A geotechnical investigation is conducted to gather information about the soil conditions at a site in order to design safe and economical foundations and other earthworks.

Grab samples are not a type of soil sample because they are not collected using a specific sampling method. They are simply collected by hand or with a shovel.

SPT and CPT are two different methods for measuring the soil's resistance to penetration. SPT uses a split-spoon sampler, while CPT uses a cone penetrometer. SPT is conducted in a borehole, while CPT is conducted in situ. SPT measures the number of blows required to drive the sampler a certain distance, while CPT measures the cone resistance.

The bearing capacity of a soil is the maximum load that a soil can support without failure. It is typically determined using a geotechnical investigation and analysis.

A foundation is a structure that is built to transfer the load of a structure to the soil. It also prevents the structure from settling and protects it from the elements.

Caissons are not a type of foundation. They are a type of deep foundation element that is used to support a structure.

Shallow foundations are used for light structures, while deep foundations are used for heavy structures. Shallow foundations are built in the upper layers of the soil, while deep foundations are built in the lower layers of the soil. Shallow foundations are less expensive than deep foundations.

A retaining wall is a structure that is built to support a slope of soil, prevent erosion, and create a level surface.

Gabion retaining walls are not a type of retaining wall. They are a type of gravity retaining wall that is made of gabions, which are wire baskets filled with rocks.

Gravity retaining walls rely on their own weight to resist the lateral earth pressure, while cantilever retaining walls rely on the bending strength of their stems to resist the lateral earth pressure. Gravity retaining walls are typically made of concrete or masonry, while cantilever retaining walls are typically made of steel or reinforced concrete. Gravity retaining walls are less expensive than cantilever retaining walls.

A slope stability analysis is conducted to assess the risk of a slope failure, determine the factor of safety of a slope, and design a retaining wall to support a slope.

The presence of water is not a factor that affects the stability of a slope. However, the presence of water can increase the risk of a slope failure by causing the soil to become saturated and lose its strength.

The factor of safety of a slope is the ratio of the resisting forces to the driving forces. It is a measure of the stability of a slope.

A drainage system in a geotechnical design is used to control the flow of water, prevent erosion, and improve the stability of a slope.

Gabion drains are not a type of drainage system. They are a type of retaining wall that is made of gabions, which are wire baskets filled with rocks.