UFC 3-260-02
30 June 2001
Therefore, the assignment of k values in increments of 2.71 MN/m3 (10 pci) for values up to and
including 68 MN/m3 (250 pci) and in increments of 6.8 MN/m3 (25 pci) for values exceeding 68 MN/m3
(250 pci) should be sufficient. A maximum k value of 135 MN/m3 (500 pci) will be used. Typical values
of k for different soil types and moisture contents are shown in Table 6-1.
Table 6-1
Typical Values of Modulus of Soil Reaction
Suggested Default
Pavement Design Values
if No Test Data is
Typical Range (lb/in.2/in.)
Available (lb/in.2/in.)
Soils
Organic Soils (OL, OH, Pt)
25 - 100
25
Silts and Clays of High Plasticity
50 - 150
50
(CH, MH)
Silts and Clays of Low Plasticity
50 - 200
100
(CL, ML)
Silty and Clayey Sands (SM, SC)
50 - 250
150
Well- and Poorly-Graded Sands
150 - 400
200
(SW, SP)
Silty and Clayey Gravels (GC,
200 - 500
250
GM)
Well- and Poorly-Graded Gravels
300 - 500
350
(GW, GP)
Pavement design should be based on test data or at least historical data of past designs and
evaluations at the same facility if at all possible. These default values are suggested for use for
preliminary calculations or for small projects or projects where better data simply cannot be obtained.
Inadequate testing or evaluation budgets are not an excuse to use these values for final design.
b. Special Conditions. Test Method CRD-C 655 requires a correction of the field plate bearing test
results to account for saturation of the soil after the pavement has been constructed. Most fine-grained
soils exhibit a marked reduction in the modulus of soil reaction with an increase in moisture content, and
a saturation correction is applicable. However, in arid regions or regions where the water table is
3.0 meters (10 feet) or more below ground level throughout the year, the degree of saturation that may
result after the pavement has been constructed may be less than that on which the saturation correction
is based. If examination of existing pavements (highway or airfield) in the near vicinity indicates that the
degree of saturation of the subgrade is less than 95 percent and if there is no indication of excessive
loss of subgrade support at joints due to erosion or pumping, the correction for saturation may be
deleted.
5. SUBGRADE COMPACTION FOR FLEXIBLE PAVEMENTS - NORMAL CASES. In general,
compaction increases the strength of subgrade soils and the normal procedure is to specify compaction
in accordance with the following requirements.
6-4
Previous Page
