Jet grouting applications in soft rocks: the Athens Metro case

摘要

The Athens Metro is an underground project, which is constructed mainly in soft rock conditions (the Athenian schist formation), and has provided extensive experience for all stages of soft rock tunnelling: the geotechnical investigation, the design and the construction. The present work gives an overview of the geological and geotechnical aspects, which are related to the design of the Athens Metro, and places emphasis on the application of jet grouting techniques for the needs of the project. Features and limitations of the applied jet grouting techniques are examined with the aid of executed full-scale trial tests in two sites of the project, where anticipated extreme surface subsidence and severe over-break incidents needed to be adequately confronted. The results from these tests are appropriately evaluated, and conclusions that can be applied to similar geological and geotechnical conditions are derived. Finally, the efficiency of the applied jet grouting techniques, relative to the acceleration of TBM tunnelling operations and to the minimisation of surface settlements, is addressed, with reference to the detailed work progress records and to the settlement measurements obtained by a comprehensive monitoring programme.