Secant Pile / Berliner Wall




		Secant Pile / Berliner Wall


		Secant Pile Wall
		Secant pile walls are formed by constructing intersecting reinforced concrete piles. The piles are reinforced with either steel rebar or with steel beams and are constructed by either drilling under mud or augering. Primary piles are installed first with secondary piles constructed in between primary piles once the latter gain sufficient strength. Pile overlap is typically in the order of 3 inches (8 cm). In a tangent pile wall, there is no pile overlap as the piles are constructed flush to each other. The main advantages of secant or tangent pile walls are:
		1. Increased construction alignment flexibility.
		2. Increased wall stiffness compared to sheet piles.
		3. Can be installed in difficult ground (cobbles/boulders).
		4. Less noisy construction.

		The main disadvantages of secant pile walls are:
		1. Verticality tolerances may be hard to achieve for deep piles.
		2. Total waterproofing is very difficult to obtain in joints.
		3. Increased cost compared to sheet pile walls.

		Soldier Pile and Lagging Wall (Berliner Wall)

		Soldier pile and lagging walls are some of the oldest forms of retaining systems used in deep excavations. These 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 "Berliner 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 and lagging walls are formed by:

		1. Constructing soldier piles at regular intervals (2 to 4m, 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 and retains soil across piles and transfers the lateral load to the soldier pile system.

		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 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.


			Special Foundation Construction


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