Numerical simulation research on the stability of transmission tower pile foundations in a karst area of Guangdong Province

The research on collaborative deformation of buried caves between transmission tower pile foundation in karst area occurred in Ruyuan county, Guangdong Province, China. The geological survey and drilling indicated that soils near the transmission tower are mainly alluvial silty clay, alluvial gravel, and residual silty clay. The bedrocks is predominately strongly weathered sandstone, moderately weathered quartz sandstone, limestone and carbonaceous limestone, which are generally greater than 30m in total thickness. Through drilling, nearly 10 different sizes of caves have been discovered in proximity to the tower. They are beaded or multi-layered in formation, and most are unfilled or half filled, where the overburden is normally 10-30 m, and a minimum of 1-4 m thick. The underlying caves have a large impact on the design, construction and operation of the transmission tower foundation. In order to study the stability and deformation of transmission tower foundations in this area, FLAC3D software was used for modele and calculations. By monitoring the stress, displacement and changes in the plastic zone at different positions, it showed that the stress distribution of the overlay is uniform and is minimally impacted by caves. However, the cave rock stress changes greatly. There is large bending down deformation in the roof of caves. Additionally, the bottom of the tower foundation moves down significantly, especially when a large stress loads are applied to the foundation and the cave roof, the cave roof would be unstable, leading to structural destruction of the pile foundation. The deformation characteristics of pile foundations with different rock-socketed depth indicate a positive correlation between rock-socketed depth and cave deformation.