Time-Varying Response Analysis of Surrounding Rock Construction Mechanics of a Double-Arch Tunnel without a Middle Pilot Tunnel and Suggestions for Tunnel Construction

Abstract

This research carries out the model test and numerical simulation, studying the time-varying response regularity of surrounding rock construction mechanics. The purpose was to ensure the construction safety of a double-arch tunnel without a middle pilot tunnel and to prevent rockburst or large deformations of surrounding rock in a stress concentration areas. To resist shear deformation of the steel arch of the first tunnel, during construction of the secondary lining of the lower step of the following tunnel near the side of the first tunnel, shear reinforcement is added to form a shear wall. To resist the stress of upward uplift in the inverted arch area, the spacing of steel reinforcements in the inverted arch is encrypted to reduce disturbance to the supporting structure. To reduce disturbance to the first tunnel caused by the blasting construction of the following tunnel, this article carried out the SHPB test on field rock samples and suggests that the reserve 2 m width of the surrounding rock (the lower heading of the following tunnel near the side of the first tunnel) is mechanically broken.

Damage and reliability analysis of double-arch tunnel without a middle pilot tunnel under blast load

“…This was conducted because, in the actual project, the distance from the palm surface of the following tunnel blasting excavation to the supporting structure of the first tunnel was especially close, and if it were not optimized for the gun holes in the following tunnel, the blasting excavation of the following tunnel would have damaged the supporting structure of the first tunnel, thus leading to cracking of the supporting structure of the concrete and to the occurrence of a safety accident. As such, the two rows of gun holes in the following tunnel near the first tunnel were omitted (they were about 1.9 m) 1 . (c) The charge of some of the auxiliary holes in the upper left step of the following tunnel of holes was changed to the same charge as that of the peripheral holes, i.e., a single-hole charge of 0.6 kg; thus, there was a reduction in the charge by 56%.…”

“…How the destruction of rock occurs and the specific manner in which it is damaged is closely related to the microstructure and macro mechanics of rock; as such, the macro mechanics should be fully considered when defining the damage variables of rock. Therefore, when defining the damage variables of rocks, we should start by considering the following two aspects: (1) The damage of rocks is determined by the expansion and development of cracks, which are often only observable from a microscopic point of view. As such, we should consider factors such as the number, length, and volume of cracks [33][34][35] .…”

“…Compared with ordinary tunnels, its advantages are obvious, but the construction process is complicated. The left and right tunnels are close to each other, and respective excavation efforts interfere with one another 1 , 2 . When a blasting excavation is used, the surrounding rock’s damaged state and the supporting structure’s stress state become more complicated, thus increasing the difficulty in the construction and design 3 , 4 .…”

“…There is a lack of research on the construction techniques for multi-arch tunnels, particularly regarding the effects of blasting excavation without a middle pilot tunnel on surrounding rock damage and the mechanical properties of support structures. The construction method for double-arch tunnels without intermediate pilot tunnels presented in this study, especially the groundbreaking pre-embedding of connection points for steel arch frames in the primary support structure of the first tunnel, is a novel contribution by our team, as detailed in referenced publications 1 . We have explored the failure patterns of surrounding rock under this method from a new perspective, as well as the dynamic characteristics of support structures in the same section of left and right tunnels after continuous blasting without a middle pilot tunnel.…”