Evaluation of movements and structural forces resulting from bored tunnelling in sand

摘要

Case histories of bored tunnels in sand in southern Taiwan are selected as a research backgroundrnin this paper. Details of these tunnels and observations of ground movement induced by tunnel constructionrnare briefly described here. By using numerical analyses, this paper aims to interpret possible ground loss raterninduced by tunnel construction. Further, structural forces on tunnel segments are further evaluated associatedrnwith different approaches and output are compared and discussed. It is concluded that less than 0.5% of groundrnloss rate is reached during tunnel construction. Larger displacement was predicted from numerical analyses andrnthe possible reason shall be mainly related to larger contraction ratio used. In addition, from exercises of the usernof two different constitutive models, the analyses using Hardening Soil model could give a better description ofrnsettlement trough since said model has an additional consideration regarding soil stiffness under unload-reloadrnconditions. Second, various approaches are adopted to explore structural forces, such as shear force, axial forcernand bending moment during tunnel construction. Under the same load condition and soil profile, it is initiallyrnfound that the analyses using the beam-spring method to predict the smallest bending moment, shear force andrnaxial forces rather than others. It is aware that ground loss rate and twin tunnel interaction would not affect anyrnresult from analyses using elastic equation method and beam-spring method since only loads and details of ringrnare considered in these two approaches. Considering analytical results, it is understood that the middle of ringrn(90 degree from top of tunnel) have to take the maximum bending moment.