Two new neolignan glycosides, davidioside A (1) and davidioside B (2), have been isolated along with six known compounds from the branch bark of Davidia involucrata. Identification of their structures was achieved by 1D and 2D NMR experiments, including (1)H-(1)H COSY, NOESY, HMQC, and HMBC methods as well as FAB mass spectral data.
Studying the propagation characteristics of blasting seismic waves in surrounding rock under different in situ stresses forms the basic framework for discussing the damage and failure laws of tunnel surrounding rock caused by deep engineering blasting vibration. To study the propagation law of blasting seismic waves under different in situ stresses, an underground engineering model test system is used to simulate tunnel blasting excavation with a nonexplosive electric spark initiation device. The vibration acceleration and strain of the surrounding rock during excavation are collected in real time. Based on the test data system, the blasting vibration response characteristics of tunnel surrounding rock under different in situ stresses are discussed. According to the results of experimental studies, the peak values of radial and axial acceleration show nonlinear attenuation with an increase in distance under different in situ stresses. With an increase in in situ stress, the attenuation rate of the peak value of radial acceleration decreases, while that of axial acceleration increases. Moreover, the peak values of acceleration and strain measured at the same point near the seismic source under different in situ stresses remain unchanged, whereas those measured at the same point far away from the seismic source gradually decrease. Moreover, the attenuation rate at the stage of low in situ stress is greater than that at the stage of high in situ stress. The farther away from the seismic source, the greater the influence of in situ stress on peak acceleration and peak strain. The research results play an important guiding role in the development of deep tunnel blasting theory and safe construction.
Cyclic blasting excavation of a deep tunnel frequently disturbs the surrounding rock, and cumulative damage effect will occur in cases multiple blasts are applied. To study the damage evolution trend of tunnel surrounding rock under multiple cyclic blasting load, a self-made physical model test system was used to test cyclic blasting excavation of a tunnel under high in-situ stress. Meanwhile, according to the characteristic that the damage of rock under frequent disturbance will appear cumulative superposition, an improved Bingham creep damage constitutive model was established. The constitutive model was applied to the numerical simulation of tunnel cyclic blasting excavation, and the numerical simulation reproduced the physical model test to study the rock damage evolution laws. The results from the physical model test and the numerical simulation revealed that the process of damage evolution of rock in in-situ stress state under the impact of multiple blasting disturbances had a non-linear cumulative characteristic. In addition, the results also shed light on the relationship between the damage zone expansion and the number of cyclic blast. This paper can provide a reference for studies of the damage evolution in deep rock under blasting impact.
In order to study the influence of tunnel excavation by a drilling and blasting method on the ground surface, a method of predicting ground surface vibration waveforms suitable for actual drilling and blasting tunnelling engineering is established. First, based on the theoretical solution of surface vibration waves caused by spherical charge blasting, a more concise surface vibration wave function of spherical charge that is suitable for practical engineering is constructed. The correctness of the constructed waveform function is verified by the measured data. Second, the waveform function of surface vibration waves caused by cylindrical charge explosions perpendicular to the tunnel working face is obtained by superposition of the spherical charge. Then, the surface vibration response of the unexcavated section during tunnel blasting is calculated using the vibration wave superposition method. In the excavated section, the influence of the hollow effect of the tunnel on the vibration wave propagation was considered, and the surface vibration response of the tunnel was analysed using conformal transformation and vibration wave superposition. Finally, based on actual engineering, the correctness of this blasting vibration prediction method is verified using field test data.
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