No abstract

During tunneling in weakly consolidated soft rock strata, lithology, joints, and fractures of rock strata play an important role in controlling overall roof stability of the roadway. A case study based on weakly consolidated soft rock roadway in Bojianghaizi mine was conducted to address disasters caused by sudden changes and collapse as well as difficulties in maintenance of weakly consolidated soft rock roadway. First, physical and mechanical properties of weakly consolidated soft rocks were investigated by X-ray diffraction mineral component analysis and scanning electron microscopy. Second, failure characteristics and instability mechanism of the roadway were analyzed by combining field survey and theoretical analysis. A mechanical model of fracture development on the composite roof of the roadway was built, and the initiation angle and critical stress for fracture development were deduced. The instability criteria of cracks based on cracking angle ( θ 0 ) were established. Moreover, the instability mechanism caused by roof falling was disclosed. Fractures were formed upon shear failure at vertex angle of the roadway. The fracture belt extended to the soft bedding plane of the separation stratum along the fracture propagation angle and connected with it, thereby inducing roof falling. On this basis, a high-strength and high-preload “inverted trapezoidal” anchoring mesh-beam string supporting structure + arched roadway cross-section with vertical walls + full-section guniting coupling control technology was proposed, which achieved good site application effects.

Previous research showed that wind characteristics were influenced by terrain. To accurately calculate the wind-induced bridge response, this article presented a comprehensive investigation of the wind characteristics of a trumpet-shaped mountain pass by long-term monitoring. Basic strong wind characteristics such as the wind rose, turbulence intensities, turbulence length scales, turbulence spectra and normalized cross-spectrum were discussed using 10 min intervals. Due to the different types of terrain on the two sides of the bridge site, this article attempted to reflect the influence of the terrain on the wind characteristics in different wind directions. The scatter plots of wind characteristics were presented directly on the terrain map. The effects of the turbulence characteristics, mean wind speed and aerodynamic admittance function on buffeting response of the composite cable-stayed bridge were discussed by the multimode coupled frequency domain. The results show that the wind profile is extremely twisted. The larger turbulent integral scale and the lower turbulence intensity appear in the direction along the river. The effect of the mean wind speed on the buffeting response is greater than that of the fluctuating wind characteristics. The aerodynamic admittance function proposed by Holmes has the largest reduction in buffeting response.