Analysis On Stability And Construction Mechanical Behavior Of Karst Tunnel Surrounding Rock

As a very typical complex geologic condition, karst caused considerable threat to tunnel construction. Due to the existence of karst caves, the stability of tunnel sur-rounding rock deterioration and likely lead to unstability and collapse of tunnel base-ment and wall, seriously it still caused secondary disasters as pour sand,water and mud gushing. Therefore analysis on karst tunnel surrounding rock's stability evaluation and construction mechanical behavior is essential in both theoretical significance and prac-tical value.Based on the construction of Naqian expressway Xulingguan tunnel, analysised and summarized the development law and characteristics of tunnel area as follow: the karst developmental feature is primarily vertical cylinder tubular shape growth with majority diameter 6～8m, mostly no fillings and water drop or water-shower drip. Combined with engineering field surrounding rock and geological conditions, perti-nently extracting three categories of secondary indexes as karst characteristics,rock mechanical characterstics,rock mass structural characteristics and fourteen first indexes. Using fuzzy theory to establish fuzzy comprehensive evaluation model and evaluate the stability of surrounding rock. The evaluation result coincides with the actual condition.According to the development characteristics of karst tunnel, established four 3D finite element models as no karst tube,vertical karst tube mutually perpendicular with tunnel,vertical karst tube mutually perpendicular with the side of tunnel,horizontal karst tube mutually perpendicular with tunnel, simulated the process of karst tunnel construction, researched the changes of vault,stress and plastic zone on each designated cross-section, analysised the influence of tunnel surrounding rock under each karst tube situation and conclude the mechanical behavior characteristics of karst tunnel construc-tion.According to the actual solution of karst tube treatment suggestion, comparative analysised surrounding rock stress,displacement characteristics and the results showed that after karst tube treatment tunnel vaults displacement,arch bottom displacement,arch foot principal stress P3,arch foot shear stress reduced greatly and side wall dis-placement,vaults principal stress P3,plastic strain zone increased. Therefore, sup-porting structure of tunnel side wall and vaults should be strengthened to achieve better effect and ensure surrounding rock stability and construction security.