Tunnel excavation in soft or weak grounds requires to be pre-supported by consolidation measures performed ahead of the tunnel’s face. The umbrella arch method is one of the most widely used techniques, consisting in a series of sub-horizontal boreholes, reinforced with steel tubes and injected under pressure, drilled to form a pre-shaped arch supporting the ground during tunnel excavation. As an alternative, jet grouting, mechanical pre-cutting and sub-horizontal fiberglass reinforcement can also be used to limit excavation-induced settlements.
The installation of pipe umbrella systems is carried out by means of conventional jumbos or special tunnelling drilling rigs, equipped with long-stroke masts to allow single pass drilling. The Comacchio MC 30 TX is ideally suited for this application and it stands out from other solutions on the market for its multi-purpose design. This unique design allows the Comacchio MC 30 TX to be converted into a ‘conventional’ articulated drilling rig, covering the entire spectrum of geotechnical engineering applications (micropiles, anchors and jet grouting).