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  Use of special jet grouting technologies for tunnel’s crown and core advance consolidation: technical aspects and case studies

  The construction of tunnels in difficult ground conditions has boomed in the last 30 years. In Italy, where the conditions are often very demanding, the ADECO-RS design approach (Analisi DEfor-mazioni COntrollate, that is Analysis of COntrolled DEformation in Rocks and Soils) was first intro-duced in the late 80’s of last century. The ADECO-RS approach is focused on the tenso-deformative behaviour of the system in “front of the excavation-advancement core”, introducing the concept of pre-containment of the cave and of the “conservative systems” The design involves a three-steps procedure: 1.investigation (or research) stage, to classify the soils according to their geotechnical pa-rameters; 2.diagnosis stage, classifying the deformations of the soil under the excavation action into three fundamental categories: A: stable front; B: front stable in short terms; C: unstable front; 3.Further on, a stage of therapy is implemented, where the designer decides the necessary in-terventions for the three behaviour categories (A, B and C), in order to obtain stabilization of the tunnel. The appropriate design for each section are assessed using computation tools. By following this innovative approach, works consid-ered impossible only few years ago have been suc-cessfully completed. This paper deals with three projects in Italy, where the ADECO method has been used in different man-ners. The first project is a challenging project in Rome, where two twin tunnels (220 sq.m front surface) have been excavated in a difficult condition using a canopy of jet grouting launched from the tun-nel face, in progressing sections. The second project is in Viterbo, where a 32 metre long pietonal tunnel has been built in one go using jet grouting columns and steel pipes. Finally, a new roadway tunnel near Pozzuoli (Naples) was built by using jet grouting columns installed from the top.

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