Abstract
Thermal expansions of 11 dry rocks were investigated. These rocks were subjected to slow cyclic temperature change (0.5K/min) between 110K and 300K. They were divided into 2 groups according to their thermal expension behavior; existence of a hysteresis in the thermal expansion and a residual strain after the thermal cycling. (1) Nongranitic rocks (sedimentary and volcanic rocks) showed neither residual strain nor hysteresis. (2) Granitic rocks and Akiyoshi marble showed the residual strain and the hysteresis. Thermal expansion coefficient of the marble was negative at almost all temperatures. The difference in the thermal expansion between these groups was explained by the thermal cracking and the cracks in the rocks. Thermal cracking which is the cause of the residual strain can be produced by the mismatch of thermal expansion among the mineral grains. Cracks are responsible for the hysteresis by frictional sliding at crack surfaces and partial crushing of asperities. Decreasing temperature cannot provide the local strain sufficient to produce the cracking in the nongranitic rocks which consist of small grains and glassy matrix. On the contrary, the granitic rocks contain large grains and a large amont of quartz that shows larger expansion than other minerals. Akiyoshi marble is the aggregation of polycrystalline calcite that expands anisotropically. Themal cracking is therefore produced in these rocks during the first cooling stage.
