Numerical Analysis Of The Influence Mechanism Of Hidden Normal Faults On Underground Utility Tunnel

The fault bedrock diastrophism of buried fault not only poses a serious security threat to urban underground space,but also seriously restricts the effective use and planning of urban construction land.As a long linear underground building structure,the underground utility tunnel will inevitably cross the hidden active fault zone during the urban construction process.The paper uses finite element software to establish a three-dimensional numerical model to study the deformation mechanism and safe avoidance distance of the underground utility tunnel during the process of buried normal fault dislocation.The research results are of great significance to the reasonable seismic planning of urban underground spaces of active fracture sites and the determination of safe escape distances.On the basis of constructing a three-dimensional numerical model of the buried normal fault and the underground utility tunnel spreading in parallel,the stress state and maximum principal strain of the underground utility tunnel under different spacing and different buried depth conditions are analyzed,and then studies the safety avoidance distance of the underground utility tunnel,and draws the following conclusions:(1)Through the analysis of the stress state of the underground utility tunnel,it is found that when the underground utility tunnel is closer to the fault zone during the dislocation of the buried normal fault,the stress state on the side of the upper plate of the fault is obviously more complicated than the side of the lower plate.When the underground utility tunnel is close to the fault(<100m)on the side of the upper plate of the fault,it is in a variety of complex stress states such as compression-shear? pure-shear ? tension-shear ? pure-shear ? compression-shear or tension-shear ?pure-shear?compression-shear?pure-shear?tension-shear.When it is far(>150m)or at the side of the lower plate,the stress state has always been in tension-shear or compression-shear.Through the analysis of the maximum principal strain,it is found that when the underground utility tunnel is located on the side of the upper plate or the lower plate of the fault,the deformation is greater when it is closer to the fault(<100m),and when it is farther from the fault(>150m),the deformation is smaller.(2)Through the analysis of the stress state of the underground utility tunnel under different buried depths,it is found that with the increase of the buried depth,thestress state of the underground utility tunnel has changed significantly.The stress state of the underground utility tunnel changes more when it is closer to the upper plate of the fault(<100m),and the stress state changes less when it is far from the lower plate of the fault(>150m)or when it is located on the lower plate.Through the analysis of the maximum principal strain,it is found that as the buried depth increases,the deformation of the underground utility tunnel also increases.(3)Taking the ultimate tensile strain and ultimate compressive strain of the underground utility tunnel material as the judgment standard,the safety avoidance distance of the underground utility tunnel is studied by whether the longitudinal strain of the underground utility tunnel at different buried depths reaches the failure standard.The research results show that for the underground utility tunnel under the same burial depth,the safe avoidance distance on the upper plate of the fault is much greater than that the lower plate fault.With the increase of the buried depth of the underground utility tunnel,the safety avoidance distance generally increases.