This report delves into the specifications and tolerances for concrete foundation construction according to the ACI 117M standards. The focus is on the acceptable tolerances for various aspects of foundation construction, such as the plumb line deviation, location displacement, and deviations from elevation, plane, and cross-sectional dimensions. The report aims to provide a comprehensive understanding of the standards and requirements for constructing concrete foundations. Additionally, Fig.1 illustrates a visual representation of a typical concrete foundation construction.
Fig.1: Concrete Foundation Construction
Tolerances for Concrete Foundation Construction as per ACI 117M-10
1. Foundation Plumb Line Deviation Tolerances
Plumb deviation tolerances vary depending on the type of material used for foundation construction and the material in which the foundation has been constructed. A table has been provided, which outlines the different tolerances for plumb deviation. Additionally, a figure has been included to illustrate the deviation of plumb.
Table 1 Foundation Plumb Deviation Tolerances
| Type of foundation | Tolerances |
| Unreinforced concrete pier extending through materials that do not provide lateral restraint | +/-12.5% of shaft diameter |
| Unreinforced concrete pier extending through materials that provide lateral restraint | +/-1.5% of shaft length |
| Reinforced concrete pier | +/-2% of shaft length |
Fig.2: Deviation of Plumb Line, A) Unreinforced Pier, B) Reinforced Pier
2. Tolerances for Location Displacement of Foundation
The allowable deviation for foundation location is determined by the size of the foundation or pier, with a set maximum limit. The maximum limit is determined by whether the foundation supports masonry or concrete structures. In other words, the deviation from the intended foundation location must not exceed a certain absolute limit, which varies depending on the dimensions of the foundation and the type of structure it supports. This is an important consideration to ensure the stability and safety of the overall structure. Therefore, it is crucial to adhere to these guidelines when constructing foundations to ensure that the structure is secure and meets safety standards.
Table-2: Foundation Location Deviation Tolerances
| Foundation Condition | Tolerances |
| Foundation supporting concrete, Figure 3 | |
| Horizontal deviation of the as cast edge with minimum dimension of 2.4m or greater | +/-50 mm |
| Horizontal deviation of the as cast edge with maximum dimension of 2.4m or smaller | Greater of 13mm or 2% of specified dimension |
| Foundation Supporting Masonry, Figure 3 | |
| Horizontal deviation of the as-cast edge | Smaller of 13mm or +/-2% of foundation width |
| Top of drilled piers, Figure 4 | |
| Horizontal deviation of the as-cast center | Smaller of +/-75mm or +/-4.2% of diameter of the shaft |
Fig.3: Location Deviation of Foundation
Fig.4: Horizontal Deviation of Top Drilled Pier
3. Tolerances for Foundation Deviation from Elevation
The given text describes the purpose and content of Table-3, which provides elevation tolerances for determining the location of any point on the top surface of a footing with respect to a predetermined plane. Additionally, the text references Figure-4 and Figure-5, which provide visual aids for understanding how elevation deviations are evaluated. Together, these resources can be used to ensure that footings are constructed with a high degree of accuracy and precision in terms of their elevation. By adhering to these guidelines and utilizing the provided tools, builders can ensure that their footings meet the necessary standards for safety and functionality.
Table-3: Elevation Deviation of Foundations
| Foundation type | Vertical tolerances |
| Footing, Figure 5 | +13mm to -75mm |
| Drilled pier, Figure 6 |
Fig.5: Vertical Deviation of Footing
Fig.6: Vertical Deviation of Drilled Pier
4. Foundation Deviation from Plane
The given context refers to the allowable slope of the base of a pier in the case of pier foundation and the top surface of a footing in the case of footing foundation. In other words, it is the maximum angle at which the base of a pier or the top surface of a footing can be sloped without compromising the structural integrity of the foundation.
The permissible slope is an important consideration in the design of foundations, as it determines the stability and safety of the structure. It is usually specified in building codes or standards, which provide guidance on the maximum allowable slope for different types of foundations and soil conditions.
For pier foundations, the permissible slope of the base of the pier is determined based on the soil properties and the load-bearing capacity of the foundation. The base of the pier must be sloped at an angle that allows for proper distribution of the load and prevents settlement or tilting of the foundation.
Similarly, for footing foundations, the permissible slope of the top surface of the footing is determined based on the soil properties, the load-bearing capacity of the foundation, and the size and shape of the footing. The top surface of the footing must be sloped at an angle that allows for proper distribution of the load and prevents excessive settlement or uplift of the foundation.
Overall, the permissible slope of the base of a pier or the top surface of a footing is an important factor in the design and construction of foundations, and it must be carefully considered to ensure the safety and stability of the structure.
Table-4: Plane Deviation of Foundation
| Type of foundation | Deviation from Plane |
| Top surface of footing at interface with supported element | largest space between the concrete and the near surface of a 3 m straightedge, measured between the support points, shall not exceed +13 mm |
| Base of bell pier | Smallest of +/-75mm and 10% of bell diameter as illustrated in Figure 6. |
Fig.7: Plane Deviation of Base of Bell Pier
5. Deviation from Cross Sectional Dimensions of Foundations
Based on the ACI specifications, the allowable errors in the size of the foundation would be specified in this section.
Table-5: Deviation from Cross Sectional Dimensions of Foundations
| Foundations | Tolerances |
| Formed foundations Horizontal deviation, Figure 8 | +50mm to -13mm |
| Unformed foundations cast against soil* Horizontal deviation, Figure 9 | +75mm to -13mm for dimension </= 600mm +150mm to -13mm for dimension >/= 600mm |
| Deviation from foundation thickness, Figure 10 | -0.05 of foundation thickness |
| *excavation shall be measured prior to concrete placement and tolerances shall apply at all locations | |
Fig.8: Formed Foundation, Cross Sectional Dimension Tolerances
Fig.9: Unformed Foundation, Cross Sectional Dimension Tolerances
Fig.10: Foundation Thickness Tolerances
References
The American Concrete Institute (ACI) Committee 117 published the “Specification for Tolerances for Concrete Construction and Materials” (ACI 117M-10) along with its commentary in 2010. This document outlines the acceptable tolerances for various aspects of concrete construction and materials.
Paragraph 2: The editorial staff of Concrete Construction in North America has also discussed the importance of tolerances in construction. Tolerances refer to the allowable deviation from specified measurements or dimensions. In concrete construction, tolerances are crucial to ensuring the proper performance and durability of the structure. Even small deviations from the specified tolerances can result in significant issues that may compromise the safety and functionality of the building.