EXPERIMENTAL STUDY ON CRACK DEVELOPMENT  OF ROCK SPECIMENS BY FREEZING AND THAWING CYCLES

 TIAN CHENG CHEN, NORIYASU MORlI, TERUYUKI SUZUKI, HITOSHI SHOJI and TAKASHI GOTO

ABSTRACT: Studying freezing and thawing mechanisms is important to understand rock slope failures in cold regions. This study investigated crack development in rock specimens by freezing and thawing action. Rock specimens were prepared from welded tuff. A freezing test was conducted in a temperature-controlled chamber where the temperature varied from + 5? to - 18?. The frozen rock specimens were thawed in distilled water. The test lasted 3.5 hours for each freeze-thaw cycle, including 2 hours for freezing and 1.5 hours for thawing. The P-wave velocity, acoustic emission, and porosity were measured, and observations on the change in appearance of the outer surface and section of the specimen were made. The results obtained are summarized as follows: (1) cracks in rock developed during the freezing of pore water; (2) the initial cracks in rock caused by freezing and thawing action formed at a weak position of the surface layer and then propagated to the inside of the specimen; (3) the patterns of cracks produced by freezing and thawing cycles depended on the rock structure, such as its geometry, porosity and pore diameter; and (4) the rate of crack development was affected by the degree of water saturation and mechanical properties of the rock.

Key words: crack development, degree of saturation, freezing and thawing, pore water migration, rock structure, welded tuff (IGC: FO)