Numerical analysis on impact of pressure cavity on karst tunnel construction safety
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Abstract:
The existence of pressure cavity with water threatens the tunnel construction safety in karst region. In order to analyze the influence of pressure cavity on tunnel construction, a simplified mechanical model was built based on the condition of the cavity located above the tunnel, considering water pressure and side pressure, the thickness of layer was calculated using structural mechanics method and variation principle , and the influence of depth-span ratio was analyzed. Combined with the condition of a karst tunnel, the thickness of prevention layer was determined to be 7.29 m, less than the actual thickness between the cavity and the tunnel, therefore the tunnel construction was safe. FLAC3D was used to build numerical simulation model, to analyze the influence of pressure cavity on the vertical displacement and the stress of the prevention layer, and further to determine the stability of prevention layer. The results showed that when the actual thickness between pressure cavity and tunnel surface was greater than the minimum thickness of the protection layer, there was no threat to the tunnel construction, but the vertical displacement and vertical stress of the prevention layer showed an increasing trend in the presence of cavity, considering the construction disturbance factors, we suggest that cavity displacement monitoring should be strengthened in construction progress and information should be fed back timely to ensure construction safety. The conclusion can provide reference for karst tunnel construction.
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