Study on Stress and Deformation Mechanism of Side Pile and Middle Column for PBA Method Metro Station in Loess Area

Abstract

[Objective] In order to ensure the stability of important vertical load-bearing components in the process of station construction with PBA (pile-beam-arch) method in loess area, it is necessary to study the stress and deformation mechanism of side piles and middle columns during construction, and put forward measures to control the deformation in the most unfavorable stress stage. [Method] With Hejiaying Station of Xi’an Metro Line 2 as the research background, the methods of numerical simulation and field monitoring are used to study the horizontal displacement, internal force of steel bar, horizontal earth pressure and strain of middle column of side piles during construction. [Result & Conclusion] Construction of buckle arch, excavation of station hall layer and platform layer are the three most unfavorable stages for horizontal displacement of side piles. During the critical stages of construction, steel support should be set up inside the structure and the disturbed stratum should be properly reinforced. During construction of pile beam and buckle arch, the main rebar of side pile bears axial pressure, while during construction of residual earthwork in the station, forces borne by the rebar of side pile back on the soil side gradually change from axial pressure to axial tension. With the increase of buried depth of side pile, the growth of axial tension pressure slows down. In the construction of the initial support of the buckle arch, the earth pressure reaches the maximum value of 34.5 kPa at the buried depth of 6.6 m of the side pile. As the aforementioned depth deepens, the growth rate of the pile side pressure is significant. Therefore, the excavation of the inner side of the station is the key stage to control the earth pressure of the side pile at the earth facing side. If necessary, grouting reinforcement of the soil behind the pile is helpful to improve the bearing capacity of the pile foundation. During the construction of the mid-span arch, the strain of the middle column shows a trend of decreasing first and then increasing.

Keywords

• metro
• station
• side pile
• middle column
• stress deformation mechanism
• pba method
• loess area