A database of 33 km of EPB tunnel records in the Barcelona area has been examined in detail from the point of view of cutting tool replacement and performance of the mechanized excavation. The database includes tunnels in soft soils, in hard and medium rocks and in mixed soil-rock conditions. Data gathered includes tool changing records, machine operation (advance, thrust, torque, etc.) and geotechnical properties, with a systematic emphasis on abrasivity measurements of the different materials perforated. To obtain a homogeneous description of abrasivity LCPC-type abrasive measurements were made in all the materials. A descriptive summary of the main trends revealed by the data is presented in this thesis. Machine downtimes during perforation can be classified into those due to planned maintenance and those due to unforeseen incidents. The latter can turn out to be decisive when assessing the success of a perforation, even though they are not usually considered in the project. One of the most demanding aspects of maintenance from an operational point of view is that of the cutting tools, since their revision and possible substitution always involves machine stops and, since it is often necessary to have access to the face, this is frequently a slow and difficult operation. Thus, it is desirable to schedule the cutter head maintenance operations with the highest possible precision.
To carry out such scheduling two aspects are necessary: the identification of "wear thresholds" of the tools and a method that allows estimating the wear for each tool as a result of the operation. The objective of this study is to investigate how to tackle this problem when the media is heterogeneous and the excavation is mechanized by EPB. Transversal and longitudinal geotechnical heterogeneity is systematically accounted for. Longitudinal heterogeneity is used to segment the database in homogeneous units. Transversal (within section) heterogeneity is gauged by a set of newly developed impact factors FI. The specific energy concept (SE) was applied to evaluate overall excavation efficiency. Previous procedures to compute SE in TBM drives were adapted to excavations by EPB machine in closed mode. Face support and rotational moment due to earth pressure at the front face are taken explicitly into account. Several existing methods to predict penetration rate and tool service life are evaluated against the database results. Recalibrations of these procedures were performed when required.
Based on a systematic analysis of the database results, new empirically based relations are proposed to estimate penetration rate from other operation parameters and section-averaged ground properties. The accuracy of some approximations involved (namely the use of an equivalent tool life time) has been found reasonable using the results of one drive were more exact computations were possible. The proposed relations would be mostly applicable as starting points in projects in which the geology is composed mostly of soils and soft rock and where the heterogeneous faces are predominant.