Geotechnical investigations are performed to obtain information on the physical properties of soil and rock at site to design foundations for different structures and for repairing or renovation of distress earthworks and structures. Geotechnical investigation includes subsurface exploration, conducting some field tests and collection of soil samples. To obtain information about the soil conditions below the surface, some form of subsurface exploration is required.
Methods of observing the soils below the surface, obtaining samples, and determining physical properties of the soils and rocks include test pits, trenching (particularly for locating faults and slide planes), boring, and in situ tests. Reliability and accuracy are the essence of geotechnical investigation. Comprehensive, precise, detail and reliable investigation can reduce construction cost and time. On the other hand, unreliable geotechnical parameters always deceive or betray engineers and entrepreneur.
The geotechnical investigation and evaluation should include a balance of methods to acquire and evaluate subsurface information, including drilling and sampling, laboratory testing, geophysical surveys, cone penetration testing, and pressuremeter testing