What Is a Secant Pile Wall?

Tips & Advice

A secant pile wall is a type of retaining wall used to ensure ground retention prior to excavation. Secant pile walls are created by constructing alternating primary and secondary piles (female and male piles) where the secondary piles partially cut into either side of the primary piles in order to form an uninterrupted, impermeable structure.

When obstructions are anticipated, secant walls make a good alternative to diaphragm walls, as they have a more flexible shape and offer relatively compact operation. Similarly, secant walls work well in urban projects with limited space.

How Are Secant Pile Walls Constructed?

Secant pile walls are built with intersecting reinforced concrete piles. The piles are reinforced with steel beams and are constructed by drilling under mud. Primary piles are installed first, with secondary piles constructed in between once the primary piles have gained sufficient strength.

There are three main types of secant pile walls, which are:

  • ‘Hard/Soft’ which uses a bentonite/cement slurry in the primary piles

  • ‘Hard/Firm’ which uses high reinforcement/low strength concrete in the primary piles

  • ‘Hard/Hard’ which uses a full strength structural concrete in the primary piles

Piles typically overlap by about three inches. Primary piles are secanted by secondary piles, thus providing a closed structure to act as a barrier in water bearing soils, and to prevent the ingress of soil between the piles.

Steel beams: wide flange, h-oile, and more

What are the Advantages of Secant Pile Walls?

The main advantages of secant pile walls are:

  1. Minimal vibration

  2. Increased construction alignment flexibility to fit complex site boundaries

  3. Less noisy or disruptive construction

  4. Ability to go through underground obstructions such as steel, concrete, etc.

  5. Increased wall stiffness compared to sheet piles

  6. Can be installed in difficult ground (cobbles/boulders)

  7. No need to install timber lagging

  8. Avoids risk of construction induced settlements to neighboring structures

What are the Disadvantages of Secant Pile Walls?

The main disadvantages of secant pile walls are:

  1. Hard to achieve verticality tolerances for deep piles

  2. Waterproofing is difficult to obtain in secant pile joints

  3. More expensive than sheet pile walls

Common Sizes for Steel Beams used for Secant Piles

Secant piles can use a wide range of steel pile sizes, including both wide flange piles and H-piles. Some common sizes include:

W8: W8x18, W8x21, W8x24, W8x28, W8x31, W8x35, W8x40, W8x48, W8x58, W8x67

W10: W10x22, W10x26, W10x30, W10x33, W10x39, W10x45, W10x49, W10x54, W10x60, W10x68, W10x77, W10x88, W10x100, W10x112

W12: W12x26, W12x30, W12x35, W12x40, W12x45, W12x50, W12x53, W12x58 ,W12x65, W12x72, W12x79, W12x87, W12x96, W12x106, W26x120, W12x136, W12x152, W12x170, W12x190, W12x210, W12x230, W12x252

W14: W14x22, W14x26, W14x30, W14x34, W14x38, W14x43, W14x48, W14x53, W14x61, W14x68, W14x74, W14x82, W14x90, W14x99, W14x109, W14x120, W14x132, W14x145, W14x159, W14x176, W14x193, W14x211, W14x233, W14x257, W14x283

W16: W16x26, W16x31, W16x36, W16x40, W16x45, W16x50, W16x57, W16x67, W16x77, W16x89, W16x100

W18: W18x35, W18x40, W18x46, W18x50, W18x55, W18x60, W18x65, W18x71, W18x76, W18x86, W18x97, W18x106, W18x119, W18x130, W18x143, W18x158, W18x175, W18x192, W18x211, W18x234

HP8: HP8x36

HP10: HP10x42

HP12: HP12x53, HP12x63, HP12x74, HP12x84, HP12x89, HP12x102, HP12x117

HP14: HP14x73, HP14x89, HP14x102, HP14x117

HP16: HP16x88, HP16x101, HP16x121, HP16x141, HP16x162, HP16x183

W-beams

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