Study On Vibration Characteristics Of Underground Pipelines Under Blasting

In the process of urban construction,there are more and more blasting operations in the subway tunnel,foundation and foundation pit engineering.These underground blasting will inevitably disturb the surrounding rock and soil,which may lead to the destruction of nearby underground pipelines.Therefore,in order to ensure the normal use of the pipeline and the construction of the project,the vibration characteristics and control measures of underground pipelines under blasting have become an important issue to be solved.In the paper,theoretical analysis,finite element numerical simulation and field test were carried out to study the vibration velocity attenuation law of the surrounding soil and the strain characteristics of underground pipelines under blasting.The main researched results were as follows:1.The results of vibration velocity in the field blasting test showed that the blasting vibration velocity decreased with the increase of distance,the attenuation of the vibration velocity increased with the increase of distance,the vertical vibration velocity was obviously larger than horizontal’s,the FFT frequency of vibrating velocity was between 30 to 50Hz and was not changed with the increase of distance.2.The strain results of the underground pipelines in the field blasting test showed that the pipeline strain increased with the decrease of distance,the decay of the strain in the pipeline decreased with the decrease of distance.And the position of the pipeline faced to the explosion was strongest.3.Used ANSYS/LS-DYNA finite element software to calculate,then gained the graph of the propagation of blasting seismic wave.The graph showed that the blasting vibration wave was approximate to the spherical wave,the existence of the underground pipelines hindered the propagation of blasting seismic wave.The results of vibration velocity showed that the peak value of vibration velocity decreased with the increase of the horizontal distance in the medium.However,with the increase of depth,the vibration velocity increased near the explosion but was basically unchanged far from the blasting.The results of the underground pipelines showed that the sequence of the pipeline strain was bottom strain<tube top strain<back surface strain<blast side strain.Along the axial direction of the pipeline,the strain decreases with the increase of the distance from the middle section.The strain became smaller as the size of the pipeline increased.4.According to the propagation of spherical wave in elastic solids,the analytical expression and distribution law of vertical vibration velocity in the elastic region of blasting was deduced.Further analysis showed that the strength of the explosive was reflected in the explosion pressure and the size of the cavity.The decay of the detonation pressure had a significant effect on the variation of the vibration velocity.And the vibration amplitude of the medium particle was closely related to the Poisson’s ratio of the material.5.Based on the formula of vibration velocity in the elastic zone of blasting,the analytical solution of the axial strain of the underground pipeline in blast zone was derived.Further analysis of the strain formula showed that the axial strain caused by the axial displacement of the pipeline decreased with the increase of density of the pipelines.The deformation of the tension caused by blasting was independent of the diameter.But the bending deformation was related to the diameter of pipe diameter.The effect of blasting on the underground pipeline was reflected by the bending action as the diameter increases.