Optimising Productivity and Climate Im pact in Complex Tunnelling Projects - A case study of how rock excavation classes impact the amount of overbreak in E05 Contract Korsvägen, Project Västlänken

Abstract

The city of Gothenburg is going through a big urban development of the city’s transport infrastructure to increase the capacity and to find more sustainable ways of travelling. Dominant in this development is the underground tunnelling project Västlänken. The project will contribute to regional growth and expansion of the labour market by shorter commuter times to satellite communities. The tunnels will be constructed beneath the city of Gothenburg, trough drill-and- blast tunnelling, in both rock and soil which involves complex challenges regarding the rock excava tion. These challenges are an opportunity for both the contractor and the client to innovate and optimise the drill-and-blast tunnelling process. Furthermore, the pro duction efficiency and optimisation of resources play an important role in reaching the future sustainable requirements and in preventing large cost overruns due to poor overbreak optimisation. The purpose of the thesis is to evaluate how the choice of rock excavation class affects the production efficiency of the tunnelling process. This by investigating op portunities and challenges of optimising the overbreak in terms of cost, time and sustainability. This to contribute to the industry’s data-driven working methods of today. To fulfil the purpose, a qualitative research methodology was developed together with a case study at project Korsvägen, Västlänken. To comprehensively analyse cost, time and sustainability in the tunnelling process, three methods were chosen. The three methods conducted are an interview study, a cost calculation, and a climate impact estimation. The study showed that Rock Excavation Class 3, in acceptable rock quality, generates a larger amount of overbreak compared to Rock Excavation Class 1. Thus, Class 3 causes larger CO2 emissions. Despite this, Class 1 was found to be the most expensive choice of excavation method. This since it disturbs the sensitive tunnelling process and thus is less production effective. Com pared to Rock Excavation Class 3, Class 1 may also have a larger negative influence on social and economic sustainability. This due to the health- safety aspects and the longer production time required, which in this large and complex tunnelling project may affect the whole city of Gothenburg.