Rock mechanical conditions at the Aespoe HRL. A study of the correlation between geology, tunnel maintenance and tunnel shape

Maintenance records including scaling, shotcreting and bolting have been kept since the excavation start of Aespoe HRL 1990 together with records of groundwater flow and all other activities taking place in the tunnels. When the facility was constructed one objective was to limit the rock support as much as possible. The reason for this was that it should be possible to go back and easily study the exposed rock surface. Support during the operational phase has only been carried out where and when necessary. This type of maintenance and its location is documented in the digital database each time. The maintenance records have been compiled and areas requiring more maintenance than average noted. An interview has also been held with one of the miners conducting scaling and bolting in the tunnel. His experiences together with the study of the database maintenance records led to the selection of certain areas in the tunnel to be studied by numerical modelling. The probable reason for the need of additional maintenance in all areas, not only these numerically modelled, has been investigated. Almost all maintenance in the main tunnel both during construction and the operational phase has been located in the widened curves of the access tunnel. The maintenance is also located in areas containing veins or intrusions of Smaaland granite or fine-grained granite. These areas are often located in fracture zones of different sizes or show an increasing fracture frequency. The areas numerically modelled indicate stress concentrations or unloaded stress conditions. The stress concentrations are created by the geometry of the niches and side-tunnels in relation to the in situ stress field. The angle between the tunnel and the major principal stress has an impact on the need for maintenance. The areas with the largest angles towards the principal stress direction need more maintenance than the areas almost parallel to the major principal stress direction. The maintenance work in the horseshoe shaped tunnel TASF at the 450 m level has been compared to the maintenance work in the adjacent TBM tunnel. No maintenance has been performed in the TBM tunnel but TASF have been scaled and bolted several time and was finally shotcreted. The TASF tunnel has some larger areas with Smaaland granite and fine-grained granite. The modelling does not indicate problems due to stress concentrations. It is therefore probable that the granites are rather fractured and therefore needs more scaling. The water flow in the Aespoe HRL is continually monitored. During the first five years of operation the water flow has had an average decrease of approximately 4% per year. The water flow in two other facilities owned by SKB, SFR and CLAB has been monitored for the last 12 years. These two facilities also show a decrease of the water flow of approximately 4% per year