Construction Methods and Mechanical Characteristics of Large Metro Stations in Expansive Soil Layers in Chengdu

Abstract

Objective In parts of Chengdu, the underlying bedrock in expansive soil area is mudstone, providing a conducive space for groundwater accumulation. This leads to the swelling of expansive soil upon water absorption, causing significant expansion pressure that can easily crack the sidewalls of station structures in the area. To prevent such occurrences, it is necessary to conduct in-depth research on the mechanical characteristics of tension-prone parts such as side walls, middle slabs, and top slabs during the construction of station main structure in this area. Method Taking the main structure Chengdu Metro Line 17 Weiling Station East Extension Line Phase II project as research object, the construction procedures of station main structure are introduced. By employing laboratory tests and numerical simulation methods, the stress variation characteristics of tension-prone areas under different construction procedures are analyzed. The most unfavorable monitoring locations for the major influencing construction processes are identified. Result & Conclusion The free expansion rate of expansive soil within the station construction area is over 40.0%, with a maximum of 48.0%, classifying it as weak expansive soil. The expansion pressure decreases with increasing natural moisture content, with the on-site soil expansion force measured at 42.8 kPa. The construction of Weiling Station main structure adopts a construction method of ′both ends closing towards the middle′, which reduces the exposure time of the expansive soil foundation pit after excavation, successfully preventing cracks in the main structure such as the sidewalls. Removing the first and second supports significantly increases tensile stress in the structure, marking it as a major influencing construction process. The most critical stress locations in the main structure are 7.23 m from the middle slab on the sidewalls of first basement level, 4.00 m from the right sidewall on both the top and bottom slabs, and the midpoint of the middle slab span, with a maximum tensile stress of 0.587 MPa, meeting safety control requirements.

Keywords

• chengdu metro
• station
• structural stress
• expansive soil layer
• numerical simulation