Abstract:

Perilous rock is one of the main geological hazards in sandstone grottoes, especially in Yungang Grottoes. The study on causes for perilous rocks is useful for prevention and cure of perilous rocks in sandstone caves. In this paper, the various influence factors of perilous rocks were analyzed in detail by engineering geology method. Box-like synclines and fractures were macroscopic tectonic origins of perilous rocks. The near E-W tensile cracks and N-E shear fissures directly controlled the perilous rocks- evolution. The differences in height between cliffs directly controlled the development scale of the unloading zone of slopes, and determined the hazard energy of perilous rocks, and the differences in weathering of soft-hard alternate multilayers generated cliffs and cavity to form perilous rocks shape. Fissure waters and rainfalls directly affected the stability of perilous rocks. The stability of perilous rocks which had undergone longterm effects of freezing and thawing, temperature differences and alternate drying-watering continued to be deteriorated, and engineering activities are the main triggering cause of the perilous rocks- instability. The result provides an important basis for prevention and cure of perilous rock masses, and is valuable to analyze the stability of Yungang Grottoes.

Key words: Yungang Grottoes, engineering geology, perilous rock, cause