Enhancements in the Virtual Support Force Method for Tunnel Excavation Problems

Abstract

In order to accurately quantify the spatial constraint effect of tunnel excavation face, a generalized and improved form of virtual support force method is proposed, and the implementation steps of the method are given in detail. This approach is capable of demonstrating the variations in load release within the excavation section as well as the evolution of load release along the tunnel axis direction under the spatial restrictions of the tunnel face. Simultaneously, the presented approach is examined from the perspective of tunnel deformation and stress, and ultimately, the impact of the enhanced approach on the support timing determination is deliberated. A numerical model of a circular tunnel is established for analysis; the results show that, in terms of deformation and stress path, the enhanced virtual support force method can more closely resemble the actual three-dimensional excavation process than the traditional method. The improved virtual support force method can reduce the volume loss rate error by up to 3.76% and the stress error by up to 15.64% compared to the conventional method. As a result, the tunnel face’s spatial limitation may be more accurately described by the enhanced virtual support force approach. The support point computed by the enhanced approach is further away from the tunnel face in the research of establishing the beginning support timing, which may more thoroughly mobilize the surrounding rock bearing and minimize support consumables.

Keywords

• tunnel excavation
• FLAC3D
• spatial constraint effect
• uneven load release
• virtual support force
• support timing