For shallow tunnels under soft grounds, it is very difficult to gain a complete understanding on all the load-bearing arch effects during excavation, since such tunnels can easily deform or even collapse. Among these effects, the tunnel face stability plays the most important role and has not been understood and handled very well; therefore, the design and construction of such tunnels under soft grounds remain as a challenge. In this work, the different failure models of face instability of the shallow tunnels were established based on the upper-bound theorem of limit analysis for the formation of clayey and sandy soils, respectively, and the analytical equations for determining the limit support force for the face stability were also derived. Furthermore, the influences of various factors on the stability were analyzed and compared. For the sandy soil formation, an equivalent pressure coefficient was proposed for the tunnel faces of bolt reinforcement. Finally, taking the face stability of the shallow tunnels in sandy soils as an example, a complete numerical simulation was conducted to verify the accuracy and effectiveness of the analytical results based on the theoretical models as well as their application conditions.

This study analyzes the phenomenon of performance deterioration in fully grouted rock bolts in tunnels with a dry, hot environment and high geothermal activity with a focus on temperature effects on interfacial bond performance. Three groups of fully grouted rock bolt specimens were designed based on similar mechanical principles. They were produced and maintained at 20 °C, 35 °C, and 50 °C. Through the indoor gradual loading tensile test of specimens, variations of axial force and shear stress between the rock bolt and mortar adhesive interface were obtained under different environmental temperatures. Distribution of the axial force and shear stress on the anchorage section were found under different tensile forces. Results showed that, with an increase in specimen environmental temperature, maximum shear stress of the rock bolt section became smaller, while shear stress distribution along the rock bolt segment became more uniform. In addition, the axial force value at the same position along the pull end was greater, while axial stress along the anchorage’s length decayed faster. With an increase in tensile force under different temperatures, the axial force and maximum shear stress of rock bolt specimens along the anchorage section has a corresponding increase.