Study on bearing characteristics of bridge piles and deformation mechanisms of karst caves in karst area
Due to the highly undulating terrain,complex geological conditions,and the widespread distribution of karst topography developed with underground karst caves in Southwest China,the construction of bridges and tunnels will inevitably traverse areas that contain these karst caves. The karst effect changes the structure of rock masses,weakening the strength and increasing the permeability of the surrounding soil. In regions where caves are developed,the construction of pile foundations will not only encounter challenges in pile formation but also will experience impacts on the load-bearing capacity of foundations due to the presence of these caves. Prolonged loads can easily result in severe deformations,tilting,or even collapses of the superstructure. To elucidate the impact mechanisms of caves on the bearing characteristics of bridge piles during construction in karst regions,this study focused on viaduct piles from a highway project in Guizhou. Numerical simulations were employed to examine the settlement patterns of piles that completely traversed the cave,those that laterally intersected with the cave,and those that were adjacent to caves. Furthermore,the axial force distribution in the piles and the deformation characteristics of the caves were analyzed,along with the stability of the caves under various working conditions.The research findings indicate as follows,(1) Caves reduce the bearing capacity of bridge piles,although the degree of this effect varies by location. When bridge piles are situated near caves,the influence diminishes with increasing distance,becoming negligible when the horizontal distance exceeds 2D (where D represents the pile diameter). Conversely,when bridge piles pass through caves,their bearing capacity decreases as the burial depth of the caves increases. The maximum impact occurs when the cave is located directly beneath the rock-embedded section of the pile,resulting in a reduction of bearing capacity by approximately 16.5% to 17.5%. Engineering practices should give due consideration to caves near the pile tips. (2) The asymmetric distribution of caves contributes to differential settlement of the foundation. The shallower the cave or the closer it is to the bridge pile,the more significant the impact. Specifically,when the cave is located above the rock-embedded section of the pile or is less than 1D away from the bridge pile,it is necessary to implement reinforcement measures such as backfilling or grouting to prevent excessive differential settlement of the foundation. (3) For end-bearing piles,the influence of the cave on the side resistance of the pile mainly manifests as a loss of side resistance in the exposed section of the pile foundation. The impact of caves on end resistance is ranked as follows:piles fully traversing the cave>piles laterally crossing the cave>piles near the cave. (4) When bridge piles fully traverse the cave,the predominant failure mode of the cave is tensile failure of the roof. When bridge piles laterally cross the cave,shear failure primarily occurs near the pile foundation. When bridge piles are in close proximity to the cave,the potential failure mode is punching shear failure from the foundation. (5) When bridge piles cross the cave,it is crucial to consider the impact of the loads on the stability of the cave and to implement appropriate reinforcement measures. Additionally,when bridge piles are near the cave,caution must be exercised regarding the potential for localized instability of the cave if the distance is too short (<0.5D).
bridge pilekarst cavebearing characteristicsstabilitykarst area