advantages & Disadvantages of Soldier Pile Walls

Soldier pile and lagging walls are the most inexpensive systems compared to other retaining walls. They are also very easy and fast to construct. The major advantages of soldier pile walls are:

1. Soldier piles are fast to construct.

2. Soldier pile construction is cheaper when compared to other systems.

3. Soldier pile installation is versatile and adjustments can be made in the field easily to accomodate changes.

4. Lagging construction can be very quick.

5. Construction of soldier pile and lagging walls does not require very advanced construction techniques.

Common lagging materials include timber, shotcrete, precast concrete panels, or steel plating. Permanent transporation walls usually utilize precast concrete panels, while temporary soldier pile walls in the US utilize timber lagging.

The major disadvantages of soldier pile and lagging systems are:

1. They are primarily limited to temporary construction.

2. Cannot be used in high water table conditions without extensive dewatering.

3. Poor backfilling and associated ground losses can result in significant surface settlements.

4. They are not as stiff as other retaining systems.

5. Because only the flange of a soldier pile is embedded beneath subgrade, it is very difficult to control basal soil movements.

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