The Ambrosero tunnel is located in The Cantabrian town of Ambrosero and is part of the Santander-Bilbao metre-gauge railway line.The works carried out for the structural reinforcement, drainage replacement and waterproofing of the Tunnel were the following:
- Special structural reinforcement located between km 564 + 208 and km 564 + 231 (23 m), which includes road protection, installation of provisional protection structure and installation of electrowelded mesh and TH-21 trusses, excavation, sealing, cleaning, reconstruction (installation of HEB-120 trusses, Bernold sheet and concreting of the backfill) coating and finally, cleaning.
- Replacement of existing lateral drainage between km 564 + 164 and km 564 + 235 (142 m). This activity includes cleaning the trench, replacement of drainage, backfill material and end of means removal.
- Tunnel vault waterproofing in sections km 654 + 100-564 + 164 and km 564 + 529-564 + 593 (128m), including tunnel waterproofing and placement of stainless steel strap to hold the waterproofing sheet
In order to carry out the work, the railway traffic had to be cut off, the access was on track and machinery had to be placed on diploris.