Abstract

The characterization, rock excavatability and volume calculation of excavations carried out during infrastructure works are extremely important given the large amount of ground movement that takes place in this type of construction. The poor characterization of materials can bring to almost any field work significant changes in the initial budget due to the high cost of excavation of rock materials as compared with the conventional soil excavation. On many occasions, a limited geological information, together with a reduced number or low quality of the specified (direct) site investigations, turns more feasible the usage of indirect methods to determine the characteristics of the materials to excavate. Given the heterogeneous characteristics of the soil layers, and the high changes of rock lithology and fracturing state, it becomes very difficult to distinguish the transition zones based solely on few punctual surveys. For this reason, indirect methods of investigation shall be specified together with the direct ones to allow a better and continuous assessment of the subsoil, possibly at a lower cost and with a nondestructively manner. With this set of field information, it is undoubtedly easier to interpret and identify the linear stratigraphy of the construction site, hence performing a tailored budget based on more realistic cut and excavation sections of soil, rock and saprolite slopes. Therefore, this paper presents a real case history where the rock excavatability and the classification methodology of 1st, 2nd and 3rd category material in a non-continuous linear (25 km) cut was interpreted through the use of an electrical resistivity survey, complemented with direct in situ investigations (SPT, rock coring and topography) and geological mapping in the same region. The cuttings were specified as part of a large railroad project design in the state of Bahia – Brazil, where great part of the construction budget was involved with the excavation phase. As it will be demonstrated, satisfactory interpretation results were found by adopting the advocated methodology, as they yielded more realistic excavation volumes than those initially forecasted solely with SPT or rock drilling soundings.

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