埋地输气管道对城市地下空间掘进爆破的力学响应

Mechanical Response of Buried Gas Pipeline to Excavation Blasting in Urban Underground Space

城市地下空间掘进爆破过程中冲击载荷对爆源近区的埋地输气管道的影响作为工程施工中的主要安全问题已被广泛关注。以某一具体施工案例为背景,采用动力有限元软件LS-DYNA建立了土体-管道-岩石流固耦合模型。对δ=0.02 m、0.04 m、0.06 m、0.08 m的4种不同壁厚条件下管道的迎-背爆面有效应力和振动合速度分布规律进行了分析;同时基于管土耦合模型,进一步研究了爆破振动速度峰值由爆源传至管道迎爆面、背爆面和地表三个关键位置时的衰减情况。结果表明:随着管道壁厚的增加,管壁质点的有效应力、振动合速度都呈现出非线性衰减规律,管道背爆面局部应力峰值数值明显高于迎爆面,而迎爆面振动合速度明显高于背爆面。当管壁厚度增量为Δδ=0.02 m时,迎爆面和背爆面有效应力峰值衰减率分别为κ_(1)=25.2%、19.2%、10.7%和κ_(2)=50%、25%、13.3%。4种不同壁厚条件下迎-背爆面和背爆面-地表质点峰值振动速度平均衰减率分别为η_(1)=24.6%、18.96%、15.04%、14.78%和η_(2)=73.46%、69.4%、66.52%、63.6%,而衰减系数α的变化明显小于衰减率。故对于存在管道的这种非均匀地质条件振动速度预测采用萨道夫斯基公式已不再准确,需要对该公式进行修正使用。

The influence of impact loading generated during the excavation blasting process on a buried gas pipeline near the blasting source has been widely concerned as a major safety issue in the engineering construction of an urban underground space.Based on a specific construction case,this issue is studied with a fluid-solid coupling model considering soil,pipeline and rock by using the dynamic finite element software LS-DYNA.The distribution laws of the effective stresses and the resultant velocities of vibration on the two sides of the pipeline towards and away from the blasting source are analyzed with four different wall thicknesses(δ)of 0.02 m,0.04 m,0.06 m and 0.08 m.At the same time,the attenuation characteristics of the peak blasting vibration velocities on the ground and the two sides of the pipeline towards and away from the blasting source are further investigated based on the established coupling model.The results present a nonlinear attenuation law of the effective stresses and the resultant velocities of vibration with the increase of the pipe wall thickness.Specifically,Moreover,the local peak stress on the side of the pipeline away from the blasting source is significantly higher than that on the side towards the blasting source,whereas the resultant vibration velocities on the side of the pipeline towards the blasting source is significantly higher than that on the side away from the blasting source.Now that the pipe wall thickness increases by an increment ofΔδ=0.02 m,the attenuation rates of the peak effective stresses on both sides(towards and away)of the pipeline are κ_(1)=25.2%,19.2%,10.7%and κ_(2)=50%,25%,13.3%,respectively.For the four different wall thicknesses,the average attenuation rates of peak particle vibration velocities from the side of the pipeline towards the blasting source to the side of the pipeline away from the blasting source and from the side of the pipeline away from the blasting source to ground are η_(1)=24.6%,18.96%,15.04%,14.78%and η_(2)=73.46%,69.4%,66.52%,63.6%respectively.However,the change of attenuation coefficient is significantly smaller than the attenuation rate.Therefore,it is no longer accurate to use the Sadovsky formula,which needs to be corrected,to predict the vibration velocities of pipelines in such inhomogeneous geological conditions.