爆破荷载作用下小净距隧道的动力响应分析

Analysis on dynamic response of small clear-distance tunnel under blasting load

隧道施工时需要控制好爆破作用下小净距隧道的安全,为此,以小净距隧道为例,基于有限元软件LS-DYNA分析了不同净距和超前距离下小净距隧道在爆破荷载作用下的动力响应和振动速度变化规律。结果表明:当隧道净距不断增大时,围岩的等效应力在爆破振动作用下逐渐减小。净距在0.5~1倍隧道直径时,围岩等效应力较大且衰减速率较快,而在2~3倍隧道直径时,后行洞隧道爆破产生的等效应力相对较小,表明在这个区间的中间岩体厚度的隧道爆破应力波传播得较稳定;当隧道中间岩体的厚度增加时,隧道的振动速度减小较快,当中间岩体厚度减小到1倍隧道直径时,振动速度迅速衰减,而当中间岩体厚度大于到1倍隧道直径时,振动速度衰减趋势变得较缓;当超前距离小于10 m时拱顶、拱腰和拱脚的振动速度随着距离的增加而减小,超过10 m时振动速度随着距离的增加减小的幅度降低,则隧道爆破施工最合理的超前距离约为10 m。

The tunnel safety under the blasting effect during the construction of small clear-distance tunnel is necessary to be well controlled,and then the dynamic response and the variation law of vibration velocity of the small clear-distance tunnels with different clear distances and advanced distances under blasting load are analyzed herein with the finite element software—LS-DYNA by taking a small clear-distance tunnel as the study case.The study result shows that the equivalent stress of the surrounding rock is gradually decreased under the blasting vibration effect along with the continuous increase of the clear distance of the tunnel.When the clear distance is 0.5~1 times the tunnel diameter,the equivalent stress of surrounding rock is larger with a faster attenuation rate,while the equivalent stress from the tunneling blasting for the subsequent driving tunnel is relatively small when the clear distance is 2~3 times the tunnel diameter,which indicates that the tunneling blasting stress wave propagation of the thickness of the intermediate rock mass for this interval is relatively stable.When the thickness of the intermediate rock mass increases,the decrease of the vibration velocity of the tunnel is faster and the vibration velocity rapidly attenuates when the thickness of the intermediate rock mass decreases to 1 times the tunnel diameter,while the attenuation trend becomes slower when the thickness of the intermediate rock mass is larger than 1 times the tunnel diameter.When the advanced distance is less than 10 m,the vibration velocities at the vault,hence and skewback decrease along with the increase of the distance,while the decreasing amplitude of the vibration velocity decreases along with the increase of the distance when the advanced distance is over 10 m,thus the most reasonable advanced distance for the tunneling blasting construction is about 10 m.