Abstract The mechanism of effects for isolation piles on reducing displacements of soil and tunnel below the ground surface needed to be studied. Field measurements were carried out in a deep excavation project in Tianjin,which adopted the isolation piles to protect the adjacent existing tunnel. The deformations of the diaphragm wall,soil outside the excavation,isolation piles and the tunnel were obtained and analyzed. Based on the measured data,a parametric study of isolation piles using finite element method considering the small strain of soil was conducted to investigate the horizontal displacements of the tunnel and the soil below the ground surface adjacent to a deep excavation. It was shown that isolation piles had both effects of isolation and drag on the tunnel adjacent to the deep excavation. The deformation of adjacent tunnel from deep excavation can be increased when the drag effect was more remarkable. The buried isolation pile could be used to minimize the effect of drag and the horizontal displacement of tunnel. Moreover,the isolation piles had higher efficiency in reducing the tunnel displacement when the piles were located closer to the tunnel.
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