Statistical Analysis of Beijing Subway Thin-walled Diaphragm Wall Foundation Pit Deformation Law

Abstract

Objective The thickness of diaphragm walls significantly affects the amount and mode of foundation pit deformation, thin-walled diaphragm walls are especially sensitive to excavation and edge loads of foundation pit. Therefore, it is necessary to study the deformation law of foundation pit diaphragm walls with different thicknesses in Beijing Subway. Method Taking six thin-walled diaphragm wall station foundation pit projects in Beijing Subway as examples, statistical analysis is conducted on monitoring data of ground vertical deformation, diaphragm wall top vertical deformation, horizontal displacement of diaphragm walls, and axial force of steel supports using statistical methods. Result & Conclusion The thin-walled diaphragm wall foundation pit ground deformation can be classified into heave-subsidence type and subsidence type, with a higher proportion of heave ground deformation. During soil mass excavation phase, the diaphragm wall exhibits a rapid upheaving trend, followed by a slight rebound of wall top uplift value after excavation completion, and eventually reaching a stable value. Based on the deformation characteristics of diaphragm walls, three types are identified: normal parabola, load parabola A and load parabola B. The maximum deformation of diaphragm walls generally occurs between 0.50H and 0.85 H (H as the excavation depth), with cumulative deformation concentrated in the range of 10 and 20 mm. The axial force variation of the first steel support is rather distinct, and its curve could be divided into four stages: rapid rise, rapid decline, slow decline, rapid rise.

Keywords

• metro
• thin-walled diaphragm wall
• foundation pit deformation