What Is A Bore Casing? How Is It Used?
Steel and concrete casing and liners are drilling equipment that play a crucial role in the construction of drilled shafts. Casings are tubes that are usually made of steel, concrete or PVC. Liners are most often made from rolled metal plate, but are sometimes made from plastic or pressed fibers. Casings are used more often than liners, but both are incredibly important to maintaining the structural integrity of drilled shafts.
To protect the internal diameters of the drilled shaft and prevent the sides of the borehole from collapsing during drilling, the bore casing is installed. The purpose of a bore’s cased section is to create a protective lining or casing for a water bore drilled vertically into the ground. This casing contains the pump that draws water from the aquifer and acts as a barrier, preventing contamination from adjacent zones. The annular space between the casing and the borehole wall helps to maintain stability and prevents soil from collapsing into the borehole.
Installation of Casings
A bore casing is often placed into a large drilled hole and then seated into the underlying foundation to provide stability. A casing can be placed through a pre-drilled hole which may be constructed by cement slurry or advanced without drilling if the soil will stand for a short time. Sometimes casings are used for further drilling. Telescoping casing is often used to perform this job when soil or rock friction is low.
A temporary casing is used to stabilise a drilled shaft excavation during the drilling process and is removed after or during the placement of fluid concrete in a shaft. Temporary casing is used to retain the sides of a borehole long enough for the fluid concrete to be placed. When the concrete has been filled to a level sufficient to withstand ground and groundwater pressures, the temporary casing is removed. Additional concrete is placed as the casing is removed to maintain the pressure balance. In some cases, temporary casing may be left in place.
The Size of Casings
If a casing size is not specified, most engineers will simply employ a casing that has an outside diameter (OD) of six inches larger than the drill shaft diameter. This is done to allow the passage of a drilling tool of proper diameter during final excavation of the borehole. The pipe wall thickness needs to be a consideration for maximum thickness.
The most common material used for bore casing is steel, although plastic and concrete materials are also used in some applications. Steel casing offers the greatest strength and durability, but can corrode over time when subjected to certain environmental conditions. Plastic and concrete casings are ideal for use in shallow boreholes, offering more cost-effective alternatives to steel but do not have as high stiffness.
The Benefits of Bore Casing
Using a bore casing provides several benefits over traditional methods of drilling and excavating a shaft. Utilising a casing can reduce the amount of time required to reach depth and provide better control over fluid pressure within the hole.
As mentioned, casings are sometimes employed as drilling tools themselves when rock excavation must be advanced below the casing in the dry rock. In such cases the end of the casing may have cutting teeth attached before a twisting or driving force is applied through the casing.
Casing must be cleaned thoroughly following use to ensure resistance due to the motion of fluid concrete is as low as possible. When temporary casings are lifted, the drag on the column of concrete may cause the concrete to lift which can manifest a void in the concrete. Therefore, casings must be free from soil, lubricants and other detritus before they are used.
If you are looking for a casings or liners for use in your construction, mining, civil or infrastructure project, just call Tebco today to place an order. We have a vast selection of casings and liners available for sale. Check out our online store or call us on (02) 4677 2649 or reach out via our contact page to ask any questions or to make an order for our casings and liners today.