Introduction

In piling and diaphragm wall construction, the casing system plays a crucial role in maintaining borehole stability, preventing soil collapse, and guiding the drilling process. As geotechnical conditions become more complex — such as loose sand, boulders, or high groundwater tables — the demand for robust casing solutions increases.

This article explains the function and benefits of Double Wall Casings and how they work in tandem with Casing Oscillators to ensure safe, efficient, and high-quality pile installation.

A Double Wall Casing consists of two concentric steel tubes — an outer pipe that provides structural strength and an inner pipe that supports the drilling fluid return or tool guidance. This design greatly improves torsional resistance and vertical stiffness compared to traditional single-wall casings.

Key advantages include:

  • Improved alignment and verticality in deep holes

  • Resistance to buckling during drilling or extraction

  • Higher torque transmission when used with casing rotators or oscillators

  • Enhanced safety and durability in harsh working conditions

    What Is a Casing Oscillator (a.k.a. Casing Twister or Tube Turner)?

    A Casing Oscillator is a heavy-duty hydraulic device used to insert or extract casings during foundation work. Unlike vibratory hammers or rotators, oscillators apply alternating torque (oscillating motion) to gently “work” the casing into the ground — a process especially useful in sensitive or hard soil formations.

     Key Functions:

    • Assists in lowering casing in gravel or dense soil

    • Applies bidirectional torque to reduce insertion resistance

    • Stabilizes casing during drilling to prevent misalignment

    • Helps extract casing after concreting by reversing the oscillation

    When paired with double wall casings, casing oscillators become even more effective, as the dual-wall structure handles high torque and compression loads without deformation.

    Where Are They Used?

    • Diaphragm wall construction

    • Large-diameter bored piles

    • Foundation piles in urban projects

    • Subway stations and retaining walls

    • Underwater foundation jobs (piers, docks)