Analysis and Field Measurement on the Internal Force Variation Laws of Steel Pipe Columns in Subway Stations

Abstract

Steel pipe columns are an important component in subway station construction and with stand stress state and internal force during the construction process. Based on the engineering background of Beijing subway, this paper introduces the geological conditions, station structure types, and internal force monitoring of steel pipe columns of 10 subway stations constructed by the PBA method. The field monitoring indicates that the greatest change in the internal force of the steel pipe column occurs during stage 1 (beam, primary support, and secondary lining buckle arch construction stage), no matter pile foundation station or strip foundation station, which accounts for about 60% to 65% of the total axial force. When the left and right spans are not synchronously arched or excavated, the steel pipe column is subjected to uneven forces and bears a large bending moment is produced. When the depth of overburden is between 7 m and 15 m, the internal force of the steel pipe changes positively correlated with the overburden depth. During the construction process, the internal force of the steel pipe varies widely in the silty sand stratum. Also, the steel pipe columns in stations affected by groundwater bears about twice of the axial force compared with other stations are not affected by groundwater. In addition, the construction period is also a factor that affects changes in internal forces. This research is conducive to update the database of the world subway projects and can serve as a practical reference for similar geological condition.

The Influence of Pile-Beam-Arch Construction on the Stratum and Station Support Structure

“…Following the completion of the secondary lining buckle arch. According to past experience, it is believed that the axial force of the middle column will not change greatly under the upper vault [25]. However, discovered through field data analysis the middle column axial force changed significantly during the digging soil stage.…”

“…Monitoring of the Middle Column by the PBA Method 3.1. PBA Method Introduce [25]. Construction process mainly involves 7 steps, as shown in Table 1.…”

“…We set up a set of monitoring points (4 string strain gauges) on the lower surface of the top longitudinal beam (TLB), the lower surface of the middle longitudinal beam (MLB), the upper surface 5 Geofluids of the bottom longitudinal beam (BLB) about 0.5 m, and between the every layer of the station, respectively. In addition, the strain gauges should be arranged at 90 degrees on the middle column and evenly spaced [25]. Both stations have the same requirement, as shown in Figure 2.…”