Study On The Stress Mechanical Of Mudstone Tunnel And The Bottom Invert Arch Drum Under Base Expansion

At present,invert heave disease is common in tunnel construction and operation at home and abroad,which has brought great trouble to the engineering and academia.The bottom arch drum of the mudstone tunnel during the operation period is one of the typical problems studied by scholars.With the large-scale development of highways and railways in the Northwest,it is inevitable to build a large number of tunnel projects.When a tunnel passes through an expansive muddy rock system,the basement often undergoes corresponding changes in its physical and mechanical properties due to groundwater migration and infiltration and erosion.The effect of basement surrounding rock on Invert bottom not only shows differences in the horizontal direction,but also unevenly distributed in the vertical direction,which results in different forces and failure modes of Invert bottom.This article mainly takes heave of invert arch of the mudstone tunnel of the expressway as the research object,through theoretical analysis,field investigation,numerical simulation and other methods to study the characteristics of the tunnel arch’s stress and failure under various operating conditions of the basement,and proposes the corresponding expansion problems.Through the review of literature and specifications and on-site investigations,the typical cases of inverted arch drum in China are sorted out,and the proportion of factors l eading to the failure of inverted arch is analyzed;Combined with the tunnel structure form,the internal force and distribution of the invert arch were calculated by structural mechanics method;the failure model and development process of the invert arch bottom drum were summarized,and the invert arch bottom drum volume was introduced according to the composition Calculation method.To study the influence of the expansion of the basement surrounding rock on the mechanical effect of the invert arch,the ABAQUS was used to set the 15%,18%,21% and 24% of the basement moisture content for various types of basement rock.Simulation analysis of the damage of the bottom drum;the increase of the uniform swelling water content of the base rock is positively correlated with the change of the bottom drum volume of the upward arch,which has a certain inhibitory effect on the settlement of the arch.The strain is the largest,and the tensile stress in the middle is the largest.Shear displacement damage is likely to occur at the 1/4 and 3/4 hole diameters of the backfill layer,and it is easy to be pulled and damaged at the midline position.The basement is unevenly expanded front and back,the damage position of the backfill layer is related to the position of the tunnel cross section,the tunnel entrance and exit center line is susceptible to tensile damage,and the middle tunnel backfill layer is easily cracked and damaged at about 2m on both sides of the centerline;the basement is unevenly expanded and backfilled With the increase of water content,the maximum stress position of the layer moves from the center line to the expansion side,that is,the 1/4 tunnel,where the backfill layer is easily damaged by tension.The increase in the vertical displacement of the invert arch caused by biased expansion is significantly greater than the change in the settlement of the vault.The stress on the left arch foot of the invert arch is the most disadvantageous.The vertical displacement of the primary support structure has a greater impact,and the horizontal displacement is manifested by the shrinking of the tunnel section.The backfill layer is easily damaged by tension at the center line of the tunnel.Secondly,the elastic modulus is reduced by 1,0.5,0.3,0.1 to explore the effect of the overall softening and local softening of the basement surrounding rock on the invert arch.The overall softening of the basement is more likely to cause the midline invert arch to be damaged and the arch foot will collapse and pull Rupture.The local softening of the base is likely to cause uneven stress on the tunnel,and the inverted arch on one side of the local softening is prone to tensile cracking and damage.Through the simulation analysis of the above various working conditions,the tunnel deformation,the development of the plastic zone,the stress of the arch and the backfill layer,the deformation characteristics and the fragile location are obtained.Taking the most unfavorable conditions as the example,the base rock surrounding the water expands evenly as an example There are two types of rectification methods: bottom anchor and bottom anchor + bottom anchor.The bottom anchor can reduce the maximum principal stress of the backfill,but it cannot control the damage of the backfill.Although the bottom foot + bottom anchor increases the bottom tensile stress,but can effectively control the maximum tensile stress of the backfill.The research results can provide reference for tunnel construction under similar engineering geological conditions.