Numerical analysis of underground displacements stirred by compaction grouting during tunnel construction

Abstract

Compaction grouting is widely accepted to mitigate the surface settlements during tunnel excavation. Currently, compaction grouting relies heavily upon field observations due to the limit understanding of the amounts of soil displacements induced by a given volume of grout. In this study, parametric studies and probabilistic investigations are performed to examine the underground displacements caused by compaction grouting during tunneling. Under high injection pressure, soils flow around the center of a circle, which is approximately 2 m ∼ 2.8 m above the elliptical grouting bulbs and 3.3 m away from the far-end elliptical grouting bulb. An influenced zone, outside which effect of the burial depth of grouting bulbs can be neglected, is determined by connecting the intersections of vertical displacements curves. Influence of burial depth of elliptical grouting bulbs on vertical displacements is greater than that of the total length of elliptical grouting bulbs. When the total volume of elliptical grouting bulbs is identical, better grouting efficiency is achieved by increasing the volume of the elliptical grouting bulbs adjacent to the tunnel center, especially for deeper monitoring points. Locations of the maximum lateral displacements in soils are within a band underground. Moreover, probability of exceedance of vertical displacements on the tunnel center line and formulas describing the distributions of heaves in soils are presented for the benefit of assessing the project risk and liability and predicting the heaves in soils.