Research On The Correlation Between Shield Tunnelling Controlling And The Masonry Structure Safety

With the massive construction of urban subway shield tunnelings in China,the shield tunneling construction under-crossing the existing buildings is becoming more and more inevitable,which will have a non-negligible impact on the existing building structure,especially the masonry structure with poor integrity.Shield tunneling construction control is not only closely related to the safety of the upper masonry,but also an important guarantee for structural safety.This paper takes the Zhengzhou metro Line 5 Huayuan Road Station～Jingsan Road Station shield tunneling under-crossing the upper masonry structure as the background,based on theoretical analysis,numerical simulation and field test,the influence of key parameters on the safety relevance of masonry structure while the shield tunneling under-crossing the upper masonry structure is studied.The main research work of the paper is as follows:(1)A field test study of shield tunneling through existing masonry buildings is carried out,meanwhile,the settlement of masonry building and the main control parameters of shield tunneling in the process of shield construction are summarized and analyzed.(2)The numerical simulation analysis of shield tunneling under-crossing the existing masonry building is carried out.A hardening model considering small strain stiffness of soil is adopted in the analysis,and a joint masonry model is adopted to consider the cohesion of horizontal ash joint mortar at the tooth seam section of masonry wall and the influence of mutual friction between adjacent brick elements.By comparing with the measured values,it is proved that the above model can better simulate the settlement and deformation of the masonry structure and the location and area of structural cracking when the shield under-crossing the masonry building.(3)Through numerical simulation analysis,the influence of the construction process of the tunnel longitudinally undercrossing the upper masonry structure on the safety of masonry buildings is studied.It is found that in this case,the shield tunneling construction has little effect on the tensile strain of the penetrated building beyond 2D in front of the excavation face;the tensile strain value of the building reaches the maximum when the tunnel shield penetrates 3/4 of the length of the building;as the shield tunneling construction continues,the maximum tensile strain value of the building does not change;during the shield tunneling construction process,the tensile strain of the building is in a constantly changing process.(4)The influence of the main shield construction parameters on the safety of masonry structure when the shield under-crossing the upper masonry structure is studied.Through comparative analysis,it is found that the possibility that the tensile strain of the masonry structure exceeds the threshold of 0.05%increases as the of the stratum loss rate increases,for every 0.2%increase in the average formation loss rate,the probability that the tensile strain of the masonry structure exceeds the threshold 0.05%increases by 4.4%,and the probability that the tensile strain of the first layer region of the masonry structure exceeds the threshold 0.05%increases by 8.7%;with the increase of the pressure on the excavation surface,the tensile strain of the masonry structure is also increasing but the increasing trend is decreasing;within a reasonable range,the increase of the grouting pressure is conducive to controlling the floating of the masonry building.The research results of this paper have important guiding significance for the safety control of masonry buildings caused by subway shield tunneling in urban areas and the process control of shield tunneling construction.