Liner or casing is one type of formwork. It gives the desired shape to green concrete. Generally, it is made of steel and circular in shape.
In the case of the cast-in-situ pile, there are two types of liner:
- Temporary liner: This type of casing is removed after the casting of concrete is complete (before the start of the final setting).
- Permanent liner: – This type of casing is concreted with the concrete and remains there for a Lifetime of Pile
Steel liners play an important role in the construction of cast in situ piles, especially in marine conditions. Temporary steel liners are used to stabilize the sides of the borehole during construction. In port and harbour structures liners become a permanent part of the foundation, which requires minimum load carrying capacity to withstand the construction loads. Liner is used to maintain the clear cover between the main reinforcement and concrete surface during the stages of construction. It is used for bored cast in situ pile that extends through very soft soils, such as marsh deposits, to reach an underlying stratum that is more stable. In such cases, the liner is used to prevent the outward bulging of the fluid concrete into the surrounding soft soils. If a bulge forms at an elevation corresponding to an extremely soft stratum, there can be a risk of defects in the concrete due to a neck in the pile above the bulge, or deformation of the reinforcement cage.
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In construction practice, there is no standardized method to fix the minimum embedment length of the liner. The embedment length of the liner depends on the stiffness of the steel liner and soil properties.
In cohesion-less soil, penetration resistance or N-values are used to determine the modulus of subgrade reaction of the soil sample, which is helpful to determine the embedment depth of steel liner in sandy soil.
In clayey soil and rocky strata, the embedment depth of liners is based on the undrained shear strength of the soil, moment of inertia of the liner and Young’s modulus of the liner material. The unconfined compressive strength is assumed as two times the undrained shear strength.
Steel liners are temporary or permanent steel casings that are installed in boreholes to prevent soil collapse and maintain the stability of the excavation. They are typically used in soft or unstable soils, or when the pile is expected to be subjected to high lateral loads.
Steel liners for piles
Steel liners are typically made of corrugated steel sheets, which are joined together with bolts or welding. The thickness of the steel liner is determined by the diameter of the pile and the depth of the excavation.
Benefits of using steel liners:
- Prevents soil collapse and maintains the stability of the excavation
- Allows for the construction of larger and deeper piles
- Protects the pile from corrosion and abrasion
- Can be reused for multiple projects
Types of steel liners:
- Temporary liners: These liners are typically used for short-term projects and are removed after the pile is constructed.
- Permanent liners: These liners are left in place after the pile is constructed. They provide additional strength and support to the pile.
Applications of steel liners:
- Pile foundations
- Bridge piers
- Retaining walls
- Utility tunnels
Steel liners are an important part of pile foundation construction. They help to ensure that the piles are safe and stable, and that they will last for many years to come.
Steel liners are temporary or permanent steel casings that are installed in boreholes to prevent soil collapse and maintain the stability of the excavation. They are typically used in soft or unstable soils, or when the pile is expected to be subjected to high lateral loads. Steel liners are an essential component of pile foundation construction, ensuring the safety, stability, and longevity of the piles.
Purposes of Steel Liners
Steel liners serve a variety of crucial purposes in pile foundation construction:
- Soil Stabilization: Steel liners effectively prevent soil collapse and maintain the stability of the excavation, particularly in soft or unstable soil conditions. Without liners, the surrounding soil could cave in, compromising the integrity of the pile and potentially causing structural damage.
- Pile Formation Enhancement: Steel liners facilitate the construction of larger and deeper piles. They provide a stable cylindrical form for the concrete to be poured into, ensuring the proper shape and dimensions of the piles.
- Pile Protection: Steel liners act as a protective barrier around the piles, shielding them from corrosion and abrasion. This is particularly important in environments where the soil is prone to chemical or mechanical damage, such as in marine environments or areas with high water tables.
- Reusability: Temporary steel liners can be removed after the pile has hardened and is no longer susceptible to soil collapse. These liners can then be reused for other pile installation projects, offering cost-effective solutions.
Types of Steel Liners
Steel liners are primarily categorized into two types based on their intended use:
- Temporary Liners: As the name suggests, temporary liners are intended for short-term applications and are removed after the pile has cured and gained sufficient strength. They are typically used in situations where soil stability is only a concern during the initial excavation and pile formation stages.
- Permanent Liners: Permanent liners, on the other hand, remain in place as an integral part of the pile structure. They provide additional strength and support to the pile, especially in situations where lateral loads are a significant factor. Permanent liners are often used for deep excavations or in areas with unstable soil conditions.
Applications of Steel Liners
Steel liners find widespread application in various construction projects, including:
- Pile Foundations: Steel liners are extensively used in pile foundation construction, particularly for bridge piers, retaining walls, culverts, and utility tunnels. They ensure the stability of the piles and provide a reliable foundation for the overlying structures.
- Drilled Shafts: Steel liners play a crucial role in the construction of drilled shafts, which are deep, circular foundations used in various structures, including buildings, bridges, and towers. Liners prevent soil collapse and facilitate the formation of the shaft, ensuring its integrity and stability.
- Microtunneling: Microtunneling, a trenchless construction technique, utilizes steel liners to guide and support the tunnel excavation process. Liners provide stability and prevent soil collapse during the tunneling operation.
- Caisson Foundations: Caisson foundations, commonly used for offshore structures and deep foundations, employ steel liners to provide structural support and maintain the stability of the excavation. Liners ensure the integrity of the caisson during construction and throughout its service life.
In conclusion, steel liners are indispensable components in pile foundation construction, ensuring the safety, stability, and longevity of piles. Their ability to prevent soil collapse, facilitate pile formation, protect piles from corrosion and abrasion, and enhance the overall strength of the structure makes them essential for a wide range of construction projects.
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