Tolerances for Concrete Foundation Construction as per ACI 117M-10

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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

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

References

1. ACI Committee 117, 2010. Specification for Tolerances for Concrete Construction and Materials (ACI 117M-10) and Commentary. American concrete institute.
2. Editorial Staff of Concrete Construction , N.A. Tolerances in construction. Concrete construction.