Abstract
In this study, we developed a tunnel excavation model test system to investigate the deformation and mechanical response of the surrounding rocks and tunnel structure during the reconstruction and expansion of an existing shallow single-hole tunnel into a twin-arch tunnel. A model test was conducted to study the variation in the ground surface settlement characteristics, surrounding rock pressure, and internal stresses of the supporting structure and midwall during the construction process. The influence of the excavation distance on displacements and structural stress between the faces of the left and right tunnels was analysed using numerical software. A comparison between the model test results and the monitoring and measurement construction results revealed a fairly consistent ground surface settlement, indicating that the system is stable and reliable and can be widely applied to laboratory model test research on tunnel excavation. Results show that the excavation of the first tunnel had a significant effect on the stability of the surrounding rock within the distance of a single-tunnel span behind the tunnel face. When the excavation distance between the two tunnels exceeded twice the length of the single-tunnel span, its effect on the stresses and deformation of the reconstructed twin-arch tunnel was negligible.
Highlights
With recent rapid social and economic development, the adaptation of existing road capacities and standards to development requirements has become challenging
(2) e existing tunnel served as the middle guide tunnel to construct the midwall, the height of which was greater than the new tunnel. e wall had a large contact area with the lining
Its structural internal stress was significantly affected by the tunnel excavations; this was applied to the second tunnel. e resulting effect on the structure was that the tensile stress exceeded the limit, affecting the stability and durability of the structure; attention should be paid to increase the structural support parameters in the design and reduce disturbances in the construction
Summary
With recent rapid social and economic development, the adaptation of existing road capacities and standards to development requirements has become challenging. Liu et al [28] combined the model test and numerical simulation methods to study the surrounding rock displacement, stress, and pressure-arch distributions of the Loess twin-arch tunnel during the construction process; they strengthened the support for the areas with multiple stress redistributions. Us, to study the deformation process and construction/mechanical response of the surrounding rocks and tunnel structures during reconstruction and expansion of an existing shallow singlehole tunnel into a large-span twin-arch tunnel, we developed a tunnel excavation model test system that could be reused and assembled ring-by-ring and conducted a model test for the construction process of the tunnel reconstruction and expansion project; we further analysed the dynamically varying characteristics of the ground surface settlement, surrounding rock pressure, and structural internal stresses of the supporting structures and the midwall during the reconstruction and expansion process. For the newly-constructed tunnel, the center of the existing tunnel is considerably higher than that of the middle guide tunnel and the top of the midwall must be well-consolidated with the top of the existing tunnel lining, resulting in a large discrepancy between the stress characteristics of the midwall structure and the new twin-arch tunnel. e disturbance caused by the existing tunnel accelerates the weathering and erosion of the surrounding rocks. erefore, it is vital to accurately assess the impact of such disturbances on the surrounding rocks and appropriately exploit it for the design and construction of in situ tunnel reconstruction and expansion. ere are almost no engineering examples that can be used as a reference for designing related parameters and construction schemes; effective, related studies need to be conducted to guide the design and construction. us, to study the deformation process and construction/mechanical response of the surrounding rocks and tunnel structures during reconstruction and expansion of an existing shallow singlehole tunnel into a large-span twin-arch tunnel, we developed a tunnel excavation model test system that could be reused and assembled ring-by-ring and conducted a model test for the construction process of the tunnel reconstruction and expansion project; we further analysed the dynamically varying characteristics of the ground surface settlement, surrounding rock pressure, and structural internal stresses of the supporting structures and the midwall during the reconstruction and expansion process. e influence of excavation distance between the left and right tunnel faces was analysed using numerical software, and the model test results were further compared and mutually verified using the construction monitoring and measurement results. e research results were subsequently used as a guide for designing the parameters and formulating the construction scheme. e research methods and results of this study can serve as a reference for similar projects in the future
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