Research on bearing capacity of post-grouting pile groups as bridge foundations in karst areas

Large-diameter rock-socketed shafts have been widely used in large-scale bridge constructions due to its higher bearing capacity and less settlement. Difficulties in pore-forming and uncertainty of pile bearing capacity have brought challenges to the construction and design of shafts in karst areas. Based on the engineering geological investigation, only parts of caves can be found in boring, however, the spanning and height of caves is not accurately identified if the comprehensive investigation was not implemented. After detailed investigations, characteristics of cave can be explored at the site of formerly-designed piles, and possibly the design scenario will be changed in usage of pile foundations. Under consideration of economy and effectiveness in the piles design, a new method, named as post-grouting pile groups was proposed to solve this problem in karst area. The post-grouting treatment can also improve the bearing capacity of pile groups. Numerical modeling for multiple small-diameter pile groups after post grouting was carried out by FLAC^3D, and the results show that the bearing capacity and settlement of the pile groups can satisfy the standards of design. It was also noted that the bearing capacity increases significantly with the depth of reinforced soils above the pile tip. However, it was found that if the depth of reinforced soils under the pile tip reaches two times larger than the pile diameter, bearing capacity of pile groups almost becomes unchanged.