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

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