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.

Concrete Foundation Construction

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

Foundation Plumb Line Deviation

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 edgeSmaller of 13mm or +/-2% of foundation width
Top of drilled piers, Figure 4
Horizontal deviation of the as-cast centerSmaller of +/-75mm or +/-4.2% of diameter of the shaft

Location Displacement of Foundation

Fig.3: Location Deviation of Foundation

Horizontal Deviation of Top Drilled Pier

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 typeVertical tolerances
Footing, Figure 5+13mm to -75mm
Drilled pier, Figure 6+25mm to -75mm

Foundation Deviation from Elevation

Fig.5: Vertical Deviation of Footing

Vertical Deviation of Drilled Pier

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.

Foundation Deviation from Plane

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

Formed Foundation

Fig.8: Formed Foundation, Cross Sectional Dimension Tolerances

Unformed Foundation

Fig.9: Unformed Foundation, Cross Sectional Dimension Tolerances

Foundation Thickness 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.

Madeh Izat Hamakareem

Madeh Izat Hamakareem

Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.