| The scale of urban subway construction in China is huge,the distribution area is very wide,and the geological conditions are complex and changeable.Among them,the sand pebble stratum has the characteristics of large quartz content,high pebble strength and strong water permeability.Its particularity and complexity bring great technical challenges to the design,construction and long-term operation safety of shield tunnel,The segment structure design and load calculation theory for this kind of stratum also need to be improved.In view of this,based on the shield tunnel project of Chengdu Metro Line 6,this paper studies the mechanical response characteristics of segment lining of overlapped small spacing shield tunnel in sandy cobble stratum by means of data investigation,field measurement,numerical simulation,model test and theoretical analysis,and discusses the calculation method of loose earth pressure of single line and overlapped small spacing shield tunnel in sandy cobble stratum,The main work and conclusions are as follows:(1)By means of field test,the load and internal force of segment structure of single line and overlapped shield tunnel with small clear distance crossing sandy cobble stratum are analyzed,and the measured time history variation and spatial distribution law of structural water and soil load,segment axial force and bending moment at different construction stages are explored.(2)The finite difference model is established to describe the whole process of single line and stacked line shield tunnel passing through sandy cobble stratum.The numerical simulation analysis of "Surrounding rock-lining structure-Water" double field coupling considering the coupling effect of stress field and seepage field is carried out.The structural water and soil loads,segment axial force,displacement of shield tail,synchronous grouting and stability stage are studied The measured time history variation and spatial distribution of bending moment are analyzed and compared with the measured data of corresponding sections.(3)We independently developed a test device suitable for the soil arching effect of Overlapped Tunnels with small clear distance,carried out the model test of soil arching effect of Overlapped Tunnels,and studied the slip surface shape of soil arching effect of Overlapped Tunnels and the law of soil loosening range.(4)Based on the investigation and analysis of the structural load calculation theory of shield tunnel at home and abroad,combined with the model test results of soil arching effect of overlapped tunnel,according to the existing load calculation theory,the analytical calculation method of loose earth pressure of single line and overlapped small spacing shield tunnel is proposed. |
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