Abstract: The internal displacements of surrounding rock are generally surveyed after the excavation of working face, which results in a certain measuring loss for the field observation. In order to get the change law of its internal displacements during tunnel construction, the multipoint-displacement testing equipment is developed, which is applicable to measuring the vertical full displacement of the vault surrounding rock. This equipment is featured by the simple test principle, the convenient field planting and the high-accuracy test data, and it has more measuring points than that of the traditional multipoint-displacement testing equipment has. The internal displacements of vault surrounding rock of the Alatan tunnel is measured by this equipment to obtain its change law in the tunnel’s shallow section. It shows that if the internal displacements of surrounding rock are generally surveyed by the traditional multipoint-displacement testing equipment, 25 percent of internal displacements of surrounding rock is lost through analysis. The range of the surrounding rock relaxation is found through surveyed data, the result is significant to the tunnel’s excavation and supporting.

Key words: tunnel engineering, surrounding rock displacement, monitoring survey, data analysis