Study On Ground Surface Settlement Law And Excavation Sequence Of Treble-hole Parallel Shield Tunnel

With the rapid development of urban rail transit in China,the metro has become the most common form of rail transportation.In the existing subway excavation projects,the parallel construction of doublehole and multi-hole tunnel is more and more common.Multi-hole tunnel excavation will cause more complex stratum disturbance and more serious surface settlement.Therefore,the thesis takes the shield tunnel project of Hai-Huan section of Nantong rail transit Line 1 as the backing project,adopts the methods of literature analysis,theoretical analysis,field measured data analysis and numerical simulation to study the surface settlement law of the treble-hole parallel shield tunnel and the influence of different excavation sequence on the shield construction.The main research contents and conclusions of this paper are as follows:(1)Based on Peck formula and the concepts of repeated disturbance range and additional settlement curve,a "three-stage analysis method" is proposed to calculate the surface settlement curve of treble-hole parallel tunnel.The calculation formulas with and without repeated disturbances are obtained respectively.The influence of net distance of tunnel on surface settlement curve is analyzed qualitatively.The settlement curve presents three peak "V" type,three peak "wave" type,single peak "U" type and single peak "V" type with the change of net distance.(2)Research on actual working conditions.The field measured data were analyzed from three angles: surface lateral settlement,surface longitudinal settlement and segment deformation.The lateral surface settlement curve caused by the three-hole tunnel shows a "V" shape deviation to the backward tunnel.The longitudinal surface settlement curve is a "S" type and goes through five stages.When the back tunnel is excavated,the front tunnel segment converges to be stable.(3)Based on the actual engineering background,the FLAC3 D model was established,and the calculated results were compared with the theoretical values and the field measured values.The results show that the "three-stage analysis method" proposed in this paper and the numerical simulation can better reflect the real construction situation.(4)The influence of the excavation sequence on the surface settlement,soil deformation and tunnel segment is simulated,and the optimal construction sequence is determined.Finally,it is suggested that the excavation sequence of condition 4 should be preferentially selected in the actual construction process,that is,three tunnels should be excavated in s-type sequence.(5)Single factor analysis method is used to study the influence of tunnel net distance and buried depth on surface settlement of three-hole tunnel.With the increase of net distance ratio,the maximum settlement decreases and the width of settlement groove increases.With the increase of the buried depth ratio of the tunnel,the width of the settlement trough and the maximum settlement value increase.