The blasting operation of newly-built tunnel has a significant impact on the adjacent existing tunnel. In view of the universality of the damping hole, the damping hole is selected as a means of vibration reduction, but the effect of the damping hole in the adjacent tunnel needs to be proved. A blasting dynamic model is established to characterize the effect of parameters of each damping hole, and the correctness of the model is verified by comparing with the field monitoring data. Furthermore, the influence law of damping hole parameters on damping rate is explored, and the relationship between damping rate and damping hole parameters is put forward, and the blasting vibration control benefit of damping hole in close tunnel blasting is demonstrated. The results show that:(1) 1~ 3 rows of damping holes were arranged respectively, and the average damping rate increases from 40.58% to 71.99%. (2) The distance between vibration reduction holes and explosion source of 0.75 m ~ 1.5 m is averaged, and the average damping rate decreases from 53.93 % to 40.21%. Changing the parameters of above has obvious influence on the damping absorbing benefit. (3) The relationship between parameters of damping hole and damping rate is shown. The significant degree of influence of damping hole parameters on blasting vibration is revealed; (4) The influence law of damping hole on blasting vibration of adjacent tunnel is shown. The vibration velocity is high and the attenuation is fast 5 m after the blasting face, and the damping hole has good vibration reduction benefit. The vibration reduction rate of each part of the central section can reach 26%-38% by a single row of damping holes.
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Open Access
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Shield tunneling parameters are an important factor affecting construction safety and construction efficiency during shield tunnel construction. Based on the three-dimensional particle flow discrete element method, a numerical model of rock breaking by full cutterhead cutter in composite stratum was established. By analyzing the rock-breaking force of the cutterhead under different tunneling parameters of the shield, the relationship between the maximum tunneling speed of the shield and the rotating speed of the cutterhead was determined, and the division range of the shield tunneling parameter control zone in the medium-strength weathered argillaceous siltstone composite formation was proposed. The values of shield tunneling parameters can be divided into three areas: maximum penetration speed control area, rock-breaking force control area and shield design parameters control area. In the maximum penetration speed control area: cutterhead rotating speed 0 < w < 0.05, maximum tunneling speed 0 < v < 175w; in the rock breaking force control area: cutterhead rotating speed 0.05 < w < 1.55, maximum tunneling speed 0<v<-8.527w2+61.058 w+5.945; in shield design parameters control area: cutterhead rotating speed 1.55<w<3, maximum tunneling speed 0<v<80.
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Large displacement misalignment under the action of active faults can cause complex three-dimensional deformation in subway tunnels, resulting in severe damage, distortion and misalignment. There is no developed system of fortification and related codes to follow. There are scientific problems and technical challenges in this field that have never been encountered in past research and practices.
This paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation based on the open-cut tunnel project of the Urumqi Rail Transit Line 2, which passes through the Jiujiawan normal fault. The test simulated the subway tunnel passing through the normal fault, which is inclined at 60°. This research compared and analyzed the differences in mechanical behavior between two types of lining section: the open-cut double-line box tunnel and the modified double-line box arch tunnel. The structural response and failure characteristics of the open-cut segmented lining of the tunnel under the stick-slip part of the normal fault were studied.
The results indicated that the double-line box arch tunnel improved the shear and longitudinal bending performance. Longitudinal cracks were mainly distributed in the baseplate, wall foot and arch foot, and the crack position was basically consistent with the longitudinal distribution of surrounding rock pressure. This indicated that the longitudinal cracks were due to the large local load of the cross-section of the structure, leading to an excessive local bending moment of the structure, which resulted in large eccentric failure of the lining and formation of longitudinal cracks. Compared with the ordinary box section tunnel, the improved double-line box arch tunnel significantly reduced the destroyed and damage areas of the hanging wall and footwall. The damage area and crack length were reduced by 39 and 59.3%, respectively. This indicates that the improved double-line box arch tunnel had good anti-sliding performance.
This paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation. This system increased the similarity ratio of the test model, improved the dislocation loading rate and optimized the simulation scheme of the segmented flexible lining and other key factors affecting the test. It is of great scientific significance and engineering value to investigate the structure of subway tunnels under active fault misalignment, to study its force characteristics and damage modes, and to provide a technical reserve for the design and construction of subway tunnels through active faults.
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