An ice lens is a survey of the soil, which occurs in frost and cohesive reason.
This is due to the capillary effect, which allows ground water from up to 50 m depth to the frost line to transport ( in Germany in winter between 20 and 120 cm). The water collects there, freezes and lifts the bottom. Since the groundwater is continuously tracked, the accumulations of ice and the overlying surveys are getting bigger.
One countermeasure is for example the use of non-cohesive soil with a foundation of 80 to 120 cm.