Study On Disaster Mechanism And Prevention Countermeasures Of Unsymmetrical Pressure In Mountain Highway Tunnel

The topography,geomorphology and geological structure of the mountainous area are complex.When the tunnel passes through the mountain or stream section,it will produce a bias phenomenon,which will cause a series of engineering problems such as cracking,deformation and damage.Based on data and literature,this article uses a combination of theoretical analysis,numerical simulation,site survey and monitoring measurement to comprehensively discuss the formation of mountain highway tunnel bias and the mechanism of disaster-causing and prevention measures,relying on the section of Zhengxi Expressway in Guizhou.Swan Cave Tunnel,carried out related research,the effect is remarkable.The main research contents and results are as follows:(1)Four types of bias hazards are systematically derived: terrain induced types,geological causes induced types,construction man-made causes induced types,comprehensive effects induced types and corresponding main influencing factors,and nine induced mechanisms.(2)Analyzed the stress distribution law of the eccentric pressure formation,obtained the horizontal,vertical and shear stress of the tunnel under the eccentric pressure formation with the transverse slope and Poisson’s ratio,and deduced the optimization of the surrounding rock load of the eccentric pressure tunnel based on the limit upper limit method According to the calculation method,it is concluded that the direct cause of the formation of highway tunnels due to biased pressure is structural asymmetry caused by topography,geology and construction reasons,and the fundamental reason for its formation is that the loads on the deep buried side are often much greater than those on the shallow buried side,and the surrounding rock And the supporting structure is caused by the significant asymmetric force.(3)Use FLAC3D finite difference software to analyze the key influencing factors of bias-induced disasters,establish a comparative model under different covering soil thickness,cross slope rate and surrounding rock grade,and draw conclusions about the different influencing factors under the control of construction man-made factors,The cross-slope is the key influencing factor of disaster;for different types of induction,the topographical cause is the key influencing factor of disaster.(4)When the inducement is single,analyze the prevention and control countermeasures according to the three aspects of terrain,geology and construction;when the inducement is coupled,the concept of asymmetric support + time-sharing grouting support is proposed,and it is concluded that it can pass time-sharing and segmented grouting in time.The load-bearing ring provides additional resistance.Spatially,the asymmetric support structure is used to offset the large loose earth pressure load of the deep-buried side vault,which is coupled with the force and formation mechanism of the biased tunnel.(5)The three-dimensional finite element software Midas GTS was used to study the application effect of prevention and control countermeasures.Establish a threedimensional numerical model of the tunnel construction stage under the three conditions of asymmetric support + time-sharing grouting,symmetric support under the same conditions,and no support,combined with monitoring and measurement data,from deformation,force,plastic failure range,and cost A comparative study of the budget estimates verifies the applicability,economy and environmental protection of the support concept.