Abstract
According to construction scheme of some weak surrounding rock large span double and multi-arch tunnel works, finite element value simulation method is adopted to research weak surrounding rock deformation characteristic, anchor bolt mechanics characteristic, preliminary support and secondary lining structure mechanical characteristics, etc, and the research result shows that: repeatedly disturbance of excavation of middle pilot tunnel and subsequent supporting excavation shall easily reduce surrounding rock strength in the range of middle wall top and middle line of arch top of left and right pilot tunnels, therefore, prior to excavation of middle pilot tunnel, surrounding rock of tunnel top shall be pregrouting reinforced to improve integrated strength of surrounding rock of arch top, max. accumulated settlement displacement of tunnel is 19.45mm, max. horizontal convergence displacement of side wall of left and right tunnel is 9.71mm, max. vertical upheaval displacement of middle wall bottom is 8.82mm, above displacement can all be within controlled range satisfying design requirement; max. plastic zone vertical depth of upper side of left and right tunnel arch top is respectively 1.23m and 2.06m, inverted arch bottom plastic zone vertical depth is 2.74m and 3.37m, radial depth of middle plastic zone of side wall of left and right tunnel is respectively 0.87m and 1.73m, mutual impact range of spatial effect of tunnel face of left and right tunnel is 3 folds tunnel span. This research shall be referred to by similar tunnel design and construction.
Highlights
With increasing of China’s traffic infrastructure construction in recent years, quantity of highway tunnel construction is increasing, new tunnel structure forms and related construction methods emerge in large number, due to restriction of topographic condition, multi-arch tunnel becomes the main form of middle and short distance expressway tunnel [1]
The project is located in the border of Huangshan Mountain, Anhui Province of China, and is straight line large span multi-arch tunnel, the tunnel area belongs to construction erosion middle mountain area, the tunnel axial line sea level elevation is 3670.0-499.0m, the mountain relief is steep, the middle part is fluctuated and uneven with developed vegetation, inlet topographical slope angle is 35o, outlet section topographical slope angle is about 45o, the developed stratum in the tunnel site mainly includes: lower segment metamorphic sandstone of Daguyun Group of Jixianian System of mesoproterozoic erathem, landslide accumulation formation
The surrounding rock, middle partition, sprayed concrete and secondary lining unit shall all be simulated by plane unit, anchor bolt shall be simulated by truss unit, steel arch and pilot tunnel temporary support shall all be simulated by girder unit [6, 7]; related boundary displacement constraint is: left and right boundary horizontal constraint, lower boundary vertical constraint, upper boundary is free; the load calculation shall consider the deadweight of rock and earth mass, as well as excavation release load, the deadweight stress field g=9.8m/s2; without considering impact of construction stress, seism, and groundwater, etc to tunnel structure
Summary
With increasing of China’s traffic infrastructure construction in recent years, quantity of highway tunnel construction is increasing, new tunnel structure forms and related construction methods emerge in large number, due to restriction of topographic condition, multi-arch tunnel becomes the main form of middle and short distance expressway tunnel [1]. SHENG et al showed that the distribution form of the plastic zones for the different execution procedures of the double and multi-arch tunnel [2, 3]. Multi-arch tunnel structure has specificity and the design and construction technology is complicated, and is always the key research objective of tunnel engineering field of each country [4, 5]. There are less engineering experiences for building large span double and multi arch tunnel in weak surrounding rock stratum, and the construction mechanical characteristic is unclear. This paper relies on certain large span double arch tunnel works, and adopts large scale finite element analysis software to simulate construction process value of excavation
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