Study on the Effect of Multi-span Pit Excavation on Supporting Structures Based on the Cutter Soil Mixing Method

Abstract

The Cutter Soil Mixing (CSM) method, a relatively recent innovation, employs twin-wheel milling and profound agitating machinery for wall construction. In an endeavor to scrutinize the displacements and internal support stresses to the support structure during the excavation of a multi-span foundation pit founded upon the CSM method, a two-dimensional finite element model was established, utilizing the Midas GTS NX 2019 V1.2 finite element software. This model was grounded on a multi-span foundation pit excavation endeavor situated in the eastern expanse of China, where steel bracing and the CSM method assumed the preeminent mantle of support. A comprehensive scrutiny encompassed ten distinct working conditions, each juxtaposed and dissected to ascertain the displacements affecting the CSM wall and the forces exerted upon the support system during the foundation excavation process. The research findings manifest a certain interplay between the embedment depth of the CSM wall and the span of the pit excavation in shaping the displacement and support stresses within the supporting structure. While deeper embedment augments the potential for enhanced support outcomes, its efficacy remains constrained. As the embedment depth increases, the internal support moment and lateral displacement of the wall increase slightly. Taking a pit with a shallow embedded CSM wall as an example, wherein both the lateral and vertical displacements experience an ascent followed by a descent, culminating at the juncture of a four-span pit. Likewise, the axial force and bending moment exerted upon the steel supports undergo a similar trajectory, culminating with a two-span pit as the threshold. At the five-span, the maximum lateral displacement of the CSM wall exceeds that observed at the two-span by an increment of 21.14%. These findings offer invaluable insights into the embedment depth of diaphragm walls and the span of pit excavations, wielding profound implications for future undertakings akin to the foundation pits in question.