Model Test On Longitudinal Seismic Response Of Shield Tunnel Intersecting Ground Fissure

Serious ground fracture hazards in Xi’an area threaten the safety of surface buildings and underground structures along the ground fractures,and restrict the construction of Xi’an metro.The construction of subway at the ground fracture site usually adopts the mining method,which faces problems such as high construction cost and long construction period.After the survey and research found that the activity of ground fractures in Xi’an has significantly weakened,attempts have been made to adopt the more efficient and safe shield method for construction at the ground fracture sites.However,Xi’an is in a high intensity（VIII）fortification zone,and earthquakes can intensify the activity of ground fissures,leading to misalignment damage of shield tunnels,etc.There are few studies on the seismic response law of shield tunnels across ground fissures,and the damage mechanism of shield tunnels is not well understood,which causes great trouble to the seismic protection of shield tunnels at ground fissure sites.Therefore,based on the public welfare geological investigation project of Shaanxi Province,"Research on the influence of active fractures and strong earthquakes on urban underground space development in Xi’an and countermeasures for prevention and control（202109）",this paper carries out a 1:20 shaking table model test on the shield tunnel crossing1)₃ ground fracture at 75°in the section from Wangjiamun to Suwangcun of Xi’an Metro Line8 as a prototype.To study the longitudinal seismic response law of shield tunnel with tube sheet lining structure across the ground crack,the main work and conclusions are as follows:1.Based on the similarity theorem,the refined shield tunnel model is designed with the focus on the shield tunnel longitudinal joint bolts.The test includes model material selection,model production,monitoring scheme and loading scheme development,loading,and mainly analyzes the activity and acceleration response law of the ground crack site,acceleration,strain,earth pressure,bolt axial force,and activity seismic response law of the shield tunnel.2.The longitudinal seismic response law of the ground fracture site was studied in terms of surface fracture development characteristics,activity volume characteristics and soil acceleration response characteristics,etc.The results show that（1）during the longitudinal seismic process,the activity volume of the upper disk is larger than that of the lower disk,and the activity of the ground fracture has three-dimensional spatial deformation characteristics,which synchronously produce vertical misalignment,tension traction and horizontal shear,and synchronously reach the maximum,and their size relationship is:vertical misalignment（2）the peak acceleration amplification coefficient of the upper disk near the ground crack is greater than that of the lower disk,and the upper disk has an amplifying effect on acceleration;（3）the closer the acceleration peak amplification coefficient is to the surface vertically,the surface has an amplifying effect on acceleration;（4）the acceleration amplification coefficient decreases with the increase of seismic intensity;（5）after the end of loading,the upper disk in the vicinity of the ground crack 50cm settlement occurs within the range.The longitudinal seismic response of the shield tunnel was analyzed in terms of acceleration response,strain response,soil-structure interaction,bolt axial force,deformation,etc.The results showed that:（1）during the longitudinal seismic process,the maximum activity of the upper shield tunnel tube ring near the ground crack,the longitudinal deformation of the tunnel is"S"shaped,similar to"This is extremely unfavorable to the longitudinal joints,and the seismic design should be based on the principle of improving the tunnel toughness;（2）near the ground crack,the acceleration peak amplification coefficient of the upper tunnel ring is larger than that of the lower tunnel,and the tunnel The acceleration variation law is consistent with the surrounding soil,and the acceleration peak amplification coefficient is slightly smaller than that of the surrounding soil;（3）the time course curves of circumferential strain,earth pressure,and longitudinal bolt axial force of the shield tunnel are consistent with the acceleration time course curves of seismic waves,and the magnitude relationship is consistent under the action of different seismic waveforms of the same seismic intensity"Xi’an artificial wave<El-Centro wave<Taiwan set set wave";（4）the distribution of the peak circumferential strain in the tunnel vault and arch bottom has a double-peak pattern in the longitudinal direction,and the peak point in the upper plate is larger than that in the lower plate.The tensile strain at the bottom of the arch is greater than that at the top of the arch in the lower tray,and the opposite in the upper tray;（5）the overall earth pressure at the top and bottom of the arch in the upper tray is greater than that in the lower tray;（6）the longitudinal bolt tension is greatest at the location of the ground crack,and the overall tension of the bolt at the top of the arch in the lower tray is greater than that in the upper tray;（7）the shield tunnel is severely strained at the top of the arch 50 cm from the ground crack in the lower tray,and the influence range of the ground crack is 10 rings each in the upper and lower trays near the ground crack.