Study On The Mechanical Characteristics Of Tunnel Invert Under The Condition Of Uneven Surrounding Rock

The development of infrastructure construction in transportation industry is related to the timeliness of economic and cultural exchanges in various regions.The road and railway construction network has gradually expanded to cover remote areas,and many engineering problems have followed.The northwestern region of China is dominated by plateaus and mountains,with complex terrain.Tunnel construction has incomparable advantages in this terrain.The proportion of tunnel length in the line is getting higher and higher.Due to the complexity and spatiotemporal variability of surrounding rock conditions,many disease problems often occur during tunnel construction,and the bottom arch and cracking of the arch are one of them.The importance of the inverted arch to the overall structure of the tunnel is self-evident,it bears multiple loads simultaneously,and the force situation is complex and changeable.Therefore,disease problems often occur and affect project safety.This has also attracted the attention of many scholars.Aiming at the problem of the stress of the inverted arch under the condition of uneven surrounding rock,this paper proposes a classification method for the failure mode of the inverted arch by consulting related research results and engineering cases,using MIDAS software to carry out numerical simulation of the four working conditions,and the tunnel is reinforced with asymmetric support measures in the case of lateral uneven surrounding rock,and its feasibility is analyzed.The main research results are as follows:(1)Several typical cases of inverted arch damage are summarized.Among the factors that cause inverted arch damage,the unevenness caused by the variation of surrounding rock properties is one of the key points;Based on the classification of the existing inverted arch damage modes,starting from the dominant factors of inverted arch damage,it is divided into primary and secondary damage,and based on the stress type of the inverted arch,it is further subdivided into pulling-bending failure,bending-shearing failure,and pulling-shearing failure.The surrounding rock conditions corresponding to various failure modes are analyzed.(2)The longitudinal heterogeneity model of surrounding rock was established,and the characteristics of displacement and force of the inverted arch in the surrounding rock of Grade ?and Grade?were compared and analyzed.The tunnel settlement displacement in the soft rock section and the uplift displacement of inverted arch are greater than those in the hard rock section,and the displacement difference between the two sections increases as the surrounding rock level increases,the difference of displacement between the center position and the both sides of the inverted arch will affect the failure mode.The interface between soft and hard rocks is a dangerous cross section,where the tensile stress of the inverted arch suddenly increases,and the plastic zone also increases significantly.(3)Based on the lateral heterogeneity model of surrounding rock,the pressure and plastic zone of the surrounding rock on both sides of the soft and hard rock,and the uplift displacement and stress of the inverted arch in the cross section are analyzed.According to the lateral change law of the major principal stress and plastic zone,the location and failure mode of cracks in the inverted arch are discussed.The vulnerable parts are located at 3.6 m on both sides of the centerline.(4)Aiming at the lateral unevenness of the surrounding rock,a numerical model of asymmetric support was established,the feasibility of asymmetrical support was verified by comparing the deformation the plastic zone of the surrounding rock and displacement and stress of inverted arch before and after the support,This kind of support method has a significant effect in controlling the displacement of surrounding rock and inverted arch and improving the stress of the inverted arch.