Abstract:

Large deformation often occurs to surrounding rock during construction of soft rock tunnel with high ground stress, and it usually develops to uncontrollable. Hence, comparison is made between Muzhailing Tunnel on LanzhouChongqing Railway in China and Saint Gotthard Base Tunnel in Switzerland from the aspects of large deformation mechanism of soft rock, classification of tunnel surrounding rock with high ground stress and deformation control technology. Some conclusions are drawn as follows: (1) The large deformation of the surrounding rock in soft rock tunnel with high ground stress is mainly caused by plastic shearing and sliding due to the excavation unloading and secondary distribution of stress, which is the consequence of a combination action of lithology, groundwater, ground stress and surrounding rock geological structure. (2) The classifications of soft rock with high ground stress of Saint Gotthard Base Tunnel and Muzhailing Tunnel on LanzhouChongqing Railway adopt BQ method; and the classification of soft rock of the Muzhailing Tunnel is more comprehensive while that of Saint Gotthard Base Tunnel is more specific. (3) Under the condition of soft rock with high ground stress, the fullface excavation method used in Saint Gotthard Base Tunnel is superior to the bench method used in Muzhailing Tunnel in terms of construction management and cost control.

Key words: high ground stress, soft rock tunnel, surrounding rock classification, deformation control technology