Abstract
At present, there are an ever-increasing number of tunnel expansion projects in China. Studying the mechanical properties of the expanded tunnels is of great significance for guiding their safe construction. Through model testing and numerical simulation, the mechanical properties of a double-arch tunnel constructed through the expansion of the middle pilot heading from an existing single-tube tunnel were studied. The variation characteristics of the surface subsidence, surrounding rock stress, and stress and strain of the middle partition wall and lining during the tunnel reconstruction and expansion were investigated. The mechanism for transferring stress and strain between the left and right tunnel tubes was studied by a numerical simulation method. The results showed that the surface subsidence caused by the excavation of the left (i.e., the subsequent) tunnel tube was larger, and the maximum surface subsidence occurred at the right (i.e., the first) tunnel tube. The surrounding rock on the middle wall was the sensitive part of the tunnel excavation, the stress of the surrounding rock at the left spandrel of the right tunnel tube fluctuated and exhibited the most complex variation, and the stress of the surrounding rock at the right spandrel of the left tunnel tube exhibited the largest variation. The excavation of the left tunnel tube had a great influence on the forces of the middle partition wall and the lining structure of the right tunnel tube, the middle partition wall was subjected to eccentric compression towards the left tunnel tube, and the stress at the left spandrel under the initial support of the right tunnel tube exhibited complex variations. The excavation of the left and right tunnel tubes had a great influence on the stability of the surrounding rock, as well as on the force-induced deformation of the middle partition wall and the support structure, within the width of the single tunnel tube span behind the tunnel working face. Due to the different construction sequences, the stress and strain at the symmetric measurement points of the middle partition wall, as well as the left and right tunnel support structures, were very different.
Highlights
In recent years, the traffic volume has increased rapidly, and the road capacity built in earlier years has become increasingly insufficient
After the excavation of the left tunnel tube, its initial support stress time history curve is shown in Figure 11. e following can be observed from the gure. e initial support of the left tunnel tube near the middle partition wall at the right spandrel (CZ-1) was always in compression, and the compressive stress increased with time, with the maximum value being 9.58 Minimum principal stress (MPa), which was much larger than the stresses at the other three measurement points. e vault
It can be seen from the gure that, except for the right haunch (Z-7) of the secondary lining of the left tunnel tube being in tension, the other measurement points were all in compression
Summary
The traffic volume has increased rapidly, and the road capacity built in earlier years has become increasingly insufficient To this end, while building new roads, China has vigorously carried out the reconstruction and expansion of the original roads. Researchers have extensively studied the effects of the single-tube tunnel excavation on the surface deformation and the mechanical response of the tunnel itself by using theoretical calculations [5, 6], numerical simulation [7, 8] and on-site monitoring [9, 10]. Extensively researches were carried out to predict the surface subsidence caused by the excavation of tunnels [14, 17,18,19,20,21] None of these studies evaluated the mechanical response of the tunnel during expansion.
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