The Bearing Capacity of Soil in Construction Projects

The bearing capacity of of soil is an important consideration in construction projects. The bearing capacity of soil is the pressure that a soil sample can support without collapsing. Bearing capacity varies with different soils cohesion. Cohesion is the force that holds together molecules and particles inside soil.

Rock is a continuous mass of solid mineral material, such as granite or limestone, that can only be removed by drilling or blasting. Rock is never completely formed of a single large segment, but is crossed by a system of joints that divide it into irregular blocks. Despite these joints, rock is generally considered the strongest and most stable material on which a building can be founded.

Soil is a general term referring to earth material that is particulate. If an individual piece of soil is too large to lift by a singular hand it is considered a boulder. It it takes the whole hand to lift a particle, however, it is a cobble. If a particle can be lifted without difficulty with thumb and forefinger, the soil is classified as gravel. If the individual particles can be viewed but are too small to be picked up individually, the soil is known as sand. Both sand and gravel are coarse grained soils, meaning at least half the material is retained on a Number 200 sieve.

Peat, topsoil and other organic soils are not reliable for the support of building foundations. Due to the high concentration of organic matter, they are spongy and are easily compressed. Their properties can change over time due to changing water content or biological activity in the soil.

Clay soils are usually referred to as very cohesive, as they retain a measurable shear resistance (a materials ability to resist forces that can cause the internal structure of a material to slide against itself), in the absence of confining forces. The ability of a cohesion-less or frictional soil such as sand or silt to support a building depends on the friction between its particles. Sand confined by surrounding soil within the earth can support a heavy building, whereas a conical pile of sand on the surface of the earth can support nothing, because there is little or no shear resistance between the particles.

Beneath every building site lies a number of superimposed layers, also known as strata, of different soils. In ancient times, the actions of natural forces allowed for the deposition of the strata one layer on top of another.