What Is the Difference Between Contiguous Piles and Secant Piles?

What Is the Difference Between Contiguous Piles and Secant Piles?

Piling in general is one of the most useful and versatile construction techniques, used for everything from strengthening your home’s foundations to anchoring major engineering projects such as bridges or oil rigs. However, the number of different types of piling can be confusing.

Two types you may have come across are contiguous piles and secant piles. So what are these, and how are they different?

Bored Pile Walls

Both contiguous and secant piles are types of bored pile walls. These offer an easy, cost-effective way of inserting a retaining wall, to hold back a mass of soil and prevent movement, with minimal disruption. Bored pile walls have a wide range of applications, but are most typically used to construct basements or foundations for substructures that are close to main structures.

Whichever approach is used, bored pile walls are created by drilling a series of holes close together, using either continuous or sectional steel flights, which are then filled with concrete or grout. The wall of piles effectively holds back the pressure from one side while the other side can be excavated with a retaining wall already in place.

Contiguous Piles Forming a Bored Pile Wall

Of the two main methods of creating a bored pile wall, contiguous piling is the simplest. The bores are made so close together that the piles will be touching, forming a virtually unbroken wall. In practice, there will be tiny gaps between piles, filled with earth, which can be grouted for extra strength. A contiguous pile wall may need a second wall in front of it if it’s going to be a permanent structure.

Because it relies on soil packed between the piles, contiguous piling is most commonly used where the subsoil is stiff and cohesive. It’s also advisable that the water level is below the bottom of the wall.

Secant Piles Forming a Bored Pile Wall

Secant piling, on the other hand, is preferable where the soil is less firm, and particularly when water needs to be retained. In this case, secondary piles are bored, with the main piles then added in between to form a more resilient wall.

In most cases, the secondary piles are formed of softer concrete than the main piles, but an alternative is to make both sets of piles from the same reinforced concrete. This is a more difficult procedure, but it does usually avoid the need for an extra wall.

Find Out More About Contiguous and Secant Piles

Contiguous piles and secant piles are both powerful and effective tools for excavating basements or foundations, and each has its own particular strengths. Give us a call to find out more about how they can be of use to you.