AUTHOR=Li Xinzhe , Li Xiulei , Yang Chao 

TITLE=A comparison study of face stability between the entering and exiting a shallow-buried tunnel with a front slope

JOURNAL=Frontiers in Earth Science

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2022.987294

DOI=10.3389/feart.2022.987294

ISSN=2296-6463

ABSTRACT=<p>Worldwide, it is a great challenge to tunnel in portal section, where excessive deformation, cracking, or even collapse often occurs during the construction process. This paper presents a comparison study of face stability between entering and exiting a shallow-buried tunnel with a front slope. Firstly, the theoretical solutions of support pressure <italic>σ</italic><sub><italic>T</italic></sub> and safety coefficient <italic>FS</italic> of the excavation face considering surface slope are derived by upper-bound limit analysis method. Secondly, for different slope angles, buried depth and surrounding rocks of the exit and entrance sections, the <italic>σ</italic><sub><italic>T</italic></sub> and <italic>FS</italic> are obtained. The results show that when the burial depth of the tunnel crown <italic>h</italic> remain constant, the <italic>σ</italic><sub><italic>T</italic></sub> increased first and then decreased while the <italic>FS</italic> increased gradually, and both become steady when the slope angle <italic>α</italic> arrive at a certain value. In addition, the thicker the <italic>h</italic> is, the smaller the certain value <italic>α</italic> is. When the <italic>h</italic> and <italic>α</italic> remain constant, the loose area in front of the excavate face will decreased apparently with the increase of the internal friction angle <italic>φ</italic>, thus the <italic>σ</italic><sub><italic>T</italic></sub> will decrease and <italic>FS</italic> will increase. Moreover, the <italic>σ</italic><sub><italic>T</italic></sub> decreased linearly with the increase of cohesion <italic>c</italic> and unit weigh <italic>γ</italic> of surrounding rock, while the <italic>FS</italic> is the opposite. Compared with the entrance section, the construction risk at the exit section is greater.</p>