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For tunnel-support engineering, the bed separation of surrounding rock has a great influence on the support performance of bolts. In order to reveal the mechanical properties of the full-grouted prestressed bolt under the influence of bed separation, three typical working conditions of single-separation, multi-separation and different separation positions were set up, and theoretical models and numerical models were established. Furthermore, the characteristics of bolt axial force and anchorage–interface shear stress were analyzed by numerical method, and the sensitivity based on an orthogonal test was studied by means of range analysis and variance analysis. The results showed that: (1) under the single-separation condition, the separation value has a significant effect on the mechanical properties of the bolt, and with the increase in the separation value, the sliding failure unit of the bolt increases; (2) for multi-separation conditions, if the total separation value is the same, the increase in the number of separation interfaces is beneficial to the force of the bolt; (3) for the case where the separation layer is located at different positions, the separation layer on the right side is more likely to cause the overall slip failure of the bolt; and (4) for the above three influencing factors, the separation value has the greatest influence on the mechanical properties of the bolt, and the separation position has the least influence. [ABSTRACT FROM AUTHOR]

In order to obtain the dynamic stress of invert and its filling in the high-speed railway tunnel under the vibration load of the train, this paper uses the field measurement method to arrange the resistance strain gauge inside the invert of the Lanzhou–Urumqi high-speed railway Fuchuan tunnel. The dynamic stress of the invert and its filling was measured, and the measurement results were verified by numerical analysis, the results obtained by the two were consistent. The results show that under the action of CRH5 electric multiple units, the dynamic stress time history curve of the invert and its filling has 16 peaks, with V-shape on both sides and W-shape in the middle. When the train load speed is constant, the dynamic stress in the tunnel invert and invert filling decreases with the increase of the depth. The dynamic stress at 0.5 m below the track bed is attenuated by about 23.1% compared to 0.2 m, the dynamic stress at 2.0 m below the track bed is attenuated by 67.5% compared to 0.2 m. Tunnel invert and its filling are the main carriers of train vibration load. The dynamic stress attenuation law of the invert and its filling conforms to the exponential function distribution. Through the data fitting, the calculation formula of the dynamic stress in different depths is given. The research results provide a new method for obtaining the dynamic stress of the invert and its filling in high-speed railway tunnel. [ABSTRACT FROM AUTHOR]

To monitor the changes in the force of the tunnel invert steel bars after the groundwater level changes, field tests were performed to accurately and comprehensively characterize the stress acting on the rebar of a tunnel invert. Changes in stress and temperature were monitored for two layers of rebar (upper and lower) in an actual tunnel invert during its repair. The results showed that the changes in stress followed different paths for the upper and lower layers. After the groundwater is replenished, the maximum tensile stress of the rebar was 17.3 MPa, and the maximum compressive stress was 120 MPa. Major changes in stress were observed 2–6 days after rain. Based on this, the seepage path of groundwater is analyzed. During this period, the compressive stress increased threefold, and the tensile stress increased 9.5-fold. The rebar stress in the tunnel invert followed a Gaussian distribution after stabilizing. Four phases of stress progression are identified and discussed. The results can provide data support and theoretical basis for the treatment of invert floor heave in enriched water tunnel. [ABSTRACT FROM AUTHOR]

In order to ensure the safety of horseshoe-shaped pipeline during tunnel blasting excavation, the vibration test and dynamic response of horseshoe-shaped pipeline were investigated. The velocity and frequency of tunnel blasting vibration were analyzed. Sodev's empirical formula was used for regression analysis of the velocity of blasting vibration. 3D numerical model of a horseshoe-shaped pipelines was established with ALE algorithm using ANSYS/LS-DYNA. The propagation law of a blasting seismic wave was analyzed, and the transverse and longitudinal vibration response characteristics of pipelines under tunnel blasting vibration were studied. The velocity of the pipeline increases gradually and the frequency tends to decrease with the decrease of the distance away from the explosion source center under the same charge. The principal frequency of vibration in the Z direction is mainly distributed from 50 to 80 Hz, which is difficult to generate resonance with the pipelines. The maximum relative error between the simulated and measured velocity of X, Y and Z directions was 8.2%. It was reliable to study the dynamic response of pipelines under blasting vibration based on this numerical model. The blasting seismic wave first reached the bottom of the pipeline right above the explosive. Subsequently, seismic waves propagated along the transverse and the longitudinal axes of the pipeline, and the pressure on the pipeline increased gradually. And when it attenuated completely in the soil, the pipeline stopped its response. The peak value of tensile stress of each element of the vault is the largest. However, the velocity of the bottom plate and the arch roof of pipeline are the largest. The peak values of velocity and tensile stress exist in 0 to 4 m away from the explosion source, and gradually decrease as the distance away from the explosion source increases. [ABSTRACT FROM AUTHOR]

Abstract: The construction of digital city provides powerful data support for the large-scale underground engineering construction. Analysis on the effect of underground excavation on surface building damage based on GIS data management can quickly evaluate the effect of underground excavation on surface building damage, and provide technical support for the disaster prevention and mitigation of underground engineering during excavation. The data management of GIS platform was first reviewed and called through professional model, which predicted the deformation of wallrock and subsidence of overlying rock mass caused from tunnel excavation. The range disturbed by excavation and numerical analysis model of underground engineering and surface buildings were determined and also the stress-strain relationship of surface buildings caused by deformation were obtained. The feedback of the analysis results to the data management of GIS platform was received. Through comparison with corresponding standard damage evaluation rules, it can provide technical support for decision makers. By analysis and verification of an example about the effect on buildings caused by the excavation of an undersea tunnel terminal, it can ensure the safety of surface buildings influenced by the excavation. [Copyright &y& Elsevier]

• Heave-induced failure is a primary type of failure in inverted arches. • Crack propagation behaviour must be analysed to determine failure modes. • Thickness and curvature of inverted arch affect crack propagation. • The centre of the arch is the structural weak point. • A rise-to-span ratio of 0.10 maximizes crack resistance. Floor heave-induced failure is a primary type of failure in the inverted arches of tunnels. In this study, the crack propagation behaviours in an inverted arch during floor heave were investigated using model testing and numerical simulations. In particular, the study analysed the effects of the thickness and curvature of the inverted arch on crack propagation. The analysis revealed that the centre and sidewalls of the inverted arch experience high contact pressures, while its feet experience bending shear and concentrations of stress. Tensile cracks first form at the centre of the arch, which then rupture the arch in the longitudinal and vertical directions to ultimately form a W-shaped failure mode. Furthermore, the centre and feet are the structural weak points of inverted arches. Increased arch thickness helps to reduce crack development but not linearly. Tensile crack development at the centre of the arch progressively weakens with increasing arch thickness. By contrast, crack development at the feet initially increases and then decreases with increasing arch thickness. Generally, crack growth in the inverted arch of a tunnel depends on its curvature. However, it does not progress monotonically; crack growth initially decreases, and then increases with increasing radius of curvature. The results of the study show that a rise-to-span ratio of 0.10 is optimal for crack resistance, as crack development is minimal at this ratio. In conclusion, we expect that the results of this study will inform the optimization and design of inverted arch structures. [ABSTRACT FROM AUTHOR]