4.1.2 The Hazard of Shield Construction to the Sur...
Shield construction inevitably disturbs the surrounding soil and causes surface settlement.When the local surface settlement is too large，it usually causes the settlement，inclination and even cracking of adjacent buildings（structures），which has become one of the most noteworthy problems in the shield construction process.The research on the influence of surface deformation on buildings（structures）was first carried out in the coal mining area.Many scholars have made in-depth studies on the deformation damage of buildings（structures）in the coal mining area，and have formed the damage evaluation standard of buildings（structures）in the mining area.However，the damage evaluation standard of buildings（structures）in the tunnel construction area has not been established.
At present，relevant studies have shown that the main damage modes of buildings（structures）caused by shield tunnel construction include uniform settlement damage，damage caused by ground curvature，damage caused by inclination，and damage caused by horizontal deformation.Usually，the compression and negative curvature of the surface appear at the same time，and the tensile and positive curvature of the surface occur at the same time.In practice，the deformation of buildings（structures）is often a comprehensive manifestation of various forms.Among them，the curvature，inclination and horizontal deformation caused by differential settlement damage to buildings（structures）is more obvious，and distortion，subsidence，cracking and even collapse will occur.In the process of shield tunneling，the influence of shield construction disturbance on buildings（structures）is restricted by many factors，among which the most important are the engineering geological conditions，the foundation form of buildings（structures），the position relationship between buildings（structures）and tunnels and the relative distance.
In 1956，Skempton et al.combined with nearly 100 tunnel construction examples，determined the allowable total surface settlement and differential settlement of the project，and summarized that the main reason for the cracking and failure of the building structure during tunnel construction was the excessive curvature radius of the settlement trough.However，compared with the curvature radius of the settlement trough which is difficult to measure，the measurement of the deformation angle is much easier，so the measured deformation angle is usually used as the main criterion of the deformation of the building structure.
In 2010，Zhang Zhongmiao and others based on Hangzhou Qingchun Road crossriver tunnel，combined with surface subsidence monitoring data，the Peck formula was used to fit the surface subsidence curve caused by shield construction，and the surface subsidence of the dam section and other sections were compared and analyzed.It is proposed that due to the complexity of the embankment structure，the disturbance of shield construction，the cyclic load of the vehicle on the top of the embankment and the combined action of rainfall，the settlement of the embankment is aggravated，which leads to the surface settlement caused by shield crossing the embankment is larger than that of other sections.
In 2014，Zhouyunjiang and Jieyu established a three-dimensional numerical analysis model for Shanghai Yangtze River shield tunnel crossing the levee section.The numerical calculation results were compared with the measured data to analyze the rationality of the numerical calculation.On this basis，the settlement law of the tunnel and the dam under different cross angles and different buried depths was analyzed.The results show that the larger the cross angle is，the smaller the maximum settlement value is，and the greater the uneven settlement is.The greater the buried depth，the smaller the settlement，the smaller the uneven settlement.
In summary，the formation loss caused by shield construction，the deformation of shield lining and the consolidation of soil after disturbance are the internal causes of land subsidence.There is a regular process of settlement，and the settlement of each stage is closely related to the state and location of the shield.The influence of shield construction disturbance on buildings（structures）is controlled by many factors，including the basic form of buildings（structures），engineering geological conditions and the position relationship between buildings（structures）and tunnels.In practical engineering，due to the influence of buildings（structures），especially its self-weight and structural stiffness，the deformation curve of buildings（structures）is very different from that of free ground.The existing research methods are mainly measured data regression method，indoor model test method，numerical analysis method and intelligent decision method.Through certain assumptions and simplification，the model is established by numerical analysis，and the relevant laws of shield construction are summarized.Combined with indoor test and field measured data，the correction and analysis are carried out，which has important guiding significance for practical engineering and theoretical research.