土岩交错地层隧道爆破施工的振动响应及空洞效应分析

Analysis of Vibration Response and Cavity Effect of Blasting Construction of Tunnel in Soil-Rock Interlaced Strata

以汕湛高速揭博段水墩隧道为工程背景,运用数值模拟计算的方法,建立上软下硬地层下爆破振动的有限元计算模型,对爆破荷载作用下上部初期支护和围岩的振动响应及空洞效应进行研究。结果表明:1)掌子面下部基岩爆破施工的振动荷载主要通过支护结构传递给拱顶围岩,而掌子面上部前方围岩(未成洞区)和后方围岩(成洞区)振动分布并不对称,其中成洞区围岩的振动速度和振动范围远大于未成洞区,说明上软下硬地层隧道爆破振动存在空洞效应;2)成洞区单向约束是造成振动加剧的根本原因,围岩振动的纵向最不利位置为掌子面后方约2 m处,径向为软硬交界结构面与隧道外轮廓的切点处;3)振动方向以径向为主,即拱顶围岩振动以竖向振动为主,初期支护拱脚以水平振动为主;4)距离掌子面1倍(洞径)范围的拱顶围岩及初期支护拱脚是控制爆破振动的关键部位。

The vibration response and cavity effect of upper primary support and surrounding rocks of Shuidun Tunnel on Shantou-Zhanjiang Expressway under the effect of blasting load is studied by finite element calculation model of uppersoft and lower-hard ground based on numerical simulation method. The study results show that：（ 1） The vibration load of the bedrock blasting of lower part of excavation face is mainly transmitted through support structure to the arch rock;while the vibration distributions of surrounding rock ahead of upper excavation face（ non-cavity area） and behind excavation face（ cavity area） are not symmetrical; the vibration velocity and range of cavity area are much larger than those of non-cavity area,which illustrates that there is a cavity effect in the blasting vibration of tunnel in upper-soft and lower-hard ground.（ 2） The unidirectional confinement of the cavity is the root cause of the increase of vibration; the most unfavorable position of the vibration along longitudinal direction is about 2 m behind the excavation face; and that along the radial direction is the tangency point between contact surface of soft soil and hard soil and tunnel outer contour.（ 3） The vibration is mainly along radial direction,i.e. the vibration of crown top of surrounding rock is mainly along vertical direction and that of arch foot（ arch springing） of primary support is mainly along horizontal direction.（ 4） The crown top of surrounding rock and arch foot of primary support are the key points to control blasting vibration where is 1D,where D is tunnel diameter,away from excavation face.