Life cycle assessment of Norwegian hard rock tunnels

Abstract

This study investigates the environmental impact of the construction phase of hard rock tunnels using a life cycle assessment approach. The study examines which components and design criteria are critical for the environmental performance in six different impact categories. Special focus has been given on the impacts of global warming potential, and identifying the distribution of the carbon dioxide emissions of the components in the construction.A literature review of previous LCA studies on tunnel structures has been done in order to make comparisons and to evaluate recommendations of the LCA structure. The product studied in this thesis is a generic tunnel placed at a non-specific site in Norway. The tunnel is modelled with two different excavation methods and three levels of installed rock support. No interior installations have been added in the tunnel since the intended purpose of the tunnel is undefined. The rock mass conditions have been modelled to be a hard rock, representative of an averaged geological condition in Norway. Development of the Life Cycle Inventory of the excavation methods was done by reports and software produced by the Department of Civil and Transport Engineering at NTNU. The data from the reports and software is based on compiled data and experiences from a large number of hard rock tunnel projects in Norway and is well suited to describe the construction process of generic tunnel.The studied rock support levels was chosen to represent a spectre of rock support scenarios. The rock support inventories of the model is based on inventories compiled for the current high-speed rail assessment in Norway and the estimated rock support amounts from the subsea tunnel project Rogfast.The amount of installed rock support, and the accompanying quantities of concrete and steel, has been identified as the major source of greenhouse gas emissions and in general the environmental impact for the majority of tunnel alternatives in the study. The findings is supported by the compiled information in the literature review.