Abstract: In order to solve the problem that the designer′s understanding of the building boundary of the opencut/shed tunnel and the subgrade, comparative analysis of the crosssectional composition of the tunnel building boundary and the highway building boundary are conducted. According to the functional requirements of the same width in the specification, it is inferred that the independently set highway opencut/shed tunnel building boundary and the subgrade width should be understood as the sum of the width of the roadway and the lateral width of the two sides, and the same width standard should adopt the larger values of the highway building boundary (general value) and the tunnel building boundary (lane + lateral width). Due to the need of laying maintenance roads or sidewalks in the tunnel, the basic width of the building boundary of the independent opencut/shed tunnel will be equal to or greater than the width of the highway subgrade when meeting the abovementioned requirements for the same width, resulting in the problem that the structure of the opencut/shed tunnel exceeds the width of the subgrade. To address this problem, the function of the maintenance lanes or sidewalk is analyzed, and the analysis results show that the independent opencut/shed tunnel can set the sidewalk on the outside of the structure, so as to effectively reduce the structural span of the tunnel, improve the internal force of the top beam, and facilitate the layout and construction of the structural foundation.

Key words: highway, opencut tunnel, shed tunnel, identical width, building boundary