Rockdrain for maintenance of tunnel drainage systems

Abstract

Rockdrain is a new type of tunnel drainage that has been developed as an alternative to the traditional underground drainage systems with drainage mats of foamed polyethylene used today. This research study is part of the Swedish Transport Administration's efforts to investigate Rockdrain as an alternative drainage method. So far, the Rockdrain technology has been evaluated and compared to traditional underground drainage systems in a research study [3, 4, 5]. This research has, so far, mainly been focused on new construction of tunnels and large-scale renovation, where a tunnel can be closed for a long time. In Sweden, the present type of underground drainage was first used in the 1990s and its life expectancy has been calculated to be about 40-60 years. Already in the 1960s, plastics covered mineral wool drainage was tested however with poor technical results. Narrow (0.5 m) and thin (10-20 mm) polyethylene foam drainage mats were first used in 1980s. This means that in the near future and even today there is a great need for maintenance of these drainages in the Swedish tunnels. In this research study, we have tried to investigate the possibilities and consequences of using Rockdrain for maintenance of old and worn out underground drainage systems. In this limited study, a maintenance operation (100 m2) of the drainage in the Lundby tunnel in Gothenburg has been assessed using Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCC). Methods and models from previous studies have been used in this project. Many tunnels cannot be closed for a long time. Thus, the maintenance has to be carried out during operation of the tunnel in short time slots (e.g. during night) but during a long time period of may be weeks or months (small-scale maintenance). In this study, Rockdrain has been investigated as a possible way to simplify small-scale maintenance. Only Rockdrain has been tested and no evaluation of small-scale installation of conventional drainage has been carried out. The test results have shown that Rockdrain very well can be used for small-scale maintenance of tunnel drainage. The technical processes used for the small-scale maintenance does not differ much from the techniques used for large-scale maintenance. The primary energy resource use and the emissions per m2 drainage are therefore not very different. However, the amount of labour work needed is very different. Much more labour work is needed for the small-scale maintenance due to an increased amount of establishment and unprovisioning. The life cycle cost (LCC) is therefore higher for the small-scale maintenance compared to large-scale maintenance of Rockdrain. However, compared to large-scale maintenance of and with conventional drainage, Rockdrain shows significantly lower values. The long term effect of Rockdrain for maintenance has not been investigated. Future evaluations are needed to show these effects.Rockdrain is a new type of tunnel drainage that has been developed as an alternative to the traditional underground drainage systems with drainage mats of foamed polyethylene used today. This study is part of the Swedish Transport Administration's efforts to investigate Rockdrain as an alternative drainage method