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210 – National Engineering Handbook
Part 650 – Engineering Field Handbook
Chapter 17 – Construction and Construction Materials
E. Construction Tolerance Guidance for Constructed Practices
The following tables provide recommended tolerances for constructed field office conservation practices. The
tolerances presented below do not apply if specific tolerances are identified on the site-specific construction plans.
For more information, consult the References listed at the end of this section, as numerically footnoted in the
tables.
Table 1: General Earthwork TolerancesA
Dimension Minimum (minus) Maximum (positive)
-0.3 ft. from planned line/grade +0.3 ft. from planned
1,B
Deviation from design slope line (if gradual) line/grade
(if gradual)
Overall slope no steeper than Flatter slope must not
Side slopesC designed interfere with function of
appurtenances
1
Top of Fill Height 00 +0.5 ft.
(including settlement allowance)
Finished Top Width of Fill 00 +15%
Depth of Excavation -0.3 ft +0.1 ft
Notes:
A.
Earthwork tolerances presented in Table 1 apply to all conservation practices but not spoil areas. These
tolerances would not apply if there are specific tolerances on the site-specific construction plans.
B.
Deviation planned line and grade is measured in feet and represents the distance between the
constructed surface and the ideal surface when built exactly as designed.
C.
When measuring side slope right after construction, adjust the design side slope to accommodate the
settlement allowance.
(210-IV-EFH, Notice IL 118, November 2020)
IL17.E-1
210 – National Engineering Handbook
Table 3: Auxiliary Spillway Tolerances
Dimension Minimum (minus) Maximum (positive)
1
Control Section Elevation -0.1 ft. +0.3 ft.
Inlet Section Deviation from design -0.3 ft. +0.3 ft.
1,A
slope line
Outlet Section Deviation from design -0.3 ft. +0.3 ft.
1, A
slope line
Outlet Section Level (Across Channel -0.2 ft. +0.2 ft.
1
Bottom)
Notes:
A.
Deviation planned line and grade is measured in feet and represents the distance between the
constructed surface and the ideal surface when built exactly as designed.
Table 4: Concrete Placement TolerancesA
Dimension Minimum (minus) Maximum (positive)
1
Formwork (Wall thickness) -0.25 in. +0.5 in.
1
Flatwork (Slab thickness) 0.00 in. +3 in.
-1.0 in. +1.0 in.
1
Finished Surface Variation (over a 5 ft section if gradual) (over a 5 ft section if
gradual)
1
Cover Over Rebar -0.25 in. +0.5 in.
1
Rebar – Length -2 in. +2 in.
1
Lap and Splice Location -3 in. +3 in.
(minimum 12” splice length)
Rebar Spacing –Distance between -0.5 in. +0.5 in.
1
bars
1
Rebar Spacing – Uniform Spacing -2 in. +2 in.
Rebar Position-Tension
Reinforcement (typically vertical bars -0.375 in. + 0.375 in.
1
in the direction of wall thickness.)
Notes:
A.
These tolerances for concrete apply except for concrete associated with certain practices that have their
own table in this guidance document.
(210-IV-EFH, Notice IL 118, November 2020)
IL17.E-2
210 – National Engineering Handbook
Table 5: Grassed Waterway and Surface Drains Tolerances
Dimension Minimum (minus) Maximum (positive)
B +0.2% with no grade
Bottom Grade (design <0.5%) -0.1% with no grade reversals C
reversals
Bottom Grade (design 0.5%-2.0%) -0.2% with no grade reversalsB +0.3% with no grade
reversalsC
B +0.5% with no grade
Bottom Grade (design >2.0%) -0.5% with no grade reversals C
reversals
1,A
Side Slope-Trapezoidal Waterway -0.2 ft. +0.2 ft
(deviation from design slope line)
2
Quarter Point Depth -0.2 ft. +0.2 ft.
2
Total Channel Depth -0.2 ft. +0.2 ft.
Center Point of Parabolic Waterway2 Is Lowest Is Lowest
2
Top Width 00 +10%
Notes:
A. Deviation planned line and grade is measured in feet and represents the distance between the constructed
surface and the ideal surface if built exactly as designed.
B. Minimum Tolerance on bottom grade refers to how much flatter is allowable for the slope. This
minimum tolerance is zero if the design velocity is at the lower limit allowed by the standard.
C. Maximum tolerance on bottom grade refers to how much steeper is allowable for the slope. This
maximum tolerance is zero if the design velocity is at the upper limit allowed by the standard.
(210-IV-EFH, Notice IL 118, November 2020)
IL17.E-3
210 – National Engineering Handbook
Table 6: Basin (Terrace and WASCoB) and Diversion Tolerances
Dimension Minimum (minus) Maximum (positive)
Top (Elevation at design top width, 00 +0.5 ft.
1
including settlement allowance)
Side Slope deviation from design -0.3 ft. from planned line/grade +0.3 ft. from planned
1,A line/grade
slope line (if gradual) (if gradual)
Channel deviation from design slope -0.2 ft. with No Grade +0.2 ft. with No Grade
1,B
line Reversals Reversals
Notes:
A.
Deviation planned line and grade is measured in feet and represents the distance between the
constructed surface and the ideal surface when built exactly as designed.
B.
The tolerance on channel slope applies to terrace channels outside of the basin storage area, and to the
gradient terraces. The restriction on grade reversals applies to all channels.
Table 7: Underground Outlet/Subsurface Drain Tolerances
Dimension Minimum (minus) Maximum (positive)
Riser Flowline (Elevation) -0.2 ft. +0.2 ft.
Orifice Depth below riser flowline 00 +0.2 ft. more depth
Overall Grade (deviation from design -0.2 ft. with No Grade +0.2 ft. with No Grade
slope line)A Reversals Reversals
Notes:
A.
Deviation planned line and grade is measured in feet and represents the distance between the
constructed surface and the ideal surface when built exactly as designed.
(210-IV-EFH, Notice IL 118, November 2020)
IL17.E-4
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