The decision to use double wall casing or single wall casing in drilling operations depends on various factors, including the specific project requirements, soil or rock conditions, and drilling method employed.
Here are some considerations for the use of each type:
Double Wall Casing:
Unstable or Loose Formations: Double wall casing is often employed when drilling through unstable or loose formations, such as sands, gravels, or water-bearing strata. It provides increased stability and helps prevent collapse or caving of the borehole.
Well Control and Fluid Circulation: The annular space between the drive pipe and casing in double wall casing allows for effective circulation of drilling fluids, such as drilling mud. This helps to remove cuttings, maintain pressure control, and prevent influxes of water or other fluids into the borehole.
Grouting Requirements: Double wall casing facilitates the injection of grout into the annular space, if needed, to enhance the integrity and load-bearing capacity of the drilled shaft. Grouting can improve the bond between the casing and surrounding soil or rock, providing additional support.
Deep Drilling: In deep drilling applications, where greater stability and support are required, double wall casing can be beneficial. It provides an extra layer of reinforcement and can help withstand the higher pressures and loads associated with deeper drilling operations.
Single Wall Casing:
Stable Formations: Single wall casing is often used when drilling through relatively stable formations, such as stiff clays, competent rock, or consolidated soils. In these cases, the primary purpose of the casing is to maintain the integrity of the borehole rather than provide additional stability.
Casing Extraction: If the extraction of the casing after drilling is required, such as for installation of reinforcement or pouring of concrete, single wall casing is typically used. It allows for easier extraction compared to double wall casing, as there is no inner drive pipe to be removed.
Smaller Diameter Shafts: For smaller diameter drilled shafts or when the loads are not exceptionally high, single wall casing may be sufficient to provide the necessary support and stability.
It's important to note that the selection of casing type should be made based on a thorough evaluation of site-specific conditions and engineering considerations. Consulting with geotechnical engineers and drilling experts is crucial in determining the appropriate casing system for a given project.