岩溶地区富水压力溶腔的存在威胁着隧道施工安全。为分析压力溶腔存在对隧道施工安全的影响，以溶腔位于隧道上方的不利工况为例建立了防突层的简化力学模型，并考虑水压力和侧压力的共同影响，采用结构力学方法和变分原理推导了防突层最小安全厚度，分析了防突层高跨比对最小安全厚度取值的影响。结合某岩溶隧道，推算出防突层安全厚度为7.29m，小于溶腔与隧道临空面的实际厚度，判定该隧道施工是安全的。运用有限差分软件FLAC3D建立数值分析模型，分析了压力溶腔存在对防突层竖向位移以及受力的影响，进而判定防突层稳定性。结果表明：当压力溶腔与隧道临空面实际岩层厚度大于防突层最小安全厚度时，不会威胁隧道施工安全，但溶腔存在时防突层竖向位移和竖向应力均有增大趋势，考虑施工扰动因素建议施工中应加强溶腔处位移监测，及时反馈信息，确保施工安全。研究结果可为岩溶隧道施工提供借鉴。

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.

西部交通科技项目（2011318797600）