Albula Tunnel II: Ground Freezing in the Raibler-Rauwacke

Quelle/credit: Kartengrundlagen/Map basis: www.schweizerweltatlas.ch; www.wikipedia.org

1 The geographic location of the Albula Tunnel

Quelle/credit: Kartengrundlagen/Map basis: www.schweizerweltatlas.ch; www.wikipedia.org

Quelle/credit: Rothpletz, Lienhard + Cie AG (Geologische Grundlage/ Geological basis: Sieber, Cassina + Handke AG, Chur)

2 Geological longitudinal profile (top) and horizontal section (bottom)

Quelle/credit: Rothpletz, Lienhard + Cie AG (Geologische Grundlage/ Geological basis: Sieber, Cassina + Handke AG, Chur)

Quelle/credit: Rothpletz, Lienhard + Cie AG

3 Geological sub-division of the Raibler-Rauwacke on the basis of the probe drillings

Quelle/credit: Rothpletz, Lienhard + Cie AG

Quelle/credit (3): Rothpletz, Lienhard + Cie AG

4 Standard cross-sections in the area of the Raibler-Rauwacke in Albula Tunnel II (left, with full seal and ring closure) and Albula Tunnel I (right, draining)

Quelle/credit (3): Rothpletz, Lienhard + Cie AG

5 Aims of the sealing mass: reduction of permeability (a) and increase in stability (b)

6 Concept of injection mass (a) and freeze body (b)

Quelle/credit: Rothpletz, Lienhard + Cie AG

7 Situation with depiction of the freezing concept from the cavern

Quelle/credit: Rothpletz, Lienhard + Cie AG

Quelle/credit: a) & b) Rothpletz, Lienhard + Cie AG; c) Dr. W. Orth

8 Cross-sections: arrangement of the holes (a), depiction of the required freeze body (b), typical thermal calculations (c)

Quelle/credit: a) & b) Rothpletz, Lienhard + Cie AG; c) Dr. W. Orth

Quelle/credit: a) Rothpletz, Lienhard + Cie AG; b) Dr. W. Orth

9 Schematic diagrams for clarification of the creep process

(ε: single-axis expansion, σ: single-axis stress, T: temperature, t: time, t_m: critical time) (a); typical creep curves from the laboratory tests (b)

Quelle/credit: a) Rothpletz, Lienhard + Cie AG; b) Dr. W. Orth

Quelle/credit: Züblin Spezialtiefbau Ges.m.b.H, Wien/ Rothpletz, Lienhard + Cie AG

10 Lost drill bit (a) and parts of the release mechanism (b)

Quelle/credit: Züblin Spezialtiefbau Ges.m.b.H, Wien/ Rothpletz, Lienhard + Cie AG

Quelle/credit: Rothpletz, Lienhard + Cie AG

11 Start oft he excavation through frozen ground in the cavern, using a 42 t excavator on a heavy-load frame

Quelle/credit: Rothpletz, Lienhard + Cie AG

Quelle/credit: Bauleitung Los 106

12 Excavation through frozen ground; tunnel face and excavation support (section III of the Raibler-Rauwacke)

Quelle/credit: Bauleitung Los 106

An inrush of mud in the running ground causing excavation to come to a standstill for 15 months: this incident was documented during the construction of the existing metre gauge railway tunnel 117 years ago. To avoid a similar inrush of mud during the construction of the Albula Tunnel II in the Raibler-Rauwacke, a freezing mass was created for the drive in this geologically challenging zone, which is composed of silty fine sand and exposed to high hydraulic pressure. The present report was part of the Swiss Tunnel Congress 2017 conference programme.

1 Introduction

The 5864 m long Albula Tunnel I is located in the canton of Grisons and connects the northern valleys of Grisons to the Engadin (Fig. 1). It has been in operation since 1903 as a single-track metre gauge railway tunnel and was made a UNESCO World Heritage Site in 2008 as part of the Rhaetian Railway (RhB) in the Albula/Bernina countryside.

The assessment of the condition of the tunnel in 2006 demonstrated a significant need for renovation as well as a need to bring the level of safety up to current standards. In 2010, it was decided in the course of the preliminary project to...