Subgrade preparation

UFC 3-260-02

30 June 2001

The reduced subgrade strength method produced the more economical design for all traffic areas.

A comparison must be made with the nonfrost pavement thickness. With F4 subgrade soils, in lieu

of drainage layer under the PCC pavement, a drainage layer between the subbase and the

separation layer should be considered. The divisions shown are one of many possibilities.

Judgment must be used when layer thicknesses are selected.

Separator

Drainage

S1 or S2

Total "Combined

Layer

Subbase Layer

Base" Thickness

NFS Base Layer

mm (in.)

Traffic Area

A

1,168 (46.0)

610 (24.0)

356 (14)

102 (4)

B

1,156 (45.5)

622 (24.5)

330 (13)

102 (4)

C

965 (38.0)

508 (20.0)

250 (10)

102 (4)

D

775 (30.5)

419 (16.5)

152 (6)

102 (4)

(3) Subgrade preparation. The depth of subgrade preparation D will be the lesser of the

following:

(a) D = 610 millimeters (24.0 inches).

(b) D = [2/3 @ (maximum frost penetration)] - (Combined thickness of PCC, base,

subbase and drainage layers).

Frost Penetration

Combined Pavement

Subgrade Preparation

Traffic Area

mm (in.)

Thickness, mm (in.)

Depth, mm (in.)

A

2,235 (88)

1,168 (46.0)

330 (13.0)

B

2,235 (88)

1,156 (45.5)

330 (13.0)

C1

2,285 (90)

965 (38.0)

178 (7.0)

D1

2,311 (91)

775 (30.5)

381 (15.0)

1

Use one-half rather than two-thirds frost penetration for traffic areas C and D.

(c) D = 1,829 millimeters (72 inches) - (Combined Pavement Thickness).

Traffic Area

Combined Pavement Thickness, mm (in.)

D, mm (in.)

A

1,168 (46.0)

660 (26.0)

B

1,156 (45.5)

673 (26.5)

C

965 (38.0)

864 (34.0)

D and Overruns

775 (30.5)

1,054 (41.5)

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