Research on Construction Safety Techniques for Shield Under-passing Brick-concrete House in Fracture Zones and Soft Rock Based on Air Pressure-assisted Tunnelling
To solve the construction problem that the earth pressure balance(EPB)shield based on the auxiliary air pressure mode starts to underpass through the old brick-concrete building with shallow foundation in the fractured soft rock stratum,a section of Guangzhou Metro is taken as a case.Firstly,the key and difficult points of this construction were analyzed in accordance with the surrounding environment and geological conditions.Then,the key construction technology was studied from three aspects,namely,pre-construction preparation,process control and post-construction protection.Finally,a comprehensive evaluation of the construction technology was carried out from the perspectives of engineering,economic and social benefits.The results show that the auxiliary air pressure method allows the formation to have a certain degree of development cracks,but other auxiliary measures need to be applied to meet the pressure requirements of the soil bin.Meanwhile,it is necessary to actively adjust the height of the soil bin residue in combination with the pressure retention of the formation.In the shield launching stage,it is necessary to adjust the foam air flow rate or the screw machine speed frequently to effectively reduce the instantaneous pressure fluctuation in the soil bin.After the muck is improved to a certain flow plastic state,the gate opening and the screw machine speed are taken as the double control indices,and the auxiliary air pressure method can be used to ensure the tunneling speed.When tunneling in soft rock strata,properly increasing the cutterhead speed and reducing the penetration can reduce the settlement of buildings induced by shield tunneling.
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