Investigation phases in geotechnical investigation:
There are four phases for the investigation of a site. These phases are given below along with their details:
- Phase 1, feasibility or reconnaissance.
- Phase 2, preliminary exploration.
- Phase 3, detailed exploration.
- Phase 4, Construction stage exploration.
Usually the first thee phases also known as pre-construction Phases are lumped together into a single exploration operation.
- Reconnaissance (phase 1):
This phase of the investigation is in fact the over view or the flying visit of the site. In this phase generally the background information of the site are collected.
It usually contains:
The type of structure to be constructed, expected structural loads, intended use of the structure, construction methods and approximate construction period.
Surface and subsurface conditions of the site:
This may be obtained by study of topography or geological maps of the site. Aerial photographs and data from previous investigations may also be use for this purpose. For large projects, geophysical methods of exploration may be used.
Study of the existing structures of the area:
The existing structures of the area near the site are studied during this phase. Its behaviour is studied during this phase.
- Preliminary investigation (phase 2):
By drilling holes and recovering the disturbed soil sample from each stratum bedrocks and hardpan are established for identification and classification of soils only. Position of GWT may also be established during this stage.
- Detailed exploration, (phase 3):
This phase may include, test pits excavation, boreholes, in-situ testing and collection of both disturbed and undisturbed soil samples. These samples then test in laboratory and analyzed. GWT fluctuations may also be checked regularly during this phase by installing peizometers.
- Construction/Post construction stage exploration, (phase4):
During construction, additional exploration may also be required to deal effectively with the un-expected subsoil conditions. Sometimes monitoring of structure both during and after construction may be required.