| Because of the special geological background and geographical environment the tunnel entrance section as an important part of the tunnel building is the throat of the tunnel entrance and exit and it is also the weak link of the entire tunnel seismic fortification The geological conditions around the tunnel entrance section are complicated and the bearing capacity of the foundation is usually weak In case of strong earthquakes earthquake damage such as damage to the door wall tilt cracking and axial cracking of the tunnel body are prone to occur The western part of our country is a mountainous region.There are many railways and highways that need to pass through the mountains and canyons.It is inevitable to build many tunnels to complete the plan.The dynamic response of different underground structures under seismic loads is still being studied.Need to explore further.Based on the concrete engineering example of Fang jia wan Tunnel,This paper studies the dynamic response laws of structures under seismic loading,finds important parts of seismic fortification analyzes the seismic effect of steel fiber concrete on the tunnel structure,and obtains reasonable results.The seismic fortification length of the tunnel provides an important basis for the earthquake resistance of the tunnel structure.The specific content includes the following aspects:(1)By reading a large number of literature,understand the main results of anti-seismic analysis and anti-seismic research at home and abroad,and introduce the commonly used dynamic analysis theory of underground structures.Determine the constitutive model of the materials required for modeling and the input seismic waves,damping conditions,boundary conditions,etc.,and consult the data and calculations to determine the values of various parameters.(2)A three-dimensional model of the tunnel was constructed using finite element software,and three different seismic waves were input horizontally,vertically,and vertically(three directions).The simulation leads to the following conclusions:(1)The overall displacement of the tunnel structure tends to decrease with increasing distance from the entrance of the tunnel.When the Wen chuan earthquake wave is input the maximum displacement is 7.34783cm.At the entrance,the structural displacement is relatively large Acceleration shows a similar law to displacement and its maximum value is2.6541m/s~2.When the Kobe seismic wave was input,the maximum displacement was 8.94407cm,and the structural displacement was relatively large at the entrance.Acceleration shows a similar law to displacement,and its maximum value is 3.40477m/s~2.When the EL-Centro seismic wave is input,the maximum displacement is 33.3248cm,and the structural displacement is relatively large at the entrance position.Acceleration shows a similar law to displacement,and its maximum value is 3.66977m/s~2.(2)When the Wen chuan earthquake wave was input in the location where the soft and hard rocks of the tunnel structure changed greatly,The internal force and stress at the monitoring surface of the tunnel structure suddenly increased and then decreased at the next monitoring surface.The maximum principal stress was 5.96MPa,which appeared at the left and right arch feet of the structure.The peak axial force is 363.907kN,which appears at the left and right arch shoulders at the interface of soft and hard rocks.The peak shear force is43.05kN,which appears at the arch foot of the interface between soft and hard rocks.The peak moment size is 6.04008kN·m,and it appears at the arch foot of the interface between soft and hard rocks.From the graphs drawn from the results of extracting data from each point of the tunnel structure monitoring surface every 3m along the longitudinal direction of the tunnel,it can be seen that the internal force and stress of the tunnel structure are gradually reduced to varying degrees.When the kobe seismic wave is input,the structure’s internal forces and stresses are abruptly changed at the locations where the soft and hard rocks of the tunnel structure change greatly.The maximum principal stress is 10.604MPa,which appears at the left and right arch feet of the structure.The peak axial force is 887.324kN,which appears at the left and right arch shoulders at the interface of soft and hard rocks.The peak shear force was 73.4779kN,which appeared at the arch foot of the interface between soft and hard rocks.The peak moment size is 8.34331kN·m,and it appears at the arch foot of the interface between soft and hard rock.From the graphs drawn from the results of extracting data from each point of the tunnel structure monitoring surface every 3m along the longitudinal direction of the tunnel,it can be seen that the internal force and stress of the tunnel structure are gradually reduced to varying degrees.When the EL-Centro seismic wave is input,the structural internal forces and stresses change abruptly at the locations where the soft and hard rocks of the tunnel structure change greatly.The maximum principal stress is 10.177MPa,which appears at the left and right arch feet of the structure.The peak axial force is 632.642kN,which appears at the left and right arch shoulders at the interface of soft and hard rocks.The peak shear force was 83.6893kN,which appeared at the arch foot of the interface between soft and hard rocks.The peak moment size is 9.70695kN·m,and it appears at the arch foot of the interface between the soft and hard rocks of the structure.From the graphs drawn from the results of extracting data from each point of the tunnel structure monitoring surface every 3m along the longitudinal direction of the tunnel,it can be seen that the internal force and stress of the tunnel structure are gradually reduced to varying degrees.(3)By adding steel fiber concrete seismic materials to the lining part under the action of steel fiber concrete the stress at most monitoring points has increased and the peak value of the maximum principal stress appears at the vault1664.82kPa,an increase of 9.5%compared with ordinary concrete.The peak value of the minimum principal stress appears at the left and right arch shoulders,with a size of-133.24kPa,which is an increase of 41.2%compared with ordinary concrete.It can be seen that when steel fiber concrete is used as an earthquake-resistant material,the structure can be enlarged to a certain extent Stress can effectively dissipate seismic energy under the action of earthquakes.(4)According to the numerical simulation results of this thesis and the latest specifications,it can be known that for the ClassⅤsurrounding rock section of the loess tunnel,the seismic fortification length can be set to 27m.The fortification length of the tunnel structure where the hard rock meets should be appropriately lengthened.The recommended fortification length is 26-30m to ensure the safety of the entrance. |
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