On Hydrogeomechanical Causes of Accident in the Subway of Saint Petersburg

A scheme is developed for the deformation of tunnels in the “Lesnaya - Muzhestvo Square” station-to-station block of Saint Petersburg subway during incipience of accident in 1995. It is shown that the main cause of the repeated accident in the washout section was the rise of level of submorainic water-bearing horizon waters. The tunnels supporting soil massif reinforced by freezing column pipes were subjected to additional bending load, which resulted in cracks appearing in the tunnel lining.