The Line 1 extension was undertaken in the Madrid Underground Extension. Excavation work was carried out by two methods: a) the Milan method (cut-and-cover) and b) underground excavation using the Traditional Madrid Method, a varient of the old Bellgian Method. In order to reduce damage to building, two ground improvement systems were used: a) Compaction grouting, where the tunnel is located under buildings and b) Jet-grouting walls, between the structures and the tunnel, where the tunnel centre line was parallel to the buildings. This paper describes the ground characteristics, excavation process and ground improvements designed. The results obtained from the special treatment and auscultation work are also included.
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