EPB tunnelling in mixed geological formations: A case study

摘要

Tunnels for the new Barcelona Metro Line 9 are being constructed in a densely built urban area,rnclose to sensitive structures. The paper presents a case history involving tunnelling in difficult mixed geologicalrnconditions belowan existing Metro Line (Line 4).Tunnellingwas performed with a dual EPB boring machine andrnthe closed mode of operation was prescribed beneath all sensitive structures. Despite this original prescription,rnan open mode excavation (with a partially filled pressure chamber) had to be adopted to avoid the interruptionrnof the boring process in the area below the existing Metro Line 4. The paper describes the geological conditionsrnof the site, presents some of the ground movement observations prior to the change of excavation mode andrndiscusses the rationale that allowed the change in the prescribed tunnelling mode as well as the results obtained.rnObservations of displacements during the excavation in open mode confirmed that no soil inrush into the headrnchamber occurred and that in addition, with the new excavation procedure, ground movements were reducedrnsignificantly.