Prior to construction of a structure, soil investigation is done in order to get the idea of subsurface condition. The scope of a soils investigation is generally depends on many factor, such as
- Type, size & importance of the structure
- The client
- Engineer’s familiarity with the soils at site
- Local building code
- Economy
If an engineer is familiar with a site, then he/she may undertake a very simple soil investigation to confirm his/her experience.
High rise buildings usually require a more through soil investigation than a foundation for a house.
The 5 phases involved in any soil investigation work are as follows
- Desk study
- Preliminary reconnaissance
- Detailed soil exploration
- Laboratory test
- Report writing
Let us discuss each of the above phases in detail.
Phase-1 (Desk study)
This is the phase where all the information that are available, are collected. The information which needs to be collected are as follows
- Site plan
- Type, size & importance of the structure
- Loading conditions
- Previous geo-technical reports
- Topographical maps
- Still photographs etc.
Phase-2 (preliminary reconnaissance)
In this phase a site visit is made to get a general idea of the topography and geology of the site. You need to take with you all the information gathered in phase-1 to compare with current conditions of the site. Make a note of everything while visiting the site. You must note down the following things
- Photographs of the site and its neighborhood
- Access to the site for workers and equipments
- Sketch of all fences, utility post, walkways, drainage etc
- Available utility services such as water and electricity
- Sketches of topography including all existing structures, cuts, fills, ground depressions, ponds & so on.
- Exterior and interior cracks on existing buildings or any tilt
- Geological features from any exposed area such as road cut or excavated portions
Phase-3 (Detailed exploration)
The objectives of a detailed soils exploration are
- To determine the geological structure, which should include the thickness, sequence and extent of the soil strata
- To determine the ground water condition
- To obtain disturbed and undisturbed samples for laboratory tests
- To conduct in situ tests
Phase-4 (Laboratory testing)
The objectives of laboratory tests are
- To classify the soils
- To determine soil strength, failure stresses and strains, stress-strain response, permeability, compaction properties and settlement parameters.
Phase-5 (Report writing)
The report must contain a clear description of the soils at the site, methods of exploration, soil stratigraphy, in situ and laboratory test methods and results, and the location of the ground water, recommendation regarding construction operation.