Methods to Calculate Rock-Embedded Depth of Bridge Pile Foundation Passing Through Karst Caves
This paper presents three methods that can accurately calculate the rock-embedded depth of pile foundation in a karst zone,which consider the effects of vertical ultimate load bearing capacities of the piles,stability of the piles and cave dissolution amount in the bridge life cycle.The pile foundation of the bridge carrying a section of the Putian-Yanling Expressway in the karst zone is used as a case.34 representative piles were selected to verify the reliability of the three methods.The design rock-embedded depths of these piles were compared with the calculated depths,and a trial pile was selected to perform comparison of rock-embedded depth given in the specifications and depths calculated by the three methods.As per the analysis,the rock-embedded depth of one pile is smaller than the calculated rock-embedded depth considering the cave dissolution amount in the bridge life cycle,accounting for 2.9％.The design rock-embedded depths of 10 piles meet the requirements of vertical load bearing capacity of piles,stability of piles and cave dissolution amount in the bridge life cycle,with rational safety margin,accounting for 29.5％.The safety margins of 23 piles are large,accounting for 67.6％,among which,14.7％of the piles own safety margin five times larger than the design data.There exist great differences among the suggested rock embedded depths of pile foundations in different codes.To ensure the load bearing safety of pile foundation and reduce the construction complexity and costs,it is recommended to sufficiently consider the cave dissolution amount in the bridge life cycle,when calculating the effective rock-embedded depths of piles passing through karst zones.
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