Settlements control in driving a shallow tunnel

Abstract

This paper will introduce an experience of tunnelling through a difficult ground, under low overburden and in the presence of some buildings located less than ten meters above the tunnel crown. The tunnel portion is in very weak clayey marl and marly clay. A clayey and sandy weathered surface affected the crown increasingly as the overburden decreased. The design provided a full section excavation with the RPUM. In this case RPUM (Reinforced Protective Umbrella Method) is a steel pipe roof protection of the opening boundary, a fiberglass tube face consolidation, a first phase lining consisting of shot concrete and steel ribs, invert casting close to the face and crown lining completion at the least possible distance from the face. All these devices had to be performed in subsequent advancement fields of reduced length. With the aim of safeguarding the buildings and their inhabitants, a measuring system, to monitor both superficial and deep ground movements, had been installed. This system allowed us to set up the design working phases and the suitable expedients to progressively reduce the settlement basin extension and the settlements entity despite the constant reduction of the overburden as the tunnel progressed. Particularly, for every main working phase, the ground deformation results were verified. Cavity boundary and surface movement were also checked, with the purpose of fixing the operative choices which have allowed the successful completion of the job. For more details you can visit the website www.sinc.it. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.