Soil Investigation is carried out for designing a right type of foundation safely and economically, a designer must possess sufficient information about the physical properties and the arrangement of underlying materials. The field and laboratory investigations required to get this essential information is known as soil exploration. The study of complete soil investigations can be grouped under the following heads,

1. Objectives or purposes,
2. Preliminary investigations,
3. Methods of site exploration,
4. Depth and spacing of trial pits and borings,
5. Choice of a method,
6. Recording of data.

Objectives of Soil Investigation :

The objectives of an engineer, before starting the exploration work, should be to collect the following information:

1. The nature, thickness and variation of soil strata in the region.
2. Procuring representative samples for assessing the physical properties of the soil strata encountered, which in turn will help in the design and mode of construction of the propsed foundations. 
3. The seasonal variations in ground water table and their possible effects on the soil .
4. The approximate values of strength and compressibility of soil bed.
5. The depth of underlying rock bed, when necessary.