Geotechnical investigations in Estonia are technically regulated by European Standard EN 1997: Eurocode 7: Geotechnical design: Part 1: General rules and Eurocode 7: Geotechnical design: Part 2: Ground investigation and testing.

In engineering practice are used many synonyms for geotechnical site investigation as for example engineering geology, soil investigation or ground investigation. According to Eurocode 7 ground investigation is the component part of geotechnical design.

In geotechnical field investigation different techniques and measurements are used- visual observation, inquiry, trial pits, boreholes, soil sampling for laboratory tests, static cone penetration, dynamic probing, field shear tests and load tests, measurement of depth of groundwater table and groundwater sampling for laboratory analysis, etc.

The results of field investigation and laboratory tests shall be compiled in ground investigation report. This report should consist of presentation of all available geotechnical information including test results and geological data, evaluation of information, assumptions made in the interpretations of test results.

As regards prediction of geological structure and soil conditions for design of new structures we can use it as if we have in near vicinity reliable geological data and sufficient geotechnical experience. The design without ground investigations could be considered only for simple and light structures and with safe and consistent use of standard factors. In these situations geotechnical design without ground investigations usually leads to over dimensioning of structures which is expensive for customer.

But design without ground investigations could be potentially dangerous especially when geotechnical conditions happen to change. The practice of ground investigations has shown that geological structure or soil conditions can largely differ on neighboring sites or even unexpectedly alter within small area of one structure. In these situations geotechnical design without proper ground investigation may lead to undesirable consequences such as flood, accumulation of humidity, undesirable settlement and deformations of the structure, danger of collapse of structure, etc.

Therefore it is important to clarify basic geological and geotechnical conditions in early phases of planning of structures in order to estimate all risks for design and construction.

Preliminary investigation shall be carried out for instance to assess general suitability of the site, to detect possible soil or groundwater pollution by contaminants, to detect underground structures etc. Preliminary investigation gives oportunity to plan subsequent design investigation and ground conditions check during supervision of construction.

Design investigation shall be carried out to provide reliable information for an adequate design, to plan the method of construction and identify any difficulties that may arise during construction.

Ground conditions check shall be carried out as a part of supervision of construction. The aim of this checking is to detect possible deviations from ground type and properties, groundwater conditions assumed in the design (investigation). The principles used in design shall be checked to ensure that they are appropriate for geotechnical features of the ground and groundwater, which are encountered.

For simple structures and conditions (geotechnical category 1) the soil type and groundwater conditions are checked visually and compared with earlier recordings. For complex structures (geotechnical categories 2 and 3) geotechnical properties of the soil or rock in or on which the structure is founded or located should be checked. Additional investigations may be needed for determination of soil type, strenght and deformability parameters. Direct observations of groundwater conditions should be made if these greatly affect the method of construction or performance of structure, and also if dewatering, grouting or tunneling during construction strongly affects groundwater regime.