Field Test on the BFW Active Joint of Steel Support in Foundation Pit Engineering

Aiming at the weak link of the active joint in the support system in the foundation pit, a BFW (Bolt Fasten Wedge) active joints were developed and 8 sets of full-scale test specimens were manufactured, and the application test was carried out at a deep foundation pit project in a station construction of Beijing Subway. Based on the field monitoring data, a comparative analysis was carried out with the steel wedge (SW) active joint, which was used to verify the bearing performance of the BFW active joint and the supporting effect of the foundation pit. Under the same construction conditions, the on-site monitoring results show that: 1) Within 24 hours after erection, the axial force of the three steel supports in the BFW test section is 86%~101% of the pre-added axial force, while the SW control section is only 67%~92% of the pre-added axial force; 2) The maximum axial force ratios of the second and third tracks of the BFW test section and the SW control section are 149.11% and 120.43%, respectively. It shows that the BFW active joint has better ability to maintain the pressure, which can play the load-bearing performance in time, and also has better supporting effect.