Soldier pileS And lagging walls overview
Soldier piles and lagging walls, also called Berlin Walls or king piles, are an earth retention technique that retains soil. The way that soldier piles and lagging walls retain soil is through vertical steel piles and horizontal lagging.
Driven prior to excavation, the steel piles are made of wide flange steel, shaped in H sections and placed roughly 2 to 3 m apart. As the excavation proceeds, the lagging, generally made out of timber sheeting, is inserted behind the H pile flanges horizontally.
The horizontal earth pressures are concentrated on the soldier piles because of their relative rigidity compared to the lagging. Soil movement and subsidence is minimized by maintaining the lagging in firm contact with the soil.
Soldier piles and lagging walls are one of the oldest forms of deep excavation used in retaining systems, used in cities around the world since the 18th century. They are also one of the least expensive techniques used and are very fast to construct.
Soldier piles are most suitable in conditions where well-constructed walls will not result in subsidence, such as over-consolidated clays, soils above the water table if they have some cohesion, and free draining soils which can be effectively dewatered, like sands. Additionally, they are often used when property lines dictate exactly where construction must be.
Although there are many benefits to Soldier Piles and Lagging Walls, there are also some downsides. Often times they can only be used for temporary systems because of many unsuitable soil conditions and long term sustainability.
Unsuitable soils and soil conditions include soft clays, as well as weak running soils that allow substantial ground shifts, such as loose sands. It is also not possible to extend the wall beyond the bottom of the excavation. Dewatering is also often required because of the type of construction and because of water making the ground less stable.
Learn more about the different types of Soldier Piles & Lagging Walls: