Bearing Behaviors and Reasonable Rock-Socketed Depth of Bridge Pile Foundation in Karst Areas

Abstract

The force of bridge pile foundation in karst areas is complicated. In order to determine the bearing capacity of bridge pile in these areas, the static load test is carried out. Bearing behaviors of the bridge pile in karst areas is analyzed using the displacement meter and strain gauge set respectively at the pile top and bottom. Furthermore, in combination with results of the static loading test for the rock-socketed pile, an optimization method for the socketed depth of the pile is proposed aiming at overcoming the shortcomings of existing pile-designing methods of bridge piles in karst areas. The results show that (1) The Q–s curve has a slowly-varying development under various vertical loads which shows a typical friction pile characteristic though the pile has been embedded in the depth of the limestone. Under a load of 8400 kN, the maximum settlement on the pile top is 3.69 mm, which is much less than 0.03 D or 40 mm, and the pile tip resistance is only 1.6% of the load on pile top. The tip resistance and shaft resistance of the pile are synchronized but with fairly different degrees of response. (2) The hyperbolic curve model is of high precision, and the forecast value is conservative when predicting the ultimate bearing capacity of a single pile, therefore, the hyperbolic model could be better for prediction in similar projects. (3) Based on the wide beam-pile mechanical model and the anti-bending failure mode, an optimal calculation method for rock-socketed depth of bridge piles in karst areas is proposed, which provide a theoretical reference for the design of pile foundation in karst areas.