No abstract

No abstract

The stability of surrounding rock near the tunnel face is very important to the safety of constructors and the tunnel itself. The vibration law of surrounding rock obtained from the vibration data in the far-field of tunnel blasting is not suitable for the near-field. Therefore, in order to guarantee the safety of tunnel drilling and blasting, it is important to study the vibration law of surrounding rock near the tunnel face. Taking Zhaitang Tunnel, the New Line Expressway of China National Highway 109, as the engineering background, acceleration sensors were installed in the surrounding rock near the tunnel face to test the blasting vibration acceleration of the surrounding rock at the arch waist of the tunnel, to study the blasting vibration attenuation law near the large section tunnel, to modify traditional blasting vibration formula, and to improve the vibration prediction accuracy. The research will bring some guidance for the construction of similar projects.

Dynamic mechanical properties of granite were tested by a split Hopkinson pressure bar system at constant strain rates. The experimental results show that granite behaves linearly elastic at the initial loading stage, followed by a significant plastic deformation after yielding, and yield strength, ultimate strength and elastic modulus are all rate dependent. On this basis, the simplified Zhu-Wang-Tang (ZWT) constitutive model is applied in this paper, assuming elastic and high frequency viscoelastic elements only. The damage evaluation equation is introduced to the simplified ZWT model to investigate the effect of damage on the dynamic strength of granite due to impact load. Finally, the proposed model is applied to fit the experimental data. It is known that the fitted stress-strain curves at different strain rates are in agreement with the experimental ones. Compared with experimental data, the error of yield stress, peak stress and corresponding strain obtained by fitting method are all not larger than 10%. This demonstrates that the proposed dynamic constitutive model can accurately describe the dynamic mechanical properties of granite under impact loading.

In this study, a C-ALS underground cavity scanner was used to detect the shapes of mining goafs. In addition, GTS software was adopted to establish a three-dimensional geological model based on the status of the stopes, geological data, and mechanical parameters of each rock mass and to analyze the roof areas of the goafs. In regard to the morphology of the study area, based on a thin plate theory and the obtained field sampling data, a formula was established for the thicknesses of the reserved protective layers in the goafs. In addition, a formula for the thicknesses of the protective layers in the curved gobs was obtained. The thickness formula of the protective layers was then successfully verified. The detection results showed that the roof shapes of the goafs in the Yuanjiacun Iron Mine were mainly arc-shaped, and the spans of the goafs were generally less than 20 m. The stability of the arc-shaped roofs was found to be greater than that of the plate-shaped roofs. Therefore, by reducing the thicknesses of the protective layers in mining goafs, the ore recovery rates can be increased on the basis of safe production conditions. The formula of the thickness of the security layers obtained through the thin plate theory was revised based on the statistical results of the roof shapes of the goafs and then combined using GTS and FLAC3D. The modeling method successfully verified the stability of the mined-out areas. It was found that the verification results were good, and the revised formula was able to improve the recovery rate of the ore under the conditions of meeting safe production standards. Also, it was found that the revised formula could be used in the present situation. At the same time, it was also determined that the complexity of the rock masses obstructed the full identification of the joints and fissures in the present orebodies. Therefore, it is necessary to incorporate C-ALS underground cavity scanners to regularly observe the shapes of the goafs in order to ensure that stability and safety standards are maintained.