Effect of Chemicals in Clogging Risk Reduction for TBM‐EPB Application

Over the last decade several tunnel excavations in difficult conditions were successfully performed using TBM-EPB technology with the help of soil conditioning agents that, in fine-grained soils, have proved to be particularly effective in reducing the clogging risk. TBM excavation performances are strictly related to the management of the injection of these products. Consequently, a preliminary study on the typologies and dosages of chemicals required to reduce the clogging risk in the soil to be excavated has become a key component of good tunnel design. Several methodologies and laboratory test equipment were developed worldwide to quantify the effects of the interaction between chemicals and soil particles; even if often there are no commonly accepted standards for the execution of these tests, several charts for the classification of the clogging risk have been provided. The scope of the research presented is to underline how specific features of natural soil (grain size distribution, mineralogical content, plasticity and consistency) affect the clogging tendency of fine-grained soil and how the injection of chemicals can modify it. Adherence was studied through mixing tests and pull out cone and plate tests, performed on several samples of different soils from actual tunnel excavation projects, untreated as well as treated with several commercial products from the main European suppliers. The results of the analyses and laboratory tests performed provide useful data that can help improve the currently available clogging risk classification charts as well as propose a classification for the reduction of the clogging risk related to the injection of chemicals specifically suited for EPB applications.