Everywhere in Saint Petersburg the top strata are represented by quaternary deposits, and the ground water level is approximately 2,5 m down from the surface. Below the quaternary deposits, at depths of 40 to 60 m, are Cambrian (Proterozoic) clays. There are many ancient buildings of a historic and architectural value on the day surface that cannot tolerate day surface settlements. The construction of underground stations, and especially inclined escalator tunnels, causes surface settlements. Technologies of construction of escalator tunnels and station tunnels have been developed in Saint Petersburg to minimize such day surface settlements.
