Preliminary analysis of the dynamic interaction between Norra Länken and a subway tunnel for Stockholm, Sweden

A large infrastructure project called “Ring road Around Stockholm” is presently being planned. A large proportion of the roads will be constructed underground. All kinds of hazardous materials; even explosive gases and liquids, will be allowed to be transported. At Roslagstull, which is located at the northern boundary of the city, five underground road tunnels will cross over an existing subway tunnel, with only about 3 m of rock between them. A scenario in which a truck loaded with explosive gas or liquid starts to leak and then explodes has been proposed by Stockholm's Street and Traffic Administration. Consequently, the effect on rock and the reinforcement surrounding the subway tunnel must be evaluated. This paper presents the results of a study based on two-dimensional distinct element modelling of the rock mass and reinforcement response to a load caused by an exploding truck as described above. Two different assumptions regarding the explosion load have been simulated—namely, static load and fully dynamic load. The study (i) provides general information about the rock mass and reinforcement response for a specific assumption regarding the rock mass conditions, and (ii) compares the results from the two different assumptions regarding the representation of the explosion load. Both unreinforced and reinforced conditions have been modelled for each loading condition (i.e., a total of four models). The results indicate that for the unreinforced models, the differences in the model response are not dramatic when compared to the models with static and dynamic representation of the explosion load. On the other hand, the reinforced models indicate major differences, particularly in the reinforcement response. All numerical analyses presented in this paper were performed using the two-dimensional distinct element code UDEC (Itasca 1992).