Consistency Index and Its Correlation with EPB Excavation of Mixed Clay–Sand Soils

Abstract

The behavioural properties of excavated ground have significant influence on the excavation process performed by an Earth Pressure Balance Machine (EPBM), as they are among the main factors responsible for maintaining the pressure ahead of the face, which affects face stability. Therefore, understanding the characteristics of the excavated material along with its flow behaviour is essential for a successful EPB tunnel drive. In scenarios involving the excavation of fine-grained soils containing clay minerals, the consistency index has been widely used as a guideline to define the ideal state of the excavated material. However, there are certain restrictions for the use of this index, the first of which are the Atterberg limits. These limits become more restrictive when mixed soils are involved. This study presents a brief review of the application of the consistency index and Atterberg limits in order to predict the performance of an EPB excavation. This study presents the results of a laboratory testing campaign with artificially mixed clay–sand soils by using a flow table as a preliminary flow assessment of cohesive soils.