Abstract
During the construction of the underpass of a new tunnel, the excavation unloading effect disturbs surrounding rock masses and promotes surrounding rock deformation, inevitably changing stress and displacement in the existing tunnel. Taking Yangtaishan tunnel excavation of Shenzhen Metro Line 6 as an engineering example, effects of excavation programs of left and right lines on the deformation characteristics of newly excavated and existing tunnels were evaluated based on Midas numerical model and priority excavation advantages of the left line were determined. The settlement and horizontal deformation characteristics of the existing tunnel were analyzed using the construction monitoring method. Results showed that maximum settlement and horizontal deformation of the existing tunnel were 1.35 and 0.23 mm, respectively. Settlement of invert and inverted top along axis direction was from growth to decline, and then a V-shaped settlement trough was formed with maximum settlement values of 1.36 and 0.97 mm, respectively. Maximum settlement and uplift of the newly built tunnel appeared on the upper and bottom parts of invert, respectively. In the newly built tunnel segments, the top settlement was dominated and deformation was mainly distributed in both side areas. At the top of the existing tunnel segment, convergence settlement was 3.09 mm and settlement rate was slow first which was accelerated, then stabilized, and finally slowed down again which was opposite to the uplift development trend of the bottom of tunnel segment. The top of the existing tunnel segment showed four settlement stages, slow, rapid, stable, and slow settlement stages. Compared with the right line, preferential excavation of the left line had obvious advantages in terms of tunnel stability. The unloading effect of TBM excavation created vault settlement in the existing tunnels where actual settlement values were 1.12 and 1.13 times, which theoretically calculated settlement. The horizontal deformation of the existing tunnel was varied first linearly and then nonlinearly with maximum deformation in the convergence stage of 1.47 mm.
Highlights
Keeping in mind that the transportation infrastructure of China has been rapidly developed during the past 20 years, the construction processes of railways, highways, and subways are no longer similar to what they were before: only consider its own construction conditions and not close to other projects [1,2,3,4,5,6]
Yangtaishan tunnel is located on the interval line between Dalang and Shiyan stations of Shenzhen Metro Line 6
To investigate the influence of different excavation programs on the deformation characteristics of the existing tunnel, cloud diagram of the vertical settlement of the existing tunnel lining obtained based on numerical simulation results was considered, as shown in Figure 5, where D represents settlement displacement
Summary
Keeping in mind that the transportation infrastructure of China has been rapidly developed during the past 20 years, the construction processes of railways, highways, and subways are no longer similar to what they were before: only consider its own construction conditions and not close to other projects [1,2,3,4,5,6]. During the construction of the underpass of a new tunnel, the excavation unloading effect disturbs surrounding rock masses and promotes surrounding rock deformation [4, 5, 8], inevitably changing stress and displacement in the existing tunnel. Such engineering problems has continuously attracted the attention of a great number of engineers and researchers around the world [20, 21]. We hope that the results reported in this work provide a reference for the construction of double-shield TBM underpassing the existing tunnels in shallow-buried composite strata
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