Abstract: Ground settlement induced by tunnelling can affect the safety of ground building facilities. To study the deformation law of sandy soil strata under the influence of tunnelling at different burial depths, a model test system consisting of a model frame and a non-contact monitoring system was designed. Using this system, the stratum loss under the influence of tunnelling was simulated with dry sand as the filler. The deformation law at different depths of the stratum was then derived. Results elucidate that i) as the tunnel depth increases, the soil arching effect occurs within the stratum, the maximum settlement of ground gradually decreases and the surface settlement evolves from being narrow and deep to wide and shallow. However, the disturbed area of the ground gradually expands from the central axis of the tunnel to both sides. ii) At any buried depth, the settlement curves of the surface and within the strata all conformed to Gaussian distribution. The width coefficient of surface settlement trough increases with the increase of burial depth of tunnel, while that of deep soil decreases with the increase of depth. iii) For both clayey soil and sandy soil, the ratio of the width coefficient of deep soil settlement trough (i_z) to that of surface settlement trough (i_s) is linearly dependent with the relationship (1-h_z/h) between soil depth and tunnel's burial depth. Therefore, the law of settlement inside the stratum can be derived from the law of surface settlement in shallow buried sandy and clayey strata, thus providing reference and guidance for tunnel construction and support structure design.

Key words: tunnel engineering, surface settlement, model test, PIV technology, settlement trough