| With the large amount of investment in infrastructure construction,the development of underground space has become an inevitable trend of urban traffic development,and subway has gradually become the first choice for major cities to develop traffic.At the same time,drilling and blasting method has been widely used in the subway construction of many cities with hard rock.However,it is very difficult to carry out the blasting construction in the urban area with large population and dense buildings,and the blasting seismic wave generated by the construction will cause potential damage to the surrounding buildings.Supported by the National Key Research and Development Program of Theory and Method of Urban Underground Space Development(2019YFC0605104),Based on the Xietaizi sub-station of Chongqing Rail Transit Line 18 and Fuxie Tunnel.By means of field test,theoretical derivation and numerical simulation,the safe allowable vibration velocity of blasting vibration,attenuation law of blasting vibration velocity,improvement of prediction formula,blasting construction method of extra-large subway tunnel and surrounding rock damage have been studied.The thesis topic selection has important engineering application value.The main research contents are as follows:(1)The monitoring and analysis of the ground vibration frequency of the field blasting construction of the interval tunnel shows that the main frequency of the surface particle vibration is mainly concentrated in the frequency range of 10-50 Hz,with 2 times exceeding50 Hz and 7 times less than 10 Hz.According to the Blasting Safety Regulation,according to the distribution range of the main frequency and safety reserve,The allowable vibration speed of subway tunnel blasting is determined to be 1.5cm/s.(2)On the basis of Sadowski formula,the least square method is used to make regression analysis,and the empirical formula of attenuation of peak vibration velocity of blasting seismic wave in the study area is obtained,and the variation rule of dominant frequency of blasting seismic wave with distance from blast center is summarized.The power spectral density is analyzed,and the PSD value decreases with the increase of horizontal distance,and the distribution range in frequency domain becomes wider.Through wavelet packet analysis,the distribution characteristics of blasting seismic wave in each sub-band are studied,and the distribution law of energy in the sub-band varies with the distance is obtained.The timefrequency energy relationship of vibration signals can be obtained by HHT,and the instantaneous energy generated by cut blasting is the largest,revealing the vibration response characteristics of blasting site.(3)Two influence parameters of free surface area and surface number are introduced,and according to t distribution in statistics,an improved formula for predicting the vibration velocity of Sadowski blasting is proposed.The effectiveness of the improved formula is verified by comparison with the measured data.Compared with the original Sadowski formula,RMSE,SSE,R-Square and Adjusted R-Square regression error evaluation indexes show that the improved formula has more accurate prediction results.(4)Based on the improved formula,the peak variation law of surface vibration velocity is obtained,and the blasting vibration response characteristics of the metro station with extralarge span hard rock in the city are studied.The variation law of particle vibration velocity and particle vibration displacement of surrounding rock is studied,and the criterion of vibration displacement for evaluating the blasting damage degree of surrounding rock of metro tunnel with extra-large span hard rock in city is put forward.By comparing the numerical results of different construction methods,the damage degree of surrounding rock and the order of vibration intensity of each construction method are obtained.According to the damage degree of surrounding rock and the safe allowable vibration velocity,the recommended blasting control technology scheme for extra-large span subway tunnel is put forward. |
PDF Full Text Request