What Is ODEX Piling?

DFE have recently completed a project in the Lake District where ODEX piling was required, but what is ODEX piling and when is it used? This guide explains how the process works and when it’s the right choice — for pile sizes, capacities and to discuss your project, see our overburden drill and case piling service page. ODEX piling is a drilling method used for installing piles in difficult ground conditions such as mixed soils, boulders and loose overburden. The name comes from the eccentric drill bit at the heart of the system. It combines drilling and casing installation into one operation, progressing a thin-wall casing through challenging soils or obstructions and into competent rock. Once competent rock is reached, the pile is progressed beneath the casing by forming a socket into the rock itself.

How ODEX Piling Works:

1. An ODEX drilling system uses an over-reaming drill bit, which creates a hole slightly larger than the casing diameter. The casing sits on the drill string, resting on a shoulder just behind the drill bit. Drilling is carried out using rotary percussive techniques, with the arisings flushed to the surface by compressed air.
2. As the drill advances, the casing is installed at the same time, which stops the hole collapsing in loose ground. Extra sections of casing are welded on as needed until competent rock is reached.
3. Once the overburden has been penetrated, casing installation stops and drilling continues into the bedrock using a smaller down-the-hole hammer to form the rock socket.
4. Once the socket is formed, the drill string is removed and the pile is filled with concrete or grout, with reinforcement placed into the pile. Depending on the project, the casing is either left in place or removed.

Where Is ODEX Piling Used?

ODEX piling tends to get specified where other methods have already struggled, or would be expected to. Common situations include:

• Former mining ground, where piles need to be founded below old workings or voids
• Brownfield sites with unknown or undocumented obstructions below ground
• Sites where a driven or bored pile has refused, or is likely to, due to boulders or cobbles
• Restricted access or low headroom sites where a large conventional rig can’t be brought in
• Projects requiring higher pile loads than a standard mini piling system can provide

When ODEX Piling May Not Be the Right Choice

It isn’t always the right tool for the job. Where bedrock is shallow and easily reached, or where there’s no reason to expect obstructions in the overburden, a simpler and quicker method — mini piling or CFA, for example — will usually do the job for less. ODEX piling is a more involved process than either of those, so it tends to earn its keep on sites where ground conditions genuinely demand it, rather than as a default choice. The only reliable way to know which category a site falls into is proper site investigation.

How Is Suitability Assessed?

Before recommending ODEX piling, we’d typically look at:

• Available site investigation data and what it shows about the ground above rockhead
• The depth to competent rock
• Any known or suspected obstructions, mine workings or voids
• The pile capacity required by the structure
• Access and headroom constraints on site

Advantages of ODEX Piling:

• Effective in Challenging Ground – ideal where cobbles, boulders or other obstructions sit above competent rock.
• Mine Workings or Voids – a strong option in areas affected by mining, allowing piles to be founded below any workings.
• Suitable for Restricted Access Sites – can be used in confined spaces while still supporting heavy loading.

If you have a project that may need ODEX or overburden drill and case piling, contact our team to discuss your ground conditions and get a free, no-obligation quote.