Designing a Tunnel

1 Chapter Designing a Tunnel Spiros Massinas Abstract Designing a tunnel is always a challenge. For shallow tunnels under cities due to the presence of buildings, bridges, important avenues, antiquities, etc. at the surface and other infrastructures in the vicinity of underground tunnels, parameters like vibrations and ground settlements must be tightly controlled. Urban tunnels are often made in soils with very low values of overburden. Risks of collapse and large deformations at the surface are high; thus negative impact on old buildings are likely to occur if appropriate measures are not taken in advance, when designing and constructing the tunnel. For deep tunnels with high overburden and low rock mass properties, squeezing conditions and excessive loads around the excavation can jeopardize the stability of the tunnel, leading to extensive collapse. The aim of the chapter is to give details on advance computational modelling and analytical methodologies, which can be used in order to design shallow and deep tunnels and to present real case studies from around the world, from very shallow tunnels in India with only 4.5 m overburden to a deep tunnel in Venezuela with extreme squeezing conditions under 1300 m overburden. Keywords: tunnel, shallow tunnelling, deep tunnels, surface settlements, tunnel squeezing, analytic solution, numerical analysis, lining stress controllers, sliding joints, monument underpassing, monitoring, plasticity, TBM, earth pressure balance shield, high overburden, high deformations, NATM, conventional tunnelling 1. Introduction The aim of the current chapter is to give details and guidance in designing underground tunnels, to be constructed with tunnel boring machines (TBM). In the sequence of paragraphs to follow, the reader will get a grasp of tunnelling principles and theory related to mountainous and urban tunnelling—deep and shallow tunnels will be explained (paragraph 2). In paragraph 3, details for designing mechanized constructed (TBM) Metro tunnels in urban environment will be given, and real cases from India will be presented. Special case for monument underpass with earth pressure balance machine (EPBM) under extreme low overburden will also be discussed, and the real case study from Chandpole Gate in Jaipur will be presented. Mountainous and deep tunnels design will be presented in paragraph 4. Squeezing and non-squeezing conditions will be explained, and methods of designing will be given, along with examples from around the world. The final paragraph will summarize the primary conclusions from the presented design methodologies. It is noted that all the examples presented herein are real cases of tunnels already constructed, with the personal involvement of the author in their designs elaboration.