| With the promotion and development of China's economic modernization,a large number of soft rock tunnels for highways and railways have been excavated in mountainous areas.However,geological disasters such as asymmetric large deformation of layered soft rock tunnels have always been difficult problems faced by the engineering community due to their high degree of danger,high treatment cost and poor treatment effect.Layered rock is a typical complex rock mass,and its deformation and failure are closely related to various factors.When these unfavorable factors are combined with each other,various unfavorable combination forms will be directly generated,and the deformation mechanisms of these unfavorable combinations are different,thus leading to asymmetric large deformation phenomenon.Rigid bolt support is one of the most commonly used tunnel surrounding rock support technologies.However,in soft rock large deformation tunnels,due to the large overall deformation of surrounding rock,ordinary rigid bolt is easily broken and damaged by external force or moves with the overall surrounding rock,and the support effect is not ideal.Therefore,it is very important to study the supporting effect of energy-releasing bolt in layered soft rock tunnel.Based on literature reading,data collection,theoretical research and numerical simulation calculation,this paper studies the energy-releasing bolt support of layered soft rock with asymmetric large deformation based on the high-speed shiziping tunnel in wenma.The main research results are as follows:(1)When the surrounding rocks slide along the stratum,the displacement of the soft interlayer is large due to the existence of the soft interlayer.When the surrounding rock of the tunnel in the near-horizontal stratum is bent and deformed,the deformation of the bottom plate and the invert occurs first.When the surrounding rock is toppling and deformed,due to the existence of the hard interlayer,the hard interlayer will have a certain inhibitory effect on the surrounding rock deformation.The deformation of the surrounding rock is small,and the key part of the deformation is at the two side walls.When the surrounding rock is plastically extruded,the side wall of the surrounding rock,the vault and the invert are prone to deformation.(2)According to the numerical simulation results of the rigid bolt support,it can be seen that the axial force of the rigid bolt in the soft rock exceeds the ultimate tensile force in the tunnel where large deformation occurs.The displacement of the rigid bolt is far more than its elastic deformation,the rigid bolt will be broken and damaged or with the whole movement of the surrounding rock,not to achieve a better supporting effect,bolt is easy to fail in the large deformation parts.Through the comparative analysis with the monitoring results of section K145 + 447 of liongping tunnel,the section is similar to the toppling deformation condition,and the deformation characteristics and axial forces are consistent.(3)Under the support of energy-releasing bolt,the displacement of surrounding rock is generally smaller than that of unsupported rock,but larger than that of rigid support;This is because the existence of the constant resistance section in the energy-releasing bolt makes the surrounding rock release part of the energy,then the surrounding rock has a relatively rigid support and produces a large stable deformation.The releasing bolt can reduce the distribution range of plastic zone and improve the stability of surrounding rock.During the support process,the energy-releasing bolt produces friction to control the surrounding rock deformation,and it can also coordinate with the surrounding rock to bear the external load,so as to keep the energy-releasing bolt in a stable state and ensure the stability of the tunnel after excavation.(4)Through the comparative analysis of the numerical simulation results of rigid bolt and energy-releasing bolt support,when the bolt is under tension,the intermediate axial force of the bolt is the largest,and it gradually decreases on both sides.The axial force of the energy-releasing bolt in the same position is smaller than that of the rigid bolt,while the deformation of the energy-releasing bolt is larger than that of the rigid bolt.This is because the existence of the constant resistance section of the energy-releasing bolt leads to a period of constant resistance deformation after being subjected to the load of surrounding rock,during which the axial force remains unchanged and the displacement increases.(5)According to the numerical simulation results and the classification of asymmetric large deformation,combining four kinds of asymmetric large deformation mechanisms,and aiming at three kinds of large deformation grades: light,medium and strong,a support scheme combining rigid bolt and energy-releasing bolt was proposed for layered soft rock tunnel.In the large deformation area,the energy-releasing bolt is used to encrypt the arrangement,while in the small deformation area,the rigid bolt is arranged. |
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