Abstract To investigate the deformation control strategy during the non-barrier launching of large-diameter dou? ble-mode shields at the shallow depth conditions, a study is conducted based on the shield-driven running tunnel section of the Zirui Tunnel on the new Chengdu-Pujiang Railway. A visual numerical model is established by using the FLAC3D software and taking into account field monitoring data and construction parameters to simulate the whole process of the non-barrier launching of a double-mode shield, and to study how the numerical characteristics of the cutterhead thrust applied when the cutterhead is cutting the retaining piles at the tunnel portal will affect the soil displacement behind the piles. The application feasibility of the traditional reinforcement theory and its improved methods under non-barrier launching are verified by comparing the displacement control effects at different reinforcement ranges. The results show that: (1) There is a stratigraphic variability in the influence of the numerical characteristics of the cutterhead thrust on the soil displacement behind the piles. Specifically, the effect in cohesive strata is significantly greater than that of non-cohesive strata such as gravel and sandy pebble strata; (2) The effect of the cutterhead thrust gradient on the soil displacement behind the piles is significantly greater than the numerical value of the thrust, regardless of the stratum types; (3) The traditional reinforcement theory and its improved methods are still applicable under the non-barrier launching, where the theoretical calculation value of the transverse reinforcement width is relatively conservative, and the length of the longitudinal reinforcement can basically meet the requirements for soil stability; (4) The choice of the location for the shift of the shield mode at the launching section has a significant impact on the surface vertical displacement caused by the subsequent construction, and the study suggests that this location shall be chosen within or near the boundary of the reinforced area.
Abstract：
To investigate the deformation control strategy during the non-barrier launching of large-diameter dou? ble-mode shields at the shallow depth conditions, a study is conducted based on the shield-driven running tunnel section of the Zirui Tunnel on the new Chengdu-Pujiang Railway. A visual numerical model is established by using the FLAC3D software and taking into account field monitoring data and construction parameters to simulate the whole process of the non-barrier launching of a double-mode shield, and to study how the numerical characteristics of the cutterhead thrust applied when the cutterhead is cutting the retaining piles at the tunnel portal will affect the soil displacement behind the piles. The application feasibility of the traditional reinforcement theory and its improved methods under non-barrier launching are verified by comparing the displacement control effects at different reinforcement ranges. The results show that: (1) There is a stratigraphic variability in the influence of the numerical characteristics of the cutterhead thrust on the soil displacement behind the piles. Specifically, the effect in cohesive strata is significantly greater than that of non-cohesive strata such as gravel and sandy pebble strata; (2) The effect of the cutterhead thrust gradient on the soil displacement behind the piles is significantly greater than the numerical value of the thrust, regardless of the stratum types; (3) The traditional reinforcement theory and its improved methods are still applicable under the non-barrier launching, where the theoretical calculation value of the transverse reinforcement width is relatively conservative, and the length of the longitudinal reinforcement can basically meet the requirements for soil stability; (4) The choice of the location for the shift of the shield mode at the launching section has a significant impact on the surface vertical displacement caused by the subsequent construction, and the study suggests that this location shall be chosen within or near the boundary of the reinforced area.
WEI Lifeng1 TIAN Yang1 ZHU Muyuan1 ZOU Kunmi2 FANG Yong1
.Study on the Deformation Control of Non-barrier Launching of Large Diameter Double-mode Shields at Shallow Depth[J] MODERN TUNNELLING TECHNOLOGY, 2023,V60(2): 149-158
2023, Vol. 60 