Study On The Mechanical Characteristics Of Segment Of Super Large Diameter Shield Tunnel Through Soft And Hard Uneven Strata

With the deepening of urban large-scale underground engineering construction,the geological conditions faced in the process of shield construction are becoming more and more complex,and the municipal tunnel project is also developing in the direction of large section and long distance.Compared with the general municipal tunnel,the cracking problem of segment structure of super large diameter shield tunnel is more significant,which puts forward higher requirements for the stability of segment structure.Among them,the mechanical properties of the segment structure are particularly important and are important factors affecting the safety of design and construction.In view of this,on the basis of summarizing the mechanical properties of super-large diameter shield tunnel segments at home and abroad,relying on the Shenzhen Chunfeng Tunnel project,through numerical simulation and model test,combined with field test data,the mechanical properties of super-large diameter shield tunnel segments in soft and hard uneven strata are studied.The main work and achievements are as follows :(1)The load-structure three-dimensional numerical model of super-large diameter shield tunnel segment is established.The influence of stratum resistance coefficient,static earth pressure coefficient,assembly point,concrete strength and stratum factors on the stress of segment structure is studied.It is found that the displacement and stress of the segment decrease with the increase of the formation resistance coefficient.The static earth pressure coefficient has little effect on the displacement of the segment,which is proportional to the stress of the segment.The assembly point has a great influence on the mechanical properties of the segment structure.With the increase of concrete strength grade,the ultimate instability load of segment increases.Weak stratum has great influence on segment deformation.(2)A three-dimensional numerical model of the segment with reinforcement is established to study the influence of reinforcement on the stress and deformation of the segment structure.It is concluded that the equivalent stress of the longitudinal main reinforcement at the bottom of the segment is the largest,reaching 116.6MPa,and the equivalent stress of the transverse reinforcement is small,only 0.016MPa;the equivalent stress at the bottom of the segment is the largest,reaching 13.3 MPa.The stress on the inner side of the bottom of the segment is greater than that on the outer side.The equivalent stress on the top of the segment is the smallest,0.075 MPa,and the stress on both sides of the waist is 7 MPa.The bolt is mainly subjected to axial force,which is 84 MPa.(3)Considering the effect of groundwater,a two-dimensional model of stratumstructure is constructed,and the influence of tunnel depth and shield gap on the stress and deformation of segment structure is analyzed.It is concluded that groundwater is beneficial to the stress of segment.Groundwater makes the stress of segment more uniform,the minimum axial force increases,and the bending moment of segment decreases.Under the action of water,the stratum deformation after excavation is mainly vertical displacement,the stratum at the top of the segment produces settlement,and the soil at the bottom rebounds;when there is no groundwater,the maximum horizontal displacement point of soil around the tunnel is located on both sides of the tunnel.When there is groundwater,the maximum horizontal displacement point of soil around the tunnel is located at 45 ° below the slope of both sides of the tunnel.(4)The physical model tests of tunnel segment deformation under different geological conditions and segment assembly methods were carried out to explore the stress and deformation characteristics of super-large diameter shield tunnel segment structure.It is concluded that under the same overburden,the segments in the hard soil layer with higher compactness are more likely to be damaged,and the segments assembled through seams are more likely to be damaged.(5)Combined with field monitoring data,the earth pressure,bolt axial force,segment steel stress and lining concrete strain of two strata sections are analyzed,and the stress and deformation law of segment structure in the whole construction process of super large diameter shield tunnel in soft and hard uneven strata is obtained.The load bias of surface buildings has a great influence on the distribution of soil pressure around the segment,and the peripheral water and soil pressure borne by the segment in the broken surrounding rock environment is greater.The stress of the outer main reinforcement is greater than that of the inner main reinforcement.The main reinforcement of the monitoring ring is under pressure,which is consistent with the numerical simulation results.The research results can guide the construction of similar projects.