Under the influence of plate collision, the high geothermal is a widespread phenomenon within the region of Tibet. Due to the aforementioned high geothermal, lining cracking is a common disaster in Sangzhuling tunnel during construction period. This paper presented the mechanical behaviour of tunnel lining under high geothermal temperature, which is studied by thermo-mechanical numerical method. The results both from field investigation and numerical analysis demonstrate that high geothermal temperature can cause the tunnel lining cracking and the variation of the stress of the tunnel lining. Thus, a novelty sandwich composite lining supporting scheme is proposed to overcome such geothermal temperature effects, in which a thermal insulation layer between primary supporting and secondary supporting is designed. The numerical analysis results indicate that the insulation layer can significantly improve the mechanical characteristics of the lining structure. In addition, the effect of the insulation layer is not linear with its thickness. For this reason, the optimum insulation thickness of the insulation layer is chosen as 0.06 m, which was optimized by a numerical parametric analysis. The research can provide a reliable reference for tunnelling works in high geothermal regions.

Because of the extreme terrain limitations and heavy traffic in congested urban areas, the supporting structures for deep excavations often undergo an asymmetric loading condition at two sides. This article reports the results of an investigation based on detailed numerical modeling of the supporting scheme and mechanical performance of a deep excavation of a metro station having different elevations at two sides. The two proposed types of design schemes for support and excavation were discussed and analyzed to evaluate the suitability of using regular or irregular supporting structures. The mechanical performance of the adopted supporting scheme was then evaluated using three-dimensional numerical analysis and verified via field observations. The results show that the irregular supporting structure functions satisfactorily when subjected to asymmetric loading, and it can also realize semicovered excavation in narrow and congested downtown areas to effectively solve the problem of traffic. The solution presented in this study can provide valuable references for the design of urban deep excavations with an asymmetric side elevation.

In this paper, we are concerned with a class of second-order half-linear delay dynamic equations on time scales. By using the generalized Riccati technique and the integral averaging technique of Grace-type, four new oscillation criteria are obtained for every solutions of the equations to be oscillatory.