To investigate the influence mechanism of synchronous grouting in shield tunnel on vertical displacement and earth pressure of sandy soil stratum

model tests were conducted to study the vertical displacement and earth pressure of the upper stratum during synchronous grouting. The results indicate that with the same filling coefficient of synchronous grouting material

the upper stratum rises and earth pressure increases after injecting small water content slurry

whereas it settles and earth pressure decreases after injecting large water content slurry. Similarly

with consistent water content in the grouting material

reducing the filling coefficient significantly decreases the uplift of the upper stratum and reduces the extrusion pressure on the upper stratum of the tunnel. Vertical earth pressure increases and passive soil arching occur when the upper stratum uplifts

while vertical earth pressure decreases and active soil arching occur when the stratum settles. During on-site synchronous grouting

the filling coefficient should be determined based on the consolidation shrinkage of the slurry and stratum permeability

and grouting parameters should be adjusted according to on-site monitoring results.