Figure 1. Bearing capacity factors of safety for different thicknesses of sand cap as a function of soil undrained shear strength

ERDC TN-DOER-N5

July 2000

Figure 1. Bearing capacity factors of safety for different thicknesses of sand cap as a function of soil

undrained shear strength (to convert soil shear strength to Pascals, multiply by 47.88)

Table 2

Soil Stregnth Required for Different Bearing Capacity Factors of Safety

Soil Strength, Pa (lbf/ft2)

Sand Cap Thickness

FOS = 1.0

FOS = 3.0

0.3 m (1 ft)

,383 (8)

1,149 (24)

0.6 m (2 ft)

,766 (16)

2,298 (48)

1 m ,(3.3 ft)

1,245 (26)

3,687 (77)

If the dredged material to be capped is too soft initially to sustain a full cap thickness, it may be

possible to construct a coherent cap in thinner lifts, i.e., use staged construction of the cap. After

placement of a portion of the cap, the dredged material will consolidate under the load and will gain

strength with time. Then the process could be repeated with additional capping material being

placed and further consolidation of the dredged material allowed to occur. In this manner, it should

be possible to design staged cap construction even for very soft sediments, so that the risk of bearing

capacity failures can be minimized.