Segment Floating Mechanism and Control Measures for Large-diameter Shield Tunnel in Coastal Water-rich Stratum
In order to explore the segment floating mechanism of large-diameter shield tunnel in complex strata with abundant water near the sea and take corresponding control measures,based on Fuzhou Binhai Express Metro project,a numerical calculation model is established considering the multi-factor coupling effect of shield machines,segments,slurry and strata,and the slurry-segment interaction mode and the segment floating mechanism with different slurry pressure distributions are analyzed.Then,the optimal material ratio for slurry is obtained through indoor experiments and on-site practical applications,and the grouting process for the shield machine wall is improved.The result shows that(1)the change in the distribution form of slurry pressure has the greatest impact on the floating displacement of the first segment behind the shield tail,the change in the distribution form of external slurry pressure has a significant impact on the floating displacement difference of the segment upper part among different working conditions,and also has a significant impact on the floating displacement difference of the segment lower part among different working conditions,while the impact on both sides is relatively small;(2)the change in the distribution of slurry pressure at the lower part of the segment has the greatest impact on the misalignment among adjacent segments near the shield tail,when the slurry pressure at the upper part of the segment is high,the axial force and bending moment at various parts of the segment structure are generally small,and the distribution range of negative bending moment at the upper part of the segment and the value of negative axial force at the lower part are relatively small;(3)the increase in the water cement ratio and cement sand ratio of the slurry lead to an increase in the consistency,flowability and initial setting time of the slurry,but there is a significant negative correlation between the powder water ratio and 3physical indicators mentioned above;(4)a material ratio of 200 kg cement,300 kg water,680 kg sand,380 kg fly ash and 90 kg bentonite per cubic meter of slurry is used,40%slurry is injected into the upper two grouting holes of the pipe segment,while 30%slurry is injected into the middle and lower two grouting holes respectively.At the same time,water glass is quickly injected into the upper part of the pipe segment after the shield tail is removed,which can significantly reduce the floating displacement of the pipe segment.
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