Specification tolerances for concrete foundation construction as per ACI 117M such as tolerances for plumb line deviation, location displacement, deviation from elevation, plane and cross-sectional dimensions of foundations are discussed.
Fig.1: Concrete Foundation Construction
Table of Contents
Tolerances for Concrete Foundation Construction as per ACI 117M-10
1. Foundation Plumb Line Deviation Tolerances
There are different plumb deviation tolerances based on the materials used for foundation construction and material in which the foundation has been constructed. Table-1 provides plumb deviation tolerances. Figure 2 illustrated 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
Permissible foundation location deviation is based on the foundation or pier dimension with an absolute limit which depends on whether the foundation carries masonry or concrete.
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
It specifies the location of any point on the top surface of a footing with respect to a determined plane. Table-3 provides elevation tolerances and Figure-4 and Figure-5 illustrate how elevation deviations are evaluated.
Table-3: Elevation Deviation of Foundations
| Foundation type | Vertical tolerances |
| Footing, Figure 5 | +13mm to -75mm |
| Drilled pier, Figure 6 | +25mm to -75mm |
Fig.5: Vertical Deviation of Footing
Fig.6: Vertical Deviation of Drilled Pier
4. Foundation Deviation from Plane
It is the permissible slope of base of bell in case of pier and top surface of footing in the case of footing foundation.
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
In this section, allowable errors in the size of foundation would be specified based on the ACI specifications.
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
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