Abstract:

Forty-two case histories in which the laterally adjacent deep excavation affects the existing tunnel are collected. The typical stratum condition, size, relative position, structure deformation and control measures of deep excavation and tunnel in each case history are counted. By analyzing the influences of important factors on vertical and horizontal displacements of tunnel, the judging criterions of tunnel heave and settlement are clarified, and then the zoning of tunnel vertical displacement outside the deep excavation is given. The comprehensive prediction index of tunnel horizontal displacement is proposed, and the practical empirical prediction formulae of tunnel horizontal displacement under three categories of stratum conditions are given. Finally, relying on a specific case study, the deformation of tunnel is predicted using the obtained empirical formula before construction, and the rationality of the prediction formula is verified by comparing the prediction results with the field monitoring results. The results show that the horizontal displacement of tunnel is towards the pit, while the vertical displacement is in the form of heave or settlement, which is related to the buried depth of tunnel crown (H_t) and the distance between tunnel springline and deep excavation (L_t). It is obtained from statistics that the critical value of H_t is H_e+R and the critical value of L_t is H_e, and then considering the vertical displacement distribution characteristics of tunnel, the area outside the pit can be divided into settlement zone, transition area and heave zone. Horizontal displacement of retaining structure (ζ_hm), excavation depth (H_e), horizontal distance L_t between tunnel and deep excavation and longitudinal width b of deep excavation along tunnel are all important factors affecting horizontal displacement ζ_hm of tunnel. ζ_hm increases nonlinearly with the increases of d_hm and H_e; z_hm/δ_hm decreases with the increase of L_t as a power function relationship; ζ_hm has an increasing trend with the increase of b, which means multiple factors should be considered to scientifically predict the horizontal displacement of tunnel. ζ_hm and bH_e/L_t have a good linear relationship under three stratum conditions using bH_e/L_t as the prediction index of tunnel horizontal displacement, and the tunnel horizontal displacement prediction formula based on it can achieve good prediction effect proved by an actual engineering case.

Key words: case statistics, deep excavation, existing tunnel, prediction formula