Thermo-Mechanical Behaviour of Refrigerated Caverns in Hard Rock

Abstract: For almost 4 decades, underground caverns in hard rock have been used to store liquefied petroleum gases (LPG) and refrigerated products, such as foods and chemicals. The design of such facilities has, however, been founded on relatively limited knowledge of the reaction of rock masses to cooling. This lack of knowledge may be detrimental to the safe containment and stability of the cavern.

According to the available experience, it is clear that one of the key issues in designing unlined caverns for low temperature products is an understanding of the disturbance in the rock fracture network. Increasing aperture and prolongation of fractures inevitably affect the rock mass stability, the heat loss from stored products, and the risk for ice growth from water invading the cavern.

The objective of the work presented here was to increase the knowledge of the mechanical and physical phenomena in a rock mass subjected to low temperatures, to enable a more reliable prediction of the behaviour of refrigerated caverns in hard rock. This thesis includes a literature survey, laboratory and field tests, prediction of behaviour and a comparative analysis.

The main investigation was performed in a pilot scale cavern in hard rock, constructed as a vertical cylinder with a diameter of 7 m and a height of 15 m. The facility was equipped with very comprehensive instrumentation, including about 200 temperature gauges and 140 deformation gauges. The temperature in the cavern was decreased in steps down to -40°C, with monitoring of relative humidity, air and rock temperatures, rock strain and fracture aperture, cavern convergence and rock mass deformation. It is considered that the thesis contains a large amount of field data of interest for future cavern design.