Rock Mechanical Consequences of Refrigeration. A Study Based on a Pilot Scale Rock Cavern

Sammanfattning: The deformation of a rock mass due to temperature decrease below freezing is very complex, since many factors are involved; thermal strain, strain due to stress change, stress re-distribution, ice formation and the temperature dependency of rock mechanical and thermo-physical properties.

The objective of this study was to achieve a better understanding of the rock mass response to thermo-mechanical loading when storing low temperature products in rock caverns excavated in hard crystalline rock masses. The study includes a literature survey, a hypothesis, a series of laboratory tests, a pilot scale field test and an analysis.

In order to investigate the rock mass response to thermo-mechanical loading, rock specimens in the laboratory were tested at low temperatures. A pilot scale rock cavern, with a height of 15 m and a diameter of 7 m, was tested under refrigerated conditions.

In the laboratory, rock cores taken from the field test area were investigated in order to estimate compressive strength, tensile strength, Young's modulus, Poisson's ratio and the coefficient of thermal contraction as a function of decreased temperature.

The pilot scale test cavern was refrigerated for about 5 months. Temperatures and deformations were measured frequently during the cooling period. Radial deformations and temperatures were measured in the rock cavern, as well as in the host rock mass. Tangential deformations were measured at the mid-height of the cavern. Stress changes were recorded in the vicinity of the rock wall. In total, the rock instrumentation system consisted of 193 instruments.