Cast-iron tunnels’ tolerance to imposed longitudinal settlement curvature

Abstract

Displacements imposed upon existing cast-iron tunnel linings attributed to new underground construction often cause changes in their alignment. The rate of change in alignment, or curvature, is a key parameter in assessing the impact of displacement. Owing to the installation limitations and the precision deficiency of conventional monitoring systems, measuring such curvature deformations, especially locally, has been a challenging task. In this paper, the curvature measurement data of the following two case studies are presented: (a) Crossrail's Liverpool Street station construction affecting the Northern Line (NL) tunnels, and (b) the Bond Street station upgrade project affecting the Royal Mail tunnel (RMT). Both new tunnels ran perpendicular to the existing cast-iron tunnels. They experienced substantial longitudinal curvatures, but the damage was limited. The NL tunnels were monitored using conventional electrolevel-beams for minimum chord lengths of 5 m, while the curvature of the RMT was monitored for chords as short as 2 m using a new photogrammetric monitoring system, called Sattar image tracking. The new system offers a high-precision measurement enabling such lengths of local measurements. This paper describes how curvatures are measured and proposes methods that need to be followed to evaluate the accuracy of curvature measurements.

A Study on the Influence of Double Tunnel Excavations on the Settlement Deformation of Flood Control Dikes

“…Furthermore, due to the high risks posed by tunnel excavation to surface and structural stability, many researchers have used theoretical analysis methods [7][8][9][10][11], field measurements [12][13][14], laboratory model tests [15][16][17], and numerical simulations [18][19][20][21] to analyze the mechanisms and patterns of ground deformation caused by tunnel excavation. In terms of numerical simulations, Mou et al [22] studied the lateral surface settlement patterns of double-line shield tunnel construction by analyzing factors such as soil pressure, deformation property of soil, internal friction angles, and tunnel burial depth based on the numerical analysis of a shield tunnel section of the Nanning Metro's Line 3.…”

Role of Shear Deformability on the Response of Tunnels and Pipelines to Single and Twin Tunneling

“…Existing tunnels and pipelines can be affected detrimentally by ground settlements caused by bored tunneling (Alhaddad et al 2020;Jin et al 2018;Mair 2008). Because of these settlements, there is potential for loss of serviceability (e.g., differential settlements, distortion of tracks, and leakages both into tunnels or from pipelines) and, in extreme cases, structural damage of linings and connections, and possible threats for safety.…”

“…The need to account for the shear flexibility of the tunnel rings in damage assessment has also been pointed out by Alhaddad et al (2020). On the other hand, Wu et al (2018) considered both shear and bending flexibilities of a buried structure using an equivalent Timoshenko beam, for tunnels resting on a Vlasov foundation, subjected to vertical external forces transferred from a surcharge load on the ground surface.…”