Dynamic evolution in mechanical characteristics of complex supporting structures during large section tunnel construction

Abstract

The shallow tunnelling method (STM) often uses temporary supports to divide large section tunnels into several closed or semiclosed sections so as to share the upper load. The complex support system composed of primary and temporary supports can ensure safety during tunnel construction. Based on the large section tunnel of Beijing Subway Line 12, the mechanical characteristics of support system by the double-side-drift method (DSDM) during excavation and demolition were analyzed through numerical simulation and monitoring. The study showed that the middle cave excavation was the most critical stage of the DSDM, during which the load on the supporting structure increased significantly. The temporary vertical support bore most of the new load during middle cave excavation. During the demolition stage, the load was redistributed, which caused arch settlement and section convergence. The removal of the temporary vertical support exerted the greatest impact in this process. The lateral temporary inverted arch changed from axial compression to axial tension after the middle and lower caves were excavated. Based on the mechanical characteristics of the support system, some engineering suggestions were proposed for large section tunnel construction. These research results can provide reference for the design and construction of similar large section tunnels.

Reliability Analysis and Risk Assessment for Settlement of Cohesive Soil Layer Induced by Undercrossing Tunnel Excavation

“…Among them, the assessment of geomechanical characteristics and stability of rock and soil strata in the metro proximity construction area is the primary key work for the safety prevention and control of existing structures [9,10]. Through geomechanical testing and assessment, the occurrence of the metro proximity construction area, the properties of rock and soil bodies, the strength of rock and soil bodies, the geological structure and formation structure, the ground stress, and the surrounding conditions of the construction area can be mastered [11,12]. It can provide a reliable basis for a safety impact assessment and disaster warning of existing structures.…”

An investigation on the thixotropic parameters and mechanical properties of loess

“…As the time develops, the filling is gradually compacted, leading the bearing capacity of the foundation to be constantly increased, which in turn, provides favorable conditions for the building height. At the same time, complex coupling effects, such as soil-water pressure and geothermal, will affect the structural stability of underground facilities with the development of time (e.g., Jiang et al, 2022;Liu et al, 2023;Yang et al, 2023). Hence, determining the variation law of the strength of the remolded loess foundation over time as well as the standard value of the bearing capacity of the foundation under different time nodes are significant issues in the urban expansion of the mountainous areas.…”

An analysis of thixotropic micropore variation and its mechanism in loess

“…During the shelving of the foundation, while the soil settles and deforms, various coupling effects such as soil water pressure and geothermal energy can also occur, affecting the strength of the foundation soil (Liu et al, 2023;Yang et al, 2023). These coupling effects also affect the structural stability of underground space engineering during shelving (Jiang et al, 2022;Xue et al, 2023c). During the period of foundation shelving, the bearing capacity of the foundation increases continuously.…”