Dynamic Response And Control Technology Of Masonry Structure Under Tunnel Blasting

In recent years, there are more and more tunnels being constructed underground which are underneath hillside buildings but extremely closed to them. In construction, drilling and blasting introduces vibration which causes local damage of buildings. Based on the engineering experiences of New Hong-Yan tunnel of Chengdu-Chongqing High-speed Railway, a typical two-story masonry building located in the upper part of the tunnel was investigated. The research contents and results are as follows:1. Blast vibration characteristics on shallow buried side (the lower part of slope) and deep buried side (the upper part of slope) have been investigated. The blasting vibration safety evaluation method functioned by the analysis of data monitored was put forward. The ground vertical and horizontal velocities separately in shallow and deep buried side depend on the distance between explosive sources, and the angle between the incident stress wave and the vertical direction. The velocity of shallow buried side is lower with lower frequency, while the velocity of the deep buried side is higher with higher frequency. Vibration safety evaluation for buildings requires a comprehensive comparison the frequency and velocity of both sides.2. The operational modal analysis (OMA) test was carried out on a typical two-story brick masonry structure under tunnel blast excitation. Modal parameters (natural frequencies, mode shapes and damping ratio) of the two-story masonry building were investigated using enhanced frequency domain decomposition method and stochastic subspace identification method. The masonry building structure model was established according to OMA modal test results. The dynamic characteristics of lower overall modes and higher local modes of the masonry building were discussed. The first to fifth natural frequencies of the structure are in the range of8.80-24.99Hz, and their modes are overall modal. But the sixth to twentieth natural frequencies of the structure are in the range of26.10-36.34Hz, the local deformation of which is much greater than the overall deformation. The first to10th natural frequencies of the structure wall and protruding parts as typical local elements are in the range of5.09-157.55Hz. The natural frequencies of the partial elements are significantly higher than the whole building. The vibration induced by tunnel blasting causes strong dynamic response of local elements of a building. 3. Dynamic response of a common two-story masonry building structure suffered from tunnel blasting was investigated. The analysis of velocity, displacement and stress response of the concrete and brick element of the masonry building were performed. The velocity and displacement amplitude of the partial elements are significantly higher than the whole building. The structure damage induced by tunnel blasting vibration is mainly controlled by instantaneous stress, rather than displacement. The structural stress increases with the rise of peak particle velocity, and also with the decrease of vibration principal frequency. When blasting vibration principal frequency and the lower level overall natural frequencies of the building is significantly different, the vertical vibration still need to be considered, while the horizontal vibration could be ignored.4. The masonry building damage mechanism and crack nucleation position under tunnel blasting were investigated. The identification and assessment of damage were put forward. Local elements of the masonry building suffer most from the tunnel blasting vibration. Great peak particle velocity might lead to the stress-induced cracks of local elements. Corners where stress concentration occurs, contact area between brick and concrete, and precast floor seams are also weak under tunnel blasting.5. A method of time-delay calculation by interval detonation using digital electronic detonators was proposed. How it works by increasing vibration frequency and decreasing vibration velocity was investigated. The interval time should not be less than the total time of the rock crushed and thrown10centimeter away of the each detonation hole. The peak particle velocity with each holes interval detonation by using digital electronic detonators is lower than the segment dose blasting, and the vibration principal frequency of that is higher than the segment dose blasting, which are close to the peak particle velocity and vibration principal frequency of single hole dose detonation.