Pile foundation construction involves manufacturing processes that can lead to errors. To ensure quality and safety, there are specified tolerances for these errors. If the errors exceed the tolerances, the pile foundations may be rejected for use.
The tolerances for fabrication differ for different types of pile foundations. Therefore, it is essential to understand the specifications for each type. By doing so, construction workers can ensure that the fabrication processes meet the required standards. This will help to avoid potential safety hazards and ensure the integrity of the structure.
Tolerances of Errors in Pile Foundation Construction
Following are tolerances for various types of piles:
1. Steel bearing piles
Steel bearing pile sections must conform to the dimensional tolerances outlined in the BS 4360. This standard specifies the allowable variations in the dimensions of steel bearing piles, which are used to support structures and transfer their loads to the ground. Compliance with these dimensional tolerances is essential for ensuring that the steel bearing piles meet the required specifications and perform their intended function effectively.
In addition to complying with the dimensional tolerances specified in the BS 4360, steel bearing pile sections and related steelwork must also meet fabrication tolerances as per the BS 5950: Part 2. This standard specifies the allowable variations in the fabrication of steel structures, including steel bearing piles, to ensure that they are manufactured with the required accuracy and precision. Compliance with these fabrication tolerances is crucial for ensuring that the steel bearing piles are fit for their intended purpose and meet the necessary safety standards.
2. Precast concrete piles
Manufacturing tolerances for precast concrete piles must meet specific requirements. Firstly, the external cross-sectional dimensions must be within a range of 0 mm to +6 mm of the specified dimensions. Secondly, the wall thickness of hollow spun concrete piles must be within a range of 0 mm to +25 mm of the specified thickness. These requirements ensure that the precast concrete piles are consistent with their intended size and shape.
There are also requirements for the surface of the pile. The face of the pile must not have any irregularities exceeding 6 mm over a length of 3 m. To measure this, a 3 m straight edge is used. Additionally, the internal face of hollow spun concrete piles must not have any irregularities exceeding 25 mm over a length of 3 m, as measured using a 3 m straight edge. These requirements ensure that the surface of the pile is uniform and smooth.
Finally, the centroid of any cross-section of the pile must not deviate more than 12 mm from the straight line connecting the centroids of the end faces of the pile. To determine the centroid, it is assumed that the pile has a solid section. This requirement ensures that the pile is balanced and has consistent weight distribution.
Overall, these requirements ensure that precast concrete piles are of high quality and consistent with their intended design.
3. Hand-dug caissons foundations
The requirement states that for each section of the shaft, its center must be located within a 50 mm distance from the centerline of the entire shaft. This implies that the positioning of each section’s center must be precise and should not deviate beyond the allowed limit of 50 mm.
Therefore, it is necessary to ensure that the shaft’s sections are positioned accurately during manufacturing or assembly processes. Any deviation beyond the specified limit may cause the shaft to be unbalanced, leading to performance issues or even failure of the machinery in which it is used.
Hence, it is crucial to adhere to the given requirement and ensure that each section of the shaft is correctly positioned within the allowed tolerance limit. This will help to ensure that the machinery operates smoothly and efficiently without any adverse effects due to improper shaft alignment.
4. Tolerances for pile installations
The installation of piles, such as hand-dug caissons and mini-piles, must adhere to the tolerances outlined in Table-1. It is crucial to ensure that the specified tolerances are met during the installation process. Any piles that do not meet the specified tolerances should not be forcefully adjusted or corrected. It is imperative to follow these guidelines to ensure the safety and stability of the structure being built.
Table-1: Tolerances of installed piles
| Description | Tolerances | |
| Land Piles | Marine Piles | |
| Deviation from specified position in plan, measured at cut-off level | 75mm (15mm for mini-piles) | 150mm |
| Deviation from vertical | 1 in 75 1 in 100 for mini-piles | 1 in 25 |
| Deviation of raking piles from specified batter | 1 in 25 | |
| Deviation from specified cut-off level | 25mm | |
| The diameter of cast-in-situ piles shall be at least 97% of the specified diameter. | ||