Study On The Mechanical Properties Of The Large Cross Section Mudstone Tunnel And The Mechanism Of The Bottom Heave

Since the reform and opening up,China's economy has developed rapidly,at the same time,the construction of transportation is also very rapid,the traffic construction in the Loess area is closely related to the construction of the loess tunnel,the cement rich rock has softened quickly after excavation and has many problems,compared with other types of tunnels,the loose earth pressure in rich cement rock is generally larger,especially in the large section of the tunnel,this kind of loose earth pressure is bigger,therefore,the tunnel with large section is more prone to tunnel diseases,the most common tunnel disease is the bottom of the tunnel invert,therefore,it is necessary to study the mechanical properties and the mechanism of the bottom heave of the large cross section tunnel.The main research results are as follows:(1)The research status of the bottom drum type,the bottom heave mechanism and the control measures of the bottom drum at home and abroad are studied,the stress characteristics of mudstone tunnel are analyzed,the mechanism of bottom heave of mudstone tunnel invert is summarized,based on the actual engineering characteristics,in view of the existing problems,this paper puts forward the research ideas and content.(2)Based on the test data of the earth's composition,chemical composition and microstructure of the mudstone samples retrieved from the tunnel,and the expansion of the tunnel mudstone is determined,It can be concluded that there is almost no swelling in the mudstone of the tunnel,but it is disintegrated.(3)Through the analysis of the monitoring data of tunnel,it can be concluded that the tunnel is subjected to large loose pressure,moreover,the stress of the arch and arch of the tunnel is the largest,which is more dangerous,the reason of the bottom heave of the tunnel invert is likely to be the result of the joint action of the two invert arch foot under the large loose extrusion pressure and the groundwater.(4)By model test,in the construction of large section mudstone tunnel,arch waist,arch foot and arch bottom are the most easily damaged parts,this is similar to the measured results,and the bearing capacity of the foundation is insufficient,the tunnel will sink,through the model test,it is verified that the pressure of large loose surrounding rock is one of the main reasons leading to the bottom heave.(5)Based on Midas-GTS 3D finite element model and structural mechanics method,in order to further analyze the mudstone tunnel under large pressure load,stress characteristics and deformation law of tunnel lining,compared with the results of indoor model test,furthermore,it is verified that the pressure of large loose surrounding rock can cause the cracking of the bottom heave of tunnel invert.(6)Based on the full text analysis,it is concluded that the cracking mechanism of the bottom heave of the tunnel invert is mainly due to the poor nature of the surrounding rock mass,the tunnel is subjected to a large amount of loose pressure,and the role of groundwater,because of the effect of some engineering factors,the bottom heave of the invert arch was increased,which led to the cracking of the invert arch,at the same time,according to the specific conditions of the tunnel,this paper puts forward the reasonable control measures.To provide reference for practical engineering application.