Control of pile movements induced by tunnelling using micropiles

The effect of installing micropiles between the existing piles and the tunnel is not well understood. This paper discusses the effectiveness of micropiles as a means to control tunnelling-induced ground movement and movements of an existing pile, located at a distance of one times the tunnel diameter from the tunnel axis. Laboratory physical model tests had been conducted in dry sand of 50% relative density using a row of 3·7 mm dia. micropiles with two different lengths (110 and 145 mm), embedded in between the tunnel (overburden ratio of 3) and the existing pile at four different locations. During the tests, settlement, the bending moment and axial force of the existing pile have been monitored. The results show that the micropiles reduced by more than 85 and 75% of the piles’ lateral and axial movements, respectively. Within the limitation of the study, it has been concluded that the most suitable length and location of the micropiles are 145 mm (tip of the micropiles is closest to the tunnel crown), located exactly in the middle between the tunnel axis and the pile. It is based on the reduction observed on the vertical and lateral movements of the pile as well as in the bending moment, and the axial force.