| With the rapid improvement of China’s comprehensive national strength,the construction of transportation and other infrastructure in western China has developed rapidly,and a large number of railways and highway tunnels have been built in the western high-intensity mountainous areas.However,the terrain in the western high-intensity mountainous area is dangerous and the terrain is complex,and the seismic activity is frequent.Especially in the soft and broken mountain areas,it is easy to produce adverse geological disasters such as landslides and collapses under the action of earthquakes,which brings great danger to the construction of tunnel engineering.At present,there are relatively few studies on the dynamic response and prevention measures of soft rock tunnels in high-intensity earthquake areas.Therefore,it is a key scientific problem to be solved urgently in geotechnical earthquake engineering to clarify the dynamic response characteristics of soft rock tunnels in highintensity earthquake areas and propose corresponding prevention measures.Therefore,this paper takes a soft rock tunnel project in the Lalin railway section of the Sichuan-Tibet line as the research background.The dynamic response characteristics of the soft rock tunnel are studied by means of data investigation and shaking table model test,and the damping measures based on the tunnel energy dissipation structure are proposed.At the same time,the damping effect of the energy dissipation structure is evaluated by model test.The following main conclusions are drawn:(1)Under the action of earthquake,the acceleration response of soft rock tunnel at vault and inverted arch is relatively strong,and the closer to the portal section,the stronger the tunnel response.With the increase of seismic wave intensity,the peak acceleration of each part of the tunnel increases radially in the “S” trend,and the peak acceleration amplification coefficient decreases with the increase of the buried depth of the tunnel.The peak acceleration of the surrounding rock of the slope is roughly the same as that of the tunnel,but the acceleration amplification coefficient of the slope shows a certain elevation amplification effect,and it will change with the change of seismic intensity.The acceleration amplification coefficient of the measuring points in the slope generally shows a trend of increasing first → decreasing →increasing again → decreasing again,and there are two peaks in general.(2)Under the action of the earthquake,the strain response of different parts of the soft rock tunnel has the transformation of tension and compression characteristics,which easily leads to the uncoordinated failure of the tunnel near the entrance section,and the tunnel far away from the entrance section produces the failure of the upper and lower middle compression.The failure of the tunnel shows the spatial coupling deformation continuous effect of regional damage and failure,and the deformation range of the tunnel gradually expands from the local to the whole.However,with the increase of tunnel depth,the probability and degree of tunnel failure are smaller.The longitudinal failure develops from the portal section to the deep surrounding rock,which makes the inverted arch and side wall of the tunnel easy to become the weak link of seismic design.(3)Under the action of earthquake,the seismic Hilbert energy of soft rock tunnel is mainly distributed in 20s-40 s,but the spatial distribution of Hilbert spectrum peak and the change of frequency are closely related to the intensity of seismic wave.At the same time,the marginal spectrum peak and frequency of different parts of soft rock tunnel are obviously different;The failure mode of the slope of the tunnel-surrounding rock system undergoes four stages of initial cumulative deformation,micro-dislocation deformation,dislocation slip deformation and caving slip deformation.For the tunnel slope without weak interlayer,under the continuous action of the earthquake,the interface of the surrounding rock soil will form a natural sliding surface,and the slope will evolve from local failure to global instability.(4)The Hilbert energy spectrum of the earthquake mainly reflects the overall energy transfer characteristics of the soft rock tunnel.The marginal spectrum has rich frequency components and high recognition degree,which can clearly reflect the energy transfer and local seismic damage characteristics of the tunnel.The Hilbert spectrum and marginal spectrum energy identification method can reveal the instability mode of the tunnel and the regional response characteristics of the particle space position,which is of great significance to the study of the seismic failure characteristics of the tunnel and the seismic design of the tunnel.(5)The low-frequency and high-frequency components of the seismic wave play a controlling role in the overall and local deformation of the tunnel structure,respectively.The tunnel energy dissipation structure has the best damping effect on the strain of the vault and inverted arch,but it does not change the time effect and spectrum response characteristics of the dynamic response of the tunnel.It only reduces the amplitude,but the tunnel energy dissipation structure will change the damage form of the tunnel.(6)On the basis of fully considering the plastic deformation characteristics of soft rock tunnel,the plastic deformation law of soft rock tunnel is mainly divided into three stages: elastic deformation stage,elastic-plastic deformation stage and plastic deformation failure stage.The energy dissipation structure of tunnel can weaken the plastic deformation effect of tunnel and delay the tunnel from entering the plastic deformation stage prematurely,which greatly improves the seismic capacity of soft rock tunnel. |
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