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2‐8 General Information MN2408
Table 2‐1 Approximate Load Bearing Capacities of Various Soil Types
Soil Type
Safe Bearing Capacity
lb per ft
2
kilo Pascals
Hard Rock - Granite etc. 50,000 - 200,000 2,395 - 9,576
Medium Rock - Shale etc. 20,000 - 30,000 958 - 1,436
Hardpan 16,000 - 20,000 766 - 958
Soft Rock 10,000 - 20,000 479 - 958
Compacted Sand and Gravel 10,000 - 12,000 479 - 575
Hard Clay 8,000 - 10,000 383 - 479
Gravel and Coarse Sand 8,000 - 10,000 383 - 479
Loose, Medium and Coarse Sand 8,000 - 10,000 383 - 479
Compacted Fine Sand 6,000 - 8,000 287 - 383
Medium Clay 4,000 - 8,000 192 - 383
Loose Fine Sand 2,000 - 4,000 96 - 192
Soft Clay 2,000 96
Table 2‐1 shows approximate load bearing capacities for various types of soil if the actual load
bearing capacity of the soil under the foundation is not known.
Caution: Check the local building codes for load bearing capacity requirements.
Caution: If the soil is subject to freezing and thawing, the foundation must be extended below the frost
line. Check the local building codes.
S Reinforce the foundation with No. 8 gauge steel wire mesh placed horizontally on
6in (150mm) centers. As an alternative, use No. 6 re-bars on 12in (300mm) centers
horizontally. Minimum cover over the bars should be 3in (76mm).
S Suggested concrete mixture by volume is 1 part cement, 2 parts sand, and 3 parts
aggregate. Maximum slump of 4in (100mm) and a 28-day compressive strength of
3000 psi (20,600 kPa).
S The size of the bolts holding the sub-base to the foundation should be sized to fit the
mounting holes shown on the Installation Diagram.
S Three-inch (76mm) iron pipe sleeves should be placed around the bolts in the
foundation to allow for any mislocation of the bolts after the foundation hardens. “J” or
“L” type bolts are recommended for the foundation bolts.
S After the foundation is cured and the genset is located, the sleeves are filled with grout.
Figure 2‐5 shows a typical foundation installation.
Figure 2‐5 Typical Foundation Installation