在隧道施工过程中,地质超前预报技术是必要手段和工序,也是制约隧道施工技术发展的关键技术难题。地震波法隧道超前地质预报施作是一个力学过程。本文将隧道围岩假设为固、气(孔隙)双相介质,在Biot波动理论的基础上,通过分析人工地震波引起的围岩应力应变关系,结合反射面处的地震波入射、折射、透射连续方程及波阻抗与反射系数关系,得到了围岩广义应力梯度与地震波瞬时振幅与瞬时频率之间的关系表达式,并建立了围岩应力信息与地质信息的联系。在此基础上,将隧道围岩广义应力梯度作为评价地质灾害的重要指标,形成了基于围岩应力信息的地震波超前地质预报方法,解决了现有预报多解性问题。经过现场试验验证,围岩应力信息能够很好地表达地质岩性变化,结合波速和走时,可以准确判定地质灾害规模、类型及位置。
The technology of geological advance prediction is a necessary means and one of process during tunnel construction, and it is a key technical problem restricting the development of tunnel construction technology. The implementation of seismic wave method for advanced geological prediction of tunnels is a mechanical process. In this paper, we regard the application of seismic wave method as a mechanical trial and assume that the surrounding rock of the tunnel is a two-phase medium including solid and gas (pore). By analyzing the stress-strain relationship of the surrounding rock caused by the artificial seismic wave, the continuous equations of the incident, refraction and transmission of the seismic wave at the reflecting surface are obtained. According to the relationship between the wave impedance, the reflection coefficient and the dynamic stress of the surrounding rock, the expression of the relationship between the pressure gradient of the surrounding rock and the amplitude and frequency at different times is derived. The stress gradient of surrounding rock is regarded as one of the important indexes to evaluate the geological disaster. On this basis, a method of seismic wave advances geological prediction based on the stress information of surrounding rock is formed. Through the field seismic wave test, the stress information of surrounding rock can well express the change of geological lithology, which is proved to be accurate and reasonable and has important application value.
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