Soil Bearing Capacity & Calculating Safe Bearing Capacity of Soil

Soil Bearing Capacity & Calculating Safe Bearing Capacity of Soil

Soil Bearing Capacity & Calculating Safe Bearing Capacity of Soil

Soil Bearing Capacity & Calculating Safe Bearing Capacity of Soil

Soil Bearing Capacity (SBC) is the soil’s capacity to support the applied load to the ground. The soil bearing capacity is the highest contact pressure between the soil and the foundation, which should not result in shear failure in the soil.

The bearing capacity depends typically on the ground or soil’s behavior under the building and the interaction with the structure’s foundation. The structural weight of a building must be economically and safely transferred to the soil or ground without significant foundation settlement.

Site ground investigation should be done to determine what type and size of structure it can support, the ground loading, and the measurement of movement that can be tolerated. 

Soil Bearing Capacities Chart

Class of Materials
Load-Bearing Pressure
(pounds per square foot)
Crystalline bedrock12,000
Sedimentary rock6,000
Sandy gravel or gravel5,000
Sand, silty sand, clayey sand, silty gravel, and clayey gravel3,000
Clay, sandy clay, silty clay, and clayey silt2,000

Source: Table 401.4.1; CABO One- and Two- Family Dwelling Code; 1995.

For large buildings or structures constructions, a geotechnical site investigation should be done. 

The requirements for categorizing a site and the planning and construction of a footing for a building of a single residential house or a townhouse. 

Ultimate Bearing Capacity

The ultimate bearing capacity for a typical foundation is the average vertical pressure on the soil leading to a shear failure. it is the moderate contact pressure between the ground and foundation that will produce shear failure in the soil

Maximum Safe Bearing Capacity 

The maximum safe bearing capacity is the maximum amount of contact pressure to which the soil can be exposed with no risk of shear failure. This is usually based entirely on how strong the soil is and is the ultimate bearing capacity divided by an appropriate safety factor.

Allowable Bearing Pressure

The allowable bearing pressure is the maximum pressure that can be beared sustainably by the structure’s foundation from the footing under the loads over a different range of soil moisture conditions.

Allowable bearing pressure should be taken into account for both the site conditions and the building system’s ability to accommodate settlement.

Allowable Bearing Capacity Table

The table below indicates the presumptive bearing capacity numbers for different types of soils. This table is a guide to a conclusion after doing conducting the test.

Type of Soil / RockSafe / Allowable Bearing Capacity (kg/cm2)
Rock32.40
Soft rock4.40
Coarse sand4.40
Medium sand2.45
Fine sand4.40
Soft shell / Stiff clay1.00
Soft clay1.00
Very soft clay0.50

 

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