Effects of Thickeners Polymers Used in Tunnelling on the Physical and Mechanical Properties of Fine-Grained Soils

The most effective, safe and controlled way to perform tunnel excavations is through the use of Tunnel Boring Machines. This technology often requires the injection of chemicals to modify the soil properties, enhancing the control on the pressure applied at the front-face and consequently reducing the risks related to unexpected surface settlements, to excessive abrasion of the excavation tools and to clogging phenomena inside the working chamber. Since the reuse of the excavated soil is rapidly gaining importance, studies focused on the effect of these chemicals on soil properties, from both the geotechnical and environmental points of view, begin to be carried out more frequently in support of the design. This study addresses the evaluation of the effects of chemicals on the physical and mechanical properties of fine-grained soils: laboratory measurements of the effects on soil plasticity and on the associated variations in compressibility and undrained and residual strength of several samples of fine-grained soils from real tunnelling projects are presented. The results provide interesting insights on the interaction between the soil and the injected chemical, useful to better understand the most suitable use and dosage of the chemical and to consider its effects when reusing the conditioned soil.