Abstract:

To investigate the influence of shield tunneling on the bearing behavior of the composite foundation, a case study and a field test are conducted on the shield tunneling through composite foundation of cementsoil pile group in a section on the Zhengzhou metro line 5. The variation trends of the ground settlement, pile top pressure stress, and soil stress between the piles are analyzed for the entire process of shield tunneling via piles. Moreover, the pile shaft axial force and side friction are further analyzed using numerical simulations based on the comparison and verification with the field test results. The conclusions inferred from the present findings are stated as follows: (1) During the entire process of shield tunneling through single pile composite foundation, the development law of loadingplate settlement can be generally classified into six stages, i.e., before shield tunneling, cutterhead cutting, shield tunneling through residual piles, shield tunneling away from residual piles, filling and condensation of synchronous grouting layer, and shield tail away from residual piles. (2) The pilesoil stress ratio initially decreases but later increases with the pile cutting construction process; the axial force of the pile shaft varies with the pile cutting process, and the axial force value in the final stage increases compared with that before pile cutting. (3) As the length of the residual pile shortens, the stress redistribution of the pile body induces two neutral points on the pile body, above which the pile body experiences positive friction and compression, and below these points, it endures negative friction and tension. (4) Compared with the final cumulative settlement, the loadingplate settlement in each stage increases by 20% before shield cutting, 60% during the condensation of the shield cuttinggrouting layer, and 20% for the shield situates farther from composite foundation. The increase ratio of the pilesoil stress ratio is －8%, －16%, －53%, 3%, 25%, and 66%.

Key words:

 , tunnel engineering, undercutting, composite foundation, bearing behavior, field test, numerical simulation