Using Electrical Resistivity Tomography (ERT) as a tool in geotechnical investigation of the substrate of a highway

Geological and geotechnical engineering field tests, like structure drillings and dynamic (DPL, DPSH) or static probing (CPT), are considered for a fundamental source of information about soil and water environments. Since Eurocode 7 has been introduced, it has become more common to use also dilatometers (DMT) or pressure meters (PMT). Results obtained using all the mentioned tests are always of a discrete nature – information is provided in certain points in the field. However, they determine the basis for creating spatial models of geological structure and geotechnical conditions of a substratum. The range and number of investigations conducted (including drilling, probing and laboratory tests) influence precision, in which a geological structure is identified and thus, also affect probability of compatibility between spatial model and real geological conditions of a substratum. In the paper, results of non-invasive electrical resistivity tomography (ERT) method are presented, comprising 2-dimensional image of a soil medium resistance. Electrical resistance is a parameter that reflects diversification of a soil medium, considering its lithological aspect. In addition, when combined with drilling results, it can be used to accurate determination of boundaries between soil layers. Carrying out of ERT tests in the field during expressway construction contributed to identification of weak, low-strength soils like organic soils (peat, aggradated mud) and of soft consistency cohesive soils. These kinds of soil are the main cause for unacceptable deformations appearing in the new road engineering structure.