The Effect On The Tunnel Structure Caused By Surrounding Rock Deterioration At Tunnel's Bottom Of Heavy Load Railway Tunnel

At present,the development of heavy-haul freight transportation technology for freight trains around the world is very rapid.Heavy haul railway transportation has received extensive attention from railways all over the world because of its large capacity,high efficiency,and low transportation costs.With the continuous improvement of China's railway network,"heavy cargo and passenger high-speed" have become the two major directions of railway development nowadays.As a key component of heavy haul lines,heavy railway tunnel's structural stress form and disease characteristics are quite different from ordinary railway tunnels.The bottom of a heavy haul railway tunnel is the foundation of the train's dynamic load and structural load,coupled with the groundwater and other geological factors,the disease at the bottom of the heavily loaded railway tunnel are particularly prominent,such as cracking,emptying,sinking,ditch squeezing,mud pumping,etc,and resulting in a shortened service life of the tunnel and a decrease in safety reserves in terms of structural strength,stiffness,and stability.These diseases worsen the driving conditions,limit the speed of traffic,endanger the safety of vehicles,shorten the maintenance period and service life of tunnels,and restrict the safe and efficient service of railways.In view of the harm caused by the loss of surrounding rock mass at the bottom of heavy haul railway tunnel.In this paper,numerical methods,theoretical analysis,on-site investigations and laboratory tests are used to study the deteriorating effects of surrounding rock mass on the bottom of heavy-load railway tunnels and their impact on the structure.The main results are as follows:1.By using the methods of data investigation and field survey,the features of heavy haul railway tunnels and their disease characteristics were clarified.Based on this feature,the influencing factors of tunnel bottom diseases were summarized.According to the survey results of heavy haul railway tunnel diseases,a method for classifying tunnel diseases was proposed.2.Through the indoor model test,the evolution process of the voids of different types of surrounding rock mass at the bottom of heavy haul railway tunnels has been explored.The stress characteristics of different forms of tunnel bottom structures were compared,and the degradation rules of the surrounding rock mass and the formation mechanism of voids at the bottom of heavily haul railway tunnels were defined.By using the discrete element method,a method for calculating the attenuation of mechanical parameters of the surrounding rock of the tunnel bottom was established.3.By means of numerical simulation,the process of seepage erosion degradation of the surrounding rock at the bottom of the tunnel was analyzed.The law of the stress characteristics and safety of the tunnel structure under the loss of surrounding rock particles at the bottom of tunnel was proposed.The transformation relationship between the elastic resistance coefficient of tunnel surrounding rock and the vertical displacement of tunnel is obtained.The above achievements have been used to formulate specifications for heavy haul railway tunnels and to design standard plans for heavy haul railway tunnels which provide technical support for improving the key technology of design and construction of heavy haul railway tunnel.