When should I use the single-walled casings? When do I need to use the double-walled casings?

When should I use the single-walled casings?

- Small hole diameter: When the pile diameter is small (usually less than 600mm), single-wall casing is a suitable choice. This is because the structure of single-wall casing is relatively simple, light weight, and convenient for operation in smaller hole diameters.

- Cost considerations: Compared with double-wall casing, single-wall casing is generally lower in material cost and processing cost. Therefore, single-wall casing may be a more economical choice when the budget is limited or the cost needs to be reduced.

- Convenience of construction: In some cases, the installation and removal of single-wall casing may be more convenient. For example, when using a rotary drilling rig for pipe lowering and pipe pulling operations, single-wall casing may be easier to cooperate with the power head and other components of the drilling rig.

Then when do I need to use the double-walled casings?

- Complex geological conditions: In the case of complex or unstable geological conditions, such as thick rock layers, large rock fragmentation, and abundant groundwater, double-wall casing provides better support and protection. Its inner and outer double-layer wall design can effectively improve the rigidity of the casing and reduce the frictional resistance of the outer hole wall on the casing. At the same time, the inner wall can play a better guiding role for the drilling tool.

- Strict construction requirements: When the construction requirements are very strict, such as ensuring the verticality of the borehole and preventing the occurrence of hole collapse or shrinkage, double-wall casing is a better choice. Its structural stability and strength can ensure the safety of construction.

- Environmental protection needs: In some areas or projects with high environmental protection requirements, the use of double-wall casing can reduce the use and discharge of mud and reduce pollution to the environment. This is because double-wall casing can better control the loss and diffusion of mud.

- Special engineering needs: For some special projects, such as offshore drilling oil platforms, port bored piles, etc., when axial and lateral bearing capacities need to be simultaneously borne, double-wall casing can provide better support and guidance.

- When using a hammer grab: When using a hammer grab, the uncertainty of the hammer grab's fall may cause it to collide with the inner wall of the casing, and causing the inner wall of the casing to bulge outward. If it’s a single-wall casing, since the casing body has only one layer, once it is hit by the hammer grab and bulges outward, the casing may be unable to be pulled out, resulting in increased costs and delayed construction time. However, if a double-walled casing is used, even if the inner wall of the casing is deformed by impact, the outer wall of the casing will not be affected, so the casing can still be pulled out normally after use.

- Large or deep piles: When the pile diameter is large or the depth is deep, the torque required to drive the casing is large. At this time, a casing oscillator or a casing rotator is needed. The single-wall casing may not be able to withstand excessive torque and cause deformation. The double-wall casing can withstand greater torque, so when the pile diameter is large or the depth is deep, the double-wall casing is more suitable.