Design of an experimental platform for investigating the structural response law of tunnel models crossing unfavorable geological zones
[Objective]In China,the rapid development of tunnel and underground engineering construction has led to an increasing number of design challenges,particularly when these structures interact with unfavorable geological conditions,such as water-rich faults,karst formations,and gullies,etc.During construction in areas with high water content under high geostress,projects often encounter high stress,high water pressure,and strong disturbances.These conditions make tunnels prone to disasters such as water and mud inrushes,collapses of the surrounding rock,rock bursts,and extensive deformation,etc.Given the extremely complex terrain and geological conditions often encountered in mountain tunnels,conducting reasonable and scientific research on the structural stress characteristics of tunnels crossing unfavorable geological zones is both theoretically and practically valuable to further enhance the safety of tunnel construction.[Methods]To investigate the structural response characteristics of tunnels crossing such unfavorable geologies,a model experimental platform was designed and developed,inspired by the Yangzong Tunnel of the Fuyi Expressway.The platform comprises a physical model box system,a sensing and data acquisition system,and a system to simulate unfavorable geological conditions.The model box measures 1.5 m(length)×1.0 m(width)x 2.0 m(height),fixed by a steel frame composed of sections made of 0.5 m(length)× 0.5 m(width)transparent tempered glass and steel bars.Several scaled simulation experiments of tunnel engineering were carried out under different types of unfavorable geological zones.Based on the experimental platform,the structure and functions of all systems were introduced,and corresponding experimental plans were developed for four types of unfavorable geological conditions.[Results]The paper also describes a typical case of unfavorable geological conditions as a fault fracture zone to demonstrate the entire process of the model experiment.Gypsum and other materials were used to simulate the surrounding rock and tunnel lining,with mechanical performance tests conducted accordingly.Then,three monitoring sections were established along the direction of tunnel excavation,such as the entrance,interior,and exit of the fault fracture zone.When filling the model box with similar materials,the method of layered filling and compaction was used to simulate the surrounding rock and fault fracture zone.After the model was cured and formed,the tunnel area of the model was excavated to complete the experiment.The structural response of the tunnel passing through the fault fracture zone was analyzed.Initial observations during excavation showed stable displacement changes in the surrounding rock at each monitoring point until significant increases were noted as the excavation approached the monitoring cross-section,which was more significantly affected by the fault.[Conclusion]The radial pressure of the surrounding rock before tunnel excavation near the monitoring section generally exhibited a negative change.As the tunnel face approached,the decrease in pressure gradually increased,reflecting a redistribution of stress in the surrounding rock and the formation of a"leading arch".Excavating up to the monitoring section led to a significant reduction in surrounding rock pressure at each measuring point,especially in the tunnel vault.The surrounding pressure in the fractured zone of the fault underwent significant changes,making it prone to instability and failure.Ultimately,the experimental results were compared with numerical simulation results to verify the effectiveness of the model experiment.
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