ADECO full-face tunnel excavation of two 260 m super(2) tubes in clays with sub-horizontal jet-grouting under minimal urban cover

• Published in: Tunnelling and underground space technology Vol. 26; no. 2; pp. 253 - 266
• Main Author: Tonon, Fulvio
• Format: Journal Article
• Language: English
• Published: 01.03.2011
• Subjects: Clays; Construction industry; Emptying; Excavation; Grounds; Roads; Tubes; Tunnels (transportation)
• DOI: 10.1016/j.tust.2010.09.006
• ISSN: 0886-7798

With a cover of 5-30 m, a 260 m super(2) cross-sectional area, and a 4-m wide pillar, the Cassia twin road tunnels underpass Cassia road (main road to/from Rome), the remnants of a 2000 year-old Roman villa, and two existing tunnels. Stiff silty clay dominates the alignment. According to the Analysis of Controlled DEformations (ADECO) principles, each tube was excavated full face to 260 m super(2). Compared to Sequential Excavation Method (SEM), this highly simplifies construction, leads to construction industrialization, and allows for full control of the ground ahead of the face, which is used as a stabilization measure. In order to pre-confine the tunnel core, Trevi roto-injection technique was used to create an umbrella of overlapping sub-horizontal reinforced jet-grouting columns ahead of the face, while avoiding up heave of the ground or emptying of the columns. Stiff preliminary lining sitting on sub-horizontal jet-grouting columns, final invert close to the tunnel face, and final lining no more than 50 m behind the face ensured that the pre-confinement ahead of the tunnel face became effective confinement around the cavity. The tunnels were finished on schedule and within budget with a mere 1 cm of settlement.