Tunnel excavation with EPB: Development of new conditioning agents to reduce the amount of water required for soil conditioning

Tunnel excavation with TBM requires large amounts of water that are necessary for several different applications. When EPB machines are used, an important contribution to the water consumption is due to the soil conditioning, in particular when the excavation is in cohesive formations. The proper amount of liquids necessary for the soil conditioning depends on several aspects (such as geology, type of conditioning agents used, configuration of the TBM, earth pressure applied at the tunnel face, etc.), however values of WIR (Water Injection Ratio = Volume of pure added water/Volume of soil excavated) in the range of 10%-30% are common. The development of new conditioning agents allows to significantly reduce these amounts of water. The laboratory of the University “Politecnico di Torino” carried out a thorough campaign of tests using a reference clay, whose results show that new conditioning agents allow to save water in a range between 20 and 33% compared to the traditional products. This reduction of the WIR means thousands of tons of water saved for tunnel excavation, with consequent advantages under several points of view: technical, economical, and environmental. The reduction of water means lower volume of tunnel muck, less trucks necessary to transport the muck to its destination, which means lower CO2 emissions due to downscaled logistics, etc. All these advantages are more and more rele- vant nowadays, especially in those countries where water has become a precious and scarce resource. The paper describes the tests carried out and obtained results.The advantages of these new conditioning agents are presented in detail and contextualized in the view of a sustainability approach in tunnel construction.