Geotechnical Engineering and Innovative Support System for Shallow Urban Subway Caverns in Rock, in Confined Built Environment
- 78 Downloads
The Ottawa Light Rail Transit project involves the construction of a new transit facility that will comprise approximately 12.5 km of new electrified Light Rail Transit between Tunney’s Pasture and Blair Road in the City of Ottawa. The mined tunnel runs from the West Portal at STA 100+617 to the East Portal at STA 103+149 for 2532 m. There are three mined stations along the tunnel route, namely the Lyon Station, the Parliament Station and the Rideau Station. The paper focuses on the geotechnical engineering and design of the excavation and the temporary support of Lyon and Parliament stations. Both stations have a horseshoe section (in order to utilize the cross section in an optimum way) and they are excavated in shale and limestone with a minimal cover to the soil layer. In the vicinity of the stations exist some of the city’s tallest buildings (reaching or exceeding 100 m of height) with deep basements, which are finally connected with the stations. In order to minimize the impact to the existing buildings, an innovative construction sequence together with a tension tie system has been designed. Specifically, this paper presents the geotechnical conditions at the area of the two stations, the proposed construction methodology and the design and impact assessment considerations including a description of the implemented Finite Element Models. The design calculations for each station were based on a set of 2D models at critical sections and a set of 3D models incorporating all the critical elements of the interaction, i.e. non-linear soil/rock behavior, interfaces between the building and the soil/rock, building stiffness, staged excavation and tension ties. The models deliver calculations of the convergence, displacements and settlements due to the excavation of the cavern and the internal forces and dimensioning of all the structural elements (shotcrete shell, tension ties and buildings). The assessment of the adjacent structures has considered all the available structural data and was based on the imposed displacements as well as the additional internal forces and pressures developed on the building walls and slabs due to the cavern excavation.
KeywordsUnderground cavern Tunneling Urban subway Metro Sprayed concrete Impact mitigation Numerical analysis
The authors would like to acknowledge the support and good close collaboration with Mr. Christian Karner of Dr. Sauer and Partners, and the Dragados—SNC Lavalin—Ellis Don JV. Background geotechncial, geological, and project information which was used as a basis for the execution of the design described in this article (particularly in Sect. 1 and 3) have been the product of work by the City of Ottawa and the City’s technical advisors.
- Fernandez E, Herrer H (2015) Mined tunnels to solve urban problems Ottawa’s choice. In: Rapid excavation and tunneling conference (RETC) 2015, 7–10 June 2015, New Orleans, Society for Mining, Metallurgy and Exploration (SME)Google Scholar
- Fortsakis P, Nikas K, Marinos V, Marinos P (2011) Anisotropic behaviour of stratified rock masses in tunnelling. Eng Geol 141–142:74–83Google Scholar
- Galera JM, Alvarez M, Bieniawski ZT (2007) Evaluation of the deformation modulus of rock masses using RMR: comparison with dilatometer tests. In: Romana M, Perucho A, Olalla C (eds) Underground works under special conditions, proceedings of the ISRM workshop W1, Madrid, Spain, 6–7 July, pp 71–77. Taylor & Francis Group, LondonGoogle Scholar
- Hoek E, Carranza-Torres C, Corkum B (2002) Hoek–Brown failure criterion. In: Proceedings of the 5th North American rock mechanics symposium and 17th tunnelling association of Canada: NARMS-TAC, Toronto, Canada, vol 1, pp 267–273Google Scholar
- Marinos P, Marinos V, Hoek E (2007) Geological Strength Index (GSI). A characterization tool for assessing engineering properties for rock masses. In: Romana M, Perucho A, Olalla C (eds) Proceedings of the international workshop on rock mass classification in underground mining held in 1st Canada–US rock mechanics symposium, also permitted to be published in underground works under special conditions, Taylor and Francis publ. pp 13–21, LisbonGoogle Scholar
- Marinos V, Fortsakis P, Prountzopoulos G (2011) Estimation of geotechnical properties and classification of geotechnical behaviour in tunnelling for flysch rock masses. In: Anagnostopoulos A et al. (eds) Proceedings of the 15th European conference on soil mechanics and geotechnical engineering, part 1, pp 435–440, AthensGoogle Scholar
- Mitri HS, Edrissi R, Henning J (1994) Finite element modelling of cable-bolted slopes in hard rock underground mines. In: SME annual meeting, Albuquerque, New Mexico, pp 14–17Google Scholar
- Volkman GM, Schubert W (2010) A load and load transfer model for pipe umbrella support. In: Proceedings of the European rock mechanics symposium EUROCK 2010, 15–18 June 2010, Lausanne, International Society for Rock Mechanics and Rock Engineering (ISRM)Google Scholar
- Wilhelmstoetter F, Karner C (2016) Construction progress of the Ottawa LRT line from early design stages to current construction milestones. In: ITA world tunnel congress 2016, 22–28 Apr 2016, San Fransisco, Society for Mining, Metallurgy and Exploration (SME)Google Scholar