Frost shattering and ice problems in rock tunnels from a maintenance perspective

Paper in proceeding, 2012

Every winter a number of railway tunnels in Sweden are affected by problems with ice. When ice is allowed to form in the rock fracture network and interface between the rock and shotcrete, degradation of both materials occur which can cause fall-outs of rock debris and shotcrete. To reduce maintenance costs it is necessary to improve knowledge of frost penetration along tunnels and the effect of frost shattering on the load bearing structures. Temperature measurements in Swedish railway tunnels have shown that frost penetrates much deeper into tunnels than previously assumed. By field observations it has been confirmed that ice problems often occur throughout the entire tunnel, even for longer tunnels (>1.5 km). If the load bearing structures are subjected to alternating freezing and thawing the shotcrete can be exposed to frost shattering. In a similar manner as frost action in soil, water tends to migrate in rock and cause ice bodies to grow inside pores and cracks. Laboratory tests show that when a rock/shotcrete sample has access to water during the freezing process, degradation occurs that affects adhesion between the materials. Therefore the load bearing structures exposed to water leakage should be designed for freezing temperatures along the entire length of the tunnel.